IELTS Online Practice Materials

Did human pheromone use die with colour vision?

A) Pheromones are similar to hormones but they have one main function: to attract a mate. Animals are very dependent on these specialized scent molecules, but according to evolutionary geneticist Jianzhi George Zhang, humans barely recognize them or make use of them. Zhang and colleagues at Michigan University have conducted research which points to a fascinating reason for this abandonment of pheromones: the development of colour vision.

B) They used a gene called TRP2, which is unique to the pheromone pathway, to track the evolution of the pheromone 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 In humans, TRP2 has accumulated so many errors in its DNA sequence that is now a "pseudogene" that is no longer active. Using a computer simulation of random gene decay, they have estimated this inactivity began around 23 million years ago, just before the hominoid super-family that eventually produced humans separated genetically from the original primate group. Crucially, the timing is approximately the same as the development of full colour vision in Old World primates. Today, this group, including chimpanzees and gorillas, are also unable to detect pheromones using TRP2. However, New World primates such as tamarins, squirrel monkeys and sakis, still have not developed colour vision and retain their ability to utilise TRP2.

C) To see things in full colour, we need two copies of a colour vision gene: one red, one green. These genes are present on the female X chromosome, so female monkeys have had full colour vision much longer than males. Then, around 23 million years ago, Old World males developed the 2nd gene...and suddenly noticed the bright, colourful patches of skin that signalled female reproductive fitness and fertility. Unlike pheromones, colour can be seen from a distance, a definite advantage in spotting likely partners.

D) Interestingly, approximately 7% of European males suffer red/green colour blindness; a higher ratio than in Old World monkeys and apes. Zhang postulates that this may be because humans no longer need to select mates primarily by visual means. We consider appearance to be important but also now use criteria such as lifestyle and personality...and may disguise our pheromonal scent completely with perfumes and deodorants.

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Journal reference for Zhang's research: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas. 1331721100)