School papers, Essays, Dissertations/biology questions...
How could human activities lead to speciation? Provide a specific example of how this could happen over time.
I assume this question has to do with speciation among human populations, so I'll deal with that most directly.
Speciation most often occurs when two populations of the same species become separated for many generations. Both selective pressures in their different environments and simple genetic drift over a long enough period of time will eventually lead to their becoming reproductively isolated genetically and behaviorally, as well as geographically. If two or more populations of humans remained sufficiently separated that there was no genetic or cultural flow between them, they could, over a very long period of time, become separate species that were unable to reproduce even if they later came back into contact.
I think such an event is unlikely now that the world is so interconnected and long-distance travel is so commonplace. It would take a catastrophic event to reduce human populations to small, isolated pockets of survival, and the isolation would have to continue for many generations--a very long time for a species with such a long reproductive cycle.
That said, I think the differences in races that are apparent, especially regarding such things as physical stature, skin color, and facial structure are the result of different populations of humans having been effectively isolated for many generations with very little, if any, gene flow among them. Homo sapiens may very well have been in the process of speciation when it was halted by modern exploration and travel that re-exposed these populations to each other and enabled a resumption of significant gene flow worldwide.
And the selection would not only have been a result of selective pressures in the physical environment such as those that produced short and stocky Inuits in the Arctic and tall and lanky tribesmen in hot climates. In any species that is strongly sexually dimorphic, it is highly likely that sexual selection plays a role as well, and H. sapiens is strongly sexually dimorphic.
Had the different races remained geographically separated forever, they would eventually have become so different genetically, physically, and behaviorally that they would have been reproductively isolated from each other. And that kind of reproductive isolation is how we most often define "species" in sexually reproducing critters.
Now, if the question has to do with how human activities might bring about speciation in other animal populations, I think we need to look no further than the dog. Certain pure breeds of dog have been kept apart deliberately for quite a long time and have become quite dissimilar physically. While they are not genetically incompatible as yet, I think it is reasonable to say as a practical matter that Great Danes and Chihuahuas are mechanically incapable of reproducing with each other entirely of their own volition. It would have to be done by artificial insemination or by members of the two breeds copulating with critters nearer their own size until reproduction produced a male and a female close enough in size to achieve physical mating. But if dog breeders keep populations of the two breeds separate for a sufficient number of generations, they will eventually become genetically, as well as mechanically, isolated.
Incidentally, the wild morphological differences among dog breeds is a very strong argument in favor of evolution. It has not taken very long at all to produce such differences via human selection. It certainly gives the lie to the religionists' insistence that there has not been enough time on earth for evolution to account for the biological diversity we find.
Hope this helps.