It's something most women intuitively knew:
the louder the man, the smaller the genitals. Now science has more or less
ticked off on the assumption - in monkeys, at least. According to a study
published by the Current Biology journal, male howler monkeys with a louder and
deeper roar are more likely to have tinier testicles. The researchers, from
Cambridge, Utah and Vienna universities, said it marked the first evidence in any
species of an "evolutionary trade-off" between the vocal tract and
the testes. "This means that different species of howler monkeys either
invest in one of these traits or the other, but not both," said Jacob
Dunn, a biological anthropologist at the University of Cambridge. "I think
the main message is that when it comes to reproduction, you can't have
everything."
Howler monkeys produce one of the loudest
vocal calls of any terrestrial animal, owing to their highly-modified larynx
and its large, cup-shaped bone called the hyoid. An air sac inside the bone is
thought to function like an echo chamber for the animal's mating calls. But
researchers found that those monkeys with the biggest hyoid were also the
least-equipped for sperm production, and vice versa. Not that this is
necessarily a disadvantage: Charles Darwin suggested the plus-sized vocal
organs of the species were sexually selected.
Males living in groups where they were the
lone male tended to have smaller testicles and bigger hyoids, whereas those who
were competing against other males in their group tended to have larger
testicles. "This is probably because the females in these species will
mate with several males, and so the males have evolved to produce more sperm to
increase their chances of fertilising an egg," explained Dunn. As for the
celebrated sub-species of human known as "that really loud guy at the bar
tonight", the study had nothing to report. But feel free to draw your own
conclusions.
No comments:
Post a Comment