Thursday, February 13, 2014

The Human's guide to being human: Evolution and adaptation

If you look at the 3 aspects of your genome, you can see that each allows adaptability but over differing time periods and scales.  Your coding genes don't change during your lifetime so they don't help to make you, as an individual, adapt to the environment.  What they do is allow the species, as a whole, to change as the environment changes and provide a framework for adaptation to occur.  The epigenome gives you some ability to adapt to the environment by changing the way genes are expressed, but you are still restricted to what you can do by your coding genes.  Finally, the microbiome allows you to adapt to the environment quickly based on the microbes you come in to contact with and the food that you eat.

If you truly think about it, adaptation is going on everywhere here.  The environment in your gut causes your microbiome to adapt which changes the internal environment, your internal environment makes your cells adapt via the epigenome, and the species as a whole adapts via evolution as certain coding genes make some people more successful at interacting with the environment than others and those people pass those genes on to future generations.  But what is the difference between adaptation and evolution?

The difference between evolving and adapting

There is a distinct difference between evolving and adapting.  Adapting occurs in individuals and is brought about by the environment affecting change on that individual.  A good example of this can be seen in weightlifting.  When you begin lifting weights and don't wear gloves, you develop calluses on your hands.  This makes the skin stronger and less likely to rip the next time you lift weights.  You are basically adapting to the stress being placed on your hands by making the skin a little stronger for next time.  The adaptation doesn't stop at the hands, over time your nervous system becomes more efficient, you lay down more muscle fibers to make you stronger, and your bones become more dense as a load is placed through them and/or the muscles you are using cause deformations of the bone which signals them to get thicker.  These are all adaptations and they make you better at lifting weights.

Evolution, on the other hand, doesn't happen to an individual, it happens to a population.  Over the course of your life you adapt to the environment, but you don't evolve.  The species as a whole, or a sub-population of the species, evolves over long periods of time as it becomes better suited to the environment, but individuals within the population are not evolving, they are adapting.  I only bring this up because many ill-informed people discredit evolution by saying that it cannot be true because we don't see humans actively evolving in to monkeys.  The human species evolves, individual humans adapt.

Let's take a look at an example of each.  Let's say we have a population of mice where half are white and half are green.  If we take this population of mice and place it in an environment where the ground is covered in green flora, the green mice would have an advantage over the white mice because predators would be less likely to see the green mice.  As a result, the number of white mice would begin to dwindle and the green mice would begin to outbreed the white mice, leading to most of these mice being green.  Let's say some of the white mice were exceptionally smart and were able to realize that looking for food at night allowed them to procure food AND reproduce without being killed by some of their predators.

This would allow a few white mice to still be kicking around when an ice age came about and the white mice became better suited to being able to hide in this new environment where the ground was mostly white.  As a result, you would see the white mice begin to outbreed the green mice and eventually become more numerous.  The change from equal parts white and green mice to mostly green mice to mostly white mice is evolution of that species.  The individual white mice who were able to adapt to the environment by hunting at night allowing that segment of the population to stick around long enough for the white color trait to be beneficial, that is adaptation. 

How evolution affects our health

Evolution is important to understand because the environment our ancestors lived in caused our species to evolve.  This is not the same thing as saying the environment molded us to become well adapted to it, that never happened.  It's also not the same thing as saying we were perfectly adapted to any particular environment from our past, as far as evolution goes there is no such thing as perfect and environments change quickly which can cause formerly beneficial traits to quickly become a liability, as seen above.  I don't think anyone would argue that our cravings to devour high sugar/high fat/salty foods is no longer beneficial to us in an environment where food is plentiful and food companies exploit these cravings to get us to buy and overconsume their products.

This also doesn't mean that we cannot be better suited to a different environment, it just means that if we are not doing well in a particular environment we can look at the environment our ancestors lived in and compare that to the environment we are currently in to identify aspects of the new environment that we may not be well suited for.  Since we are individuals, adaptation is our primary concern because we do not evolve, but remember that our ability to adapt is constrained by our genome, which was developed through evolution.  There is no doubt that the environment we are in is drastically different from the one most of our ancestors adapted to and the human genome as a whole evolved in, and science is beginning to allow us to peel back the onion and take a look at this from a genetic perspective.


The environment our species evolved in for the vast majority of time on this planet was devoid of processed foods, high in physical activity, and low in sedentary behavior.  Being a couch potato is a relatively new option for individuals of our species since our ancestors actually had to procure their food through more physical means than calling Domino's.  Furthermore, our bodies are not well suited to experiencing stress the way we do today.  For most of our time on the planet, stress has been intermittent and resolved very quickly.  If you encounter a bear in the woods and it wants to make you lunch, you either get away or become lunch, you may become more conscious of bears in the area but you don't lament about it for a month.  Stress was more acute back then, it's more chronic now.

Chronic stress is a more recent physiological problem that's been brought about through society.  All of these things have an impact on our internal physiology and, thus, the environment our cells are in.  It's not too big of a reach to think that these lifestyle factors can impact our health by causing our cells to adapt in a way that isn't healthy for us.  New studies on the way lifestyle decisions impact genetic expression are beginning to open up our eyes to the way our lifestyle choices impact our health.  In my next blog we will look at how our new environment is clashing with our old physiology and what the research shows about how this affects our health.

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