What Is the Evolutionary Significance of Medicines?

What is the evolutionary significance of medicines for curing and treating diseases? Allow me to explain my question…

Your body automatically guards against foreign substances when it comes to things like bacteria and viruses. If one of those foreign bodies enters your system, your body goes haywire. Antibodies are immediately dispatched, and your body does just about everything else it can to fend off the intruder. This ofcourse has always been the case for humans since our entering of the earth ecosystem thousands of years ago. And it is closely related to how we evolved. If we couldn’t fend off diseases, or most diseases in any event, we would have never passed on our genes to subsequent generations.

Now think of all the medicines we take. These are foreign things to our bodies too, although they aren’t always intruders per se of course. But thousands of years ago, a good defense against any foreign substance might be of help to our ancestors. Eat the wrong berry or root, and having your body recognize it as foreign might have done our ancient parents good. Right? And yet our body does accept medicines. In fact it does more than that. With some medicines, our bodies may become acclimated to them, and miss them if they are gone. And I am not just talking about addictive drugs here. This is true of many benificial medicines. (All of what I just said is true of other animals too of course.)

So our bodies are clearly designed to allow medicines in them, which is good. But what advantage did that give us when we were just evolving?

:slight_smile:

Being TOO selective about what substances the body would tolerate can be just as bad as allowing anything in. Having some leeway allows one to consume new food sources, which would would otherwise be unavailable. There is such a thing as overprotection.

IANAEvolutionary Biologist, but maybe I can add something until Darwin’s Finch or some-one else who knows more shows up.

In no particular order:
Many medications either are chemicals that the body produces or are analogous to natural body chemistry. Steroids, for instance, or epinephrine.

You mention the body becoming tolerant of medication, and steroids are also a good example of this. If you have ever taken prednisone for an extended period, the doctor may have titrated up the dosage to start and then weaned you off at the end of the course. This is because there is a risk that your body can stop producing its own steroids during treatment and when you stop treatment, you develop Secondary Adrenal Insufficiency. This is specifically because these medicines are not foreign substances. Many other medicines are also “natural” to the body.

On another level, the active immune system responds primarily to foreign organisms, rather than substances. The white blood cells recognize “self” based on surface markers on the other cells. Therefore, virii, bacteria, or even other human blood cells lacking these markers are “non-self”. Some white blood cells even “remember” the surface markers from previous “non-self” cells previously encountered, thus speeding the response to, for example, chicken pox.

Last point: although this really isn’t the question asked, I though it was relevant. Medicines that could have an affect on the evolution of people would treat diseases that:[ul]are heriditable
convey a higher-than-normal risk of death
strike in childhood[/ul]

Asthma, juvenile diabetes, and hemophilia are possible candidates. With treatment, children with these conditions are now more likely to live into adulthood and reproduce, passing on the suseptibility to these conditions. Prior to treatment, none of these diseases were invariably fatal, but did decrease the likelihood of reproduction. Medicines that treat arthritis, high cholesterol, high blood pressure, etc. affect those who have generally already had the chance to pass on their genetic susceptibilty to, for instance, heart disease.

To expand on QED’s answer, the evolutionary advantage in being able to tolerate foreign, biologically active chemicals drifting around in our bodies is that we can actually eat food.

Organsims have been involved in chemical warfare now for a few billion years. The prey organism produces a chemical that has a negative affect on the predator, and in response the predator becomes tolerant of that chemical. The prey in turn either increases the dose or modifies the chemical to overcome the tolerance and so ad infinitum.

As a result of this ongoing process fruits and vegetables are loaded with phytoestrogens, cardiac glycosides, antioxidants, enzyme suppressors, saponins and an almost limitless list of other toxic compounds that modify our native biological processes. They evolved these substances in an attempt to stop themselves being eaten, or at least being eaten by the wrong species of animal. All fruit and vegetable matter is further contaminated with microbes which produce a range of anti-microbial, immunosuppressant and immunocompetitive substances because they are engaged in their own chemial warfare with themselves and their plant victims.

Of course the best of such chemicals are ones that modify the host’s own physiology. For example some plants produce compounds that slow the heart rate, some increase it. Some produce compounds that strip the body of calcium or cholesterol. Humans have evolved a tolerance for such physiologically active compounds just so we can eat.

Our bodies can allow medicines in them because the body has evolved to allow physiologically active plant products. It doesn’t distinguish between such a compound taken as medicine and such a compound taken as fruit. This is further aided because much of modern medicine is still based on either natural plant and microbial chemicals or close analogues. But even if that weren’t the case the body has evolved to tolerate novel compounds in circulation in order to cope with novel diseases and novel food sources as well as novel toxins as old species evolve new defences.