Louis Bolk revisited. II--Retardation, hypermorphosis and body proportions of humans.

A number of morphological particularities of humans, generally thought to be specializations produced by natural selection, arguably are instances of hypermorphosis: alterations in proportion brought about by simple prolongation of general embryonic allometries. The descended larynx, the flattened human chest, and several limb proportions are given as examples. The case of the human foot, often quoted as an example of advanced specialization in humans, is examined in some more detail. Besides, it is argued that the human growth pattern displays a unique 7-year periodicity unlikely to be the result of the erratics of Darwinian evolution. Developmental acceleration is the unavoidable correlate of animal specialization; it brings about the breakdown of the periodicity present in the generalized humanlike development and causes the embryonic allometries to be cut off prematurely in the non-human mammal.