Big brains and spineless penises

How DNA deletions may have produced uniquely human traits

By | March 9, 2011

Hundreds of deletions in non-coding DNA have helped sculpt human evolution, including an increase in brain size and the loss of sensory whiskers and penis spines, proposes a study published this week in linkurl:Nature.;
The spiny genitalia of the Callosobruchus analis beetle
linkurl:Wikimedia Commons, Johanna Ronn;
"The molecular basis of becoming human is one of the great problems in biology," said senior author linkurl:David Kingsley; of Stanford University. "There have been suggestions from multiple organisms that changes in non-coding regions were likely to be important," he added, and with the availability of the human genome sequence, "we have an incredibly exciting opportunity to start to address that question." 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. "This is a clever thing to do," linkurl:Svante Paabo,; director of the department of genetics at the Max Planck Institute for Evolutionary Anthropology who was not involved in the research, wrote in an email to The Scientist. "As with many good ideas, it seems almost obvious in hindsight." 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. "There's a good chance some of these deletions contributed to the evolution of human traits," wrote linkurl:James Noonan,; a geneticist at Yale University School of Medicine who was not involved in the research, in an email. Still, the paper's speculations about how the deletions influence brain size or penile spines are "premature," he wrote. "All we know is that these deletions remove regulatory elements; we don't know what that means for human biology yet." To find out, Kinglsey and his team are now recreating the deletions in mice to see if the removal of corresponding DNA sequences results in neural expansion or the loss of whiskers and penile spines. They will also continue to look at other deletions on the list for involvement in additional human traits. "Just 508 to go," said Kingsley with a laugh. McLean, C.Y., et al., "Human-specific loss of regulatory DNA and the evolution of human-specific traits," Nature, 471:216-9.
**__Related stories and F1000 evaluations:__***linkurl:Multicellular evolution not linear;
[22nd February 2011] *linkurl:Minor change, major difference;
[22nd February 2011] *linkurl:Evolution loves history;
[2nd June 2008] *linkurl: Neanderthal DNA sequenced;
[15th November 2006]


March 9, 2011

\nYou say: "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."\n\nI say:"Perhaps the loss of penile spines could be mourned. And sensory whiskers? Well, I pluck the odd one from the bottom of my chin. Yes, I'm looking in from a female perspective and grin! "\n\n:)\n\n\n

March 9, 2011

The playfulness of the title does not diminish the genius of the research design. Probably the playfulness frees the scientific imagination to have breakthroughs.\n\nCan we suppose that some such deletion permitted the high creativity that made this discovery possible? Truly, less is more.
Avatar of: Matthew Grossman

Matthew Grossman

Posts: 27

March 10, 2011

Nice article, nice approach to understanding the HG.
Avatar of: Michael Lerman

Michael Lerman

Posts: 8

March 10, 2011

The big brains resulting from specific deletions of regulatory conserved sequences around genes have driven human evolution that resulted in high IQ (spineless penises was probably a byproduct..?). The question is: Who was the surgeon? Michael I. Lerman, M.D., Ph.D.
Avatar of: Dov Henis

Dov Henis

Posts: 97

March 10, 2011

Horse And Wagon\n\n\n"How DNA deletions may have produced uniquely human traits"\n\n\nWith such a title you don't need to read the article, that would apparently explain how a wagon pulls the horse.\n\nSee \n"Seed of Human-Chimp Genomes Diversity"\n\n\n\nDov Henis\n(Comments from 22nd century)\n"Evolution, Natural Selection, Derive From Cosmic Expansion"\n

March 10, 2011

\n"(spineless penises was probably a byproduct..?). Human evolution\nby Michael Lerman\n\nThat could very well be. It would be very difficult, if not nearly impossible, to go back in order to stand in front of evolution unfolding. \nYet, we may come to understand a lot more by trying to focus in where we're going. Finding the drive, which in essence would be comparable to that of being 'the surgeon', would be key. \n\nInteresting process, the process of evolution. \n\n\n\n\n\n
Avatar of: Francis Nunes

Francis Nunes

Posts: 1

March 11, 2011

We know that C-value (total DNA content in a haploid genome) and G-value (total number of protein-coding-genes in a haploid genome) do not explain biological complexity. John Mattick's ideas and other authors highlight the importance and increase of both DNA and RNA non-coding to the evolution of increasingly complex organisms. Therefore, I'd like to name another index: "the nc-value". However, I also consider 'my' nc-value has found its paradox, ie, the complexity is also the result of deletion of non-coding sequences. In the next step we need to explore this breaking news. Let's go?

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