Artificial selection is the selective breeding carried out by humans to alter a population. It is a procedure often used in agriculture: artificial selection has been used to alter the number of eggs [..]

The term 'meiotic drive' refers to any process which causes some alleles to be over-represented in the gametes which are formed during meiosis. With normal Mendelian segregation at a genetic [..]

Evolutionary classification is a synthesis of the phenetic and phylogenetic principles. The school therefore describes itself as synthetic, drawing on the advantages, and avoiding the shortcomings, of [..]

A homology is a character shared between species that was also present in their common ancestor. This can be contrasted with an homoplasy, which is a convergent character shared between species but no [..]

An isolating mechanism is any property of two species that stops them from interbreeding. They are fundamental to the biological species concept. Biologists distinguish between prezygotic and postzygo [..]

Kin selection is the theory put forward by the biologist W.D. Hamilton to explain the problem of altruism. The theory is as follows: Suppose that a rare gene for altruism is present in an individual. [..]

Imagine that at any time there is an optimum state that the members of a species could have; a genotype with that optimum has fitness wopt; it is defined such that wopt = 1. But the genotype that is n [..]

The French naturalist Jean-Baptiste Lamarck (1744-1829) was one of the key influences on Darwin's thought. Lamarck's most important book was the Philosophie Zoologique (1809) in which he arg [..]

Lamarckian inheritance is a synonym for the idea of the inheritance of acquired characters. As an organism develops, it acquires many individual characters, due to its particular history of accidents, [..]

The separation of an individual's two genes at a locus into its offspring is called segregation. Mendel (pictured opposite) demonstrated that, for every character, an organism inherits an allele [..]