Like your big brain & non-spiny penis? Thank "junk" DNA.


Noncoding DNA is a weird thing. This is the stuff that's often called "junk" DNA, because it's not involved in making protein sequences—the building blocks of life. But, just because noncoding DNA isn't part of our genetic bricklaying crew, that doesn't mean it's not involved in the construction project. There's a growing body of evidence, from many different researchers, that suggests "junk" DNA might be pretty important stuff. In fact, a recent paper in the journal Nature claims that changes in noncoding DNA have been responsible for some of the important physical characteristics we humans enjoy today.

Like, say, for instance, the fact that the penis of the human male is not spiny. Megan Scudellari at The Scientist explains:

For over a decade, Kingsley's lab has studied the genetic basis of evolution in stickleback fish, and found time and again that major morphological differences can be tracked to deletions in regions of DNA surrounding key developmental genes. To see if the same was true for human evolution, Kingsley and colleagues compared the human and chimpanzee genomes, identifying 583 human-specific deletions. They then narrowed the list to sequences likely to have an important function by looking for those which are highly conserved across other organisms, including rhesus macaques, mice, and chickens.

The team's final list included 510 DNA deletions, highly conserved across animal species but absent from the human genome. All but one of the deletions mapped to non-protein coding regions, and many were near genes involved in steroid hormone signaling and neural function.

The team closely analyzed two of the deletions and their potential contribution to human evolution. One, a deletion near tumor suppressor gene GADD45G, may have removed the brakes from cell division and promoted the expansion of brain tissue, contributing to the increase in brain size of humans over other primates. A second, a deletion near the human androgen receptor gene, correlates with the loss of sensory whiskers and penile spines, which mice and other primates still have, but humans (thankfully) lack.

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