THE LINEAGE OF MAN
be little doubt as to their relatively close relationship. The alternative possibilities, either that fishes were derived from four-footed amphibious animals, much as whales have been derived from mammals, or that air-breathing fishes and four-footed animals represent entirely distinct groups of vertebrates, have been carefully considered by those best qualified to weigh the evidence and have been rejected for excellent reasons.
We must infer, then, that some adventurous pioneers among the early air-breathing fishes managed to crawl out of the muddy waters at times when either the supply of oxygen in the water or the supply of living food there was insufficient; that at such times these creatures wriggled along on their bellies much as some eel-like fishes do now under similar circumstances, except that they used the stout fore and hind paddles to increase their hold on the mud and to assist in pushing the body forward. From that time on, the stout fan-shaped fore-paddles began to be bent at the future elbows and wrists, while the hind paddles were bent in the opposite directions at the future knees and ankles; meanwhile the fan-shaped bony rods of the paddles broke into segments and gave rise to the bones of the fingers and toes.
In many of the earliest land-living vertebrates there were five principal rods or digits on each hand and foot, and possibly a small nodule or reduced ray in front of the thumb or the great toe, and another behind the little finger or the little toe; but these extra digits in most lines of animals were early reduced to vestiges, so that the five-rayed hand and foot became the standard form. Thus man in common with other vertebrates has inherited the basic pattern of his five-fingered hand and five-toed foot from the earliest land-living vertebrates, perhaps of the days
[ 279 ]
