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

Human-Guided Evolution Closer Than You Think (Skeptical Inquirer)

9 minute read

Evolution is often thought of as a solely long-term process. But the conception that its effects are only seen after millions of years ignores a crucial part of the evolutionary process: adaptation. Because we tend to fixate on the drastic changes caused by evolution over huge timescales, it’s easy to ignore the small variations between generations that add together over time to form the big evolutionary changes we focus on. This unintentional side-lining of small adaptations can blind us to the ways in which humans are directly affecting the evolutionary processes of nature. From tuskless elephants to fish that can’t smell, animals are developing specialized adaptations to allow them to live in ecosystems that have been disrupted and altered by mankind. These adaptations are one step in the evolutionary process that already bears the unmistakable marks of humanity’s influence.

Just as humans are changing the planet, they’re changing the fauna that inhabit it. Here are some examples of how.

You can read the entire article here: https://skepticalinquirer.org/exclusive/human-guided-evolution-closer-than-you-think/

Why Are There so Many Different Body Types?

3 minute read
Image made by Ada McVean
Originally posted here: https://mcgill.ca/oss/article/general-science-you-asked/why-are-there-so-many-different-body-types-among-people

While this question seems simple, it turns out there are a lot of complex processes behind your development of a particular body size or shape.

Some biologic aspects are controlled by individual genes. Take for example sickle cell anemia. This red blood cell disorder is caused by inheriting just one abnormal gene from each parent. There is, similarly, just one gene implicated in people having or not having cleft chins.

Body size is not controlled by only one gene, but many, making it hard to predict the size of individuals before they reach adulthood. To further complicate matters, it’s not only genetics that influence body size. Factors like diet, nutrition, climate and health status all change how you grow.

As Manuel Will, an anthropologist and archaeologist with the universities of Cambridge and Tübingen, explained to me: “your genes define a range for the potential body size you might achieve as an adult, and factors duringyour development determine how much you realize of it.”

So how did different ranges of body size develop in the first place? We can look to random genetic mutations, competitive living and environmental influences in early Homo species to explain how such a range of human sizes developed.

It could be that a random mutation made an individual taller-therefore able to reach more food-or the opposite. Taller individuals would likely be more successful, so reproduce more, passing these genes to the next generation, but a certain number of less-successful shorter individuals would still reproduce and pass their genes on.

A trend develops wherein the gene pool contains more “tall genes”, and when you go fishing in it, you’re more likely to catch a tall person. There is still a range of heights available to catch, but the pool is overstocked with tall. But, gene pools are often destroyed, subdivided, reduced or impacted by natural events.

Famines, earthquakes or floods can cause population bottlenecks. This means that the gene pool is reduced to include only those who survived the disaster. It could be that every tall individual was killed, so that the tall trait goes extinct in future generations.

Since gene pools only exist between breeding populations, if a few of individuals left the main group to establish their own population, they are also establishing their own gene pool. Within this new pool though, certain genes can be over represented (maybe most of the new pool’s founders happened to be short). This is called a founder effect.

As humans began to migrate around and out of Africa, founder effects and population bottlenecks would have occurred frequently. Combine these genetic effects (nature) with the environmental effects (nurture) different groups of humans would experience as they moved around, like fires or plagues, and you can see why the world has so many different types of bodies.

So, there isn’t really a hard-and-fast rule for body sizes based on genetics, since location, nutrition and other factors play such a role. But, we can pick out some general trends. Individuals from colder environments tend to have shorter limbs and larger body sizes, while those from warmer climates are taller and thinner. Those from richer countries tend to be taller than those from poorer ones.

While it may seem universally beneficial to be a larger human, there are some drawbacks. Larger bodies take longer to grow and require more resources. They’re more likely to experience joint pain, and generally put more strain on their internal organs.

As modern humans continue living in an economically successful and stable countries their nutrition and health improve, allowing them to grow larger. There will always be variation in a population (some people shorter than average, some taller) but we can expect a general increase in average heights and body sizes of Canadians as time goes on.

Why Do We Have Dimples?

Originally published here: https://mcgill.ca/oss/article/did-you-know/why-do-we-have-dimples

Orlando Bloom might have the nicest dimples around, but glance at his chin and you’ll notice a lack of a dent. Look at Demi Lovato’s chin though and you’ll see a cleft, almost like an indent there. How can somebody have one kind of dimple but not the other? And what causes dimples in the first place? 

Cheek dimples are the result of a muscle in the cheek, the zygomaticus major, splitting in two. Before birth this muscle can split into a superior bundle that is positioned above the corner of the mouth, and an inferior bundle, below the corner of the mouth. This splitting creates a hammock sort of effect where skin can hang in slightly between the two bundles. When you smile, the muscles contract and the dimples are more prominent due to the increased skin tension. Chin dimples on the other hand, have nothing to do with muscles.

Cleft chins, or butt chins are they’re colloquially called, are a result of an unfused jaw bone. The skin over the tiny gap is indented, creating the dimple. If you ever feel a cleft chin, you can actually feel the gap, but don’t worry, this anatomical feature is harmless. It is dominant genetically though, so your kids might face a few inevitable ‘butt face’ insults.