The development of colour vision may have lead to Old World primates, and hence their human descendants, to lose their ability to detect pheromones, suggests a new genetic study.
Pheromones are highly specific scent molecules that many animals rely upon to find and assess a potential mate. But humans appear to make little, if any, use of pheromone signals, says Jianzhi George Zhang, an evolutionary geneticist at the University of Michigan, Ann Arbor.
Researchers have suggested before that the primates' pheromonal abilities may have fallen by the wayside because they developed colour vision, a better way of selecting mates. "But we establish the timing for when the pheromone signal transduction pathway was shut off," Zhang told New Scientist.
It occurred about 23 million years ago, just before the hominoid superfamily that eventually produced humans branched off. Crucially, the timing approximately coincides with the development of full colour vision in Old World primates, thereby giving a major boost to the theory.
Random decay
Zhang and colleague David Webb used a gene called TRP2 - unique to the pheromone pathway - to track the evolution of the system in primates. In humans, TRP2 has accumulated so many errors in its DNA sequence that is now a "pseudogene" that is no longer active.
It is also a pseudogene in Old World monkeys, such as the baboon and guereza, and apes including the chimpanzee and gorilla. But in New World monkeys, like the tamarin, squirrel monkey and saki, the team found TRP2 was completely functional and bestows a sharp ability to detect pheromones.
A computer simulation of random gene decay estimated the time of TRP2's shutdown at just over 23 million years ago. And this matches the estimated time at which male Old World monkeys developed the full colour vision that their New World cousins still lack.
Gaudy and colourful
In order to see the world in full colour, two copies of a colour vision gene are needed - one red, one green. The genes reside on the X chromosome, so female monkeys have long had full colour vision, while males have not.
But when male Old World monkeys gained a second colour vision gene, about 23 million years ago, it meant a new approach to mate selection was possible. Rather than pheromones, "sexual swellings" - gaudy, colourful patches of skin - could be used to signal female reproductive fitness and fertility.
"We think there might be some advantage to using a vision based signalling system, compared with a pheromonal one, because you can see colour from a distance," says Zhang. With pheromones, he notes, a mate has to close enough for the pheromones to drift through the air and be detected.
Zhang adds that red/green colour blindness is relatively common in humans compared with Old World monkeys and apes - with about seven per cent of male Europeans being colour blind. This might be because the need to very carefully select mates by visual means has become "relaxed" in modern humans, he suggests.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.1331721100)
Re:Did color vision end human pheromone use?
« Reply #1 on: 2003-07-07 12:51:38 »
Interesting thought along the same lines.
If color vision was one of the more important mate selection criteria than wouldn't this make for an unequal selection pattern from dark to light skin.
If so wouldn't this lead to a non-cultural selective process that could be racially and geographically different. (think sun tan as appossed to Igloos)
Anyone seen sources on this or the greater implication this might have? Thanks Nate
I donīt think that a color based selection can be more effective than that based in molecules that can be detected miles away (as in insects). In the mammals case, itīs true that the spacial proximity is the common rule for the detection, but with the kind of sistems in which primates live, staying a bit far is always important to keep a social order.
The fact that pheromone sensitivness dissapear can lead to the development of the colors vision, but the order can be cleared so simply.
About the X chromosome, in females, exist a special kind of chromosome called "the Barr Corpuscle", which is the second X sexual choromsome very condensed and non functional. Itīs true that females have two copies of the gene, but only one is functional (as in males).
Re:Did color vision end human pheromone use?
« Reply #3 on: 2003-07-15 10:53:13 »
Theory
1. Color vision was important to mate selection. 2. Social Heirarchy is influence heavily by mate selection.. 3. Anthropomorphic Aesthetics would judge lighter skin harsher than darker. (AA) 4. Under more critique social heirarchy would diversify. 5. Lighter skin societies would have a more rigid and complex social heirarchy. 6. More rigid and complex societies (in general) would replicate faster
Could this be an important key to european rule of the last 1000 years?
The idea that color vision ended pheromones in humans is absurd given that pheromones have been proven to exist in humans.
Martha McClintock, now a professor at Univ. of Chicago proved many years ago that women produce pheromones which cause other women's menstrual cycles to synchronize, when they live together. It's also been shown that women's menstrual cycles are more regular when they live with men.
And McClintock has more recent research showing that pheromones actually affect mood: Horm Behav. 2000 Feb;37(1):57-78, Psychological state and mood effects of steroidal chemosignals in women and men.
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