Instead, scientists believe that biology played a far greater role in the evolution of species than external factors like prehistoric climate change. After conducting "DNA-clock" studies, which revealed that new species evolved at very variable rates, the scientists were able to conclude that external factors can only have had a limited impact on evolution.
This study's remit was not to put forward new theories, but Professor Jim Mallet, UCL Department of Biology, argues that his team's work shows that factors other than climate change play the greatest role in species evolution. He said: "Different types of rainforest butterflies in the Amazon basin are evolving at very different rates, not at all the pattern expected if forest refuges during the ice ages were causing the origin of new species the reason normally given. Instead, we think that idiosyncratic features of the biology of each species, such as competition for food and their individual reactions to the environment dictate the pattern of evolution in each group."
Professor Mallet and PhD student Alaine Whinnett tested the "DNA clock" using the mitochondrial DNA of nine different butterfly species groups [genera] on the eastern side of the Andes in Eastern Peru. By using a "DNA clock" the scientists were able to calculate the age of the species within each group of species. If the DNA is similar between any pair of species, they must have split recently. If the DNA has diverged a great deal between species, the species are probably ancient.