This book is a discussion about what our genes can and cannot tell us. A lot of what we can know involves comparing DNA to known sources. What we have trouble knowing is the impact certain genes have on individuals. The news will often report that scientists have discovered a gene for a certain trait. However, this simply indicates there is a statistical relationship between the gene and trait. It may be fairly useless. A large percentage of incarcerated people may have a gene. Yet, if the gene is also prevalent in a large percentage of free people, it doesn't tell us much. Genes will often work together with other genes making it unlikely a single gene will indicate much. We can consider this the start of scientific research rather than the end.
Humanimal looks at humans from an "animal" perspective. How is it that humans came to dominate the world? Use of tools helped, but many other animals have tools. The ability to pass on knowledge from generation to generation ends up being a main factor. He spends a good chunk of time looking at corollary behaviors in other animals. He cautions that people should not justify a human behavior simply because a similar behavior exists in nature. Animals may appear to rape and murder, but without a communicable thought process, there is no way to directly compare. He also spends time looking at sexual behaviors. There are a number of different reproductive mechanisms out there. There are also many instances of animals (including humans) engaging in sexual activity that will not produce offspring. Why is that so? There are some conclusions to that and the question of how homosexuality propagates. He dubunks many explanations, and cautiously presents his preferred explanations. (For example, homosexuals tend to come from larger families.) There are some areas that he decides are not worth touching, and just condemns them out of hand. There are some interesting bits, but it is overall an easily forgettable book.