Thursday, September 4, 2014

Evolution for Dummies

Very often, I come across a real knock-down drag-out discussion of evolution on the net. Usually, it involves some sort of creationist, who might, but never does, have cogent criticisms of evolution. He almost always makes a series of arguments against what he thinks evolution is, and makes no sense whatsoever.

Here's the point: Evolution is not some kind of plan. It's the simple statement that mutations occur which cause offspring to be somehow different from their parent or parents. Most such mutations are either trivial or harmful. Some, however, confer, strictly by accident, some sort of advantage which causes the mutated offspring to survive and/or reproduce better, i. e., have more offspring than his nonmutated siblings. As far as anybody knows, all this is completely random.

Let's say there's a species that only eats apples (not giraffes, please), but they're little guys, too clumsy to climb, so they only eat apples that fall on the ground, because they can't reach the apples on trees. Okay so far?  They do fine, eating plenty of apples. We'll call them pomophages. Well, due to a stray alpha particle or something, a mutation occurs, and a pomophage is born that, like a kangaroo or a tyrannosaur, can actually stand partially upright, and is able to eat the apples right off the tree. He survives every bit as well as the others of his cohort, and has some pups of his own, many of which inherit his new ability. After a few generations, there's a few upright pomophages in the herd. Then there's a drought, and the apple trees don't bear as many apples. Suddenly the upright guys can get to apples that the regular guys can't, and they begin surviving a lot better. They have a lot of offspring, the others have relatively few. In a few generations, pomophages are virtually all upright, and the others dwindle and disappear.

In the next valley over, the same thing occurs, except that instead of the upright mutation, a mutation causes a pomophage to be born with longer and more flexible toes. Instead of reaching up to get apples, this toe-pomophage can actually climb up trees and get apples. The same dynamic takes place, and after a few generations, all the toe-pomophages are living in the trees.

In a third valley, there are no advantageous mutations, and the pomophages there die off a lot, but survive the drought.

After many more generations, other genetic changes take place at random in all three groups, and finally they differ so much that they can't interbreed any more, and you have the old pomophage-A species, and two others, pomophage-B and pomophage-C.

Nobody planned anything, nobody calculated anything. Everybody just did their best to survive.

Oh, over in a fourth valley, a mutation made the pomophages more intelligent, enough that they figured out how to butt their heads into the trees to knock the apples down. So that's pomophage-D. And that species got so smart that one day, one of them asked:

"If evolution is real, how come those other three species aren't smart like we are? Huh? Huh?"
And:
"Where are the missing links? Why aren't there any half-upright pomophages, or pomophages with toes that are only a little longer?"
And:
"How come we're not evolving now?"

And other silly questions.

Here's Greg Cochran to talk about pygmies and evolution:

Pygmification

A recent paper in PNAS talks about the  evolution of the Pygmies – or, more exactly, the Pygmy phenotype, because it seems to have happened independently in the Biaka Pygmies (west Africa) and the Batwa pygmies of Uganda.  The two groups have different genetic mechanisms for being short. Their shortness really is genetic, of course. Pygmies are mixed, to a degree: the more Bantu ancestry they have, the taller they are. And although height really is affected by nutrition, Pygmies are about six standard deviations shorter: someone of normal potential height would have had to starve to death (twice!) to be that short, and there would be lots of other symptoms of malnutrition that Pygmies don’t have.
Still, there were those who thought otherwise, presumably because they’d stuck a crayon up their nose as a kid. Way up. Environment does matter!
I noticed an interesting comment on this in Science: Michael Balter said “scientists had not been sure to what extent Darwinian natural selection is actually responsible for the Pygmy body type and how many times it has arisen over the course of evolution.”  The bit about how many times it had arisen is reasonable – that takes looking at the genotype to be sure, and indeed it has occurred five or more times (in Africa and Southeast Asia).  But there was no reason to wonder whether those changes were a product of Darwinian natural selection: that was a sure bet. Not just because it has happened multiple times in similar rain-forest environments. Darwinian natural selection is always operating.
Natural selection is not an odd, unusual, poorly understood phenomenon like ball lighting.  It is not something that last occurred 50 million years ago, like a kimberlite pipe eruption.  And, of course, it applies to human behavioral traits, which are significantly heritable. Unless you think that the optimum mental phenotype (considering costs and payoffs) was the same in tropical hunter-gatherers, arctic hunter-gatherers, neolithic peasants, and medieval moneylenders (which would strongly suggest that you are an idiot), natural selection must have generated significant differences between populations. Differences whose consequences we see every day, and that have been copiously documented by psychometricians.
This notion that ongoing natural selection is not the default – that it only happens on national holidays or whatever – is fairly common among biologists.  Obviously untrue, because you can’t even have things stay the same without ongoing selection – otherwise mutations and drift would gradually ruin everything.  Only selection lets horseshoe crabs outlast mountain ranges.
Sure, some of this is because the topic of human psychological differences makes biologists upset, or threatens to impose unemployment and/or celibacy – but it also shows up in  topics that don’t seem to have much emotional or political charge. I think that only a few biologists reject those unexciting examples of ongoing natural selection because of a realization that they logically imply other, controversial conclusions.  They do have such implications, but I think that poorly understood neutral theory plays a bigger role.
The original is here:http://westhunt.wordpress.com/2014/08/24/pygmification/
And he has more to say about pygmy evolution here:http://westhunt.wordpress.com/2014/08/26/the-wrong-path/

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Quibcag: Well, because this is a science quote, I resorted to using Rika Shiguma of Haganai (はがない) again, because she's the cutest anime girl scientist I can find.

9 comments:

  1. I met a few people who believe in both creation and evolution.

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    1. There are probably a lot of them. "Creationist" seems to be a term for those who don't accept evolution, though. I have a vague notion that the Catholic Church has basically endorsed Darwinian evolution.

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    2. From memory here, no idea how to look it up: Pope John Paul II wrote a paper (not ex cathedra, just his opinion) saying if God wants to work via evolution, that's His business. Don't put God in a box, as He said to Job.

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  2. You're leaving out Sexual Selection which is certainly not "strictly by accident".

    And there's also Edward O Wilson's updated version of group selection.

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  3. Evolution is a process that changes the allele frequency in a population so, I suppose, group selection is an attractive hypothesis but it only makes sense to me if I restrict natural selection to the level of the gene. However, a gene does not exist in isolation but is part of a unique package the individual organism inherits. I reiterate an earlier observation that evolution happens to the population but selection happens to the individual. At best group selection is a mildly useful metaphor. At worst, it is Deepak Chopra playacting at being Sarah Hrdy.

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  4. Early evolutionary theory was advanced by Catholics like Jean-Baptiste Lamarck who is is mostly remembered by being spectacularly wrong on how new traits enters a species. OTOH, the Augustinian monk Gregor Mendel's humble experiments with peas led to profound insights on inheritance and laid the groundwork for the new synthesis.

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  5. Evolution is about changes within a species leading to adaptations to environments that help affected populations survive in specific environments. This leads to variation within a species or even the rise of new species. Now what happens when you have people moving between environments on a frequent basis and/or intermarrying with people from other environments as you find in the USA and in much of the rest of the Americas?

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  6. "Evolution is a process that changes the allele frequency in a population so, I suppose, group selection is an attractive hypothesis but it only makes sense to me if I restrict natural selection to the level of the gene. However, a gene does not exist in isolation but is part of a unique package the individual organism inherits. I reiterate an earlier observation that evolution happens to the population but selection happens to the individual. At best group selection is a mildly useful metaphor. At worst, it is Deepak Chopra playacting at being Sarah Hrdy."

    This makes no sense. Selection doesn't happen to the individual; selection happens to the individual's descendants, if any. In other words, selection happens to the population. You are making a distinction between evolution and selection which does not exist: evolution is selection, whether natural, artificial, sexual, or other. You can do whatever you want as an individual, but you yourself will never "evolve". Your actions can change allele frequency in a population, so you can influence evolution, but you yourself will never evolve. Evolution is about population groups, not about individuals.

    This liberatarian abhorence of groups and deification of the individual is absurd and is, in fact, far closer to Deepak Chopra's "woo" than evolutionary group psychology is. Group selection is what evolution is all about; individuals do not evolve. Whether the group is called a species, sub-species, race, or something else is not important. Its allele frequency changes; the individuals do not change, they merely act in ways that change future allele frequency within the group population. Groups compete with other groups; sometimes they cooperate; it isn't only individuals who compete (or cooperate). Evolution simply doesn't make any sense if you can't think of it in terms of group selection. The diversity of life on this planet is inexplicable if we aren't allowed to think in terms of group selection.

    "a gene does not exist in isolation but is part of a unique package the individual organism inherits" -- Yes, but an individual organism does not exist in isolation, either, but is part of a group without which the individual whould not exist...."group selection is an attractive hypothesis but it only makes sense to me if I restrict natural selection to the level of the gene"...what does this even mean, and why should it invalidate group selection?

    You literally aren't seeing the forest because all you can see are individual trees.

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  7. "Here's the point: Evolution is not some kind of plan. It's the simple statement that mutations occur which cause offspring to be somehow different from their parent or parents. Most such mutations are either trivial or harmful. Some, however, confer, strictly by accident, some sort of advantage which causes the mutated offspring to survive and/or reproduce better, i. e., have more offspring than his nonmutated siblings. As far as anybody knows, all this is completely random."

    The problem with dealing with Creationists and the general public which is ignorant of basic science, is that you are using loaded words. You know that your use of "completely random" refers to the appearance of mutations; a Creationist hears this and thinks you mean "the process of Evolution itself is completely random" which is untrue. Evolution is not random: evolution is selection, which is non-random. Nature is selecting those features which result in evolutionary fitness to a particular environment (ie, more offspring).

    The general public hears "mutation" and thinks radiation-created monsters like from the 1950s horror movies. All mutations are, are errors in DNA replication or RNA replication. In other words, a mutation is a change from the original genome, due to any cause at all - not just from radiation. It's a replication error. Most mutations are harmless but the public has been trained to think of mutations as harmful, thus, "mutation" is a loaded word, just like "random" is a loaded word, because of the popular connotations of those words.

    This underlying source of random mutations gives natural selection material to work with - and it is natural selection which is non-random. This is the important point that, once grasped, saves people from the delusions of the Creationists. If you can't get people to understand the non-randomness of evolution, then you'll never get them to understand evolution.

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