While it is unclear how intelligence evolved, it is clear that it happened sometime in the last five million years, when the to-be homo-sapiens separated from their next closest relatives - chimpanzees. It is also clear that intelligence bears costs, as well as benefits, and has so far proven to represent a very successful niche in the global web of life. It requires a large, cumbersome and delicate brain to be carried around, but also allows unprecedented dynamic adaption of behavior - and the ability to manipulate the environment instead of just adapting to it.
The link between race and intelligence has always been a contentious issue. Various tests show provocative and differing levels between average intelligences of various races, while no tests have yet been devised which measure intelligence independently of culture.
In fact it seems highly likely that intelligence (or at least the ability to think abstractly) is equally shared between most of the races on the planet. Different races have adapted differences in various characteristics for various environments - shade of skin, for varying sunlight, varying body shapes for climate, differing emotional temperaments for different environments and so on. The ability to analyse situations and to think abstractly, however, would be an advantage in any environment. Hence it seems highly likely that these genes would be selected for in all races, provided that the trade-off was not too great in other areas (eg - making the brain too cumbersome).
So it seems likely that any race which had genes for extra intelligence available, adopted them. The exceptions may have been the isolated races which did not have the genes available. The genes may have arisen naturally in these population pools of course, but we would expect to see this very occur much more slowly.
So isolated populations would adapt more slowly than those with a larger gene pool to borrow from. The human populations of Europe, Asia, and Africa were joined by land, by trade, and by frequent invasions which carried genetic riches with them. One gene could be produced in any of these continents, and be spread through all of the other populations.
The Native Americans and the Australian Aborigines did not have the same advantage. While the population of the Americas was quite large, and may have allowed a respectable rate of adaption for the local population, the small Australian Aboriginal population of 300,000 may have greatly reduced their ability to adapt. The forbears of the Australian Aborigine are believed to have arrived in Australia about 60,000 years ago when there was a land-bridge, or partial land-bridge to Papua New Guinea during one of the ice-ages. Thereafter there was almost no contact (and presumably little opportunity to share genes) with the outside world.
In Tasmania, the Aboriginal population was even lower, and it has been suggested that they were well on their way to extinction, having lost the ability to fish and the ability to make clothes (beyond throwing animal skins over themselves), in a harsh environment which may have been made considerably more hospitable with greater technology.
Ironically the inability to adapt is also one of the criticisms of the Australian Aboriginal culture - that its fragility and inflexibility have resulted in its collapse.
See