| Darwin's Second Theory: sexual selection and genetic evolution |
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| Written by Administrator |
| Tuesday, 24 July 2007 05:21 |
 Charles Darwin This asymmetry creates an enormous amount of competition between the sexes. And that pressure has consequences. Professor Cherry will be presenting a Darwin Seminar at the University of Cape Town on 6 August. The series is a joint initiative of the Africa Genome Education Institute and the Division of Human Genetics at the University of Cape Town. His topic is "Sexual Selection -Darwin's Second Theory." Charles Darwin produced two great theories on the underlying pressures stimulating genetic inheritance. The first was his "On the Origin of Species", published in 1859, which introduced the concept of natural selection. This focused on how environmental pressures and competition for resources favoured some individuals over others. The pace of evolution varies between species: extremely rapidly in bacteria and viruses as they evolve to overcome your body's defences (causing you to get sick every winter); very slowly in larger animals. Darwin's second book was "The Descent of Man", released in 1871. Here Darwin introduced the idea of sexual selection, illustrated by the characteristics of plumage in birds. Professor Cherry refers to this as Darwin's Second Theory. "Sexual selection," says Professor Cherry, "is selection for any character which confers an advantage of increased matings on individuals which have that character." The most famous sexual selection example used by Darwin is that of the peacock's tail. If the tail gets too big then it becomes dangerous for the bird as it can't escape predators, or forage efficiently. Yet, the fact that it does have such a large and showy tail indicates that it is a superior bird. Females recognise this and will choose to mate with it, so passing on these superior genes to the next generation. "We do have to distinguish between biological and cultural evolution," he says. Humans have "confused" some of the instinctive criteria used in mate choice We no longer mate exclusively to produce offspring, and we even sometimes deliberately act to disguise ourselves using perfumes, hairstyles and elaborate clothing. This isn't a new phenomenon. Clonycavan Man, a prehistoric Iron Age Irishman murdered 2 300 years ago and his body thrown into a peat bog, has his hair styled in a Mohawk with a resin that would have to have been imported from France. This ability to control our immediate environment has reinforced the idea that we can control our world. "This notion is a fallacy. We are certainly more able to modify our environment than other species, but the evidence of climate change disputes our ability to control the world." The study of sexual selection has a wide range of applications. Marketers regularly play on the differences between the sexes, along the way stimulating the production of books like, "Men are from Mars, Women are from Venus." Professor Cherry works primarily on sexual selection in sugarbirds and ostriches but will, during his presentation, be discussing human characteristics as well. "As humans, a fundamental part of our nature is a desire to understand ourselves," says Professor Cherry. Sexual selection has created immense evolutionary pressure altering not just our appearance but also our cultures, societies and interactions with each other. The Darwin Seminar on August 6 will help us to understand these forces. |