The chimpanzee is the closest living relative of humans, but just how close are they?
The last common ancestor of humans and chimps, dubbed Pan prior, lived 6-8 million years ago in Africa. Even though that's not a very long time in the grand scheme of life on Earth, it's plenty long for random mutations to make substantial changes to our respective genomes.
Genetic information evolves little by little, generation by generation because of things like recombination from sexual reproduction and random mutation.
So how does the human genome compare to the chimp genome after all this time?
On the surface, it's easy to see the similarities between the two species. Humans and chimps are both covered with hair (though it's much shorter and finer on humans) and the human face shape is pretty close to a young chimp's. Brain size is relatively large for the body size of both animals, and have relatively long childhoods during which we are entirely dependent on others.
Because physical traits and behaviors are dependent on our genomes, it stands to reason that the genetic blueprints of the two species would be very similar. It's no small surprise that when the DNA of chimps was sequenced in 2005, many began to claim that the genomes between the species are so similar that humans are essentially 99% chimpanzee.
But that's not the entire story.
While "Humans Are 99% Chimp" is a sexy headline to be sure, it's not entirely representative of what the scientists found in their paper. As a recent Minute Earth video has explained, the human-to-chimp genome comparison is not 1:1, as humans and chimps have a different number of chromosomes, and their chromosomes are different sizes, making a direct comparison difficult.
The researchers therefore focused on what could be dealt with while introducing as little error as possible. Ultimately, over a billion letters of genome were cast aside in order to conduct the actual comparison.
If humans and chimps are so different genetically, what about the previously mentioned similarities?
With mutations, their location on the gene is everything. There are large parts of the genome which don't code for protein or affect the expression of genes, so changes there won't matter much.
Many of the genetic differences that set humans and chimps apart exist in the regulatory region. For instance, humans and chimps both make hair and have bones, but human genes make less hair and slightly differently-shaped bones than our primate cousins.