To calculate when a species diverged, researchers look at the average age of members of the species when they give birth and mutation rates. The older the average age, the more time it takes for mutations to cause changes. Insects that produce offspring in a matter of months, for example, can adapt much more quickly to environmental changes than large animals that produce offspring many years after they themselves are born. To find such data for both chimps and gorillas, the research team worked with many groups in Africa that included studies of the animals that totaled 105 gorillas and 226 chimps. They also looked at fossilized excrement that contained DNA data. In so doing they found that the average age of giving birth for female chimps was 25 years old. They then divided the number of mutations found by the average age of birth to get the mutation rate. In so doing, they found it to be slower than humans, which meant that estimates based on it to calculate divergence times were likely off by as much as a million years.
The end result of the team’s research indicates that humans and chimps likely diverged some seven to eight million years ago, while the divergence of gorillas (which led to both humans and chimps) came approximately eight to nineteen million years ago. To put the numbers in perspective, humans and Neanderthals split just a half to three quarters of a million years ago.
Alu elements infiltrated the ancestral primate genome about 65 million years ago. Once gained an Alu element is rarely lost so comparison of Alu between species can be used to map primate evolution and diversity. New research published in BioMed Central’s open access journal Mobile DNA has found a single Alu, which appears to be an ancestral great ape Alu, that has uniquely multiplied within the orangutan genome.
Analysis of DNA sequences has found over a million Alu elements within each primate genome, many of which are species specific: 5,000 are unique to humans, while 2,300 others are exclusive to chimpanzees. In contrast the orangutan lineage (Sumatran and Bornean orangutans) only has 250 specific Alu.
These tiny pieces of mobile DNA are able to copy themselves using a method similar to retroviruses. But, because this is an inexact process, a segment of ‘host’ DNA is duplicated at the Alu insertion sites and these footprints, known as ‘target site duplications’, can be used to ‘identify’ Alu insertions. Alu elements can be thought of as molecular fossils, and a shared Alu element sequence and location within the genome indicates a common ancestor.