by Bryan Sykes
Adam’s Curse is a book about the Y chromosome, which carries the genes determining the sex of mammals. The title is misleading. There’s only a brief discussion in the final chapter regarding the instability of the Y chromosome (due to mutations), which Sykes predicts will lead to its eventual distinction in 5,000 generations (125,000 years). Most of the book concerns the history and evolutionary function of sex differentiation, the use of the Y chromosome and maternal DNA (carried on the mitochondria*) to trace historic migrations, the phenomenon of “group selection” (whereby individuals are genetically programmed to sacrifice themselves for their species) and the genetic basis of patriarchy and homosexuality.
Because neither maternal DNA nor the Y chromosome undergo recombination** at the time of cell division, both remain highly stable over thousands of generations. This feature been invaluable in tracing the prehistoric migration of Neanderthals, Polynesians, Vikings, Native Americans, Australian aborigines and other population groups. Sykes subscribes to the “selfish gene” theory, which asserts that most of human behavior is directed towards the survival of our unique genetic material, ie our genes drive behavior that favors their survival.
The study of thousands of Y chromosomes reveals that “super-Y” chromosomes occur much more frequently than others. In most cases they’re derived from testosterone-driven warriors (eg Vikings and Mongol warriors like Genghis Khan) who used their aptitude for violence, ruthlessness and wealth acquisition to spread their Y chromosome to a disproportionate number of women.
According to Sykes this “crazed ambition of the Y chromosome” to “multiply without limit” leads to endless wars, land annexation and enslavement of women. As he points out in his introduction, it’s quite rare for women to commitment violent crimes, become tyrants or start wars. He also has grave concerns that this unholy alliance between “super Y chromosomes” and an unchecked drive for wealth and power is leading to imminent planetary destruction.
A British financial analyst recently made the observation that the global economy would still be intact if Lehman Brothers had been Lehman Sisters. Recent studies show women make better financial traders because they’re more risk adverse.
The chapter I found most interesting concerns the genetic origin of sexual reproduction, ie the exchange of genetic material during reproduction, and male and female sexual identity. I was particularly fascinated to learn that organelles like chloroplasts (plants only) and mitochondria were originally bacteria, with their own DNA, that were captured by larger cells. This modification enabled the larger cells to produce much more energy, which allowed them to specialize and become multi-celled organisms.
My second favorite chapter concerns research into the genetic basis of homosexuality. Geneticists have identified an SRY gene on the Y chromosome that switches on testosterone production when the embryo is six weeks of age. Embryos exposed to testosterone develop male sexual organs. Those that aren’t are automatically programmed to become female.
There’s also a brain structure called the bed nucleus of the stria terminalis (BST) which determines a child’s gender identity and sexual orientation. Testosterone exposure during embryonic development causes it to be larger. It’s much smaller in women, homosexuals and transsexuals. Especially after the birth of one or more sons, women develop antibodies to the H-Y antigen on the Y chromosome. These antibodies, in turn, act to lower fetal testosterone levels, resulting in a smaller BST.
*A mitochondria is an organelle found in large numbers in each cell responsible for respiration and energy production.
**DNA recombination involves the exchange of genetic material between different chromosomes or between different regions on the same chromosomes.