Why Don’t Humans Have Whiskers? (McGill OSS)

2 minute read

Humans might not have hair as thick as chimpanzees covering their body, but our arm, leg and eyebrow hair all serves as reminders of our primate ancestry. So why don’t Homo sapiens have whiskers like other simians? To answer that, let me explain first what whiskers do, besides look adorable.

Whiskers are vibrissae, keratin filaments that grow out of different follicles than hair. Whisker follicles are much deeper than hair follicles and are surrounded by pockets of blood that amplify vibrations to better communicate information to the nerve cells beside the follicles. You may have noticed when looking at your cat that there are 2 kinds of whiskers, long and short. Long whiskers are macrovibrissae and can be moved voluntarily. Animals use these to sweep areas (called whisking) to navigate spaces and generally feel the world. Short whiskers are microvibrissae, and they cannot be moved voluntarily. These are used specifically for object recognition, whether it’s your rat’s favourite toy or your hand. 

In general, animals use whiskers to help them ‘see’ the world, navigate it and identify features. Humans used to have whiskers too (about 800 000 years ago we lost the DNA for whiskers), but have now largely integrated the function performed by whiskers into their brains, specifically into their somatosensory cortex. The human brain devotes relatively huge portions of itself to sensing and processing touch. 

Certain areas of the body, like fingertips, lips and genitals have much greater sensitivity to touch than other areas like the back or legs. A visual representation of this sensitivity to touch can be seen in the Cortical homunculus, or by performing a simple test: Have a friend use 2 pencils to touch your arm, while you close your eyes. Have them move the pencils closer and closer together. At a certain point, you will not be able to distinguish whether you are being touched by 1 or 2 pencils. Have the friend repeat this activity on your fingers, then your back. You’ll quickly notice that you have a much more sensitive sense of touch on your hands, feet and face. This test is called the 2 point discrimination test, and it’s often used to test patients for paralysis. 

So we as humans may not have cute whiskers anymore (though our simian cousins still have microvibrissae), but rest assured we’re no worse off for this loss, just slightly more dependent on our brains. 

Original article posted here: https://www.mcgill.ca/oss/article/did-you-know-history/whiskers-humans

Cats Can Get Hairballs…But so Can People!

Originally posted here: https://mcgill.ca/oss/article/did-you-know/its-not-only-cats-get-hairballs-people-can-too

Rapunzel, Rapunzel, let down your hair… 

If you’ve ever had long hair you know how it can collect just about everywhere, so I can’t help but wonder how Rapunzel kept her locks from sticking to the shower wall and getting in her coffee. One thing’s for sure though, she didn’t eat it. If she did, she’d probably be pretty sick.

Rapunzel syndrome is the result of trichophagia (compulsive hair eating), and is essentially a human hairballTrichotillomania is a psychiatric disease in which someone pulls out or cuts off their hair, and when it combines with trichophagia, Rapunzel syndrome is born. The danger lies in the human digestive system’s inability to digest hair, leaving to the formation of trichobezoars (yes bezoars like in Harry Potter), or hairballs. Generally the hairballs are not that dangerous, since humans (unlike rabbits who also get hairballs) can vomit them up, but if they grow too large they may need to be surgically removed. Much more worrying however is the psychiatric state of a patient experiencing this condition, as trichophagia and trichotillomania are commonly seen in conjunction with the difficult-to-treat obsessive compulsive disorder.