One of the greatest influences on Evolutionary Thought:
"The evolutionary biologist Ernst Mayr died on 3 February at the age of 100, after a short illness. A hugely prolific writer and researcher, he was instrumental in developing modern ideas in evolutionary theory."
"It was Mayr who defined a species as a group of individuals that are capable of breeding with one another, but not with others outside the group. This led to the idea that new species can arise when an existing species becomes separated into two populations that gradually become too distinct to interbreed; it was an answer to a biological conundrum that had eluded Charles Darwin."
Excerpts from: Nature. February 2005; | doi:10.1038/news050131-19