Since life first evolved on Earth, a huge number of species have developed only to subsequently become extinct, a key feature of Darwin's 'survival of the fittest' model of evolution. A number of species face extinction today - is it right for mankind to intervene to try and stop this process?

Saying that natural selection favors the "fittest" creatures makes it sound like interfering would obviously be bad because it would risk diminishing a good thing, namely fitness. But first of all, there is nothing in Darwin's explanation of natural selection that assigns any value, positive or negative, to reproductive fitness. The central idea, of course, is that when genetically passed-on traits cause members of a species to have more descendents than others, the traits become more common. That has nothing at all to do with whether the outcome is "for the best" in any sense. It's just what will in fact happen. And secondly, the role of humans in a way changes nothing: we are part of the enviroment, and our behavior affects the natural selection of other species fundamentally no differently from any other environmental factor. Our fondness for juicy oranges or annoyance with intrusive coyotes can explain why certain organisms have more or fewer offspring than others in the same way...