Human and Mammalian Evolution: Is There a Difference?

This short essay, by John de Vos and Jelle W.F. Reumer, is another from the book I'm reading. I found it interesting and will just sum it up.

From ancient times to the present, there has been a conceit regarding the place of humans in the world. De Vos and Reumer state this nicely as follows:

When God created the world, he did so in a succession of different steps. The creation of animals was one such step. The creation of mankind was another one. Ever since, mankind has been considered (i.e., has considered itself) not to be part of the animal kingdom. This notion—that Homo sapiens is a species next to, above, or outside the mammalian world—has long perverted science. Ernst Haeckel's famous "Stammbaum des Menschen/Pedigree of Man," published in 1874, shows "man" in the highest branch of the tree, above the rest of the living world, although part of the apes.

Commendably, these authors prefer to study humans as mammals, and their research shows that, in the past, environmental changes affected humans just as much as other mammals. The Pliocene period, 5.3 to 2.6 million years ago, entailed a cooling of the planet, during which forests were transformed to grassy plains in the American prairies, the Eurasian steppes and the African savannahs. Horses and antelopes evolved from smaller, shorter-legged animals to have longer legs, new dental characteristics and increased socialization. The Pliocene, with its increase in grasslands, was also the time of origin for early hominids such as Australopithecus.

Thus, both the evolution of human bipedalism and erect posture on the one hand, and of the long-legged running gait in horses on the other, are the result of Miocene-through-Pleistocene climate change in conjunction with the reduction of forest ecosystems and increase in open habitats....Humans, antelopes and horses are mammals that adapted to a new environment, and their evolution reflects their convergences.

There are also parallels between humans and other mammals seen in studies of island paleontology:

Although the mechanisms leading to observed phenomena remain unclear, these studies have given rise to what is called the "Island Rule." That is, in general, small mammals (shrews, hedgehogs, rodents, leporids) become larger when isolated on islands, and large mammals (elephantids, hippopotamids, bovids, cervids) become smaller....Although until fairly recently one might have wondered if humans would be an exception to the Island Rule, the possibility emerged with the discovery of the remains of a Late Pleistocene hominid on the Indonesian island of Flores....Claims of microcephaly notwithstanding, the specimens are more reasonably seen as evidence of island dwarfing and of a separate species.

During the Late Pleistocene, many large mammals became woolly: the woolly mammoth, woolly rhinoceros, musk ox and cave bear. At that time, the climate was cold and dry. But at the end of the Pleistocene, the climate became warmer, and most of the woolly species became extinct. As a speculative matter, the authors suggest that Homo neanderthalensis, which had evolved during the Pleistocene, may also have been "woolly," and became extinct along with the other woolly mammals.

The point of the authors is that large mammals are large mammals, and there are probably convergences when different species experience the same environmental changes. From a scientific point of view, I think this is fairly obvious – though it would be heresy to many.