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Darwin's theory of the [[evolution]] of [[species]] through natural selection, starts from the premise that organismic traits vary in a [[nondeterminism|nondeterministic]] among individuals, a process Darwin called "individuation". Darwin did not make any specific claims as to how variation between individuals is generated, but modern [[genetics]] has characterized several mechanisms that can generate such variation: random mutations of the genetic material ([[DNA]]), e.g., can result from errors during its [[replication]] as well as from damage to the DNA generated during the [[transcription]] of genes or caused by chemicals and physical agents (e.g. X rays); and in sexual populations genetic recombination and segregation/syngamy mix the DNA of two parents into that of offspring so that the latter are guaranteed to differ genetically from each other and from their parents.
Although darwinian fitnesss is often thought to be partitionable into an [[ecological selection|ecological ability]] (viability) component and a fecundity component (which includes the [[sexual selection]] component), many traits can be involved in determining more than one fitness component. For example, motor skills not only influence foraging success and survival but often make one attractive to mates. Sexual selection, therefore, can but need not lead to ecologically maladaptative traits. Recent modelling work moreover indicates that even sexual selection for maladaptative traits can have beneficial fitness consequences, e.g., when it leads to assortative mating according to overall gentic quality, wich reduces gentic load (Siller 2002).
Furthmroe
==Mechanisms of natural selection==
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