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Convergence: Wallabies do have placentas as well as milk that does placenta jobs


From Sara Reardon at Nature:

Wallabies are kicking over scientific conventions surrounding mammalian placentas, the organ responsible for protecting and nourishing a developing fetus. A study finds that contrary to what scientists thought previously, mother tammar wallabies (Macropus eugenii) have both a functioning internal placenta and milk that performs some of the organ’s usual roles.

Taxonomists usually separate marsupials — including kangaroos, wallabies and wombats — from placental mammals, also known as eutherians, such as mice and people. The separation is based partly on a supposed lack of a placenta in marsupials. But many researchers think that this distinction is incorrect, noting that marsupials develop simple, placenta-like structures during the end of pregnancy, just before the underdeveloped baby crawls from the uterus into the mother’s pouch. More.

Which they presumably developed without reference to placental mammals.

See also: Lee Spetner: What challenges do convergent evolution and antibiotic resistance pose to Darwinian evolution?


Evolution appears to converge on goals—but in Darwinian terms, is that possible?

From a 'teleological' point of view, all of this easily makes sense; but, not from a strictly Darwinian view, which would reckon that the marsupial reproductive system happened by chance. Just think what would happen if a pregnant mother were 'hopping around' all day long; think of all the 'g-forces' created. What would happen to the embryo? Well, when the embryo is small in size, and, hence, small in 'mass,' then the force of gravity, being proportional to mass, would not be so great. However, the point will be reached when the forces created by gravity might begin to undermine, e.g., placental attachment, and the placenta itself might get highly tangled within the womb. So, it would make sense--reason would dictate!--that the better and safer strategy for a viable offspring would be for that small-sized embryo to relocate itself to a pouch, where all the bouncing around would not dislodge it from anywhere. This would represent a 'tweak' to the placental system, but would not necessarily require changing other parts of the placental reproductive system. Now, all this would require is an "intelligent designer." PaV

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