WEIT Chap3

What are vestigial organs ?

cf. p.56

Vestigial organs occur because inherit their anatomy from their ancestors, they are traces of an organism's evolutionary history. A trait can be vestigial and fuctional at the same time. It is vestigial because it no longer performs the function for which it evolved.
Example: Flightless birds have wings and they have exaclty the same bones as in wings of species that can fly. In some birds, wings don't seem to have any function, they're just remnants. In others, wings have new fuctions. Ostriches can't fly, but they still use their wings when they run, for balance or to protect thier babies from the sun. In penguins, the ancestral wings are now flippers.

other examples might be usefulPierre.brawand 19 avril 2011 à 22:44 (CEST)

What are atavisms ?

p.56 ss.

Sporadically expressed remnants of ancestral features. Difference with vestigial traits : occur only occasionally. Has to recapitulate an ancestral trait. Come from reexpression of genes that were functional in ancestors but were silenced by natural selection when no longer needed.

These dormant genes can be reawakened when something goes awry in the development but the information is degraded during the time it remains unused in the genome.

Examples :

" coccygeal projection " known as the human tail : we still carry a developmental program for making tails but those genes are deactivated in human fetuses.

Why do all flightless birds have wings ?

cf. p.57

Are vestigial traits useless?

cf. p.58

Why haven't vestigial organs completely disappeared?

cf. p.59

---

back to Evolution_3BIbDF01-02_10/11
back to Accueil