As discussed earlier, a species is a group of closely related organisms that are capable of interbreeding to produce fertile offspring.
Speciation is the evolutionary process by which new and distinct species form. In speciation, the ancestral species splits into two or more descendant species that are genetically different from one another and can no longer interbreed. There are two major modes of speciation, explained in the table on the right:
The formation of the bonobo and common chimpanzee species from their common ancestor 2-3 million years ago is an example of allopatric speciation. Their geographical barrier was the Congo River. Scientists believe there may have been a time where the Congo River depth became so low that a small group of their common ancestor crossed over to its left bank, forming a new colony. The Congo River depth than rose again, and because the common ancestor was believed to dislike swimming (modern-day bonobos and common chimpanzees don’t like swimming), they were unable to get back. Over time, these separate groups of common ancestors evolved, until eventually the separate bonobo and common chimpanzee species were formed.
Bonobos now currently live on the southern side of the Congo River, whilst common chimpanzees live on the northern side: