Ridley asserts that the differences between species are in the genes, and while genes do not totally control behavior, they do play a part. Monogamy also shaped our hunting/gathering habits and a “sexual division of labor” began to emerge. The human population developed different methods of sexual selection from the other two species, such as a more monogamous system and attraction to more youthful mates. One population developed a genetic mutation (the fusing of two chromosomes) that prevented the two populations from breeding and thereby forming a new species that eventually became the human species. The point in time that the split occurred is unclear, but it is clear that after some barrier, whether geological or otherwise, a chimpanzee population split. This being said, humans and chimps genetically are 98% the same. However, evolution is based on the principle of optimizing one’s adaptations to one’s environment and has no pinnacle.

“Humans are an ecological success,” because our 300 million tons of biomass is only rivaled by domestic animals and we have colonized virtually every habitat.

Therefore some religious figures believe that the human soul is somewhere near the centromere of Chromosome 2. Coincidentally, apes such as gorillas and chimpanzees have 24 chromosomes to our 23, because the human Chromosome #2 is a slightly modified fusion of two ape chromosomes. In the middle part of the twentieth century, there were thought to be 24 chromosomes in the human genome.

In conclusion, Ridley says that “life has a physical history, not a genealogical one” and that the history of life is written in the genome. However, since bacteria do not conform to the laws of genetic inheritance because they “steal genes” from one another (which used to cause evolutionary competition to be between genes rather than species, but now it is more of a team sport), Luca is now believed to be more of a protozoan, because bacteria would have dropped the extra RNA in order to reproduce more quickly, playing to possibly their greatest evolutionary strength. LUCA has been believed to be a bacterium living in a hot marine environment. LUCA, the Last Universal Common Ancestor, is then introduced. RNA is much more chemically active and automatic than DNA, but it is also unstable, therefore prehistoric “ribo-organisms” came up with DNA through an evolutionary trial and error process because it was faster, more accurate, and more reliable. Ridley then begins talking about the history of life, beginning with RNA, which came before DNA. He says that DNA is analogous to written languages: it is written linearly, read from left to right (or right to left), and there is an alphabet (although it is 22 letters shorter than the English version). Ridley begins the chapter with a parody of the beginning of the Biblical book of Genesis, with “In the beginning was the word.” and later reveals that the “word” is RNA, not DNA.

Ridley genome