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“Does natural selection evolve things to perform healthily?”
July 26, 2010 8:07 AM   Subscribe

“Does natural selection evolve things to perform healthily?”

“It seems evident that natural selection evolves plants and animals to be healthy on a physical and physiological level. Does this dynamic also apply to the psychological and collective/cultural performance of animals whose psychological and collective/cultural forms have been evolved through natural selection?”
posted by plungerjoke to Science & Nature (32 answers total) 3 users marked this as a favorite
 
Homeworkfilter?
posted by afx237vi at 8:10 AM on July 26, 2010


No. Posted for a friend who is trying to see why I like this site so much.
posted by plungerjoke at 8:11 AM on July 26, 2010


I'm not sure it is entirely evident - selection is in favour of those who reproduce and whose offspring survive. If there is a trait that allows the reproduction of healthy infants whilst being less healthy for the mother, as long as the mother survived long enough to give infant care etc, then that would be beneficial. The most obvious example of this is the human head versus the human pelvic canal, giving humans a prolonged and dangerous birth; but there is obviously something in that head size that is selected for, so ending up with poorer maternal health than if there were a smaller head.

So without even going into the issues of group selection, I find the initial posit is not actually 'evident' at all.
posted by Coobeastie at 8:16 AM on July 26, 2010 [4 favorites]


I think you'd get a lot of insight into this question by reading Richard Dawkins's book The Selfish Gene. I don't think it's entirely accurate to say that collective behavior evolves through natural selection, but the idea of "memes" (units of cultural inheritance) was originally introduced towards the end of this work.
posted by vytae at 8:22 AM on July 26, 2010


The 'New Science on Morality' post may be helpful here--discussion of evolutionary & biological basis for human morality. So some scientists apparently think that evolution applies to collective/ cultural behavior like morality in humans. Moral modularity is another cognitive science/ evolutionary perspective on the evolution of cultural and innate behavior.

So not only is AskMe awesome, so is Metafilter generally.
posted by _cave at 8:23 AM on July 26, 2010


It seems evident that natural selection evolves plants and animals to be healthy on a physical and physiological level. Does this dynamic also apply to the psychological and collective/cultural performance of animals whose psychological and collective/cultural forms have been evolved through natural selection?

Any given species tends toward collective/cultural behaviors that help them produce offspring and continue to exist. A colony of ants, for instance, has obviously developed a very speciallized and efficient system of behavior that helps the colony as a collective function better in a given environment than a similar number of ants working completely independently. I'm not sure how you would measure the psychological and collective/cultural "health" of such as colony though. What would be examples of healthy versus unhealthy behaviors when referring to these kinds of collective behaviors in animals?
posted by burnmp3s at 8:26 AM on July 26, 2010


Natural selection selects for the ability to survive and reproduce. These are binary issues -- whether a plant or animal survives, or whether it is able to reproduce. Health is a much messier concept. I think of health as being dependent on how well a particular creature's traits match its particular environment. In a fixed environment, natural selection probably does select for health, since healthier creatures can probably survive and reproduce more effectively. But environments are not static. When changes occur, appropriate adaptations sometimes emerge and a certain sort of creature continues to thrive. Sometimes they don't, and the health of a population suffers.
posted by jon1270 at 8:27 AM on July 26, 2010 [2 favorites]


It seems evident that natural selection evolves plants and animals to be healthy on a physical and physiological level

Natural selection doesn't 'evolve' plants and animals to any particular end. Natural selection is the result of certain inherited traits predisposing individuals to survive to the point of producing viable offspring. In other words, I think your statement implies intent where there is none. A healthy organism is more likely in many cases to survive and reproduce than an unhealthy one, but there will be many cases where, for example, a super-fit organism turns out to be more susceptible to a particular disease than an organism that appears less fit to survive. So it's more about those organisms having just the right set of attributes to survive the various death-inflicting factors around them. Good health is just one factor in a complex set of biological and environmental variables.

Your actual question is all over the place though. What is 'psychological and collective/cultural performance'? Pretty much whatever you want it to be, I'd say. And are you saying that some animals have evolved this particular 'performance' while others have not? The closest I can come to an answer, I think, is that there's no reason to suspect that the social and psychological makeup of various animal species is not in whole or in part a result of natural selection.
posted by le morte de bea arthur at 8:28 AM on July 26, 2010 [11 favorites]


I wouldn't say that your premise is as evident as you indicate. As Coobeastie points out, the fundamental driving principle of natural selection is that genotypes that produce phenotypes that successfully reproduce are the genotypes that survive. In fact, it is often evolutionarily favorable for individuals to become sick and die after reproducing; salmon that die en masse after reproduction is complete, female spiders that eat their mates after copulation.

Psychological health is pretty closely tied to physical health, so I'd say it is governed by the same principles as physical health; i.e. selected for only so far as reproduction is concerned. Of course, the animal genome is an enormously complicated basis for an evolutionary code - the myriad mutations and genetic crossovers that occur in every individual cause many complicated changes in phenotype. What I'm trying to say is that there is plenty of room for many "sick" individuals within an evolving population.

The question of cultural evolution is much more complicated. There is a natural selection principle at work, but it's only vaguely reminiscent of the evolutionary principle for animals. I think the question of the evolution of cultural forms (let alone "healthy" cultural forms) is way to vague to be discussed with any rigor. The health of a culture or cultural form is pretty relative. One might define Fascism as a very healthy cultural form, since it is highly virulent. Perhaps if you define what you mean by the health of culture, it'll be easier to answer your question. Interesting topic though - cheers!
posted by Salvor Hardin at 8:30 AM on July 26, 2010 [2 favorites]


The book Your Inner Fish goes over several examples of evolutionary tradeoffs that have led to humans having bad knees, hemorrhoids, and hernias. These are arguably cases of natural selection not selecting for human health. However, as noted above, "natural selection" isn't an entity with a game plan.
posted by ldthomps at 8:41 AM on July 26, 2010


Premise is flawed, for example Sickle Cell Anaemia has an evolutionary advantage within certain populations but individuals could not be described as 'healthy on a physical or physiological level.'
The rest of the question is meaningless, hand-wavey bullshit.
posted by SyntacticSugar at 8:41 AM on July 26, 2010 [2 favorites]


Evolution is a "good enough" system. If you are healthy enough to produce offspring, evolution doesn't "care" if you're unhealthy in other ways (e.g., have a gene that contributes to the likelihood of developing schizophrenia? Doesn't matter, as long as you're able to reproduce).

I agree with others that assessing the "health" of population's culture/psychology is way too subjective and culture-bound itself to make any decent hypothesis (that is, one that is testable) wrt the role of evolution in its development.
posted by rtha at 8:50 AM on July 26, 2010 [5 favorites]


The question is tautological--the definition of "healthy" for any given organism depends on what it has evolved to do, and so ultimately what you're asking is: "does natural selection favor organisms that do what they do, well?" Which is, of course, what natural selection is all about.

Concretely:

natural selection has resulted in some species that compress their entire life cycle into a few days. Is this healthy? It is if you're a fruit fly. But a lifespan measured in days is not healthy if you're a tortoise. Cannibalizing parts of your own body to provide energy to survive would not seem like a healthy behavior in most organisms, but if you're a metamorphising tadpole on your way to frog-dom, that's a perfectly healthy process.

In a psychological vein, you might think of flight-response prey species like antelope or horses or rabbits. In human terms, they are paranoid as all fuck. Anyone who's ever spent much time around horses will realize that millenia of domestication has not been entirely successful in breeding out the paranoia from these creatures. This is, of course, a healthy psychological state if you're big, fast, and tasty to lions, but would be unhealthy if you were, for example, the lion. Or a prey species that is small and depends on sitting still and being camouflaged for defense.

Similarly, some species have evolved to operate in groups, and are psychologically dependent on the herd. Other species live in isolation and become psychologically stressed if there are too many others around. In the world of our familiar domestic animals, for example, rats are highly social and are psychologically healthier if they are kept with others of their kind. Hamsters, on the other hand, descend from relatively solitary stock, and it can be very tricky to keep two together in a cage, and they're notorious for killing their cagemates. A lone rat is an unhappy rat. A lone hamster is a happy hamster. They've evolved to do what they do, which is what evolution is all about.
posted by drlith at 9:10 AM on July 26, 2010 [1 favorite]


The question, as others have pointed out, is flawed to the point of being unanswerable in any meaningful way. Selection doesn't "evolve things to" anything...thinking of selection as a teleological process is a category mistake.

That is, it isn't like there's a plan, it's just that stuff that doesn't survive, doesn't survive...the things that do, reproduce and pass their genes on to the next generation.
posted by griffey at 9:15 AM on July 26, 2010


It seems evident that natural selection evolves plants and animals to be healthy on a physical and physiological level.

The unromantic, literal point of sexual reproduction — the entire reason why sexual reproduction was selected for and is so successful on an evolutionary scale — is that you die. If disease or predators don't catch up with you, being killed off by your own genes is ultimately not healthy. But you do make room for the young 'uns who may have a better set of genes than you.

One might argue that selection breeds for "health" to the point where reproduction and rearing of young is successful enough that the next generation can reproduce themselves. Beyond that, senescence, cancer, disease, wolves, etc. are fairly likely to take you out. So "health" is a pretty loaded term from the start and would need to be defined more stringently.
posted by Blazecock Pileon at 9:22 AM on July 26, 2010 [1 favorite]


“Does natural selection evolve things to perform healthily?”

Organisms are selected for their ability to make other organisms. Whether the organism is "healthy" is beside the point. If, say, you had an organism that always died on Day 2 of its life, it would do just fine ... provided it could birth two child organisms on Day 1 with a high rate of success.
posted by Cool Papa Bell at 9:34 AM on July 26, 2010


No.

Evolution "selects" for a momentary advantage. If, for example, an alien force appeared that massacred every penguin unable to recite the complete lyrics to Lady Gaga's "poker face," (Yes, I've been watching Dr. Who and listening to Lady Gaga, why do you ask?) the surviving penguins would be genetically more inclined to display an affinity for queer-friendly pop music, assuming that it's a heritable trait.

That these aliens never again return to Antarctica to murder penguins (Thanks, no doubt, to The Doctor's helpful interventions.) doesn't affect that LGQFPMA (Lady Gaga queer-friendly pop music affinity) was a trait that was, at one point, selected for.

So no, it's not evident that evolution selects for healthy critters. Consider the Cornish Cross chicken and how its primary predator (*waves*) selects it.

Regarding cultural selection, it's worth remembering that colonial Salem did a fine job of selecting for people that weren't witches.
posted by stet at 10:17 AM on July 26, 2010 [2 favorites]


I'm wondering if "healthy on a physical and physiological level" is another way of saying, "survival of the fittest" but in the case of natural selection, "fittest" is only another way of saying best adapted. As others have pointed out, the best adaptations are not always about being big, strong or resistant to disease. Sometimes just living long enough to reproduce without exhausting your immediate resources is plenty good enough. Our particular physiology is a product of the chain of apes that stretched out across the continent. There was no single environment to adapt to, and if some did adapt perfectly to a certain niche they probably disappeared along with it or were pushed out of it by our more generalist ancestors.

I've seen a couple of good documentaries about certain isolated colonies of baboons in South Africa that might apply to your question. Inbreeding and poor diet has screwed their health and behavior relative to the more robust, stable colonies in other parts of Africa but they're still surviving in this isolated location. I suppose if disease were to somehow wipe out all the other populations, then these ugly, twitchy baboons could go on to repopulate the other ranges and it wouldn't have been a result of them having been "fittest".
posted by bonobothegreat at 11:44 AM on July 26, 2010


I've heard it best described as not the 'survival of the fittest' but rather the 'survival of what ever works well enough'.
posted by buttercup at 12:33 PM on July 26, 2010


To the degree that health supports survival, yes.
posted by Mertonian at 1:26 PM on July 26, 2010


Response from friend:
I wouldn't say that your premise is as evident as you indicate. As Coobeastie points out, the fundamental driving principle of natural selection is that genotypes that produce phenotypes that successfully reproduce are the genotypes that survive. In fact, it is often evolutionarily favorable for individuals to become sick and die after reproducing; salmon that die en masse after reproduction is complete, female spiders that eat their mates after copulation.



Psychological health is pretty closely tied to physical health, so I'd say it is governed by the same principles as physical health; i.e. selected for only so far as reproduction is concerned. Of course, the animal genome is an enormously complicated basis for an evolutionary code - the myriad mutations and genetic crossovers that occur in every individual cause many complicated changes in phenotype. What I'm trying to say is that there is plenty of room for many "sick" individuals within an evolving population.



The question of cultural evolution is much more complicated. There is a natural selection principle at work, but it's only vaguely reminiscent of the evolutionary principle for animals. I think the question of the evolution of cultural forms (let alone "healthy" cultural forms) is way to vague to be discussed with any rigor. The health of a culture or cultural form is pretty relative. One might define Fascism as a very healthy cultural form, since it is highly virulent. Perhaps if you define what you mean by the health of culture, it'll be easier to answer your question. Interesting topic though - cheers!

posted by Salvor Hardin at 8:30 AM on July 26



Thank you for your insightful comments, and for pointing out the gaps in my premise. Defining health and illness is a starting point. I define illness as a occurring when a part of the whole (system) is acting in a way that damages the whole. Health is the absence of illness.



By these definitions a broken leg, asthma, diabetes and Alzheimer’s are illnesses. However, falling asleep, digesting food and losing excess weight are not illnesses. Also, from the perspective of the animal in a natural system, starvation, physiological disease, being killed by a predator and old age are forms form illness. However, from the perspective of the natural system these events are healthy as they facilitate natural selection and regulate the performance of the ecology.



What I am proposing for discussion is that natural selection (as occurring prior to the Neolithic revolution) generates healthy physiological, psychological and cultural (collective) forms. These systems need to compete to survive. They need to be fit (e.g. an uncompetitive species may become extinct). I propose that healthy performance is a prerequisite for fitness, e.g. unhealthy systems are not competitive. Therefore natural selection (again, as occurring prior to the Neolithic revolution) does not evolve unhealthy systems. This being said, from the perspective of the animal illness does occur in these systems.



As regard to genotypes: The genotype of a fit individual member of an ailing species would have little survival advantage and thereby individual genotypes depend on competitive psychological, social and species performance in order to successfully propagate. This could be referred to as the gene-trait link, i.e. how genes are linked to physiological, psychological, social/cultural/collective, species, and ecology form and performance.
posted by plungerjoke at 2:27 PM on July 26, 2010


Not exactly. There is some overlap between "health" and what evolution selects for, but evolution does not select for individual or population health on any level--physical, psychological, or cultural. Evolution acts purely on the genetic level--on average, genes that are successful at reproducing themselves increase their representation in subsequent generations.

That's it. Evolution does not act on any other level. Evolution is, however, a powerful metaphor that can be useful in thinking about other situations, like how cultures "evolve" over time with some traditions enduring and some not. This process is analogous in many ways to evolution but its mechanism is fundamentally different.

It's an interesting question and one worth thinking about; however, before embarking on it I would recommend really honing your understanding of exactly what evolution is. It is, strictly speaking, incorrect that "natural selection evolves plants and animals to be healthy on a physical and physiological level." It really looks true! But it's not precise, and it turns out there are some subtle distinctions that make precision important here. Richard Dawkins' The Selfish Gene may be a good place to start.
posted by kprincehouse at 2:40 PM on July 26, 2010 [1 favorite]


One additional thing to consider about the definition of "health." There are things that are "unhealthy" that provide inobvious benefits. For example, there's the case of sickle-cell disease and malaria, in which carrying the gene for a disease provides a benefit against another disease.

But even developing full-blown sickle-cell doesn't usually prevent reproduction in an affected individual.

This is another case of evolution pointing toward the notion of, "Us gametes don't really care what happens to you, so long as you can help us make enough zygotes before you kick the bucket."
posted by Cool Papa Bell at 2:49 PM on July 26, 2010


"Healthy" is a relative term; not even amongst different species but different times.

Evolution isn't about making things healthy; its about making things more likely to adapt to the changing environment.

If you are using "healthy" as "better AVERAGE rate of survival than the AVERAGE rate of survival for previous generations in the same environment", then yes...makes 'em healthy.
posted by hal_c_on at 8:12 PM on July 26, 2010


What I am proposing for discussion is that natural selection (as occurring prior to the Neolithic revolution) generates healthy physiological, psychological and cultural (collective) forms. These systems need to compete to survive. They need to be fit (e.g. an uncompetitive species may become extinct). I propose that healthy performance is a prerequisite for fitness, e.g. unhealthy systems are not competitive. Therefore natural selection (again, as occurring prior to the Neolithic revolution) does not evolve unhealthy systems. This being said, from the perspective of the animal illness does occur in these systems.

At the very root of it, I think you have a fundamental misunderstanding of what natural selection is and isn't. First, natural selection is a process that simply occurs with no regard to any sort of outcome or eventual end. Second, it's a process that occurs on the level of individual organisms, with results that affect gene pools. Some individuals will have more or fewer children than others, thus passing on more or less genetic material. That's natural selection.

You're focused far too much on the collective. "Health" only plays a role insofar as the health of an individual affects its ability to have children and thus pass on genetic material. There really is nothing to the idea of a species or population being "healthy" or "unhealthy"—it's the individuals that are healthy or otherwise. Systems aren't competing to survive, and, for the lifespan of any individual, nor are species. There's more than enough room for multiple species in direct competition for resources to exist at any one moment or lifespan in history. In geologic or evolutionary time, yes, competition will eliminate the less fit forms, but not in the sense that you're thinking. Either less competitive populations will become extinct—again, in thousands of generations—or they will adapt to take advantage of another ecological niche.


As regard to genotypes: The genotype of a fit individual member of an ailing species would have little survival advantage and thereby individual genotypes depend on competitive psychological, social and species performance in order to successfully propagate. This could be referred to as the gene-trait link, i.e. how genes are linked to physiological, psychological, social/cultural/collective, species, and ecology form and performance.

For the life of me, I just can't parse this.* Refer to above: individuals that are fit will pass on genes, period. What happens to the populations of which those individuals are members depends on what happens to all of the other individuals in that population and the genes they pass on too. "Systems" are human-created abstractions built around natural phenomena to help us parse the complexities of what's happening. They have no "perspectives," "desires," or any other anthropomorphic qualities.

*I have an extensive background in paleoanthropology and human evolution, and none of the framing or phrasing of the questions here are anything like those actually used in the field.
posted by The Michael The at 9:23 PM on July 26, 2010 [1 favorite]


Oh, I forgot to add: in the OP's response, he twice proscribes the question to "before the Neolithic revolution." The mechanisms of evolution, as defined, have nothing that causes them to cease applying after the shift to agriculture and urbanity. Drift, mutation, and gene flow all certainly continue, and if there's a change in the rate of natural selection, it's a result of different types and intensities of selective pressures, but it certainly hasn't ceased. That really gets me to think that the OP is phrasing a question with hopes of a result of something like "this crazy modern world is screwing up people" or some other such nonsense.
posted by The Michael The at 9:35 PM on July 26, 2010


You may want to look at the Stanford Encyclopedia of Philosophy page on Concepts of Disease and Health.

I don't exactly understand your contention that natural selection does not evolve unhealthy systems if "from the perspective of the animal illness does occur in these systems." What's this "from the perspective of the animal" bit doing? You're relativizing health to various systems and playing with different levels of selection when discussing evolution... all of this makes it pretty difficult to figure out what your claim is.
posted by painquale at 1:18 AM on July 27, 2010


What I am proposing for discussion is that natural selection (as occurring prior to the Neolithic revolution) generates healthy physiological, psychological and cultural (collective) forms.

This only works if you substitute "reproductively competitive" for "healthy." A lot of posters who understand evolutionary biology have come to this party before me, but I can't resist chiming in. Natural selection doesn't care if individuals are healthy or not. In fact, if our species had originally evolved to live for 500 years, free of all cancers or degenerative disorders, but a hypothetical mutation was introduced that shortened our lifespan to 30 and caused us to all have multiple tumors, but that mutation somehow allowed us to raise 3x as many children to maturity, what do you think would happen? Yeah. We'd all be dying young, being less healthy from an individual standpoint, but we'd be having a lot of kids. Natural selection is all about how many offspring you can pop out; natural selection doesn't care about how good we feel while we're doing it, or what happens to us when we're past the childbearing years.

(Another example: in my lab, I make a lot of genetically-engineered bacteria that produce specific pieces of DNA that I want. It's hard for the bacteria to make these pieces of DNA -- the DNA pieces are really big and long and take a lot of resources that the bacteria could be using to make more copies of itself. This bacterium is a less-healthy cell than a wild-type bacterium that doesn't have to spend half its energy making weird DNA for me. In fact, it's so weak that I have to coddle it, growing it in specially-fortified culture medium kept at body temperature whereas the wild-type bacteria can grow in almost anything that has some nutrients and isn't frozen. But, because I select for the genetically engineered bacteria using antibiotic resistance genes, the engineered bugs are much more fit from a standpoint of selection than the wild-type ones, so they are the only ones who reproduce.)

Could it be that you have some confusion between "physical fitness" (i.e., not being too fat or sick, and being able to lift heavy things and do a lot of work), and "evolutionary fitness" (i.e. being able to pass on your genes by having lots of offspring?) I see a lot of people, frequently advocates of Crossfit and the paleo diet, who are confused and conflate the "fitness" they're thinking of (which has a lot to do with being healthy), with "fitness" in an evolutionary sense (which has much less to do with being healthy on an individual level).
posted by kataclysm at 7:38 AM on July 27, 2010


More from question author:
…Evolution acts purely on the genetic level--on average, genes that are successful at reproducing themselves increase their representation in subsequent generations….That's it. Evolution does not act on any other level.



posted by kprincehouse at 2:40 PM on July 26 [1 favorite]



I propose that evolution acts on many levels, for example, the level of species. For example, Neanderthals did not survive and our species did. We were more competitive as a species and thus were selected for and Neanderthals selected against (i.e. less genetic propagate in the ecology).

***************************



…genes that are successful at reproducing themselves increase their representation in subsequent generations.



That's it. Evolution does not act on any other level.

posted by kprincehouse at 2:40 PM on July 26 [1 favorite]





I propose that the genotype’s propagation is dependent on the survival advantage (fitness) of the phenotype. And that the phenotypes survival advantage depends on the survival advantage of the psychological, social, cultural, collective, species and ecological systems that it is a part of. In this way the genes are linked to all these layers.



***************************************

Oh, I forgot to add: in the OP's response, he twice proscribes the question to "before the Neolithic revolution." The mechanisms of evolution, as defined, have nothing that causes them to cease applying after the shift to agriculture and urbanity. Drift, mutation, and gene flow all certainly continue, and if there's a change in the rate of natural selection, it's a result of different types and intensities of selective pressures, but it certainly hasn't ceased. That really gets me to think that the OP is phrasing a question with hopes of a result of something like "this crazy modern world is screwing up people" or some other such nonsense.

posted by The Michael The at 9:35 PM on July 26



Prior the Neolithic revolution the human species was a natural system, i.e. a system ultimately being regulated by natural selection. Due to the relatively limitless food supply created by the invention of agriculture the gene-trait link was broken and so after the Neolithic revolution natural selection no longer regulates the human species. That is, after the Neolithic revolution the human species can no longer be defined as a natural system. Of course genetic change still occurs in the species but calling it natural selection not precise. After the Neolithic revolution you could describe genetic change in the human species as “natural selection in a non-natural system”. I think it would be better to say it is governed by a different process than natural selection.



For example, war did not occur prior to the Neolithic revolution. Describing war a form of natural selection does not really fit.



No hidden agenda – an open book, for open discussion.



Thanks for the insights.
posted by plungerjoke at 11:34 AM on July 27, 2010


Bit more:

I don't exactly understand your contention that natural selection does not evolve unhealthy systems if "from the perspective of the animal illness does occur in these systems." What's this "from the perspective of the animal" bit doing? You're relativizing health to various systems and playing with different levels of selection when discussing evolution... all of this makes it pretty difficult to figure out what your claim is.

posted by painquale at 1:18 AM on July 27



Thanks for your comments. Sorry for not explaining what I meant. I propose that the phenomenon of health and illness are relative to the system from which they are being observed (this is inherent in the definition: illness occurring when a part of the whole (system) is acting in a way that damages the whole. Health is the absence of illness). For example, eating a banana is a healthy thing for me but a very unhealthy thing for the banana. Another example, a lion eating a zebra in the wild is very unhealthy for the zebra but from the perspective of the natural world it is a healthy way of maintaining and developing the ecology of the natural system. One could consider physiological disease, predators, old age (lifespan) and starvation as being illness from the perspective of the creatures that suffer from them. However, from the perspective of the natural system, these things can be seen as the mechanisms through which natural selection operates and so are a healthy and positive part of the system.
posted by plungerjoke at 11:34 AM on July 27, 2010


Prior the Neolithic revolution the human species was a natural system, i.e. a system ultimately being regulated by natural selection. Due to the relatively limitless food supply created by the invention of agriculture the gene-trait link was broken and so after the Neolithic revolution natural selection no longer regulates the human species. That is, after the Neolithic revolution the human species can no longer be defined as a natural system. Of course genetic change still occurs in the species but calling it natural selection not precise. After the Neolithic revolution you could describe genetic change in the human species as “natural selection in a non-natural system”. I think it would be better to say it is governed by a different process than natural selection.

1) the natural/non-natural distinction that you're making is arbitrary and meaningless. In fact, you're trying to define it circularly: it's non-natural because natural selection isn't at work, natural selection isn't at work because it's non-natural. The changes to how humans live have no impact to the processes of evolution.

2) your Neandertal example is way off. Species can not be selected for or against! Again, only traits are selected for/against.

3) no war before the Neolithic? Wrong. Even chimps war against other bands of chimps, so it's a safe assumption that humans and prehumans have been killing each other for 8 million years.
posted by The Michael The at 6:08 PM on July 27, 2010 [2 favorites]


Adding onto The Michael The's first point: We are a part of nature. The most urban urbanite living in a one-bedroom apartment with central heating and refrigerated factory-made food is a part of the natural environment. During the Neolithic revolution, humans (who had already evolved a series of traits) were able to adapt, by virtue of the traits they already possessed, to do stuff like develop agriculture and construct permanent dwellings.

Nobody would say that ants are not a natural system, even though many ant species construct permanent dwellings for themselves and several species of ant cultivate food (fungi grown on chewed leaves and aphids, to name the two examples that come straight to mind) and also enjoy a "limitless food supply".

In fact, the laws of natural selection continued to operate after the Neolithic revolution. The invention of agriculture seems to have strongly selected for traits in multiple human populations, including the ability to digest dairy (at least, in many Western Europeans), and increased resistance to multiple microbe-born illnesses.

It's a mistake to think of the Neolithic revolution -- or any other development in human history -- as a bridge separating Humans from Nature. Liberal arts students and philosophers can perhaps be excused for thinking in those terms, but that isn't how the world actually works. We are human animals, and we are inextricably entwined with the natural world. It may be that several traits that conferred selective advantage when most of the population were hunter-gatherers (e.g. a fondness for sugary and/or fatty, high-calorie foods) are no longer particularly adaptive given the ways in which we have altered our lifestyles and environments through technology, but that doesn't mean that we don't live in the natural world anymore. It might even mean that some maladaptive traits are widespread in our species, and that (for example) an individual whose high metabolism recklessly burns calories and who isn't hardwired to seek out salt, sugar, and fat might have a selective advantage NOW, whereas they probably would have died of famine in the past. It might also mean that some traits, that previously would have been lethal, are allowed to propagate (i.e. kids with rare genetic conditions can be diagnosed, treated, live to maturity, and perhaps pass their genes on to offspring if they choose to). But none of this means that natural selection doesn't work anymore -- at most, a particularly maladaptive trait might take a longer time to vanish from the population.
posted by kataclysm at 11:15 AM on July 28, 2010 [1 favorite]


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