"If those two mutations had not happened, our bodies today would have to use different mechanisms to regulate pregnancy, libido, the response to stress, kidney function, inflammation, and the development of male and female characteristics at puberty," Joe Thornton, a professor of human genetics, ecology and evolution at the University of Chicago, said in a statement. 

Tweaks in how proteins function have been key to how humans evolve, and this study demonstrates how the smallest of mutations can be responsible for vital permanent changes. It also gives some insight as to how genetic code works to change those functions, and Thornton believes discoveries such as these will have a key role to play in developing targeted drugs that combat genetic mutations -- the better we understand how genetic mutations occur, the better equipped we'll be to combat unhelpful ones. 

The team made the discovery by retracing today's steroid hormone receptor proteins' historical steps, choosing this group of proteins for their wide-ranging roles in controlling hormones for reproduction and development.