Evolution on Steroids: Bizarre Fish of the Congo - a wild evolutionary ride that shows no signs of slowing.

One piece of evidence comes from a high-velocity spot just downstream from where the kayakers had paddled. At the calmer edges of the river, Stiassny and her team sampled two groups of a slender species called Teleogramma brichardi. One group was netted from one side and the other from the opposite side. Then Stiassny and Schelly scrutinized the fish back at the Congo Project’s genetics facilities at the Museum. Although the two groups looked nearly identical to each other, at the genetic level the differences were astonishing. Five percent of their DNA units differed. (The DNA of humans and chimpanzees differs by only 1.2 percent.)

This degree of genetic separation indicates that mutations occurring in fish near one riverbank are not being passed to fish near the other bank. That’s a strong clue that the two populations aren’t interbreeding, likely because they can’t cross the powerful current in the center of the channel. Thus, each group is adapting on its own, and evolving in different directions. T. brichardi is well on its way to splitting into two species.