- News Home
6 March 2014 1:04 pm ,
Vol. 343 ,
Early in April, the first of a fleet of environmental monitoring satellites will lift off from Europe's spaceport in...
Since 2000, U.S. government health research agencies have spent almost $1 billion on an effort to churn out thousands...
Magdalena Koziol, a former postdoc at Yale University, was the victim of scientific sabotage. Now, she is suing the...
Antiretroviral drugs can protect people from becoming infected by HIV. But so-called pre-exposure prophylaxis, or PrEP...
Two studies show that eating a diet low in protein and high in carbohydrates is linked to a longer, healthier life, and...
Considered an icon of conservation science, researchers at World Wildlife Fund (WWF) headquarters in Washington, D.C.,...
The new atlas, which shows the distribution of important trace metals and other substances, is the first product of...
- 6 March 2014 1:04 pm , Vol. 343 , #6175
- About Us
The Penis Plan
1 March 2004 (All day)
When it came to phallus design, Mother Nature stuck with a good thing. Although mammals and reptiles apparently evolved penises independently of each other, they share an underlying design optimized for stiffness and form, according to new research.
A penis is essentially a "big, reinforced water balloon," says functional morphologist Diane Kelly of the University of Massachusetts, Amherst. Kelly's previous work suggested that mammals had a swell design. She found that mammalian penises--from those of rats to armadillos to elephants--have two layers of collagen fibers. One set of fibers runs along the long axis while another wraps around perpendicularly. When pumped full of blood, such an arrangement is extremely stiff--it can't bend because the fibers are stretched to their maximum length. The perpendicular fibers also help the penis hold its shape, she says. Kelly wondered whether distantly related animals such as reptiles had come to the same evolutionary solution.
To get the story straight, she examined flaccid specimens from two turtle species and from the workhorse of mammal penis research, the armadillo. Shining polarized light on the tissues revealed a similar pattern of collagen fibers, she reports in the 25 February Biology Letters. Because reptilian and mammalian penises develop from different embryonic tissues, Kelly says the two groups must have reached the same design independently.
There were differences between the species, however. While the armadillo, like other mammals, had only two perpendicular collagen layers, the turtles had multiple layers, like plywood. That means a turtle penis could withstand more bending forces than could a mammalian one, she says. Why turtles need a stronger penis, however, remains one of Mother Nature's secrets.
The study shows that evolution finds similar solutions for problems across species, says comparative physiologist Jim O'Reilly of the University of Miami. He points out that penises with perpendicularly arranged fibers are more prone to buckling than other conceivable designs, but for most species, a dependable shape may be worth that risk.