For several years now, I have experienced a slight disruption in the rhythm of my heart. “Experienced,” is a bit of an overstatement because I have no awareness of this other than the fact that doctors tell me they can hear it when they listen to my heart. My heart will occasionally contract a bit early, out of the steady rhythm. There are medicines that help to regulate the heart and I take one of them, but from time to time, doctors are interested in observing my heart a bit closer so they order an electrocardiogram. The test involves attaching electrodes on the chest to record the heart’s electrical signals. These signals are then shown as waves on a computer monitor or printer. The test is painless and takes just a few minutes. Electrocardiograms have been around for many years. In the early years of the technology, the electrodes had small clamps on them that pinched the skin. These days the electrodes are clamped to metal pieces attached to the skin with stickers.

I have a bit of a problem with the stickers. The problem is that I have a fair amount of hair on my chest. Usually in order to get the stickers to work, the technician has to shave some of that hair. I don’t mind. The hair grows back quickly. I can’t explain it, but I’m good at growing hair in all sorts of places where I don’t need it. In addition to the hair on my chest, I’ve got longer than usual hair on my arms and legs. I am annoyed by the rate at which hair grows in my ears, requiring trimming more often than than the hair on the top of my head needs to be cut. It is the hair on the top of my head that is a problem. I’m not too good at growing it up there. in fact, there are some large patches of skin on my forehead and on the top of my head where they could attach electrode stickers with no problem.

Compared to most mammals, including other primates, humans are remarkably un-hairy. There are a few other relatively hairless mammals: naked mole rats, rhinos, whales, and elephants. I’m not sure I want to be compared with any of those creatures, but we do have a bit in common with them.

So why do we not have fur like other mammals? Our hominoid ancestors had much more fur than modern humans. There is archaeological evidence that homo erectus and later hominids began to appear with less and less hair during that Pleistocene.

There are several scientific theories that seek to explain our relative lack of fur. One has to do with cooling. As humans started hunting on the open savannah, they began to run for hours to chase their prey, in order to drive the prey to exhaustion. Sophisticated hunting tools appear only later in the fossil record. Running on a hot savannah could have put our early ancestors at risk for overheating, thus the loss of fur to cool the body. Modern scientists note that certain cells can either develop into sweat glands or hair follicles. Less hair resulted in more sweat glands. We can sweat better without fur, so the benefit of losing fur was an increase in our ability to cool our bodies.

This theory doesn’t explain why other apex predators such as large cats, bears, and wolves continue to have fur while we do not. It also does not explain why we haven’t grown back our fur as we have settled into cooler climates and given up endurance running as our primary form of obtaining food.

Another theory is called the ectoparasite hypothesis. Furless apes suffer from fewer parasites. Fewer parasites is a major advantage. Certain species of flies are specialized to land on, live in, and deposit their eggs in fur. These flies carry disease. People with more fur have more parasites. Those with less fur have fewer. This could account for the development of humans with less fur.

A third theory has to do with the development of humans making clothing out of other animals’ fur. Having clothing that can be removed and washed is a real advantage. Human body lice can be removed by removing clothing and washing it.

Darwin believed that human hair loss was the product of natural selection. Basically, our ancestors preferred less hairy mates.

There are probably many other theories about why humans aren’t covered with fur. One of the problems with studying the phenomenon is that the processes that allow bones and other structures to develop into fossils doesn’t work with hair and therefore there is little evidence of hair or fur in the fossil record, making it more difficult to determine exactly where on the evolutionary timescale humans lost their fur.

I’ve learned a few tricks to deal with my own personal fuzziness. When my dermatologist notices a suspicious spot on my skin and takes a biopsy, I make sure to shave the area around that spot before I go in to have the lesion removed. This allows the adhesive tape to stick, and, more importantly, to be removed without pulling out a bunch of hair. I sometimes will shave the crook of my elbows when I know that I will be donating blood or have to have blood drawn for routine medical tests, though these days they have a kind of easily removable elastic tape that they prefer to the old-fashioned hair pulling type. Still, I have no cure for the annoying hair growth in my ears. I try to trim it between haircuts, but I’m not as good as the barber at getting rid of the unwanted hair.

In my particular case, my beard grows a lot faster than my hair. I trim it between trips to the barber, but my hand-eye coordination is limited when using a mirror and I struggle to get it as straight and neat as the barber can. Meanwhile I have less and less hair on the top of my head as each year passes. It is too bad that so far they have no need to attach electrodes up there.