Medicine as Evolutionary Expansion|
Jan 23, 2014, 12:46p - Science
We've all heard about "survival of the fittest." This saying explains why certain species thrive and others go extinct, and it captures the core of Darwin's idea of evolution by natural selection. People also use it colloquially to explain why certain individuals are successful and rich and others are weak and poor - some people are more "fit" than others.
But this saying confuses me. "Survival of the fittest" stands in stark contrast to what I see people in society actually doing: helping each other. If we really believed in this saying, we wouldn't also have the strong culture of altruism and assistance that pervades Christianity and non-religious morality. And the continuing advancement of medicine is a testament to this: with every year we discover a new way to cure or ameliorate some disease, and then endeavor to make that available to as many people as possible (ignoring corporate interests for the moment). Somehow, in spite of survival of the fittest, we make it a priority to help others.
So how does this make sense? How can we, on the one hand, think that nature and even society selects for survival of the fittest, while on the other try everything to cure sick people? If the world really operates as survival of the fittest, we would just let people who can't make it on their own die.
So clearly something else must be going on. One idea is that the unit on which selection operates is no longer the single individual. Sociality evolved because it allowed groups of individuals to survive better as an interdependent unit rather than as independent organisms. Emotions then evolved to encourage behavior that would help the survival of people an individual depends on. These emotions drive us to help an aging or sick parent. This all makes intuitive sense to me.
But I think there's a more unusual, statistical way to think about what's going on here.
To begin, let me explain the modern view of how evolution by natural selection works. The basic idea is simple. An organism's structure is determined by its genome, which consists of genes. Each gene consists of a sequence of DNA, with 4 different units (nucleic acids) per position, in a sort of linear digital code. The sequence of a gene determines its function. Genes can code for seemingly banal things such as eye color but also for functions absolutely critical to the survival of the individual, such as genes that enable you to digest food.
Evolution works as follows. At a slow, random and sustained rate, mutations are introduced into genes (e.g. from UV radiation from the sun). A mutation is just a change at one site in the sequence of a gene. So instead of having a T at position 100, the gene may be mutated to have an A at that position. Evolution works by accumulating these mutations. Some mutations will improve a gene, so for example by making it more effective at extracting nutrition from food. Such genes will persist in the population because it will give those individuals a survival advantage over those who have the older version of that gene. Most mutations probably have no effect, while some mutations can even do harm, "knocking out" a gene's function completely. If the mutation knocks out a critical gene, the organism may not develop properly, for example if it can't extract nutrition from food. Such negative mutations won't persist, because individuals with them won't successfully reproduce compared to their normal brethren.
And so it goes. Over billions of years, you get life as we know and love it today.
Now let's more carefully consider the broader impact of these negative mutations. To do this, I want to introduce the concept of evolutionary space. Let's use a simple example. Let's say that an organism has 3 genes, A, B and C, and these genes exist in 2 versions, one with a mutation and one without. If the organism can survive with the mutant forms, there are 2^3 = 8 different gene sets ("genomes") that an organism can have. So 8 different organisms can exist, and the one that's best suited for its environment can prosper. The size of the evolutionary space would be 8.
But now let's say that the organism cannot survive with the mutant form of gene C. So now there are only 2^2 = 4 different genomes that an organism can have - and now only half as many organisms can endeavor to survive!
That seems bad - by having lethal mutations, the evolutionary space has shrunk 2-fold. Intuitively, it seems that the species will persist if it has a larger evolutionary space to explore. And that's exactly what medicine provides - medicine expands evolutionary space.
As an example, take something like infertility, which often has a genetic basis. Historically, if you had a mutation that, say, prevented you from releasing sperm during sex, you could never have children. But with modern surgery you can have children by extracting the sperm and manually injecting it into the uterus. From a "survival of the fittest" point of view, this seems bad - we're just propagating people with lower fitness. But from a social point of view, we're now enabling new combinations of genes to exist in an organism. Genes can do many things, so while a mutant version of a gene may cause sperm not to be released, it's possible that it could provide a survival advantage, such as increasing intelligence or athleticism because the gene functions differently in the brain than in the penis.
So by maximizing the size of the evolutionary space through medicine, you maximize the number of gene combinations that can exist, and this maximizes the chances of producing individuals with unique combinations that have unique survival advantages, especially in a social setting.
That's one view, and one that I think I believe at the moment. An alternative, less optimistic view is that medicine just enables weak genes to survive and weakens the population by enabling such individuals to persist. This makes society more dependent on medicine and related technologies. While this may be true, it seems to me that societies with the greatest medicine might also be the most productive, and this productivity is a fitness advantage for that society as a whole.
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- Feb 7, 2014, 7:33a
I really enjoyed your post. It's a thought process I've been going over a few times and have been trying to tie together; but didn't quite finish. I like your full circle approach. I also conceptually agree with the notion of "evolutionary space" as a property of a population or society that is to be expanded. You can even popularize the concept by calling it specialization and pulling in the economic theory related to that? That would be saying that more diversity, genetically, can potentially lead to more diversity at the phenotypic level, which allows more specific ability -- as one boundary phenomenon.
On the exact point of how medicine comes into this, I think you have touched on something very technical, but profoundly important for the role of science (and medicine / "health" ) in the future of society -- my thought for a long time has been along those lines as well, which is a controversial way of phrasing this thought because it's binary for most people: affected by disease makes it a huge emotional experience, not affected leads largely to denial of personal connection - in my experience - so putting the idea of medicine and associated scientific inquiry into the context of the larger fitness picture of a population is a fabulous full-circle.
In short, thank you for this post!
- Feb 7, 2014, 7:34a
Cool, glad you read it and liked it. I've been thinking about it for maybe a year and finally wanted to write it down, so I could move on. My next post will be about food!
One thing I'm not convinced about is whether more combinations makes for a fitter population. One could argue that keeping "weak" genes in the mix (1) seems bad because they persist, and (2) allows their weakness to be exposed in the future, e.g. more likely to lead to a dead end, i.e. you're just delaying the inevitable. I think those arguments are weakened if there is a lot of pleiotropy, esp. tissue-specific pleiotropy. And not just any pleiotropy - pleiotropy where the same gene has a negative effect in one tissue (e.g. heart) but meanwhile has a positive effect in another tissues (e.g. brain). For example, maybe a specific allele of a fat-storing enzyme causes heart disease in the heart, but in the brain it provides nutrients that enable dramatic growth and increased intelligence. So solving heart disease would keep such people around, benefiting the population as a whole. If one could find some examples like this, I would be pretty much convinced that greater combinations might be a net win.
- Feb 25, 2014, 7:16p
Dengke pointed out today that there is a related area of research called "evolvability", or the capacity for an organism to evolve.
The Wikipedia page is one place to start, thought I didn't find it very clear: http://en.wikipedia.org/wiki/Evolvability
This review paper has some good points: http://www.nature.com/nrg/journal/v9/n1/abs/nrg2278.html