عصير كتاب: خرائط الزمن لـ ديفيد كريستيان David Christian: Maps of Time

بسم الله الرحمن الرحيم

Maps of Time: An Introduction to Big History – David Christian

Introduction: A Modern Creation Myth?

· “Who am I? Where do I belong? What is the totality of which I am a part?” In some form, all human communities have asked these questions. And in most human societies, educational systems, formal and informal, have tried to answer them. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 422-424). University of California Press. Kindle Edition.]

· If the Eiffel Tower were now representing the world’s age, the skin of paint on the pinnacle-knob at its summit would represent man’s share of that age; and anybody would perceive that that skin was what the tower was built for. I reckon they would, I dunno. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 495-497). University of California Press. Kindle Edition.]

1 The First 300,000 Years: Origins Of The Universe, Time, And Space

· At the very beginning, all explanations face the same problem: how can something come out of nothing? The problem is general, for beginnings are inexplicable. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 721-722). University of California Press. Kindle Edition.]

· At the smallest scales, subatomic particles sometimes emerge instantaneously from nothingness. One moment there is nothing; the next moment there is something. There is no in-between state. Quantum physics can analyze these odd jumps into and out of existence with great precision, but it cannot explain them in ways that make sense at the human level. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 722-724). University of California Press. Kindle Edition.]

· But where did the Maker come from? Each beginning seems to presuppose an earlier beginning. In monotheistic religions, such as Christianity or Islam, the problem arises as soon as you ask, how was God created? Instead of meeting a single starting point, we encounter an infinity of them, each of which poses the same problem. [David Christian; William H. McNeill: Maps of Time: An Introduction to Big History (Kindle Locations 744-747). University of California Press. Kindle Edition.]

· Similar arguments are common in modern cosmology, and what they imply is that the universe we see may be merely one tiny atom in a much larger “multiverse.” But such approaches are also unsatisfying, because they still leave the nagging question, How did such eternal processes themselves begin? How was an eternal universe created? [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 797-799). University of California Press. Kindle Edition.]

· Within Christianity, it was generally agreed that the Creator made the universe a few thousand years ago. In one famous calculation, a Dr. Lightfoot from Cambridge “proved” that God had created humans at exactly 9:00 AM on 23 October 4004 BCE. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 800-802). University of California Press. Kindle Edition.]

· Many other creation myths also introduce deities who created the world, working like potters, or builders, or clockmakers. This approach solves much of the problem, but leaves open the basic question of how the gods themselves were created. Once again, we seem forced back to an infinite regress. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 803-805). University of California Press. Kindle Edition.]

· A final position is skepticism. This entails a frank admission that at a certain point, we must run out of knowledge. Human knowledge, by its nature, has limits, so some questions must remain mysteries. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 805-806). University of California Press. Kindle Edition.]

· We will see that modern cosmology also opts for skepticism at the beginning of its story, though it offers a very confident account of how our universe evolved once it was created. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 807-809). University of California Press. Kindle Edition.]

· Though many pioneering scientists, like Newton, were Christians who believed deeply in the existence of a deity, they also felt the Deity was rational, so their task was to tease out the underlying laws by which the Deity had created the world. This meant trying to explain the world as if there were no deity. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 810-812). University of California Press. Kindle Edition.]

· Modern science, unlike most other traditions of knowledge, tries to explain the universe as if it were inanimate, as if things happened without intention or purpose. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 812-814). University of California Press. Kindle Edition.]

· The Christian view of the universe owed much to the ideas of the Greek philosopher Aristotle. Though some Greeks had argued that the earth orbited the Sun, Aristotle placed the earth at the center of the universe and surrounded it with a series of transparent spheres, each revolving at a different speed. The spheres held the planets, the Sun, and the stars. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 814-816). University of California Press. Kindle Edition.]

· Copernicus gave some powerful reasons for thinking that the earth revolved around the Sun, and the heretical monk Giordano Bruno argued that stars were suns and that the universe was probably infinite in extent. In the seventeenth century, scientists such as Newton and Galileo explored many of the implications of these ideas, while retaining as much as they could of the biblical creation story. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 819-822). University of California Press. Kindle Edition.]

· During the eighteenth century, the Ptolemaic view of the universe finally collapsed. In its place, there emerged a new picture of a universe operating according to strict, rational, and impersonal laws that could, in principle, be discovered by science. God may have created it, perhaps in time; perhaps, in some sense, out of time. But then he left it to run almost entirely according to its own logic and rules. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 822-825). University of California Press. Kindle Edition.]

· But there were problems. One arose from the theory of thermodynamics, which suggested that the amount of usable energy in the universe was constantly diminishing (or that entropy was constantly increasing; see appendix 2). In an infinitely old universe the consequence would be that no usable energy was left to create anything—yet clearly that was not true. Perhaps, this might have suggested, the universe was not infinitely old. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 827-830). University of California Press. Kindle Edition.]

· In the first half of the twentieth century, evidence began to accumulate for an alternative theory that we now know as big bang cosmology. It solved the problem of entropy by suggesting the universe was not infinitely old; it solved Olber’s paradox by describing a universe that was finite in both time and space; and it solved the paradox of gravity by showing that the universe was expanding too fast for gravity to gather everything into a single lump (yet!). Big bang cosmology described a universe with a beginning and a history, so it turned cosmology into a historical science, an account of change and evolution. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 838-843). University of California Press. Kindle Edition.]

· Evidence from the Wilkinson Microwave Anisotropy Probe (WMAP) released by NASA in February 2003 suggests the most precise date calculated so far for the big bang: about 13.7 billion years ago. See “Imagine the Universe News,” 12 February 2003 <http://imagine.gsfc.nasa.gov/docs/features/news/12feb03.html&gt; (accessed April 2003). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 10064-10066). University of California Press. Kindle Edition.]

· About the beginning, we can say nothing with any certainty except that something appeared. We do not know why or how it appeared. We cannot say whether anything existed before. We cannot even say that there was a “before” or a “space” for anything to exist in, for (in an argument anticipated by St. Augustine in the fifth century CE) time and space may have been created at the same time as matter and energy. So, we can say nothing definite about the moment of the big bang, or about any earlier period. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 856-859). University of California Press. Kindle Edition.]

· Inflation seems to ensure that most of the universe is beyond our observation, as light from most of the universe will be too distant ever to reach us. The parts of the universe we can see may be only a tiny part of the real universe. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 874-876). University of California Press. Kindle Edition.]

· Particles appeared in two forms, to make up almost equal amounts of matter and antimatter. Particles of antimatter are identical to particles of matter except for having the opposite electrical charge. Unfortunately, when the two meet, they annihilate each other and 100 percent of their mass is transformed into energy. So, during the first second after the big bang there played out a perverse subatomic game of musical chairs, in which quarks were the players, antiquarks were the chairs, and the winner was the one quark in a billion that couldn’t find an antiparticle chair. The matter left to construct our universe was made from the one in a billion particles that didn’t find an antimatter partner. The particles that did find a partner were transformed into pure energy, and that energy pervades the universe today, in the form of cosmic background radiation. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 885-891). University of California Press. Kindle Edition.]

· Relations between electrons and protons were controlled by a second fundamental force, the electromagnetic force, which also appeared within the first second of the universe’s history. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 894-895). University of California Press. Kindle Edition.]

· One of the most familiar examples in daily life is the transition that takes place when water turns into steam. Water is heated, and for a time all that seems to happen is that it gets warmer. Change occurs gradually, and we can watch it happening. Then, abruptly, a threshold is crossed; something new is created and the whole system enters a new phase. What had been liquid becomes gas. Why should a threshold occur at this particular point, in this case at 100°C (at sea level)? Sometimes we can explain transitions from one state to another, and the answer generally turns on a changing balance between different forces—between gravity, pressure, heat, electromagnetic forces, and so on. Sometimes we simply do not know why a threshold is crossed at a particular point. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 903-908). University of California Press. Kindle Edition.]

· Hubble found both types of shift. But as he worked on the remotest objects, he realized that these were all shifted toward the red end of the spectrum. In other words, they appeared to be stretched out as if they were moving away from us. And the farther away they were, the greater the extent of the redshift. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1020-1022). University of California Press. Kindle Edition.]

· We have no reason to think that we live in an abnormal part of the universe. Indeed, modern maps of the distribution of galaxies suggest that the universe really is pretty homogenous on the largest scales. So we have to assume that other observers in any other part of the universe would also observe that other parts of the universe seemed to be moving away from them. And this must mean that the universe as a whole is expanding. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1024-1027). University of California Press. Kindle Edition.]

· If the universe is expanding, then in the past it must have been much smaller than it is now. If we follow this logic back in time, we will soon see that at some point in the distant past, the universe must have been infinitesimally small. This argument leads directly to the basic conclusion of modern big bang cosmology: the universe was once infinitesimally small, but it then expanded, and it continues expanding to the present day. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1027-1030). University of California Press. Kindle Edition.]

· In the early twentieth century, most astronomers still assumed that the universe was infinite, homogenous, and stable. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1042-1043). University of California Press. Kindle Edition.]

· Einstein’s equations suggested that the universe, like a pin standing on its end, had to fall to one side or the other. It had to be either expanding or contracting; a perfectly balanced universe was very unlikely. Einstein himself resisted this conclusion. Indeed, in what he later described as the greatest error of his life, he altered his theory by proposing the existence of a force he called the “cosmological constant,” in order to preserve the idea of a stable universe. This force he imagined as a sort of antigravity, which could counterbalance gravity and thus prevent the universe from collapsing in on itself. However, in 1922 a Russian, Alexander Friedmann, showed that the universe really might be either expanding or contracting. Eventually, even Einstein accepted the idea of an unstable and evolving universe. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1045-1051). University of California Press. Kindle Edition.]

· In the 1940s, the idea of an expanding universe still seemed odd to most astronomers. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1051-1052). University of California Press. Kindle Edition.]

· between the 1940s and the 1960s, new evidence accumulated in support of the idea until, by the late 1960s, the big bang theory had become the standard account of the origins of the universe. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1052-1053). University of California Press. Kindle Edition.]

· It soon became apparent that the idea of an early, dense, and hot universe was perfectly consistent with all that was known in the emerging field of particle physics. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1062-1063). University of California Press. Kindle Edition.]

· Some of the earliest theorists of big bang cosmology predicted that there ought at that moment to have been a huge release of energy, whose remnants might be detectable today. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1069-1070). University of California Press. Kindle Edition.]

· It is a sign of the caution with which scientists still approached the idea of a big bang that no one actually looked for this background energy. It was found accidentally, in 1964, by Arno Penzias and Robert Wilson, two scientists working for Bell Laboratories in New Jersey. They were trying to build extremely sensitive radio antennae, but found it was impossible to eliminate all the background “noise” they picked up. Eventually, they realized that wherever they pointed their antennae, there was always a faint hum of weak energy. What could possibly be emitting energy from all directions of the sky at the same time? Energy coming from a particular star or galaxy made sense, but energy coming from everywhere—and so much energy—seemed to make no sense at all. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1071-1076). University of California Press. Kindle Edition.]

· Though the signal was weak, the total when all the energy it represented was added up was colossal. They mentioned their discovery to a radio astronomer who had heard a talk by a cosmologist, P. J. E. Peebles, predicting the existence of remnant radiation at an energy level equivalent to a temperature of ca. 3°C above absolute zero. This was remarkably close to the temperature of the radiation found by Penzias and Wilson. They had found the flash of energy predicted by early theorists of the big bang. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1076-1079). University of California Press. Kindle Edition.]

· Their discovery was decisive because no other theory could explain such a universal and powerful source of energy, while big bang cosmology could explain it naturally and easily [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1080-1081). University of California Press. Kindle Edition.]

· Since 1965, few astronomers have doubted that the big bang theory is the best current explanation for the origins of the universe. It is now the central idea of modern astronomy, the paradigm that unifies the theories and ideas of modern astronomy. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1081-1083). University of California Press. Kindle Edition.]

· the big bang theory predicts that the early universe will consist mainly of simple elements, above all hydrogen (ca. 76 percent) and smaller amounts of helium (ca. 24 percent). These are about the ratios we observe in the universe today (though the amount of hydrogen has fallen to ca. 71 percent as reactions within stars have converted hydrogen into helium, which now accounts for ca. 28 percent of all matter). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1089-1092). University of California Press. Kindle Edition.]

· Is big bang cosmology true? No scientific theory can claim absolutely certainty. And there remain problems with the theory, some of which are highly technical. But at present, none of these problems seems insurmountable. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1105-1106). University of California Press. Kindle Edition.]

· The rate of expansion of the universe, rather than decreasing under the influence of gravity, is in fact increasing. If these observations are correct, they are startling, for they seem to imply that there exists some hitherto unknown force that has operated constantly since the big bang to maintain and accelerate the rate of expansion, but that is too weak to have been detected before. One possibility is that this force consists of “vacuum energy,” a force predicted by quantum mechanics that would act in a way opposite to gravity, driving matter and energy apart rather than drawing them together. If so, its effects may be almost identical to those of Einstein’s speculative cosmological constant. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1110-1116). University of California Press. Kindle Edition.]

· There is also the tricky problem of beginnings. At the beginning of the big bang, all our scientific knowledge seems to go haywire. The density of the universe seems to move toward infinity, as does its temperature, and modern science has no good way of dealing with such phenomena, though it has many promising ideas. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1118-1120). University of California Press. Kindle Edition.]

· What encourages us to take the theory seriously despite these difficulties is its consistency with most of the empirical and theoretical knowledge assembled by modern astronomy and modern particle physics. And no other theory of origins can explain so much. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1120-1122). University of California Press. Kindle Edition.]

· Before about 13 billion years ago, we can say nothing with any confidence about the universe. We do not even know if space and time existed. At some point, energy and matter exploded out of the emptiness, creating both time and space. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1155-1156). University of California Press. Kindle Edition.]

2      Origins Of The Galaxies And Stars The Beginnings Of Complexity

· It seems that most of the mass of the universe (90 percent or more) is not visible, and the exact nature of this mass (known appropriately as dark matter) remains a mystery. In other words, we are in the embarrassing position of not knowing what most of the universe is made of. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1205-1208). University of California Press. Kindle Edition.]

· The first stars and galaxies were constructed from little more than hydrogen and helium. But they were a sign of our universe’s astonishing capacity to build complex objects from simple building blocks. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1215-1216). University of California Press. Kindle Edition.]

· In some sense, and at some scales, gravity can temporarily counter the second law of thermodynamics, the fundamental law that seems to guarantee that over time, the universe will become less ordered and less complex. Instead, as gravitational energy is released (as gravity clumps matter together), the universe appears to become more ordered. Gravity is thus one of the major sources of order and pattern in our universe. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1237-1240). University of California Press. Kindle Edition.]

· Gravity needs some initial differences to work with. If the early universe had been perfectly smooth—if, say, hydrogen and helium had been distributed with absolute uniformity throughout the universe—gravity could have done little more than to slow down the rate at which the universe expanded. The universe would have remained homogenous; and complex, lumpy objects such as stars, planets, and … human beings could never have formed. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1245-1247). University of California Press. Kindle Edition.]

· Evidence from WMAP released by NASA in February 2003 suggests that the first stars may have appeared as early as 200 million years after the big bang. See “Imagine the Universe News,” 12 February 2003 <http://imagine.gsfc.nasa.gov/docs/features/news/12feb03.html&gt; (accessed April 2003). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 10108-10110). University of California Press. Kindle Edition.]

· The second law of thermodynamics ensures that all complex entities will eventually die; but the simpler the structure, the better its survival chances, which is why stars live so much longer than humans. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1292-1293). University of California Press. Kindle Edition.]

· At the center of most galaxies, densities were so great that huge clouds of matter and energy kept collapsing even at temperatures high enough to start fusion reactions. Here, gravity acquired such momentum that it crushed matter and energy out of existence, thereby forming the bodies called black holes. Black holes are regions of space so dense that no matter and no energy can escape their gravitational pull, not even light. This means we can never directly observe what goes on inside a black hole, except by entering it—and then, of course, we could never return to report our findings. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1312-1316). University of California Press. Kindle Edition.]

· Galaxies and stars make up most of the visible universe. But observations of the movements of galaxies and galaxy clusters have led to the embarrassing conclusion that we are seeing only a tiny part of what is actually out there. Indeed, what we can see may constitute no more than 10 percent, and perhaps as little as 1 percent, of the matter in the universe. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1346-1348). University of California Press. Kindle Edition.]

· Using the basic laws of gravity, astronomers can calculate roughly how much matter is in a group of galaxies by studying the way they rotate, and such studies show that galaxies contain perhaps ten times as much matter as we can see. Astronomers refer to this matter as dark matter, which is really a way of expressing their puzzlement. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1348-1351). University of California Press. Kindle Edition.]

· Stars, like people, have biographies. They are born, they live, they change, and they die. And today we know a great deal about the typical life cycles of stars. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1364-1365). University of California Press. Kindle Edition.]

· In their dying phases, many stars swell into red supergiants; an example is Betelgeuse in the constellation of Orion. When our sun reaches this phase, in about 5 billion years, it will expand so much that both Earth and Mars will be within its outer layers. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1397-1399). University of California Press. Kindle Edition.]

· Momentarily, in the extraordinarily high temperatures of a supernova, a new threshold of some kind is crossed, for in this furnace it is possible to bake elements much heavier than iron. Indeed, in a few moments, supernova explosions can manufacture all the elements of the periodic table, up to uranium. These are then blasted deep into space. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1417-1419). University of California Press. Kindle Edition.]

· The gold or silver ring you may be wearing was made in a supernova. Without supernovae, we could not exist. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1426-1427). University of California Press. Kindle Edition.]

· So, the chemicals we are made from were created in three distinct stages: while most hydrogen and helium was created during the big bang, most elements from carbon (atomic number 6) to iron (atomic number 26) were formed inside medium and large stars, and most other elements were formed in supernovae. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1434-1436). University of California Press. Kindle Edition.]

· The energy that drives the biosphere is also derived largely from stars. Direct sunlight is one of the most important of all sources of energy on Earth. But for humans in the past two centuries, the sunlight stored long ago in coal and oil has been almost as important. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1438-1439). University of California Press. Kindle Edition.]

· As with all stars, many features of the Sun are determined by its size. It is a yellow star (spectral type G2), which means that it falls in the middle of the range of brightness of stars. However, most stars (about 95 percent) are smaller and cooler than the Sun. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1455-1457). University of California Press. Kindle Edition.]

· Nevertheless, our sun is not large enough to collapse into a supernova when it dies. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1458-1459). University of California Press. Kindle Edition.]

· After struggling through a traffic jam of subatomic particles for 1 million years, it takes photons of light just over 8 minutes to reach Earth, 150 million kilometers away. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1464-1465). University of California Press. Kindle Edition.]

· Without the Sun, our earth could not have existed and life could not have evolved. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Location 1466). University of California Press. Kindle Edition.]

· The placing of our earth within the universe is by no means random. We can exist only because we are in an atypical region. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Location 1507). University of California Press. Kindle Edition.]

· Our earth exists within a region unusually rich in matter, in a large galaxy, in which supernovae have generated a broad variety of elements. Within that galaxy, we live in a region of star formation, close to a mature star. Even in the densest part of the galaxy, the disk, regions of empty space normally contain only about one atom in each cubic centimeter. But in the earth’s atmosphere, there may be 25 billion billion molecules in the same space.15 And pouring though this matter is the energy emitted every second by the Sun. In other words, human history has taken place in a pocket of the universe that is dense in matter and packed with energy. It is the extraordinary richness and complexity of this environment that made life possible. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1509-1514). University of California Press. Kindle Edition.]

3 Origins and History Of The Earth

· As the Sun lit up, the inner rings of the solar nebula were heated more than the outer rings. This heat drove the more volatile (gassy) materials away from the inner regions. But farther out, from about the orbit of the future Jupiter on, it was cold enough for volatile gases to become liquids or solids. As a result, the inner orbits contained much more rocky material, while the more volatile materials accumulated farther from the Sun. This explains why the inner planets are rocky, while the outer planets (from Jupiter outward) are dominated by substances such as hydrogen and helium that are gases on earth. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1557-1562). University of California Press. Kindle Edition.]

· Earth, for example, is made up of oxygen (almost 50 percent) and smaller amounts of iron (19 percent), silicon (14 percent), magnesium (12.5 percent), and many other elements of the periodic table. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1589-1590). University of California Press. Kindle Edition.]

· Between Mars and Jupiter, the asteroids may be the remnants of a “failed” rocky planet, whose formation was disrupted by the strong gravitational pull of nearby Jupiter. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1590-1591). University of California Press. Kindle Edition.]

· If Jupiter had been slightly larger, then the solar system might have had two suns, and its structure and history would have been very different. The planets would have orbited in much less stable patterns, and it seems unlikely that life could have emerged on any of them. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1593-1595). University of California Press. Kindle Edition.]

· This means that the astronomical niche in which we exist, though unusual on the scale of the universe, is not rare. Just within the Milky Way, there may be millions of planetary systems capable, in principle, of supporting life of some kind. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1607-1608). University of California Press. Kindle Edition.]

· By about 40 million years after the formation of the solar system, most of the heavier metallic elements in the early earth, such as iron and nickel, had sunk through the hot sludge to the center, giving the earth a core dominated by iron. This metallic core gives the earth its characteristic magnetic field. The earth’s magnetic field has played an extremely important role in the history of our planet: by deflecting the many high-energy particles streaming through space, it shielded the delicate chemical processes that eventually generated life here. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1628-1632). University of California Press. Kindle Edition.]

· The lightest materials of all, including gases such as hydrogen and helium, bubbled through the earth’s interior to the surface. So we can imagine the surface of the early earth as a massive volcanic field. And we can judge pretty well what gases bubbled up to that surface by analyzing the mixture of gases emitted by volcanoes today. These include hydrogen (H), helium (He), methane (CH4), water vapor (H2o), nitrogen (N), ammonia (NH3), and hydrogen sulfide (H2S). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1641-1646). University of California Press. Kindle Edition.]

· However, as the earth cooled, water vapor that had accumulated in its atmosphere fell in torrential rains lasting millions of years. These downpours created the earliest oceans. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1650-1651). University of California Press. Kindle Edition.]

· The fact that water exists in liquid form on the earth’s surface is of fundamental importance to us, for it means that Earth’s temperatures were suitable for the appearance of the complex and fragile molecules that made up the earliest life forms. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1653-1655). University of California Press. Kindle Edition.]

· Perhaps Earth proved suitable for life because of a rare combination of circumstances, suggesting that even if the universe contains billions of planets, few may be hospitable to life. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1660-1662). University of California Press. Kindle Edition.]

· Once life formed, living organisms started making themselves at home, shaping the atmosphere and surface of the earth to make it more suitable for life. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1662-1663). University of California Press. Kindle Edition.]

4 The Origins of Life and The Theory Of Evolution

· Schrödinger therefore suggested another way of defining what is distinctive about life. Life is not just complex—it is significantly more complex than anything else in the universe; and the level of orderliness achieved by living organisms is remarkable, given the general tendency of the universe toward disorder. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1878-1880). University of California Press. Kindle Edition.]

· Chemical processes may have generated life elsewhere in the universe, though at present we do not know if this is true. But we do know that life appeared on Earth within 600 million years of the planet’s creation. By geological standards, and given the harsh conditions of the early earth, that was quick. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1897-1900). University of California Press. Kindle Edition.]

· And from the moment life appeared, living organisms have multiplied and changed in a dazzling and apparently endless cascade of new life forms, each finely tuned to handle the particular energies and resources in its immediate environment. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1900-1901). University of California Press. Kindle Edition.]

· Many societies have tried to explain life by assuming that there is a creator spirit or god who somehow breathed life into inanimate matter. Modern science regards this explanation as the easy way out, because theories that depend on deities can be made to explain more or less anything and are not subject to objective verification. Instead, modern science tries to explain the creation of life as a consequence of inanimate forces and processes, just as it approaches the creation of our sun and earth. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1947-1950). University of California Press. Kindle Edition.]

· Another naturalist, Alfred Russel Wallace, stumbled on the same idea at about the same time, and he and Darwin first presented the theory in two papers published in 1858 in the Journal of the Linnaean Society. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 10152-10153). University of California Press. Kindle Edition.]

· Darwin rarely used the term evolution, perhaps because it seems to imply some sort of mystical force that drives biological change in particular directions and thus would contradict his own view of biological change as a more open-ended process. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1953-1955). University of California Press. Kindle Edition.]

· Darwin knew that in most populations only a minority of individuals survive to adulthood and produce offspring. Yet the future of the species can be shaped only by those individuals that do survive and reproduce. So later generations of life are the offspring only of the survivors. (Evolution, like history, apparently is written by the winners.) [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1965-1968). University of California Press. Kindle Edition.]

· Adaptation is such an important notion in modern biology that it is worth defining more carefully. It refers to the fact that all living organisms seem to be exquisitely fitted for the environments in which they live. Indeed, so perfect is the fit between organisms and their environments that many of Darwin’s opponents argued, as some still argue, that organs such as the human eye or the elephant’s trunk must have been designed by a benign creator. Darwin tried to show that blind processes could do the job equally well. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1975-1979). University of California Press. Kindle Edition.]

· Modern biologists use the idea of evolution to explain the colossal variety of life-forms on earth. They also use it to try to explain the initial emergence of life on earth, for it seems that nonliving substances may also have evolved by some simplified form of natural selection. And, given a favorable environment and enough time, they eventually evolved into living organisms. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1988-1991). University of California Press. Kindle Edition.]

· We have seen that in the seventeenth and eighteenth centuries, some European scientists began to doubt the creation myth of the Judeo-Christian Bible. The Bible seemed to say that species were created by God, about 6,000 years ago, and that they remained essentially as God had created them. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 1994-1996). University of California Press. Kindle Edition.]

· By the late eighteenth century, some biologists were considering the possibility that living organisms changed over time by natural mechanisms of some kind, as it seemed messy to suppose that God was continually tinkering with his creation. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2017-2019). University of California Press. Kindle Edition.]

· To understand his argument fully, it is vital to understand the random nature of many of these processes. Individuals vary from their parents in minor but essentially random ways. They do not, in any sense, “try” to adapt. It is not the individuals that “evolve,” but the average features of the species. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2071-2073). University of California Press. Kindle Edition.]

· These were astonishing conclusions, for they implied something utterly revolutionary: all the beautiful and complex organisms on Earth, from amoebae to elephants to hummingbirds to human beings, can be created by blind, repetitive processes. Unconscious processes can create not just stars and galaxies, it seemed, but even life itself.8 Such reasoning seemed to deprive God himself of any reason for existence, which is why Darwin’s theory has met, and still meets today, such profound resistance. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2079-2083). University of California Press. Kindle Edition.]

· Most of his readers were traditional Christians. They believed that God had created distinct species, and the thought that species might have emerged through blind processes shocked them. So it was to this audience that Darwin directed most of his arguments. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2094-2096). University of California Press. Kindle Edition.]

· What reason could a god have for preserving such useless organs, rather than redesigning each species from scratch? [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2112-2113). University of California Press. Kindle Edition.]

· Darwin understood that natural selection needed huge periods of time in which to generate the immense variety of creatures present on Earth, and he conceded that 100 million years was probably not long enough. He believed that evolution worked extremely slowly. Indeed, he was convinced it worked so slowly that it could never be observed directly, and thus all the evidence for evolution would have to be indirect. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2122-2125). University of California Press. Kindle Edition.]

· One reason why his theory is now so widely adopted is that in the twentieth century it proved possible to see evolution at work directly. It is easiest to watch evolution when studying small species that breed rapidly, such as fruit flies. We have also seen evolution at work when new forms of bacteria have appeared in response to the use of antibiotics (as further discussed below). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2136-2138). University of California Press. Kindle Edition.]

· His experiment seemed to prove, finally, that life could not be generated spontaneously and that there was no life force floating through the air. Life could be generated only from life. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2190-2191). University of California Press. Kindle Edition.]

· Paleontologists knew that life seemed to appear quite suddenly in the so-called Cambrian era, which we now know began less than 600 million years ago. How could this sudden burst of life be explained? Were biologists forced back to the idea of a creator deity? Many nineteenth-century biologists felt they were, because any purely scientific explanation of the origins of life had to suppose that life could be generated from nonliving material, and Pasteur seemed to have shown that this was impossible. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2192-2195). University of California Press. Kindle Edition.]

· But precisely how chemical evolution generated the first living organisms remains unclear. To understand these difficulties, we must break the problem into several levels. First, we need to explain how the basic raw materials of life were created: the chemical level. Second, we need to explain how these simple organic materials were assembled into more complex structures. Finally, we need to explain the origins of the precise mechanisms of reproduction encoded in the DNA that is present in all living organisms today. At present, we have reasonably good answers to the first question; we have plausible answers to the second question; and we are still puzzled by the third question. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2206-2211). University of California Press. Kindle Edition.]

· Some claimed that Miller and Urey had come close to creating living organisms. It is now clear that this was not so. Many difficult steps lie between the creation of simple organic molecules and the creation of life. In any case, the atmosphere of the early earth probably contained less ammonia and methane than the two chemists had supposed, and more carbon dioxide and nitrogen. Such an atmosphere would have been less fertile in simple organic molecules. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2232-2235). University of California Press. Kindle Edition.]

· The second task is more difficult. It is to explain how these simple chemicals, containing no more than a few tens of molecules at the most, were assembled into the vast and complex structures necessary for life to exist. Even viruses contain up to 10 billion atoms organized in highly specific patterns, while the complex cells of plants and animals each contain between 1 and 100 trillion (i.e., 1012 to 1014) atoms. At present, there is little certainty about where or how this great leap in size and complexity was achieved. Yet it was this change that created true life from organic chemicals. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2250-2254). University of California Press. Kindle Edition.]

· Yet at present it seems unlikely that life itself could have originated in space, where both energy and raw materials are in short supply, thereby ensuring that chemical processes are normally very slow. Besides, many of the chemical reactions vital to life seem to require water in liquid form, and this cannot be found in space. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2260-2263). University of California Press. Kindle Edition.]

· As early as 1871, Darwin suggested that life might have begun in “some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc.” [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2265-2267). University of California Press. Kindle Edition.]

· All these theories are plausible, but none can explain all the steps leading from nonlife to life. And there are problems with the “warm pond” theory, including the fact that the early atmosphere may not have been as favorable to organic evolution as Miller and Urey had supposed—particularly if, as some evidence suggests, the earliest living organisms appeared before 3.8 billion years ago, when the earth’s surface was still being bombarded regularly by extraterrestrial material. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2286-2289). University of California Press. Kindle Edition.]

· The third task, to explain the origins of the genetic code, is even trickier than the previous two. In a sense this is the most fundamental problem of all, for the key to all modern forms of life appears to be a division of labor between nucleotides, which store and read the instructions for making an organism (the genome), and the proteins that use those instructions to construct each individual organism. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2315-2318). University of California Press. Kindle Edition.]

· Crudely speaking, nucleotides handle replication, while proteins handle metabolism. The distinction is almost exactly analogous to the distinction between hardware and software in computing. So, which evolved first, metabolism (chemical activity) or replication (the genetic code)—or did they evolve together? [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2318-2321). University of California Press. Kindle Edition.]

· As Cesare Emiliani points out, the odds of a monkey typing the entire Bible by tapping away randomly for millions of years are almost infinitely low. But if a rule is added saying that each time a correct letter is typed it is locked into position, then the odds change radically, and we can expect a Bible to be produced within a decade. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2328-2330). University of California Press. Kindle Edition.]

· DNA, the key to the genetic code in all living organisms today (except for a few viruses), is a fantastically complex molecule, containing billions of atoms. Untwisted, a single molecule of human DNA would be almost two meters long. The atoms of DNA are arranged in precise patterns that, like a piece of software, contain all the information needed to create a living organism. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2344-2346). University of California Press. Kindle Edition.]

· Explaining how this complex, elaborate, and elegant mechanism was constructed is one of the most challenging tasks facing modern biological theory. One problem is that DNA appears to be helpless on its own. Like any software, it is useless without hardware. So it is difficult to imagine how it could have evolved independently. But there are also problems with the notion that metabolism (the “hardware”) evolved first—in particular, it is hard to see how rough-and-ready evolutionary processes could generate a high level of complexity. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2359-2362). University of California Press. Kindle Edition.]

· life cannot achieve significantly new levels of complexity without a capacity to replicate more precisely. And that leads us back to the argument, despite its difficulties, that perhaps the genetic code came before complex metabolism. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2364-2366). University of California Press. Kindle Edition.]

· Unfortunately, RNA copies itself less accurately than DNA, and this ereates real problems. A system of replication that is good but not quite good enough may be the worst of all possible worlds, because it may be bad enough to accumulate errors and good enough to transmit those errors faithfully to later generations. It has been shown that such a system may lead to breakdown more rapidly than the sloppier forms of replication required in “metabolism first” models of the origins of life. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2373-2377). University of California Press. Kindle Edition.]

· If none of these theories is totally persuasive, we should not be surprised. There doesn’t yet exist a complete theory of the origins of life. In explaining the origins of the genetic code, the key to the emergence of really complex organisms, we are still in difficult territory. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2393-2395). University of California Press. Kindle Edition.]

5 The Evolution of Life And The Biosphere

· After almost 4 billion years of evolution, most living organisms are still simple and small. Bacteria rule, as they always did, and few bacteria are more than a hundredth of a millimeter in diameter. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2426-2428). University of California Press. Kindle Edition.]

· Stephen Jay Gould has argued that even if the appearance of life marks the emergence of new forms of complexity, the history of life on Earth is not merely a story of entities becoming complex. The simplest genetic recipes still work well, so there is no particular evolutionary virtue in complexity. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2431-2434). University of California Press. Kindle Edition.]

· Indeed, in some cases organisms have evolved toward greater simplicity: snakes have lost their legs, moles have lost their eyes, and viruses have lost even the ability to reproduce independently. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2434-2435). University of California Press. Kindle Edition.]

· The story of increasing biological complexity can be told as a series of major transitions. These include the origin of life itself, the appearance of eukaryotic cells, sexual reproduction, the construction of multicellular organisms such as ourselves, and the appearance of organisms that join together in social groups. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2443-2445). University of California Press. Kindle Edition.]

· paleontologists have learned how to find and analyze the tiny “microfossils” of bacteria, and the oldest of these date back 3.5 billion years, close to the earliest signs of life on Earth. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2460-2461). University of California Press. Kindle Edition.]

· Either way, life appeared early. Living organisms probably existed by 3.8 billion years ago, for rocks of this age from Greenland contain a level of the C12 isotope that is normally associated with the presence of life. Life was certainly present by 3.5 billion years ago, the date of rocks from South Africa and Western Australia that seem to contain microfossils of bacteria similar to modern cyanobacteria (i.e., blue-green algae). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2468-2472). University of California Press. Kindle Edition.]

· By 2 billion years ago, free oxygen may have accounted for 3 percent of the gases in the atmosphere; in the last billion years, the level has risen to about 21 percent.12 If there were much more oxygen around, we’d self-ignite if we rubbed our hands together too hard! [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2544-2546). University of California Press. Kindle Edition.]

· In addition, free oxygen, floating high in the atmosphere, eventually created the ozone layer. Though only a few millimeters thick and about 30 kilometers above the earth’s surface, this layer of three-atom oxygen molecules (O3) shielded the earth from much ultraviolet radiation and thus made it easier for life to spread on land as well as in the sea. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2567-2570). University of California Press. Kindle Edition.]

· The first extensive fossil evidence of multicellular organisms dates from the Ediacaran era, ca. 590 million years ago. But the fossil record of multicellular organisms really becomes abundant during the Cambrian era, from ca. 570 million years ago. Quite suddenly, in geological terms, there appeared organisms with protective shells, made from secretions of calcium carbonate. Their shells have survived exceptionally well as fossils. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2683-2686). University of California Press. Kindle Edition.]

· The worldwide appearance of shells marks the beginning of the Cambrian era, but it is hard to tell whether this signals a real flourishing of multicellular organisms or merely the appearance of organisms more likely to be preserved as fossils. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2686-2687). University of California Press. Kindle Edition.]

· The asteroid impact of the late Cretaceous period counts, therefore, as a crucial event in the prehistory of our own species. If the asteroid had been on a slightly different trajectory, say a few minutes faster or slower, mammals would have remained limited in numbers and variety, and our own species could not possibly have evolved. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2815-2817). University of California Press. Kindle Edition.]

· The fossil record suggests that the earliest hominoids appeared roughly 25 million years ago in Africa. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2830-2831). University of California Press. Kindle Edition.]

· Besides, it is abundantly clear that living organisms really have transformed the earth’s surface. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Location 2896). University of California Press. Kindle Edition.]

· For more than 3 billion years, life consisted only of single-celled organisms. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 2973-2974). University of California Press. Kindle Edition.]

6      The Evolution of Humans

· We are animals, we evolved according to Darwinian rules as did any other living organism, and we are remarkably similar to closely related species, such as the other hominoids (the great apes). Yet we are also radically different from even our closest relatives. Somehow or other, our species has moved beyond the Darwinian rules. And this is why our impact on the earth has been far greater than that of any other large organism. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3009-3012). University of California Press. Kindle Edition.]

· Human history marks the sudden and unexpected emergence of a new level of complexity, as did the first appearance of stars, of life on Earth, or of multicelled organisms. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3014-3015). University of California Press. Kindle Edition.]

· Increasing human control of energy has shaped human history and the histories of many other species as well. It has also enabled humans to multiply at an accelerating rate. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3039-3040). University of California Press. Kindle Edition.]

· Resources used by humans are, by definition, unavailable to other species. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Location 3047). University of California Press. Kindle Edition.]

· All species adapt to their environments, but most have only one or two adaptive tricks in their repertoire. In contrast, humans seem to constantly develop new ecological tricks, new ways of extracting resources from their environments. In the jargon of economists, humans seem to have a highly developed capacity for “innovation.” And they innovated not on the Darwinian scale of hundreds of thousands or millions of years, but on a scale ranging from thousands of years to decades and even less time. Our challenge is to explain how, when, and why human beings acquired their new level of ecological creativity. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3087-3091). University of California Press. Kindle Edition.]

· Like many other transitions of this kind, the emergence of our species was quite sudden. On the paleontological scale, it was an almost instantaneous event. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3098-3099). University of California Press. Kindle Edition.]

· we know of no animal that can describe what to do in the abstract—no animal that could explain how to fish for termites without giving a demonstration, or give an account of a pathway without walking along it; and we certainly know of no animal that could describe abstract entities such as gods or quarks or pink elephants. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3104-3106). University of California Press. Kindle Edition.]

· animals without symbolic language may lack the ability humans have to deliberately think about the past and imagine the future. These are severe limitations. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3107-3108). University of California Press. Kindle Edition.]

· Human language, however, allows more precise and efficient transmission of knowledge from brain to brain. That means that humans can share information with great precision, creating a common pool of ecological and technical knowledge, which in turn means that for humans, the benefits of cooperation increasingly tend to outweigh the benefits of competition. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3111-3113). University of California Press. Kindle Edition.]

· Human language, however, allows more precise and efficient transmission of knowledge from brain to brain. That means that humans can share information with great precision, creating a common pool of ecological and technical knowledge, which in turn means that for humans, the benefits of cooperation increasingly tend to outweigh the benefits of competition. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3111-3113). University of California Press. Kindle Edition.]

· Among the most important of these pre-adaptations are sociability, preexisting linguistic skills, bipedalism and dexterous hands, meat eating and hunting, a long period of childhood learning, and large forebrains. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3254-3255). University of California Press. Kindle Edition.]

· At present, most paleontologists are agreed that the decisive feature distinguishing hominines from apes is bipedalism: all known species of hominines are bipedal, while no known species of apes are (though chimps can stand for short periods). [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3291-3293). University of California Press. Kindle Edition.]

· Whatever the causes of bipedalism, the fossil evidence, thin as it is, shows that within 2 million years, a number of bipedal species had appeared. These include the species known as Ardipithecus ramidus ramidus, whose remains were found in Ethiopia in 1994 and dated to ca. 4.4 million years ago. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3313-3315). University of California Press. Kindle Edition.]

· Though australopithecines walked on two legs, close study of their anatomy and particularly their hands has shown that they remained well adapted to life in the trees, and their walking was not yet as efficient as that of modern humans. Even more important, they had small brains, ranging in size from ca. 380 to 450 cubic centimeters. This contrasts with the 300 to 400 cubic centimeters of modern chimps, and an average brain size of 1,350 cubic centimeters for modern humans. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3335-3338). University of California Press. Kindle Edition.]

· in 1960, Jonathan Leakey—the son of Louis Leakey, one of the pioneers of modern studies of human evolution—found a hominine fossil about 1.4 meters tall. Louis Leakey claimed that it belonged to the same genus as human beings (Homo) and therefore christened it Homo habilis, or “handy man.” This made it the oldest species of the genus that includes modern humans. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3377-3379). University of California Press. Kindle Edition.]

· First, associated with Homo habilis he found the earliest evidence for the systematic manufacture and use of stone tools. The skills involved in these activities seemed significantly more complex than those evident among earlier hominines. Second, the brains of habilis were a lot bigger than those of the australopithecines, ranging from 600 to 800 cubic centimeters. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3381-3383). University of California Press. Kindle Edition.]

· Homo habilis seemed to be a tool-using, learning animal, like modern humans; so perhaps the appearance of the new species, about 2.3 million years ago, marked the real beginnings of human history. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3383-3385). University of California Press. Kindle Edition.]

· Making such tools requires considerable planning and experience, much more than is needed to make the simple tools used by chimpanzees. Modern experiments in stone knapping have shown that the original stones need to be chosen carefully, and struck with precision. In fact, making stone tools requires precisely those skills that are the forte of the prefrontal cortex, that part of the brain that was to expand most significantly in human evolution. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3399-3402). University of California Press. Kindle Edition.]

· Why should hominine brains have grown so quickly? Explaining brain growth is harder than it may seem, for large brains are rare—and with good reason. The modern human brain is arguably the most complex single object we know. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3488-3489). University of California Press. Kindle Edition.]

· Each human brain contains perhaps 100 billion nerve cells, as many cells as there are stars in an average galaxy. These connect up with each other (on average, each neuron may be connected to 100 other neurons) to form networks of astonishing complexity that may contain 60,000 miles of linkages. Such a structure can compute in parallel. That means that although each computation may be slower than that of a modern computer, the total number of computations being carried out in a particular moment is much, much greater. While a fast modern computer may be able to complete one billion computations a second, even the brain of a fly at rest can handle at least a hundred times as many! [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3491-3496). University of California Press. Kindle Edition.]

· Neanderthals first appear in the archaeological record about 130,000 years ago, and they vanish from the record as recently as 25,000 years ago. Their brains were as large as, and perhaps even larger than, those of modern humans, but their bodies were tougher and stockier. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3539-3541). University of California Press. Kindle Edition.]

· There are hints of Neanderthal art or burial ritual, both of which might have signaled an increased use of symbolic communication (but the evidence is ambiguous). And there is little sign of great social complexity. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3545-3546). University of California Press. Kindle Edition.]

7 The Beginnings of Human History

· This is murky territory, for language leaves no direct signs in the fossil record; our attempts to understand the evolution of human language depend on ambiguous hints in the fossil record, padded out with a heavy wadding of theory. Not surprisingly, experts disagree even on the fundamental question of when human language first appeared. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3580-3582). University of California Press. Kindle Edition.]

· Human infants acquire language with a speed and fluency that is incompatible with any process of learning by trial and error and that has no parallel among our closest relatives, the chimps. In some sense, it seems, the human capacity for language must be hardwired into our brains, and it must have been wired in quite recently, in evolutionary terms. If so, those interested in hominine evolution must try to explain how a language module evolved. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3592-3595). University of California Press. Kindle Edition.]

· Human brains are certainly different in significant ways from those of apes (not just in their size), but it has proved impossible to locate a distinct “language” module. Language skills appear to be distributed through many different parts of the mind, and their location differs even between individuals. Language seems to be a product of networks of interactions between different parts of the brain, rather than the work of any one language area. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3599-3602). University of California Press. Kindle Edition.]

· Large brains are not enough, however. Symbolic language also requires many other intellectual and physiological skills. These include a capacity to quickly make and process symbolic gestures or sounds and to understand rapid sequences of symbolic sounds uttered by others. How and why could such a coherent and complex set of skills develop together in the comparatively short period of a few million years? [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3618-3621). University of California Press. Kindle Edition.]

· The relatively high larynx of all early hominines suggests that they could not produce the range of sounds (particularly vowels) used by modern humans. If they spoke, they probably did so with a limited vocabulary of words dominated by consonants. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3661-3663). University of California Press. Kindle Edition.]

· Neanderthals had brains as large as humans (see figure 7.1), but studies of the base of Neanderthal skulls suggest that they, too, lacked the capacity to manipulate sounds in the complex ways demanded by modern human languages. And this, combined with the absence of any other unequivocal evidence for extensive symbolic activity among Neanderthals, leads us to believe that Neanderthals did not use a fully developed form of language, though their presence in parts of Ice Age Eurasia indicates that they did have an enhanced capacity to adapt to new environments. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3667-3671). University of California Press. Kindle Edition.]

· When do we first get evidence for the existence of humans that not only looked like modern humans but also behaved and communicated with each other like modern humans? [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3680-3681). University of California Press. Kindle Edition.]

· In recent years, two rather different answers have been available. The first is now a minority position, though it is still defended vigorously by some scholars, including Milford Wolpoff and Alan Thorne. They argue that humans evolved slowly toward their modern forms throughout Afro-Eurasia, over almost a million years. Thus all the hominine remains found throughout Afro-Eurasia in the past million years should be treated as examples of a single, evolving species with regional variants, some of whose features, including skin color and facial characteristics, survive to the present day. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3682-3686). University of California Press. Kindle Edition.]

· A second view, which is currently more popular, is that modern humans appeared more abruptly, somewhere in Africa, between 100,000 and 250,000 years ago. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3691-3693). University of California Press. Kindle Edition.]

· But there is a problem with this theory, too, for most of its supporters agree that evidence of distinctively modern behaviors, including human language, does not appear before the Upper Paleolithic, which began about 50,000 years ago. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3710-3711). University of California Press. Kindle Edition.]

· Fourth, and in some ways most important of all, are indirect signs of symbolic activity, such as the appearance of artistic activity of various kinds, which would have accompanied the use of symbolic language. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3717-3718). University of California Press. Kindle Edition.]

· On the basis of evidence for all these types of change, a number of archaeologists and prehistorians have argued that there was a “revolution of the Upper Paleolithic”: a late, and remarkably sudden, flowering of human creative activity, beginning ca. 50,000 years ago, which marks the true beginning of human history. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3718-3720). University of California Press. Kindle Edition.]

· But why the apparent gap between the appearance of modern humans and the appearance of modern behaviors? This has remained a tantalizing puzzle. It has tempted some scholars to suppose that critical changes may have taken place in the wiring of human brains within the last 100,000 years; [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 3721-3723). University of California Press. Kindle Edition.]

· Recent research suggests that modern humans, equipped with a symbolic language and the capacity for collective learning, appeared in Africa about 250,000 years ago. [David Christian; William H. McNeill, Maps of Time: An Introduction to Big History (Kindle Locations 4175-4176). University of California Press. Kindle Edition.]

الحمد لله الذي بنعمته تتمّ الصَّالِحات