Friday, March 17, 2006
Waddington's "The evolution of adaptations" gives a logical explanation of how ostrich callosities may have become hereditary but specifically refers only to those found "fore and aft" on the underside of the body.
On page 37 of "The Great Evolution Mystery" Gordon Rattray Taylor goes on to say:
Curiously, it [the ostrich] also has calluses on its ankles which are of no use to it, as it turns its foot sideways when sitting. They may, however, have been functional long ago when the ostrich had three toes and probably did not turn its feet over.
Yesterday's post, Re: The evolution of adaptations (Waddington) (2), describes how the callosities could have become hereditary from the perspective of the proposed internal evolutionary mechanism (the end result of the process being restoration of the 'localized area of equilibrium' to its initial state).
There is, of course, no "Law of Use and Disuse". But if, for example, consideration is given to the degeneration of the eye and loss of pigmentation in cavefish, then why have the ankle calluses of ostriches 'persisted' if they were "functional long ago"?
The answer is simple: When the ankle calluses became hereditary in the three-toed ostrich then contact between those areas and the ground would no longer have affected the 'localized area of equilibrium at the apex of the homeostatic hierarchy'.
During the transition from the three-toed to the two-toed ostrich the ankle calluses would still have had no affect upon the localized 'area of equilibrium'. Consequently, they are still there.
Eye degeneration and loss of pigmentation in cavefish, on the other hand, are examples of 'negative equilibrium' affecting the localized area and will be discussed in a future post.
This is the third of three posts on Waddington's "The evolution of adaptations". The other two are at:
The title link of all three posts goes to the Main Blog entry for Waddington's paper and this link goes to the paper itself.