Mors-
Well, the reason why some monkeys stayed and others grew on is because the was tectonic activity and they got sepperated by the mountans. Some were still living in the forest (today's apes), but some were living in the newly created plane. Where natural selection occured and the most fit to survive did ( the upright apes).
Yes, good response.
Let me elaborate on this.
Thousands of years ago a catastrophic event of some sort had happened, and as a result, the land which was primarily covered by forests, was now turned to mostly flatlands.
Now, the primates that had developed bipedalism, were better adapted to this new enviornment, thus the excelerated growth that they experienced. The bipedal and non-bipedal primates diverged paths and took up different patterns of growth.
Bipedalim was the main key to our superiority on this planet. A common misconception, is that it was a larger brain. But bipedalism allowed the primates to carry various items and as a result they adapted in various new and exciting ways. This lead up to a larger brain in some primate species.
Mostly when one thinks of evolutionary change, what comes to mind is gradual change. But the idea of Punctuated Equilibrium has gained intellectual ground.
According to this idea, new species usually do not arise within the main body of a population, because the genetic exchange between organisms rapidly swamps any new variations. Instead, small subpopulations which are genetically isolated from the main population are more likely to change, because an evolutionary novelty has a much better chance of dominating a small population than a large one.
If a species isolation is long enough, they become so genetically different that when they are reintroduced or reinvade their original homeland (become sympatric), they can no longer interbreed with the ancestors; they have become a new species. This new species may die out quickly, or it may drive its ancestor to extinction, or both may persist side-by-side, typically by exploiting slightly different ecological niches. In paleontological terms, the allopatric speciation model predicts that species arise rapidly (a few hundred to a thousand years, but instantaneous in a geological sense) on the periphery of their range (where they are rarely fossilized). It predicts that the main population (most likely to be fossilized) will show little or no change, but will be suddenly invaded by new species with no apparent transitions between them.
