A fascinating end to a fascinating book, in these last two chapters, Moalem tackles the science behind overweight mice, premature aging, planned obsolescence, the angle of human noses, and water births, while explaining why my iPods always seem to die out after the warranty expires. He ends the book by reflecting on what the evolutionary sciences have done for us, and how understanding of them may help us in the future. While I’ve always been interested in evolution, I feel that this book, more than anything else, has helped me to appreciate it.
Chapter 7 begins by discussing America’s obesity epidemic, and suggesting that genetics, along with diet and exercise, may play a large role in child obesity. Evidence suggests that pregnant womens’ diets have an impact on their childrens’ metabolism. This seemingly Lamarckian idea is illustrated by an experiment conducted in Duke University involving overweight yellow mice. Normally, these mice would mate to produce overweight offspring with yellow fur. However, when a pregnant fat yellow mice was given vitamin supplements, she produced thin brown mice. Though the thin, brown mice’s genes were the same as its parents, the “agouti” gene that had made its parents fat and yellow was turned off through a process called DNA methylation. In methylation, a methyl group binds to a gene and keeps it from expressing itself, effectively turning it off. This study sparked interest in the field of epigenetics, the study of how genes express themselves and how this can be affected by external factors. Lamarckian examples of evolution in nature include voles whose coat is thick or thin depending on when it was born, desert locusts whose size depends on the availability of food detected by their mothers, and a species of lizard whose size depends on whether or not its mother smelled a lizard-eating snake while pregnant. David Barker, a medical professor, proposed the thrifty phenotype hypothesis. This hypothesis states that fetuses that are given poor nutrition develop metabolisms that store energy faster. Further research has shown that though methylation, children can even be affected by the environment their grandparents lived in. In my opinion, the most interesting example of how the environment of pregnant women can affect their children is that the male birthrates tends to drop in times of stress, and increase in times of conflict. These studies convinced scientists to start the Human Epigenome Project (the successor to the completed Human Genome Project) to find every spot on the human genome where methyl markers can attach.
Chapter 8 deals with aging and childbirth; death and life. It introduces Seth Cook, a twelve year old with a tragic condition known as progeria that causes premature aging. Scientists have identified the gene that, when defective, causes progeria. This gene produces lamin A, a protein that provides structural support for the nuclear membrane. The existence of this gene is taken by many scientists to mean that we are “programmed to die”; dubbed biogenic obsolescence. The purpose of biogenic obsolescence is to “make room” in a population for younger organisms, and eliminating members of the population that have accumulated parasites. The second half of the chapter discusses human childbirth. Moalem explains that human childbirth is much more difficult than that of other animals because compared to our primate cousins, our adults have smaller pelvises, and our infants have larger heads and exit the birthing canal facing away from their mothers. It is accepted in the scientific community that humans have smaller pelvises because they are bipedal. However, there is debate as to why exactly we evolved to be bipedal. The conventional theory states that when humans left the dense African forests for the savanna, they needed a way to scan for food and their height gave them this advantage. It also claims that we lost our fur because with it, human males would be too hot while hunting, and that being bipedal made humans faster. Elaine Morgan challenged this theory in her book The Descent of Woman, believing that this theory was centered on the male. She pointed out that there are many fast quadrupeds with fur, and that women have even less hair than men, even though they don’t hunt. The marine biologist Alister Hardy proposed a different theory. He claimed that water played a large role in early human evolution. According to Hardy’s theory, we lost our hair to be able to swim better, and became bipedal so our heads could come over the surface of the water. There is even evidence to show that women can safely give birth in the water.
If water births have so many advantages over “conventional” births, why aren’t they the medical standard? How is the aquatic ape hypothesis received in the scientific community? Is there a way to slow aging by keeping the Lamin A-producing gene active?