Lack of spines may be the key to longer-lasting loving

StephenW

                    
http://www.smh.com.au/technology/sci-tech/lack-of-spines-may-be-the-key-to-longerlasting-loving-20110310-1bo6i.html
Lack of spines may be the key to longer-lasting loving                                                                                    Deborah Smith SCIENCE EDITOR                 March 10, 2011   

                                IT IS what men have lost, rather than gained, during evolution that helps make humans unique, new research shows.
            Men's penises lack the prickly spines found on the surface of the penises of many other mammals, including chimpanzees, due to the loss of a small chunk of DNA, scientists have found.
            The spines increase sensitivity, and their absence in men is thought to have contributed to longer-lasting intercourse and monogamous relationships, underpinning a society where fathers help raise children.
                                    Advertisement: Story continues below                           
            "We often think of brain size and bipedalism as key characteristics of what makes us human," said Philip Reno, a member of the research team. "But another difference is our sexual behaviour."
            He said chimpanzees, our closest living relatives, have quick intercourse because many males have sex with one or a few receptive females, in a competition to fertilise them.
            Having tactile penile spines may enhance this rapid action, and "their loss in the human lineage may be associated with the longer duration of copulation in our species relative to chimpanzees," said Professor Reno, of Pennsylvania State University.
            The same missing segment of DNA also explains why men do not have sensitive whiskers on their faces, like mice and cats, which also have penile spines.
            Research on the Neanderthal genome shows these extinct relatives also lacked the DNA segment, he said. This meant the deletion occurred between 7 million years ago, when human ancestors split from chimpanzees, and 800,000 years ago, when human ancestors split from Neanderthals.
            The results of the study are published in  Nature.
            The researchers compared the genomes of chimps and humans and identified 510 segments of DNA which are present in apes and other mammals, but completely missing in humans.
            The hundreds of deletions are in stretches of the DNA code which regulate the action of nearby genes, by turning them on or off during development.
            Another deletion that they discovered is thought to have allowed parts of the human brain to grow larger.