Like individuals in a population, species also struggle amongst themselves to survive, and most become extinct over time. Species can also die out in mass extinctions, such as the one that caused the demise of the dinosaurs. Today we may be in the throes of another mass extinction, caused by human overexploitation of habitats... Secret code
Darwin was able to establish natural selection, without any understanding of the genetic mechanisms of inheritance, or the source of novel variation in a population. His own theory on the transmission of traits, called pangenesis, was completely wrong.
It was not until Gregor Mendel and the start of the 20th century that the genetic mechanism of inheritance began to be revealed. We now know that most traits, such as skin colour, eye colour and blood group are determined by our DNA and genes. During the 20th century, evolutionary biologists such as Ernst Mayr, J.B.S. Haldane, Julian Huxley, and Theodosius Dobzhansky combined Darwinian evolution with our emerging knowledge of genetics to produce the "modern synthesis" that we call evolutionary biology today.
Most genes come in a variety of forms, one inherited from each parent. The varieties are known as alleles, and encode slightly different traits. The incidence of different traits, or alleles, in a population is driven by natural selection and genetic drift, which can randomly reduce genetic variation. Today, evolution is defined as the change in the frequency of alleles in populations over time.
New traits are introduced into populations by gene flow from other populations or by mutation. Mutation is a change in the structure of a gene and can be caused by errors in copying DNA, carcinogenic chemicals, viruses, UV-light and radiation. Most mutations are neutral, having no effect on gene function; others are harmful, such as the ones that cause inherited diseases like cystic fibrosis. Rarely mutations can lead to beneficial new traits, such as increased resistance to malaria.
Today evolutionary biologists are largely divided into two camps. The pro-selectionists such as Richard Dawkins, Stephen Pinker, Edward O Wilson, Matt Ridley, Mark Ridley and Jared Diamond believe in the primacy of natural selection as the principle guiding evolution. Others such as Niles Eldredge, Stephen J. Gould, Brian Goodwin, Stuart Kauffman and Steven Rose argue that we are still missing something big, and that natural selection does not explain the full complexity of evolution. Instant Expert: Evolution 11:41 04 September 2006 NewScientist.com news service John Pickrell