What makes two species different?

For most of the 20th century, scientists believed that the reproductive incompatibility between species evolved gradually as a by-product of adapting to different environments. New research has shown there are more factors at play – specifically the presence of ‘selfish genes,’ whose flow among species may dictate whether two species converge or diverge.

There is much in that article that represents bad science journalism. Part of it may be due to reliance on university press release hype, and part of it may be due to the pressure on scientists to hype their research. Perhaps the original paper is better?