| UP A GUM TREE WITH A DOWN POUCH. Dawkins notes that the koala pouch "opens downwards, instead of upwards as in a kangaroo." This
is "not a good idea in an animal that spends its time clinging to tree trunks." Dawkins' explanation for this apparent anomaly is: "Koalas are descended from a wombat like ancestor. Wombats are champion diggers." He then goes on to explain that it has not been
possible for evolution to change the back facing wombat pouch into a forward facing one. Dawkins suggests "the embryological
upheaval attendant on such a major change would render the intermediates even worse off than the koala coping with the existing
state of affairs."
(Dawkins, Greatest Show, pp 369-370) ED. COM. Since us Aussies who live with Koalas in our backyards don't ever worry about "drop bears" hitting us on the heads when we walk under gum trees, perhaps some local knowledge will help. It is obvious that Dawkins' faith in evolution as the explanation for all things is rather limited as he is able to believe evolution could turn the wombat pouch around when it was evolving from a possum-like creature with front facing pouch, so that the wombat pouch does not fill with dirt while it digs burrows. But evolution has not been able to do the reverse when the wombat evolved into a tree climbing Koala. He ignores the fact that a back facing pouch is also a good idea for a gum tree climber. Koalas have short legs, so when they climb trees their abdomens are close to the surface of the tree, if not actually scraping it. If the koala pouch opened upwards the pouch would collect bark and other detritus as the koala moved about the tree. When they are not moving (which is most of the time) they sit, well supported, in forks of trees, rather than spending their time "clinging to tree trunks". And lastly the koala pouch is well equipped with a strong muscle around the opening to keep it closed so the babies are not in danger of falling out, Dawkins should consider the whole animal, including its behaviour, not just one feature when assessing what is good and bad design. (Ref. marsupials, mammals, reproduction) |
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