This book was published in 1998, which is a long time ago in the fast-moving field of paleoanthropology, so I hesitated before checking it out. However, I like Ian Tattersall’s books, and decided I would take a chance on it. It turned out to be worth reading, because much of the book focuses on the big picture of how we became the humans we are today, which is not likely to be overturned by new developments in the field. Even the parts which are out of date based on current scholarship are worthwhile for the light they shed on the experts’ evolving ideas of our relationships with humanity’s distant ancestors.
The key characteristics which make humans different from all our relatives, living and dead, are physiological, social, and mental. The causal factors behind them are climate change, migrations that isolated certain populations, walking upright, and the ability to master fire, which allowed meat to be cooked, increasing its nutritional value and providing an energy surplus that led to larger brains. Bigger brains, in turn, allowed for more complex social behaviors such as improved weapons (stone-tipped spears instead of sharp sticks), and a more sophisticated ability to coordinate complex behaviors such as hunting. These, along with modifications to the larnyx, paved the way for speech. The nightly campfire was more than just a safety feature to keep wild animals away; it also facilitated group social developments such as storytelling, teaching, and the creation of myths which coalesced into religions.
Since this book was published the scholarly opinion about Neanderthals’ mental capabilities has changed significantly. They now seem to have been much closer to Homo sapiens than was previously thought, with an ability for speech and symbolic thought. If you are of European ancestry about 1.5% of your genome comes from the Neanderthal lineage, so interbreeding was clearly possible. There are, however, still important differences, some of them the result of indirect and circumstantial evidence, such as the fact that Neanderthal bones show far more damage than contemporary human ones. The fact that many of the broken bones were healed indicates that they had a social organization sufficiently advanced to take care of their injured, but it also seems to indicate a more primitive hunting style, where the hunters had to get within stabbing range of large, angry animals. An alternative could have been the atlatl, or spear-thrower, which could launch attacks from up to 100 meters away, though it was most accurate when used at shorter ranges. It has been attested in H. sapiens sites as far back as 30,000 years ago, and it may be much older, but there is no evidence Neanderthals ever used it.
Ian Tattersall is a strong proponent of the Out of Africa hypothesis. In it Homo erectus is believed to have evolved from H. habilis about two million years ago, and several H. erectus migrations from Africa are known from the fossil record, one of which, about 600,000 years ago, gave rise to the Neanderthals and Denisovans (who were unknown when this book was written) and possibly other species that exist today as ghosts in our genome. H. sapiens evolved from the African branch of H. erectus about 300,000 years ago and 50,000 years ago one group of them led the great migration west into Europe, north into Siberia, and east into Asia. Out of Africa is still, without a doubt, the dominant theory supported by most paleoanthropologists. There is a minority opinion, however, the multi-regional hypothesis, which has some archaeological evidence to support it. Madelaine Böhme’s 2020 book Ancient Bones discusses the theory for a general reading audience.
Tattersall is also a proponent of a critical mass theory of consciousness. Our closest cousins, the chimpanzees and bonobos, show impressive mental abilities, including tool use and complex social behaviors. They are however, very different from humans, particularly in their ability to use symbolic thinking. Part of this is no doubt because of the physical limitations imposed by a brain of only about 450 cm3 (about the same as our Australopithecine ancestors five million years ago), while in modern humans it is around 1400 cm3.
What caused the dramatic increase in humans, with all its attendant consequences? Tattersall believes in the punctuated equilibrium model proposed, in its modern form, by Stephen Jay Gould and Niles Eldredge. It says that stable environments evolve animals which are ideally suited for them, so there are no ecological pressures that would give survival and reproductive advantages to the kind of minor mutational differences that evolution produces. Two things, however, could cause rapid evolutionary changes, one of which is a population that gets isolated from the rest of its species, so that whatever random mutations were originally present in it, and which otherwise would have been merged back into its larger parent population, get passed down and enhanced if they are beneficial, leading eventually to new species.
The other possibility is an external environmental change, such as early humans faced when East Africa went through wet and dry cycles in what was geologically very quick succession. Under such situations evolution would favor even minor changes so long as they helped improve survival chances. It is possible that under these environmental pressures larger brains, with their greater cognitive and social capacities, might have been selected for, and if a slightly larger brain has advantages, an even larger one has even more, and so on. Our chimpanzee relatives, safe in their jungle forests, did not face similar pressures, and had no reason to evolve larger brains.
Eventually, as brains got larger and more sophisticated, a threshold was crossed and one of the Homo species, probably H. erectus, gained an ability for abstract thought, speech, complex social arrangements, and much more. It has been a long, strange trip to the present, and while modern humans have much to be proud of in our achievements, it is a sobering thought to consider that all of our progress and sophistication may have been the result of random changes in weather patterns millions of years ago. A bit of humility is definitely called for.