Addition by Subtraction: Penile and Brain Genetic Deletions Makes Us Human

Perhaps you’re familiar with the term, “addition by subtraction.” The term is often applied for athletics like when the New England Patriots got better by getting rid of the Randy Moss plague or perhaps to your diet by ridding it of unhealthy snacks like mouth-watering, deliciously fried macaroni and cheese bites.

Whatever the societal application, it appears that nature has again beat humans to the punch. The term also applies to genetics. In a paper recently published in Nature, Philip L. Reno from Penn State University helped show how the deletion of non-protein-coding segments of DNA in the human genome has contributed greatly to two of the greatest human characteristics that there are: sexual stamina and a giant brain.

A decent bit of the genetic material encoded in our DNA is used for actually producing proteins that make our biological machines run. Enzymes that spark chemical reactions and globules that attack harmful bacteria are just a couple of the thousands of types of proteins that DNA blueprints. However, there are even more genetic strands that don’t encode squat. The purpose of a lot of this DNA – if indeed there is any at all – is still speculative.

But some of it isn’t.

Some of this genetic material is regulatory. It turns on and off or amplifies the genetic codes that create proteins. It is these types of DNA segments that the scientists looked at.

With help from Cory McLean and Alex Pollen at Stanford University, Reno scanned these sections of DNA for segments that appear in the chimpanzee genome but not in ours. After cross-correlating these segments with other mammals, the scientists were able to identify on 510 segments for which their disappearing act in human evolution helps distinguish us from all other mammals.

The authors of the paper then decided to focus in on two segments in particular because they were near genes they suspected might be involved in the evolution of particular human traits. By knocking out the genetic segments or enhancing them in the fetuses of chimps and mice, they were able to determine what it is that they do.

One section turns on the tissue production responsible for the development of prickly surface spines found on the penises (click at your own risk) of mice and many primates, but not humans. (Ladies, aren’t you glad this gene got deleted?) Because these spines are extremely sensitive, the deletion of the feature allows for human males to have sex longer before ejaculating.

The other gene doesn’t turn on tissue growth, however, it stunts it. The genetic sequence is responsible for regulating a gene that suppresses tumor growth in the brain. However, turning the off switch on this feature is part of what has allowed the human neocortex to evolve into the giant supercomputer that it is today.

On the other hand, maybe these characteristics aren’t so great. The authors speculate that the increased duration of sex contributes to the human tendency to be monogamous. So not only do these genetic deletions cause us to get tied down and married, they give us the mental capacity to lament about what sorry suckers we are.

Thanks a lot evolution.


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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