I was getting my mare, Six ready for a video shoot this morning, for a series of videos to be part of a membership site I will be launching shortly.

As I groomed her before saddling, handfuls of hair clogged up the brushes. My goodness, Six is going bald, I thought. But I calmed down and realized she has started to shed her winter coat.

It’s been cold here, with the nights approaching freezing temperatures. The winter equinox was about 3 weeks ago and the days are starting to get longer. I thought to myself what a stupid trigger for controlling coat length and thickness, day length seemed to be. It’s still bloody cold and horses are losing their coats. It seemed that if the purpose of a horse’s coat is to regulate body temperature, then surely changes in seasonal daily temperature would be a more useful way for a horse to decide if it needed to grow hair or shed hair. But instead of using temperature, the body uses photoperiod - day length. My first thought was that this was another example of where evolution allowed inefficient genes to creep into a species and be perpetuated in subsequent generations. More proof that nature does not have to be efficient, it just has to allow genes to exist long enough to be passed to the next generation.

But then I thought about it for another couple of minutes and realized that even if using day length to determine seasonal changes in a horse’s coat was not ideal, using temperature would be even worse.

The thing about using day length is that the pattern of changes in how long the days are is consistent. By that I mean, as summer approaches each day is longer than the previous day until it reaches the equinox. It’s not longer one day and shorter the next. The pattern is consistent and reliable. Then as winter approaches, each day is shorter than the previous. The central control mechanisms in the brain that regulate the growth of a horse’s coat can count on this. It’s reliable.

But this is not true of temperature. Temperatures fluctuate tremendously both between days and within a day. Temperature is rarely consistent for more than a few days and is never reliable. The hormonal mechanisms that control coat growth would go haywire trying to figure out the right strategy. From day to day it would be deciding on whether it needs to stimulate more hair, less hair, shed hair, thicken hair. It’s enough to pull your hair out worrying about it.

When I pondered a little more on this problem this morning, it occurred to me that evolution added a few refinements to help compensate for the failings of using day length as the determinant of coat growth.

It evolved that horses are more comfortable at colder temperatures than warmer ones. Their thermal neutral temperature range varies between 5 and 12 deg C. Whereas humans have a comfortable temperature around 20-22 deg C. I won’t go into how this works, but the way a horse’s coat grows is part of the mechanism. It also helps that horses primarily breathe through their nose and not their mouth when it comes to reducing heat loss.

But perhaps the most important mechanism that nature created to help horses combat cold weather was to engineer the evolution of humans with enough spare cash to afford to spend hundreds of dollars on buying horse rugs/blankets. And it instilled in those humans a brain mechanism that triggers overwhelming feelings of guilt if the temperature falls below 25 deg C and their horse is not rugged. It is a brilliant strategy that nature devised to protect horses from the shortfalls of photoperiod being the determinant of the growth of a horse’s coat. Isn’t Mother Nature and evolution amazing?

So those are the sort of things that occupy my thoughts daily. Aren’t you glad you don’t live in my head?