Human Evolution: A Very Short Introduction (Very Short Introductions) 2nd Edition
For an author used to the luxury of lengthy academic papers, the occasional 500-page monograph, and to the protection afforded by technical language and multiple qualifications, boiling down human evolutionary history to the size constraints and style of a VSI is a considerable challenge. Much has changed in our understanding of human evolution in the decade or so since the first edition, and I am grateful to my undergraduate and graduate students for helping me keep up with those advances. One of the main differences between now and thirteen years ago, apart from the recovery of new fossils, is methodological developments. Advances in molecular biology have made a major impact on human evolution research. Molecular biology has not only helped resolve the relationships among the great apes, but improvements in the recovery and analysis of ancient DNA have added a powerful tool to help us understand more recent (less than a million years) human evolution. Special thanks to Brenda Bradley for helping me understand the implications of these developments. I am also grateful to Eve Boyle, Matthew Goodrum, David Patterson, Osbjorn Pearson, Peter Ungar, and Mark Weiss for their advice and expertise.
This book is for my family and my teachers, young and old, living and dead.
Finally, many thanks to Carol for her understanding.
Reason is replaced by faith
After the collapse of the Roman Empire reason-based explanations for the creation of the world and of humanity were effectively replaced by faith-based ones. The Genesis narrative is well known: God created humans in the form of a man, Adam, and then a woman, Eve, and, because they were the result of God’s handiwork, Adam and Eve must have come equipped with language and with rational and cultured minds. According to this version of the origin of humanity, the first humans were able to live together in harmony, and they possessed all the mental and moral capacities that, according to the biblical narrative, set humanity above and apart from other animals.
The biblical explanation for the different types of modern humans is that they originated when Noah’s offspring migrated to different parts of the world after the last big biblical flood, or deluge. The Latin for ‘flood’ is diluvium, which is why we call anything ancient ‘antediluvial’ (i.e. it came ‘before the flood’). Explanations involving successive floods had implications for the study of fossils. All the animals created after a flood must inevitably perish at the time of the next flood, so ‘antediluvial’ animals should never coexist with the animals that replaced them. With very few exceptions Western philosophers living in and immediately after the Dark Ages (5th to 12th centuries) supported a biblical explanation for the origin of humanity, yet not long after the scientific method began to be applied to the study of human origins (see below) some religious groups doubled down on biblical literalism. This resulted in the movement we call ‘Creationism’, and in the enterprise described, ironically, by its participants as ‘Creation Science’.
During the Dark Ages some of the Greek classical texts that had survived in Europe were translated into Arabic. Some of these were later translated into Latin, which made them accessible to people like the 13th-century Italian Christian philosopher Thomas Aquinas, who integrated Greek ideas about nature and modern humans with interpretations based on the Bible.
The move away from reliance on biblical dogma was especially important for those who were interested in what we now call the natural sciences, such as biology and the earth sciences. English philosopher Francis Bacon was a major influence on the way scientific investigations developed. Theologians use the deductive method: they begin with a belief, then deduce the consequences of that belief. Bacon, who summarized his suggestions about how the world should be investigated in aphorisms that are set out in his Novum Organum or True Suggestions for the Interpretation of Nature, published in 1620, suggested that scientists should use the ‘inductive’ method. Induction begins with observations, also called evidence or ‘data’, then scientists devise explanations, or ‘hypotheses’, to explain those observations. They test the hypotheses by making more observations, which in sciences like chemistry, physics, and biology means conducting experiments. This inductive way of doing things is the way the sciences involved in human evolution research are meant to work, but in historical sciences like palaeontology you cannot conduct experiments. So, as far as you can, you test hypotheses about processes by gathering evidence about how the world works today, and then assume it worked the same way in the past.
Anatomy starts to become scientific
Nearly three-quarters of a century before Bacon published this advice, a major change had already occurred in anatomy, one of the natural sciences that contributes to understanding human evolution. That change was brought about by Andreas Vesalius, who was born in 1514 in what is now Belgium. Vesalius’ own anatomy education was typical for the time: the professor sat in his chair (hence professorships are called ‘chairs’) and read out loud from the only locally available textbook a safe distance from a human body that was being dissected by an assistant. After finishing his medical studies in 1537, Vesalius moved to Padua, Italy, to teach anatomy and surgery. Although Chinese, Greek, and Islamic scholars had begun to assemble reliable descriptions of human anatomy, it did not take long for Vesalius to realize that the textbooks used by his professors were based on a confusing mixture of human, monkey, and dog anatomy that had been assembled by Galen, so he resolved to write his own, accurate, human anatomy book. Vesalius’ seven-volume De Humani Corporis Fabrica Libri Septem, or ‘On the Fabric of the Human Body’, was published in 1543. The Fabrica is one of the greatest achievements in the history of biology, and Vesalius’ careful recording of his own dissections meant that researchers had access to reliable information about the structure of the human body.
One of the implications of interpreting the Genesis narrative literally is that the world, and therefore humanity, had a remarkably short history. The best-known biblically based chronology was published in 1650 by James Ussher, then archbishop of Armagh in Ireland. Ussher used the number of ‘begats’ in the Book of Genesis to calculate the precise year of the act of Creation: according to his arithmetic it was 4004 bce. Subsequently another theologian, John Lightfoot, part of the University of Cambridge in England, refined Ussher’s estimate and declared that the act of Creation took place at precisely 9 a.m. on 23 October 4004 bce.
The Industrial Revolution hastened the development of geology in the sense that the excavations involved in making the ‘cuttings’ for canals and railroads exposed previously hidden rock formations. Pioneer geologists such as William Smith and James Hutton paved the way for Charles Lyell in 1830 to set out a rational version of the history of the earth in The Principles of Geology, a book that profoundly influenced Charles Darwin. Lyell’s book promoted fluvialism and uniformitarianism as alternatives to biblically based diluvial explanations for the state of the landscape. Fluvialism suggested that erosion by rivers and streams had played a major role in shaping the contours of the earth, and the principle of uniformitarianism suggested that processes such as erosion and volcanism that we see in action today were the same ones that shaped the earth’s surface in the past. Lyell also championed the principle that, barring obvious major upheavals, rocks and strata increase in age the further down they are in a geological sequence. The same principle applies to any fossils or stone tools contained within those rocks, so unless there is evidence that fossils were deliberately buried, the lower in a sequence of rocks a fossil is, the older it is likely to be.
The implications of the new science of geology were profound. There was no need to invoke the biblical floods or divine intervention to explain the appearance of the earth. The pioneer geologists of the time also suggested that it would have taken the processes that shape the earth’s surface a lot longer than the 6,000 years implied by the Genesis narrative to produce the valleys, canyons, and mountain ranges we see today.
Classical Greek and Roman writers had recognized the existence of fossils, but they mostly interpreted them as remnants of the ancient monsters that figure prominently in their myths and legends. By the 18th century geologists began to accept that life-like structures in rocks were the remains of extinct animals and plants, and there was no need to invoke supernatural reasons for their existence. As noted earlier in the chapter, the diluvial theory does not allow for any mixing of modern and ancient, or antediluvial, animals, so the presence in the same strata of fossil evidence of extinct animals together with fossils of creatures similar to living forms effectively refuted the diluvial explanation.
In addition to the conclusions reached by pioneer geologists about the age and history of the earth, several other factors influenced 17th- and 18th-century scientists to consider alternatives to the Genesis account of human origins. Explorers were returning from distant lands with eye-witness accounts of modern humans living in crude shelters, using simple tools, and existing by hunting and gathering. This was so far from the state of humanity in their homeland that European travellers described the people they observed as living in a state of ‘savagery’. According to the Genesis narrative, no human beings created by God should be living in such a state.
List of illustrations
2 Finding our place
3 Fossil hominins: their discovery and context
4 Fossil hominins: analysis and interpretation
5 Early hominins: possible and probable
6 Archaic and transitional hominins
7 Pre-modern Homo
8 Modern Homo
9 The future of human evolution
Timeline of important events and discoveries relevant to human origins and evolution
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