Geographic isolation is one of the traditional mechanisms invoked for triggering the rise of new species; some experts therefore flatly say that human evolution has ended because in the modern world, no one is really isolated from the rest of humanity. And depending on how it might be applied, culture and technology could either isolate some people from others, or it could help to renormalize them to the rest
Humans haven't really changed the rules of natural selection. We might think that because we have culture--and with it all kinds of medical interventions and technologies--that we are immune from natural selection, but nature proceeds as usual. Evolution is defined as a change in gene frequencies over time, which means that over generations, there will be changes in the gene pool, and humans experience those changes as much as any other organism. Some people live and some people die, and some people pass on more genes than others. Therefore, there is a change in the human gene pool over time.
"But we might suggest that with all that cultural and technological intervention that there would be some kind of influence in the composition of the gene pool, and there is. Take smallpox, for an example. Years ago millions of people died from smallpox, and their genes were not passed on because many of them died before reproductive age. The human gene pool was then missing the genes of those people. But now, since smallpox has been wiped off the planet, people who normally died of the disease now live, probably have children, and thus contribute to the human gene pool. In another example, the birth rate always goes down the more developed, and economically affluent, countries become. Today the highest birth rates are in Latin America, Africa and Asia. People in these places are now the major contributors to the human gene pool. In many generations, the human species will be more composed of genes from those groups than from developed countries.
And so culture, development and medicine might change the tenor of the human gene pool, but they do not take away the force of evolution, the force of change. Also, keep in mind that culture may not seem a 'natural' force, but because it is part of our environment, it is just as natural as disease, weather or food resources. We in developed nations may think we are immune from natural selection because we are so surrounded by material goods and high technology, but this immunity is an illusion. Technology protects us from nothing, and medicine surely hasn't cured all the diseases--just ask the people in Nebraska near the Red River what they think!
