Saturday, March 27, 2010

The Battle of the Hominins

Fossil records give evidence that humans evolved from common ancestors with chimps. Several species of hominins arose from this common ancestor. H. erectus was the first species of hominin to leave Africa. "H. erectus was a highly successful species, not only in population size but in longevity. It was around for one and a half million years, disappearing from the fossil record about 300,000 years ago" (Coyne, 205). Also, it is thought to have left two decendents: H. heidelbergensis, and later H. neanderthalensis (around 230,000 years ago). Then, they disappeared around 28,000 years ago. Their disappearance is associated with the rise of another species: Homo sapiens. There are two theories surrounding the disappearance of the other hominins. Explain both the Multiregional theory and the Out of Africa theory. Also, describe the selective advantages of H. sapiens.

1 comment:

  1. The multiregional theory is that H. erectus (and possibly H. neanderthalensis) populations evolved into H. sapiens independently in several areas. This could of happened if "natural selection was acting in the same way all over Asia, Europe, and Africa" (Coyne 206) on hominins. This theory is very similar to the idea that there was an EEA: the "Environment of Evolutionary Adaptedness." This is because under the multiregional theory, conditions in Europe, Africa, and Asia had to be very similar for a while, in order to have natural selection work in several places in the same way, and the EEA proposes that "over the millions of years of human evolution, the environment, both physical and social, was relatively constant" (Coyne, 245). The first proposes that much of the world was the same before H. sapiens, and the latter proposes that much of the world was the same after they arrived. Components of this theory are that H. erectus are direct ancestors to modern humans, and that modern human variation has been accumulating for over a million years, since when the first H. erectus populations split up.
    The out of Africa theory is that after H. sapiens originated in Africa, they spread to Europe and Asia, and then caused the extinction of all other hominins, by either killing or outcompeting them for food. Components of this theory are that H. sapiens arose in only one place(Africa), and that modern human variation has only been accumulating for less than a 100,000 years, ever since H. sapiens first left Africa.
    The multiregional theory predicts fifteen times more genetic difference between races than the out of Africa theory.
    Selective advantages of H. sapiens included their height: early H. sapien males were anywhere from 4-12 inches taller than Neanderthals. This was an advantage because they could reach new food sources (for instance, trees whose lowest branches were still high), and gave them better climbing skills (longer limbs makes it easier to climb). Also, early H. sapien skeletons and musculature are in general less massive than Neanderthals. This was an advantage because H. sapiens would have carried less weight, and thus had more speed. Also, an advantage for H. sapiens was that they were better with tools. Whereas Neanderthals used stone tools with little variation between them, early H. sapiens used diverse stone tools, along with tools made from bone, antler, and ivory. This advancement in tools allowed for more available food for H. sapiens, because they could hunt more dangerous animals and could fish.

    Why Evolution is True