Raevmo
Posts: 235
Joined: Oct. 2006
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| Quote (Zachriel @ Nov. 10 2009,12:37) | | Quote | jerry: it takes over 20 million years to form a new species
Mark Frank: Where did you get that figure? |
Most likely by reading a quote-mine somewhere.
| Quote | Prager & Wilson, Slow evolutionary loss of the potential for interspecific hybridization in birds, PNAS 1975:
Birds have lost the potential for interspecific hybridization slowly... it is inferred that the average hybridization species pair diverged from a common ancestor about 22 million years ago. The corresponding period for frog species pairs capable of hybridization is about 21 million years, while for hybridizable placental mammals it is only 2 to 3 million years. Thus birds resemble frogs in having lost the potential for interspecific hybridization about 10 times as slowly as have mammals. |
The key phrase is interspecific hybridization (meaning between different species). |
A plausible explanation is that in mammals there is more scope for mother-offspring genetic conflict while the offspring are in utero. Offspring genes (especially those inherited from the father) are selected to suck lots of resources from mom, while maternal genes might prefer to spread them around more evenly over multiple litters. This might lead to a kind of genetic arms race that might in turn lead to interspecific genetic divergence and incompatibility. This wouldn't work in frogs or birds, where the offspring have much less opportunity to 'force' the mother in handing out the good stuff.
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After much reflection I finally realized that the best way to describe the cause of the universe is: the great I AM.
--GilDodgen
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