Asked by: Hector E Qintero, Puerto Rico
The genes in a modern human don’t all date back to a single point in our history. When a new species evolves, it has almost exactly the same genes as its ancestors, with just a few crucial mutations that set it apart. The genes that gave early humans their larger brain size, for example, evolved around 500,000 years ago but we still share lots of genes with other primates and mammals.
DNA is constantly mutating. The egg and sperm that originally created you probably contained 100 to 200 new mutations that weren’t in your parents’ DNA. Each of those mutations created a new gene, so you have quite a few genes that are only slightly older than you.
At the other extreme, the oldest known functioning gene is the one that codes for the enzyme glutamine synthetase, which creates the amino acid glutamine from glutamate and ammonia. As this enzyme is a crucial part of the way cells make protein and remove excess nitrogen, natural selection has preserved it unchanged. Every living thing uses this same gene that first evolved more than two billion years ago – before even the first cells with a nucleus emerged.