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Loss of external genitalia in bird evolution

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Published on Jun 6, 2013

External genital anatomy evolves rapidly and is remarkably diverse among animals that reproduce by internal fertilization. One of the most intriguing evolutionary transitions is the reduction and loss of the penis in most birds, despite their dependence on internal fertilization. A new study by evolutionary developmental biologists at the University of Florida reports that embryos of bird species with reduced genitalia have increased activity of genes that control programmed cell death (apoptosis) in the developing phallus. This leads to a wave of cell death that arrests outgrowth and causes regression of the phallus at embryonic stages. These findings identify a potential mechanism for reduction of the phallus during bird evolution.

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