Radcliffe Emerson

The latest scientific studies say homo sapiens first appeared 100,000 years ago, rather than 10,000.

GeoTheo

I agree that discussions on Eugenics becomes very controversial very quickly and usually has racist undertones. I am not an advocate of it at all.
To some extent though, I have no reason to believe, that the selective breeding of humans would not produce similar effects as the selective breeding of domestic animals. The serious ethical problems involved is what prevents this. Interestingly though, domestic animals have lots of genetic problems. They are bred with different goals in mind and various trade offs occur. What would be the goal of how humans should be bred to be like and what would be the trade offs?
Another aspect of human evolution is that reproductive success is not related to other measures of success. Many people lead very fulfilling lives and contribute much to the success of society and never bear children.
There are other social animals of which this is true, like wolves, various mongooses, ants and other animals that posess a type of altruism but none to the same degree as humans.

Dr S

I have no reason to believe, that the selective breeding of humans would not produce similar effects as the selective breeding of domestic animals.
Sure it would, humans are just as much an animal as every other animal on this planet.
Anyway there has been selective breeding of humans through evolution. Just like Galapagos tortoises and Darwin's finches humans of the same species (there once were other species of humans but they are now extinct) have become geographically separated. This isolation forces selective breeding. Eventually these groups would evolve into separate species. But there hasn't been enough time for that at this point. I'm sure you would have no trouble telling if a person was from Africa or Asia or Europe just by looking at them. You could probably tell the difference between someone from Spain and someone from Ireland just by their appearance. Not unlike separate breeds in dogs and cats. If these breeds were controlled long enough Saint Bernards and Pugs would become different species altogether.
Interesting enough in the past hundred years this geographic separation of humans has ceased to be an issue due to technology. This will probably alter the course of human evolution as much as the initial separation of groups did.

MrDarwin

Yes, I suppose that's what I was saying, except not about the likelihood, just about any possibility of a segregate population becoming isolated from a parental population. But my main point was not about the large population, it was about the small population. Speciation is made possible by (and may only be possible with) the establishment of a relatively small population somewhere apart from a larger population of the same species with which it might otherwise interbreed, e.g., a pregnant female fly that lands on an oceanic island thousands of miles away from the mainland, and the population from which that fly came.

I don't necessarily agree that "large populations may tend to resist adaptive evolution". In plants, at least, large populations (usually meaning a species occurring over a wide range) tend to be quite diverse, with local populations being adapted to slightly different climates or habitats than other populations of the same species at other geographic localities. In other words, different parts of the population are evolving under slightly different selective pressures, and working with slightly different raw material (mutations). But overall these populations are more or less continuous, as is the range of variation. Now, if the climate changes or the species is otherwise forced to shrink into several smaller populations that are isolated from each other, these populations will already differ because they were already adapted to different climates or habitats. And under unfavorable or rapidly changing conditions, in combination with a smaller population size, natural selection may greatly speed up the genetic makeup of these populations, even in the absence of new mutations.

But even locally, many species show a high degree of heterozygosity, possibly due to gene flow from other populations. And a very common pattern in the group I work with is that a genus will have a few common, widespread, and variable species, with several locally restricted and morphologically distinct species that seem to be derived from one of those species. I think this is one reason why cladistic analysis is so difficult with plants: a single original population may give rise to several segregate species, all drawing from more or less the same original pool of genetic variation, and in many cases the parental population may remain relatively unchanged (if genetically diverse) even as multiple new species (which are genetically more uniform) segregate from it over time.

This may also account for the fact that closely related species are often morphologically very distinct, even though they are capable of interbreeding and may even produce fully fertile progeny when they are artificially hybridized. In the wild, however, they don't interbreed, because they are isolated geographically, or use different pollinators, or flower at different times of the year.

GeoTheo

Dr. S:
Sorry for the lack of clarity. This another way of saying what I said without the double negative: I have reason to believe, that the selective breeding of humans would produce similar effects as the selective breeding of domestic animals. So, We agree.

Peez

Certainly it is thought that speciation would be rare (and might require particular circumstances) unless populations are reproductively isolated, but population size is not necessarily part of the equation. For example, a large population in North America isolated from a large population of the same species in Asia could easily evolve to become separate species. Of course, it is also possible to have large evolutionary changes without speciation (although the punk eek people might not agree). It depends on the level of gene flow. Different parts of a "continuous" population may be essentially reproductively isolated. However, if there is appreciable gene flow then large evolutionary changes are unlikely (that is why speciation typically requires reproductive isolation). It is not the small size of the population per se that makes it prone to rapid evolution (I presume that this is what you meant), rather it is the homogeneity of its habitat. A smaller population is more likely to inhabit a relatively homogenous habitat than a larger one, simply because the larger one will probably cover a greater area and so will be more likely to live in some areas with different conditions. A large population that is all under the same selection regime is expected to evolve adaptations just as fast as a small one (unless you go with punk eek), and might move faster if you take mutation rates into account. Very interesting, this demonstrates how simple models of bifurcating speciation should not blind us to more complex patterns of descent. It also brings up the issue of selection at higher levels, but let's not go there just now. [quote]This may also account for the fact that closely related species are often morphologically very distinct, even though they are capable of interbreeding and may even produce fully fertile progeny when they are artificially hybridized. In the wild, however, they don't interbreed, because they are isolated geographically, or use different pollinators, or flower at different times of the year.[quote]Defining species in plants is always a challenge, that's why I work with animals.

Peez

lpetrich

Part of the dating discrepancy consists of how various Late-Pleistocene fossils are to be classified. Are the Neanderthals and similar forms members of our species or members of different ones? (Homo sapiens neanderthalensis vs. Homo neanderthalensis).

It's the old problem of where variation inside of a species ends and a new species begins, but with the difficulty of not having many specimens to work from.