Chapters 10-12


Language is a medium of culture that allows us to think more effectively about the world we live in, just as it did for our ancestors. There is no question that language emerged from evolutionary forces, but the answer to why or when it arose is unable to be discovered, to a degree.

Language may not be uniquely human, as it is commonly believed. Chimps have been proven to be able to invent new names for objects by generalizing, and they show a preference for ordering the words in their conversation. This was all discovered through experimentation with trying to teach them language, which was a success, despite their inability to speak. This inability to speak does not mean that we can dismiss their capability for language due to the factors mentioned above.

Leakey and Lewin make a point that the structure in which people operated was provided by a group culture that would have been impossible without a language to construct it. We can see the sign of emerging language in our history by looking at both the brains and the tools of our ancestors. There are structural changes to the brain, specifically the Broca’s and Wernicke’s areas that indicate a shift toward language. It is also clear to the authors that somewhere along the way, our past social and economic needs would have been much more easily satisfied if language were prevalent. They also suggest that language development may have followed a similar pattern to stone tool development, mirroring advances in technology.


Homo sapiens is the only creature for which sex is an activity rather than just a preoccupation. The aim of individuals in evolution is to produce as many surviving offspring as possible. When it comes to evolutionary pressures, it is becoming clear that evolution acts on the individual rather than the population, because it is about an individual’s genes being passed on into the gene pool, which can only be accomplished by maximizing the number of offspring. For simple biological reasons, this often leads to female investment in offspring to be significantly higher than male investment, a pattern that is repeated throughout the animal world.

This fact has led to a “battle of the sexes”, of sorts. The female has a higher investment in her offspring, meaning that she has less of a chance to desert her mate. The concept of polygamy more often leads to one male with many females (polygyny) due to his ability to release a large amount of sperm in a short time period. In the animal kingdom, this is far more frequent than either monogamy or polyandry.

Depending on the species, it may be seen as more beneficial to have offspring of a specific sex, which leads to systematic infanticide being common. This also happens in specific social structures involving harem owners who want all the offspring in their group to be their own, as they would not want to have any investment in another individual’s offspring.

It is likely that early Homo had a sex life similar to chimpanzees, in which the men were fully promiscuous and there was nothing even close to monogamy. There would have been competition among the males, although the extent was not known at the time this book was written due to lack of information about the sexual dimorphism that was present. Yet, as time went on, males started to have more investment in child rearing as kinship became more prevalent. Somewhere along the way, human females became interested in sex all the time, contrary to what is seen in other primates. The female orgasm is also something that is unique to humans in the animal world. One theory states that the evolutionary force that caused us to become naked could have been in order to increase stimulation during sex. This increased sexuality may have been a way to increase the bond that led to more male investment. Despite all these findings, the authors do not take a stance on whether or not monogamy is the natural state of humans.


If it was not already clear throughout the book, this chapter finally summarizes the authors’ views on the Hunting Hypothesis, which they are against. They mention that the widely held view that the transition to Homo sapiens did not take place in Europe as believed by many. They discuss the evolutionary failures of the period in which Homo sapiens came about, including the Neanderthals, primarily brought about by increased competition for resources when one species had a distinct advantage.

With the retreat of the ice sheet, agriculture was able to develop, launching the world into an industrial and technological revolution. This agriculture was developed simultaneously around the world and diffused from there rather than being concentrated in just one place.

The final topics covered in the book are those of aggression and warfare, and whether or not these are innate human things. It was widely believed that it is in our nature to be aggressive, and that once stone tools were developed, it would be impossible to prevent them being used as deadly forces against others of the same species. Leakey and Lewin acknowledge that human evolution has been driven by aggression and warfare, but they also point out a number of examples in which one would expect aggression that does not come about, such as in submitting to a superior fighter. They claim that the costs of fighting are, in many cases, too high too justify. This leads them to decide that it is not an unwavering instinct that humans must take out on each other through violence and warfare. They also differentiate between aggression and organized warfare, as well as explaining away traditions of cannibalism that have been prevalent throughout history.