Researchers Asger Hobolth (North Carolina State University, Raleigh, NC, USA), Ole Fredslund Christensen and Mikkel Heide Schierup (University of Aarhus, Jutland, Denmark), and Thomas Mailund (University of Oxford, UK) published their conclusions in the Public Library of Science journal PLoS Genetics. Their research article is entitled “Genetic relationships and speciation times of human, chimpanzee and gorilla inferred from a coalescent Hidden Markov Model”. (The abstract of the paper appears at Public Library of Science: PLoS Genetics.)

They stated within their paper that the “recent speciation time of human-chimp” (that is, the time when humans and chimps genetically separated with respect to their common ancestors) was about 4.1 million years, plus or minus 0.4 million years.

The researchers used a statistical calculation that, although commonly used elsewhere, had not been used before in genetics research. The hidden Markov model (HMM), developed in the 1960s, is a statistical model that assumes the modeled system (in this case, evolutionary progression of humans and chimps) is a Markov process; that is, a random process where all future states of the process depends only on the present state and not on any past states.

Based on this mathematical technique, the researchers showed that beginning about four million years ago humans were able to become a separate species within a span of only 400,000 years. Even though this occurred, humans and chimpanzees still today are over 95% identical with respect to their DNA (deoxyribonucleic acid)—the substance that possesses an organism’s genetic information.

Past studies have generally shown that humans and chimps separated on the evolutionary ladder around five to seven million years ago. Most evolutionary theorists contend that humans and chimpanzees became separate species after the separation of orangutans and gorillas, the next nearest relative to humans.

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