Is it possible for humans and chimpanzees to interbreed?
Genetic analysis suggests there may have been a long period of crossbreeding between early ancestors of the humans and chimpanzees, before they finally split into the Homo and Pan (chimp) genera around six million years ago. But today, although humans and chimpanzees share 99 per cent of the DNA sequences that code for proteins, that DNA is packaged differently into the chromosomes. The human chromosome number two is actually two ape chromosomes joined end-to-end, and nine other chromosomes have inverted sequences of genes compared with their equivalents in chimps. Humans and chimps also have differences in their individual genes that are far bigger than the differences between any two unrelated humans.
These are big obstacles, but not necessarily insurmountable. Other animals with comparable genetic differences, such as zebras and horses, have bred successfully in the past, although the offspring are almost always sterile. There are documented cases of Soviet experiments in the 1920s where artificial insemination was attempted using female chimps and human sperm. However, none of these experiments resulted in a pregnancy, much less the birth of a ‘humanzee’. There are various urban legends of other later experiments in different labs worldwide, but there’s no evidence that the result was ever any different.
Chimp skull (left) compared to a human