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

From tiny bodies to giant ears, rabbits have super specialized physiologies

Originally posted here: https://mcgill.ca/oss/article/did-you-know/tinies-bodies-giant-ears-rabbits-have-super-specialized-physiologies

We’ve already seen that rabbits and hares have quite interesting physiology, but for certain species of leporidae the adaptations get even more extreme.

The smallest rabbit in existence is the pygmy rabbit, who weighs on average only 450 grams! They’re found in the western US,and are one of the only rabbit species who dig their own burrows, as opposed to repurposing the found burrows of other animals.

Hares on the other handdon’t use burrows at all,but make nests in grass and underbrush. Part of the reason for this is their impressive ability to run away from predators, as opposed to hiding from them in the first place. Some species of hares can run as fast at 80 km/h! This speed requires some serious shock absorption to keep their brains from being rattled, so they’ve actually developed hinged skulls.

Rabbits are generally known for their massive ears, but they actually do a lot more than just hear predators and friends. Rabbits ears are crucial for thermoregulation! Their large surface areas allow bunnies to release their heat and keep cool, that’s why bunnies that live in hot areas tend to have the largest ears.

Platypus are Electrifying

Originally posted here: https://mcgill.ca/oss/article/did-you-know/platypus-hunt-tracking-their-preys-electrical-outputs

If you thought that echolocation or vegetarianism were the only options available to vision-impaired animals, you’re in for a surprise.

Platypuses (the plural “platypus” is also correct, but technically “platypi” is not) have almost 40,000 special cells in their bills called electroreceptors that are activated by the electric fields created by other marine animals’ muscles moving. This is quite useful for the platypus, who tend to live in murky or dark waters but are able to follow the electric fields of their prey to catch their dinner.

It’s not only platypuses that can sense electricity: there are many electric fishthat also do this, as well as some sharks, bees, echidnas and a newly discovered species of dolphin!

While platypuses might not be blind, they are functionally blind when hunting. They close their eyes, noses and ears whenever they dive, and then swing their heads back and forth to sense electrical currents and move towards them (here’s a great video of that!)

But why are there only 3 species of mammals with these electric abilities? Well, it’s partly due to ecological niches. If a species develops a method to hunt where no others can (like in dark murky water) they flourish, but since that niche is now filled, the new skills don’t extend beyond that species.

Otherwise, you can thank evolution for non-electric animals. Sensing electric fields is only really useful if you live in the water (like electric fish) or at least hunt in it (like platypuses). Once you live and eat on land, there’s no real reason to keep your electroreceptors, and with less water comes even fewer reasons. This is reflected in echidnas: Western long-beaked echidnas have about 2,000 electroreceptors on their beaks (20x less than platypuses), and the short-beaked echidnas, who tend to live in even drier climates, have only about 400.

It’s worth pointing out, though, that all animals use electric signals to make their muscles work, so in a sense, we’re all electric!