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Parts one and two discussed the genetically specified foundations of our unique cultural traits. We saw that those foundations include our familiar skeletal hallmarks, such as our large braincase and our adaptations for upright gait. They also include features of our soft tissues, behaviour, and endocrinology concerned with reproduction and social organization. But if those genetically specified features were our sole distinctions, we would not stand out among animals, and we would not now be threatening the survival of ourselves and other species. Other animals, such as ostriches, walk erect on two legs. Others have relatively large brains, though not as large as ours. Others live monogamously in colonies (many seabirds), or are very long-lived (albatrosses and tortoises).

Instead, our uniqueness lies in the cultural traits that rest on those genetic foundations and that in turn give us our power. Our cultural hallmarks include spoken language, art, tool-based technology, and agriculture. But if we stopped there, we would have a one-sided and self-congratulatory view of our uniqueness. The hallmarks I just mentioned are ones that we are proud of. Yet the archaeological record shows the introduction of agriculture to have been a mixed blessing, seriously harming many people while benefitting others. Chemical abuse is a wholly ugly human hallmark. At least it does not threaten our survival, as do two of our other cultural practices: genocide, and mass exterminations of other species. We are uncomfortable about whether to regard these as occasional pathological aberrations, or as features no less basic to humanity than the traits we are proudest of.

All of these cultural traits that define humanity are seemingly absent in animals, even in our closest relatives. They must have arisen some time after our ancestors parted company from the other chimpanzees around seven million years ago. Furthermore, while we have no way of knowing whether Neanderthals spoke or indulged in drug abuse and genocide, they certainly did not have agriculture, art, or the capacity to build radios. These latter traits must therefore be very recent human innovations of the last few tens of thousands of years. However they could not have arisen from nothing. There had to have been animal precursors, if we could, only recognize them.

For each of our defining cultural traits, we need to ask, what were those precursors? When in our ancestry did the trait approach its modern form? What were the early stages of its evolution like, and can those stages be traced archaeologically? We are unique on Earth, but how unique are we in the universe?

Our two most dangerous traits, genocide and environmental destruction, will be reserved for discussion in Parts Four and Five. Here we will consider some of the above-mentioned questions for our noble, two-edged, or only mildly destructive characteristics. Chapter Eight takes up the origin of spoken language, which I suggested in Chapter Two might have triggered the Great Leap Forward, and which anyone would list among our most important distinctions from animals. On first reflection, the task of tracing the development of human language appears plainly impossible. Language before the dawn of writing left no archaeological remains, unlike our first experiments in art, agriculture, and tools. There seems to be no surviving simple human language, no animal language, that could exemplify the early stages.

In fact, there are innumerable animal precursors: the vocal communication systems evolved by many species. We are just beginning to appreciate the sophistication of some of these systems. We shall also see that there really are some simple languages that modern humans have unconsciously invented and that prove unexpectedly instructive. Taken together, these complex animal 'languages' and simple human languages begin to bridge, from both sides, the apparent chasm with respect to speech between animals and ourselves.

Chapter Nine turns to the origin of art, the noblest human invention. There seems to be a gulf separating human art, supposedly createdjust for pleasure and doing nothing to perpetuate our genes, from any animal behaviour. Yet paintings and drawings created by captive apes and elephants, whatever the motives of those animal artists, look so similar to work of human artists that they have fooled experts and have been bought by art collectors. If one nevertheless dismisses those animal artworks as unnatural productions, what is one to say about the carefully arranged coloured displays of normal male bowerbirds? Those bowers play an unquestioned crucial role in passing on genes. I shall argue that human art also had that role originally, and often still does today. Since art, unlike language, does show up in archaeological deposits, we know that human art did not proliferate until the time of the Great Leap Forward.

Agriculture, the subject of Chapter Ten, has an animal precedent, but not precursor, in the gardens of leaf-hopper ants, which lie far off from our direct lineage. The archaeological record lets us date our 'reinvention' of agriculture to a time long after the Great Leap Forward, within the last 10,000 years. That transition from hunting and gathering to agriculture is generally considered a decisive step in our progress, when we at last acquired the stable food supply and leisure time prerequisite to the great accomplishments of modern civilization. In fact, careful examination of that transition suggests another conclusion: for most people the transition brought infectious diseases, malnutrition, and a shorter lifespan. For human society in general it worsened the relative lot of women and introduced class-based inequality. More than any other milestone along the path from chimpanzeehood to humanity, agriculture inextricably combines causes of our rise and our fall.

Abuse of toxic chemicals is a widespread human hallmark documented only within the last 5,000 years, though it may well go back much earlier into pre-agricultural times. Unlike agriculture, it does not even rank as a mixed blessing but as a pure evil threatening the survival of individuals, though not of our species. Like art, drug abuse seems at first to lack animal precedents or biological functions. I shall argue in Chapter Eleven, however, that it fits into a broad class of animal structures or behaviours that are dangerous to their owners or practitioners, and whose function depends paradoxically on that danger. While animal precursors can thus be identified for all of our hallmarks, they still rank as human hallmarks because we are unique on Earth in the extreme degree to which we have developed them. How unique are we in the universe? Once conditions suitable for life exist on a planet, how likely are intelligent, technologically advanced life forms to evolve? Was their emergence on Earth practically inevitable, and do they now exist on innumerable planets circling other stars?

There is no direct way to prove whether creatures capable of language, art, agriculture, or drug abuse exist elsewhere in the universe, because from Earth we could not detect the existence of those traits on planets of other stars. However, we might be able to detect high technology elsewhere in the universe if it included our own capacity to send out space probes and interstellar electromagnetic signals. In Chapter Twelve I shall examine the on-going search for extraterrestrial intelligent life. I shall argue that evidence from a quite different fieldstudies of woodpecker evolution on Earthinstructs us about the inevitability of evolving intelligent life, and hence about our uniqueness, not only on Earth but also in the accessible universe.

SEVEN WHY DO WE GROW OLD AND DIE? | The rise and fall of the third chimpanzee | EIGHT BRIDGES TO HUMAN LANGUAGE