Some species, such as giraffe or bottlenose dolphin, are immediately recognizable and might seem absolute, whereas other species, such as bonobo and chimpanzee, seem very closely related. In fact, Darwin in his 1859 book wrote about “strongly-marked varieties” as contrasted with “doubtful species”––when he was considering the boundary between what we would now consider “conspecific populations” (or subspecies) and sibling species (i.e. distinct “sin-offs”).
In this latter category, regional populations of giraffe with distinct patterns of their coats have only recently been recognized as four different species, and the number of species represented by what we recognize as “the bottlenose dolphin” (20 or one?) is still open to question. Authors [see attached article] describe the relationship between two other iconic species in unprecedented detail, comparing whole genomes from populations of bonobo (Pan paniscus) and chimpanzee (Pan troglodytes). They report evidence for gene flow between these species––contributing to our increasing appreciation for the complexities of the process of speciation.
Authors analyzed (in high-coverage) whole genomes of 75 wild-born chimpanzees and bonobos from 10 countries in Africa. They found that chimpanzee population substructure makes genetic information a good predictor of geographic origin at country and regional scales. Multiple lines of evidence suggest that gene flow occurred from bonobos into the ancestors of central and eastern chimpanzees between 200,000 and 550,000 years ago––probably with subsequent spread into Nigeria-Cameroon chimpanzees. Together with another, possibly more recent contact (after 200,000 years ago), bonobos contributed less than 1% to the central chimpanzee genomes. Admixture thus appears to have been widespread during hominid evolution.
Science 28 Oct 2o16; 354: 477–481 and editorial, pp 414–415