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The big issues

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Development is the process through which an embryo becomes an adult organism and eventually dies. Through development, an organism's genotype is expressed as a phenotype, exposing genes to the action of natural selection.

Studies of development are important to evolutionary biology for several reasons:

Explaining major evolutionary change
Changes in the genes controlling development can have major effects on the morphology of the adult organism. Because these effects are so significant, scientists suspect that changes in developmental genes have helped bring about large-scale evolutionary transformations. Developmental changes may help explain, for example, how some hoofed mammals evolved into ocean-dwellers, how water plants invaded the land, and how small, armored invertebrates evolved wings.

Mutated fly with two pairs of wings Mutated fly with legs instead of antennae
Mutations in the genes that control fruit fly development can cause major morphology changes, such as two pairs of wings instead of one. Another developmental gene mutation can cause fruit flies to have legs where the antennae normally are, as shown in the fly on the right.

Learning about evolutionary history
An organism's development may contain clues about its history that biologists can use to build evolutionary trees.

Developmental stages of embryos
Characters displayed by embryos such as these may help untangle patterns of relationship among the lineages.

Limiting evolutionary change
Developmental processes may constrain evolution, preventing certain characters from evolving in certain lineages. For example, development may help explain why there are no truly six-fingered tetrapods.

Embryos image after an original by Michael Richardson et al; Fruit fly images courtesy of Jean-Michel Muratet, Syndicat National des Ophtalmologistes de France (SNOF).

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Learn more about evolution and development in context: Why the eye?, a case study.

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