« WEIT Chap3 » : différence entre les versions
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Examples: Flightless birds have wings and they have exactly 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 their babies from the sun. In penguins, the ancestral wings are now flippers. Another vestigial feature that proves evolution is the appendix. This organ, also known as the vermiform, is a thin cylinder that forms the end of the pouch that is situated at the junction of our small and large intestines. It was used before by the herbivorous animals and our leaf-eating ancestors but has no value for humans any more. This is why it's a vestigial organ. | Examples: Flightless birds have wings and they have exactly 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 their babies from the sun. In penguins, the ancestral wings are now flippers. Another vestigial feature that proves evolution is the appendix. This organ, also known as the vermiform, is a thin cylinder that forms the end of the pouch that is situated at the junction of our small and large intestines. It was used before by the herbivorous animals and our leaf-eating ancestors but has no value for humans any more. This is why it's a vestigial organ. | ||
== How come the vestigial organs appear? == | == How come the vestigial organs appear? == | ||
=What are atavisms ?= | =What are atavisms ?= | ||
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cf. p.59 | cf. p.59 | ||
Version du 12 mai 2011 à 10:30
What are vestigial organs ?
cf. p.56
Vestigial organs are so called not because they have no function but because "it no longer performs the function for which it evolved".
These organs are present because our organim has inherited them from the anatomy of their ancestors. They are traces of an organism's evolutionary history.
Examples: Flightless birds have wings and they have exactly 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 their babies from the sun. In penguins, the ancestral wings are now flippers. Another vestigial feature that proves evolution is the appendix. This organ, also known as the vermiform, is a thin cylinder that forms the end of the pouch that is situated at the junction of our small and large intestines. It was used before by the herbivorous animals and our leaf-eating ancestors but has no value for humans any more. This is why it's a vestigial organ.
== How come the vestigial organs appear? ==
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.
Dead genes
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