Colour leaves smell behind in mating game

MUMBAI: India’s original empress of scent was an enchantress called Yojana-Gandha in the Mahabharata.
She was famous for leaving a mile-long swathe of suitors swooning in her trail before she settled down to be the stepmother of Bhishma. Yojana-Gandha’s unique brand of perfume could possibly have originated in a heady mix of natural substances that are now known as pheromones.
These chemical messengers and attractants were first named after the Greek word for ‘carrier of excitement’ in 1959.Originally found among female silk moths, which used a compound named bombykol to pretty much strip the males of their free will, pheromones have also been proposed for all sorts of animals ranging from mice to elephants, not to forget humans and their nearest cousins.
Today, if no chemical brew has been found to have effects similar to bombykol in humans and primates, it’s not for want of trying.
For scientists have known for decades that human pheromonal effects, which range beyond mere vibes and basic chemistry, wreak all sorts of molecular magic, including synchronisation of menstrual cycles among women who spend a lot of time together.
Similarly, people exposed to cotton underarm pads worn by moviegoers can tell if the viewer was scared or amused.
Now, however, a new genetic study provides tantalising clues to the so-called last mystery of the senses —why men don’t behave like love-crazed moths. It seems the development of colour vision may have led to a loss of ability to detect pheromones among Old World primates and their human descendants, according to a new genetic study.
Earlier researchers did speculate that the primates’ pheromonal abilities may have become redundant because they developed colour vision as a better way of selecting mates.
“But we establish the timing for when the pheromone signal transduction pathway was closed,’’ said Jianzhi George Zhang, an evolutionary geneticist at the University of Michigan, Ann Arbor.
Dr Zhang and colleague David Webb homed in on a gene called TRP2, which is unique to the pheromone pathway, to track the evolution of the system in primates.
In humans, TRP2 is riddled with so many errors in its DNA sequence that it is now deemed to be a ‘pseudo-gene’ that is no longer active. Similar is the case with Old World monkeys like baboons and apes like chimpanzees and gorillas.
However, the gene is active and kicking in New World monkeys such as the tamarin and the capuchin, bestowing a sharp ability to detect pheromones, the scientists have found.
A computer simulation of random gene decay estimated the time of TRP2’s shutdown at just over 23 million years ago. This coincided with the estimated time at which male Old World monkeys developed the full colour vision that their New World cousins still lack.
This also gave rise to a new approach to mate selection —to visual communication via gaudy and colourful patches of skin, which worked accurately over longer distances. Still, that did nothing to stop the birth of the multi-billiondollar perfume industry, which is another story.