Testing Evolutionary Explanations


Recommended Posts

Evolutionary arguments have been invoked to defend or attack various positions here and elsewhere. The typical form of these arguments has been to link some phenomenon with natural selection via a "just so" or story scenario, expressing a qualitative and intuitive model of causation. Many biologists, such as Brian Goodwin, have criticized this method for being arbitrary. (See Goodwin's "Evolution and the Generative Order" in Theoretical Biology: Epigenetic and Evolutionary Order from Complex Systems, edited by Goodwin.)

An example of this might be why did wolves come to be pack animals. The "just so" story might go along the lines of this offers a competitive advantage, so wolves must have evolved along this path and that explains it. In in this example, the story is tenuous and there's no other evidence offered. Note that no attempt is made to find the exact evolutionary path the wolf ancestors took to arrive at their current arrangement. Instead, a story is offered as an explanation and the explanation ends with that.

One might argue that using a flawed method of explanation is better than using none at all. Science can work with faulty explanations. Instances of such abound in the history of science. Bohr's model of the atom, e.g., is now known to be wrong, but it did focus attention on the important traits of atoms at that time, and hacked a path over which later thinkers could travel toward better theories.

It can also be argued that any explanation we have at any point will always be flawed. Human knowledge will never be perfect or complete. I agree with this and that a "just so" explanation can be a starting point for further inquiry.

Still, in evolutionary biology there are better means of evaluation than making up a good scenario of how things came to be. They are not perfect, though they are almost all better than "just so" explanations in that they offer a testing methodology. Some of these methods have the benefit, so important in science, of being independent of particular causal theories of evolution – such as the neo-Darwinian "Synthetic" Theory, the entropic "Unified Theory" (see Brooks' and Wiley's Evolution as Entropy), and the Neutral Theory (see Motoo Kimura's The Neutral Theory of Molecular Evolution). These methods include paleontology, population biology, phenetics, and cladisitics. Here I will concentrate on cladistics, though I'm doing so to illustrate the point and not because cladistics is the best method of all. (I'm also using it because it's the method I'm most familiar with both in terms of application and theory.)

Cladistics uses the traits of biology groups, such as populations, species, and genera to reconstruct the lineage of the groups. The method aims at a transparent recovery of the history of "cladogenic" events – that is of splits in ancestral groups. By "transparent" is meant a method that does not rely on intuitive notions and should allow others to quickly and repeatedly get the same results without bias. This is akin to addition or multiplication. If someone adds one number to another to generate a third, anyone should be able to repeat the process and clearly see how the third number is generated. (See Wiley et al. The Complete Cladist: A Primer of Phylogenetic Procedures.)

To give an example of this, Barbara A. Block et al. test the hypothesis that endothermy evolved only once in fishes in "Evolution of Endothermy in Fish: Mapping Physiological Traits on a Molecular Phylogeny" (Science (260) 1993 April 9). Endothermy is, in lay terms, warm-bloodedness. Put simply, the hypothesis is that warm-bloodedness came about once and was passed along to all other warm-blooded fishes. This would mean that all warm-blooded fishes should be more related to each other than they are to non-warm-blooded fishes – in the same way that I'm more related to my brother than I am to his wife. Another way of saying this is that all warm-blooded fishes can be traced back to a common ancestor -- that one particular fish species developed warm-bloodedness and passed it along to all its descendants and all living warm-blooded species are descended from this line.

Block et al. examine the distribution and changes in DNA to determine that endothermy in fact has evolved independently three times in fishes. This is the equivalent of saying that not all warm-blooded fishes are more related to each other than they are to non-warm-blooded fishes. Thus, they tested the above hypothesis and it failed. A "just so" explanation most likely would not have revealed this. In fact, it's hard to see how one might have tested any "just so" explanation. Chances are, the creator of the explanation would merely stated and those who accepted it would see the trait of warm-bloodedness as explained and move on to the next topic.

I don't have enough space here to cover the whole method, but cladistic methods work by comparing traits (which can be anything from a complex behavior to DNA sequences) between groups (e.g., species) and seeing in terms of these which groups are more closely related. This allows one to recapture the history of evolution as the sequence of branchings between traits. For instance, two species of fish which are closely related in many their of traits might differ in endothermy, giving evidence that endothermy evolved separately.

To illustrate: imagine three sister species (species sharing a common ancestor) which form a clade (meaning there are only these species and no other that share this common ancestor): A, B, and C. Cladistically, this set can give rise to four hyptheses. The first is that they all evolved directly from their common ancestor, meaning there were no intermediary splits in their line. The evidence for this would be that none of them shared any other traits besides the ones all of them shared. Let's call their ancestor M (for mother species). M has among other traits five traits that we can list as (0,0,0,0,0) – each 0 representing a binary trait: you have it or you don't have it. These traits can be anything, from having a certain stripe on the back to warm-bloodedness. Let's say A has traits (1,0,0,0,0), B (0,1,0,0,0), and C (0,0,1,0,0). They all share the last two traits (the last two 0s), but differ completely in the others. Graphically this could be modeled by on point M with three lines leading to points A, B, and C.

Imagine now instead that while A, B, and C share a common ancestor, A and B share another common ancestor which C does not share. In other words, between M and A-B, there lines another species which is the mother of the A-B sister pair. We'll call this M'. Evidence for this would be something like M and C have the same traits as above, but A has traits (1,0,0,0,0) and B has traits (1,1,0,0,0). Note A and B share that first 1 with each other, but not with C; they also differ by the third 0 with C and share 0s four and five with C. Graphically, this could be pictured as a point M with one line leading to C and another leading to M' AND two lines leading from M' to A and B. Thus M evolved into M' and C, and M' then evolved into A and B. The two remaining possibilities here, which I won't cover in such detail, are that B and C are more closely related or that A and C are more closely related.

Aside from the order in which the branches happened, why would this be important? One might, say, have an evolutionary hypothesis like long-billed hummingbirds in South America evolved from shorter billed ones in response to environmental pressure. I bring up this example because not only has someone done the analysis but it seems obviously to be true. But, in actual cladistic analysis, it was found this was not the case. The short-billed ones actually came later, evolving from their longer billed cousins. If we had stuck with "just so" stories of evolution, I doubt we'd have uncovered this one. (The article in which this was covered was in an issue of BioScience several years ago.)

Another example is that of skull size in certain fishes in Lake Victoria. Robert Dorit covers this in his "The correlates of High Diversity in Lake Victoria Haplochromine Cichlids: A Neontological Perspective" (in Causes of Evolution: A Paleontological Perspective, edited by Robert Ross and Warren Allmon). Dorit shows particularly how one might assume skull size and shape varied gradually from one species to another in this closely related fish group. However, when molecular cladistics methods (specifically, using mtDNA to map relationships), one finds the two species with extreme skull sizes (the largest and the smallest) actually are more closely related than any of the intermediary ones. This again clearly illustrates how "just so" explanations can go wrong. (It also shows that morphological data and phenetic analyses can lead one astray.)

The lesson of these examples is that "just so" stories can at best be starting points to explaining the evolution of a particular phenomenon. The can be completely misleading, however, is one confuses them with scientifically valid explanations. At best, they're a starting point and must be tested using methods like cladistics -- else all the would be explanation ends up being is a sort of mythical account that might blind one to the truth.

Link to post
Share on other sites

I wonder how many of the examples from Darwin's books would be regarded as 'just so' stories. Darwin (as I'm sure you already know) didn't even have the gene concept much less the ability to compare dna. I suppose with the genome of all species is known the evolutionary history of everything will be known or guessed. Darwin's birthday just passed (feb. 12) so you could see the scientist working to sell Evolution ("Darwin's Ancestry Traced to Cro-Magnons!")but in my view Evolution sells itself; Darwin was a hero of factuality and seeing what he saw, writing it down and explaining it.

Link to post
Share on other sites

I wonder how many of the examples from Darwin's books would be regarded as 'just so' stories. Darwin (as I'm sure you already know) didn't even have the gene concept much less the ability to compare dna. I suppose with the genome of all species is known the evolutionary history of everything will be known or guessed. Darwin's birthday just passed (feb. 12) so you could see the scientist working to sell Evolution ("Darwin's Ancestry Traced to Cro-Magnons!")but in my view Evolution sells itself; Darwin was a hero of factuality and seeing what he saw, writing it down and explaining it.

I don't think "Evolution sells itself." Just look at all the people who aren't buying over 150 years after Darwin first published his book. Also, evolution should be distinguished from evolutionary theory or evolutionary mechanisms. I do think that evolution is a fact -- or maybe more precisely an very abstract fact since it collects many observations under one concept; the fact being that life has undergone much change over time. Evolutionary theory is the attempt to explain that fact. Darwin's theory, in particular, attempts to explain it via "descent with modification" and natural selection. (Other theories propose other mechanisms or causes.)

Regarding Darwin's books, I think he was attempting to test his hypotheses, so he wasn't stopping at just concocting a story and leaving it at that. In my view, just so stories can be great starting points for investigation, but the problem occurs when someone stops at a just so story and doesn't attempt to test it against the evidence -- particularly by constructing a "null hypothesis" and looking for conflicting evidence, and also seeking out independent lines of evidence.

By the way, to do cladistics, one doesn't need to know genetics. For instance, in Phylogeny, Ecology, and behavior: A Research Program in Comparative Biology, Daniel Brooks and Deborah McLennan come up with a way of coding behavior to do cladistic analyses on it. One could imagine someone in Darwin's time doing the same -- without the benefit of post-Medelian genetics -- just by observing organisms. In fact, anything can be grist for the cladist's mill -- any trait.

It's even been applied to fossils! A few month ago, I went to New York City and visited the American Museum of Natural History. They actually have cladistic diagrams there to categorize their dinosaurs. The only thing to compare in this case is, of course, fossilized remains -- not DNA and rarely anything directly like behavior. So what workers are doing is looking at, e.g., a skull and comparing to other skull and generating a cladogram from this to reveal evolutionary relationships -- things like dinosaur X is more closely related to dinosaur Y than to dinosaur Z because they both share the same type of teeth and jaws. (I'm dinosaur nutter.rolleyes.gif )

Edited by Dan Ust
Link to post
Share on other sites

Dan,

I think you have a very valid point here. It's often too easy just to build a plausible-sounding story loosely based on evolutionary ideas and pretend it has justification.

Any theory on how altruism can develop must be falsifiable. It would seem reasonable that anyone making this claim would have to show at least the following:

1) A pattern of true altruistic acts (survival disadvantage to the actor, advantage to the recipient) and not just simple tit-for-tat or delayed benefit.

2) A mathematical model that makes sense for these traits to develop and grow.

3) Genotype identifiers/connections to behavioural tendencies.

Behaviour is linked to evolution and genetics as much as morphology. Rand's human nature proclamations repeadetly fail the 'reality' test. Mathematical models do exist that model the development of altruism in it's strictist form (non-kin, clear net loss to actor).

Bob

Link to post
Share on other sites

Dan,

I think another powerful way to avoid just so stories in evolution is to evaluate survival strategies mathematically. If scientists are going to theorize certain behavior patterns confer an advantage, they should look to game theory to see if this is actually so. Robert Axelrod goes into this in depth in The Evolution of Cooperation.

Jim

Link to post
Share on other sites

Dan,

I think you have a very valid point here. It's often too easy just to build a plausible-sounding story loosely based on evolutionary ideas and pretend it has justification.

Any theory on how altruism can develop must be falsifiable. It would seem reasonable that anyone making this claim would have to show at least the following:

1) A pattern of true altruistic acts (survival disadvantage to the actor, advantage to the recipient) and not just simple tit-for-tat or delayed benefit.

2) A mathematical model that makes sense for these traits to develop and grow.

3) Genotype identifiers/connections to behavioural tendencies.

Behaviour is linked to evolution and genetics as much as morphology. Rand's human nature proclamations repeadetly fail the 'reality' test. Mathematical models do exist that model the development of altruism in it's strictist form (non-kin, clear net loss to actor).

Bob

Yes, you need a clear definition of what an altruistic act -- in this context -- would be. A problem here, though, is that Rand's view of altruism (and egoism) do differ in some respects from the biological view usually taken for altruism in two respects. One is that, for her, there's no genetic determinism for human action. (I'm not saying mainstream biology posits there is one. I think there's much debate in the field about this and, yes, some do argue that human action can be traced back to genetics or to some biologically deterministic mechanism.)

The other is that Rand waffles, I think, on just what's supposed to be in one's self-interest -- is it survival ("life as the standard of value" tout court) or flourishing ("man qua man")? But even with her waffling, if we select either view of self-interest, I'm not sure what you mean by her "proclamations repeadetly fail[ing] the 'reality' test." Do you just mean her views of human nature are wrong? In what way? That people are basically altruist by genetic programming because natural selection selected for some altruism?

Maybe we should step back and discuss just what all of us -- not just you and I -- believe are Rand's and the evolutionary biologist's views of human nature, altruism, and the like.

Link to post
Share on other sites

Dan,

I think another powerful way to avoid just so stories in evolution is to evaluate survival strategies mathematically. If scientists are going to theorize certain behavior patterns confer an advantage, they should look to game theory to see if this is actually so. Robert Axelrod goes into this in depth in The Evolution of Cooperation.

Jim

Yes, though one must be careful with such models. Game theoretic models are often used, for example, in economics. They're good as long as one remembers they're idealized and baked in many assumptions that might not hold in real world cases. I believe Axelrod covers some of this, but I've only skimmed his work... I'm thinking of, for example, how people will argue against free markets using the traditional "prisoner's dilemma" reasoning, which assumes things like people only think about immediate gains, can't signal each other, and the game does iterate. (Of course, there are approaches that try to make up for this by allowing these factors to creep into the model.)

Population genetics models have the same problem, of course, but these models all can be used to create null hypotheses to test a just so story against. Still, one must be careful that the mathematical model is capturing something real and is not merely a formalism that looks cute. This is not typically a problem, though, in biology as the case study approach is still alive and well there, in my experience, and they don't seem to have gone model-crazy like economists. (To be sure, too, cladistics is usually done not by someone listing out traits and then having at it. Instead, a lot of the work is coding up traits, developing algorithms, and letting the computer program have at it. A lot of these studies I've read about involve dozens of species, so one person trying to develop a phylogenetic tree would likely take years were it done without some computational power.)

Link to post
Share on other sites

Do you just mean her views of human nature are wrong? In what way? That people are basically altruist by genetic programming because natural selection selected for some altruism?

Yes, I believe that "qua man" - human nature according to Rand is wrong. Life as the standard of value is not correct, based on reality. We need to look at what evolution teaches us about what it is to be human, not what Rand says it is.

Humans are partially altruistic. Any ethical system, "objective" or not must account for this. In my opinion, this has huge downstream implications if we follow her reasoning, but based on more correct premises. In other words, this should change everything wrt Objectivist Ethics.

Bob

Link to post
Share on other sites

Do you just mean her views of human nature are wrong? In what way? That people are basically altruist by genetic programming because natural selection selected for some altruism?

Yes, I believe that "qua man" - human nature according to Rand is wrong. Life as the standard of value is not correct, based on reality. We need to look at what evolution teaches us about what it is to be human, not what Rand says it is.

I'm unsure what that means in this context. If one is looking to draw ethical conclusions from evolution, what would that mean? Evolution, by itself, is merely history -- what came to pass. I believe it might be helpful, but I'm not sure it's the sum of knowledge one brings to the table to formulate an ethical system. And one must be very careful here. Evolution as the record of what came to pass is mostly hypothetical and mostly only records some more or less partial success stories.

Humans are partially altruistic. Any ethical system, "objective" or not must account for this. In my opinion, this has huge downstream implications if we follow her reasoning, but based on more correct premises. In other words, this should change everything wrt Objectivist Ethics.

I think it'd be more accurate to say some humans are partly altruistic. Looking at human behavior, I see a range from probably fully altruistic to non-altruistic behaviors and people.

I'm also not sure arguments about survival of genes and the like would have to lock in any objective ethical views -- unless you're going to presume gene survival is the standard of value, which is open to debate, don't you think?

Anyhow, my point in this topic was not to get into Objectivist ethics or even ethics in general, but merely to show that certain types of evolutionary speculation -- just so stories -- need to be vetted via some valid method -- e.g., cladistics.

Link to post
Share on other sites

Do you just mean her views of human nature are wrong? In what way? That people are basically altruist by genetic programming because natural selection selected for some altruism?

Yes, I believe that "qua man" - human nature according to Rand is wrong. Life as the standard of value is not correct, based on reality. We need to look at what evolution teaches us about what it is to be human, not what Rand says it is.

I'm unsure what that means in this context. If one is looking to draw ethical conclusions from evolution, what would that mean? Evolution, by itself, is merely history -- what came to pass. I believe it might be helpful, but I'm not sure it's the sum of knowledge one brings to the table to formulate an ethical system. And one must be very careful here. Evolution as the record of what came to pass is mostly hypothetical and mostly only records some more or less partial success stories.

Humans are partially altruistic. Any ethical system, "objective" or not must account for this. In my opinion, this has huge downstream implications if we follow her reasoning, but based on more correct premises. In other words, this should change everything wrt Objectivist Ethics.

I think it'd be more accurate to say some humans are partly altruistic. Looking at human behavior, I see a range from probably fully altruistic to non-altruistic behaviors and people.

I'm also not sure arguments about survival of genes and the like would have to lock in any objective ethical views -- unless you're going to presume gene survival is the standard of value, which is open to debate, don't you think?

Anyhow, my point in this topic was not to get into Objectivist ethics or even ethics in general, but merely to show that certain types of evolutionary speculation -- just so stories -- need to be vetted via some valid method -- e.g., cladistics.

Talking past each other a little I think.

My main point is not whether we should or shouldn't draw objective ethical conclusions from evolution, but just that Rand begins her argument in this vein on premises that conflict with current evolutionary thought, and if we correct the premises according to what we know (or think we know) now, but follow her reasoning, we get very very different ethics. And yes, some people are more altruistic than others, for sure, but I think you'd be hard-pressed to find many at the far ends of either side of the spectrum.

But in a different line, I do believe human morality evolved just like our bodies did and a great deal of human behaviour and morality can be explained this way, and mathematically so, not just story-telling. Still doesn't make anything Objective though...

Bob

Link to post
Share on other sites
  • 4 weeks later...

Dan,

I think another powerful way to avoid just so stories in evolution is to evaluate survival strategies mathematically. If scientists are going to theorize certain behavior patterns confer an advantage, they should look to game theory to see if this is actually so. Robert Axelrod goes into this in depth in The Evolution of Cooperation.

Jim

A game theoretical explanation for the doings of a non-reasoning non game playing animal or plant is the ultimate in "just so" stories.

Ba'al Chatzaf

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now