GeologyRocks

Individuals with extreme trait values have greatest fitness. E.g. selection on bill size in the black-bellied seedcracker – Pyrenestes o. ostrinus. This species of African finch exhibits non-sex related polymorphism in bill size. Members of the species have either one of two bill morphs; bills are relatively small or relatively large. The morphs feed on different sized seeds and this is directly related to natural selection on bill size.