Uncovering the Truth: The Power of Predictions in Evolutionary Evidence

[bobze]

I think that this is the difference between most evidence for evolution and evidence for physical theories. Of course it's possible to come up with ways that evolution could have been falsified [the famous rabbit in the Cambrian for example], but that isn't as powerful as an experiment designed such that one of two possible outcomes is incongruous with evolutionary theory. Has such an experiment ever been done?

Sure you can design experiments to test individual parts of evolutionary theory (remember evolutionary theory is a big unifying theory, as such it incorporates many parts).

Suppose we wanted to test speciation, using evolutionary theory we predict that for a population, in which subsets become divide off each individual subset will continue to undergo selective pressures exerted by the environment until such a time that the populations no longer interbreed even if brought back together eventually.

Just such a famous experiment was carried out byhttp://evolution.berkeley.edu/evolibrary/article/_0_0/evo_45". What she found was that when a population is isolated to two different environments, even after they're brought back together, reproductive isolation starts.Another good example would be if we wanted to test the idea of selection itself. We could predict with evolutionary theory that allele frequencies in a population may not change randomly, but rather as a result of selection. How could we test this?

Suppose we wanted to look at how predation affected allele frequencies, after all evolution says that population under selective pressure should show adaptive changes due to the differential survival and reproduction of those changes. We could for instance, take a population of animals in the lab, let them live without selective pressure from predation for a time. Then introduce to the population, a predator which would provide a selective pressure. If evolutionary theory is right, we should see a change in allele frequencies over time (generations). We could even test this in the wild by introducing a new predator to a population which had not seen said predator before. That is to say, we have experimental (both dependent and independent) variables we can go in and manipulate.

Again, such a thing has happened in both the lab and in a "natural lab".http://evolution.berkeley.edu/evosite/evo101/IVB1bInthelab.shtml" Suppose we wanted to test the foundation of evolutionary theory; descent with modification. Evolutionary theory says that some clades of organisms should share common features because of shared ancestry and this should be to the exclusion to other clades. Here we can even get maths involved!

We could then use homology (evolutionary derived shared features) as a null hypothesis; "Such and such structure is not homologous in these two organisms".

We could then go out into the world and gather data, say the gene sequence (molecular genetics), the embryonic development (Evodevo) of said feature, the protein structure (proteomoics) etc.

We could then array these features in a matrix (lots of them!) and apply statistical tests to our observations and based on those tests accept or reject the null hypothesis.

If we were unable to reject the null hypothesis ever (that structures aren't homologous), you would certainly falsify evolutionary theory. There must be homologies shared between clades if evolution were true. Low and behold we do find homologies throughout clades of varying sizes (the continuity of the mammalian arm, the development of the notochord in vertebrates, etc).

We can then use everything we know about evolutionary theory to predict or make models of lineages and of course, some of those models are falsified from time to time. Say for example the common derived characteristic of the mammalian and mollusk eye, which was falsified on the basis of homology. There are literally thousands of examples of these different tests of evolutionary. So many, that I'm not even sure you could find a collective source for them all. I'd suggest, barring taking a upper level evolutionary biology course, you start with authors like Sean B. Carrol, Jerry Coyne, Steven Pinker, Richard Dawkins (at least his stuff involving evolution, not religion), Stephen Gould, Matt Riddley, etc

Honestly, I can't think of (with the exception of quantum physics) a scientific theory that has been more tested and scrutinized than evolutionary theory (And we don't even understand quantum physics in the way we understand evolutionary theory!)

 

[DaveC426913]

It occurs to me that evolution is not what we should be talking about. Evolution is fact. We see it happen all the time.

The thing that is in question is natural selection - what drives the evolution of critters.

eg. We know that there are finches on Galapagos that have evolved specialized beaks. The question is not whether they have evolved them over time, the question is what forces led to the variation.

Is it, indeed, that for example, ones who ate certain types of berries and who had longer beaks were able to take advantage of a food source and thus proliferate, eventually out-breeding other, more general types?

The mechanism by which an entire population changes, and the mechanism by which new species diverge from old ones - these are the things hotly contested.

 

[daniel_i_l]

bobze:
Thanks for those links, John Endler's guppy experiment is fascinating.

Now I take back what I said before. I think that my mistake was that I failed to recognize a distinction similar but not identical to the one that DaveC426913 pointed out. I was looking at evolution as more of an historical question, i.e are all the organisms we see today byproducts of natural selection as explained by evolution. And while this is also possible to prove, it's much harder to experiment with than sciences like physics because we're pretty much limited to natural experiments where we're not in control or even aware of all the factors. But the theory "organisms evolve through natural selection and that could conceivably account for life on Earth" can be tested with definitive experiments.
In addition, I think that I was a little fixated on evidence from fossils and, as I said before, nothing guarantees that we find what we're looking for. On the other hand, homology might be a better approach to this kind of experiment.

Even though this is a minor issue in comparison, I think that part of the problem was that in the book I was reading [in one of the first posts I said which one] the author repeatedly said things like "evolution predicts that fossil A will be found and we really found it" which in my opinion isn't entirely honest. Because like I said, sometimes biologists search for certain fossils without actually find them and this poses no problem for evolution. So I think that if the author wanted to give examples of fulfilled predictions he should have chosen examples similar to the ones posted in this thread.

 

[gerben]

I do not know the book, but I guess when the author says "evolution predicts that fossil A will be found and we really found it", he means "evolutionary theory predicts that species A existed and we found a matching fossil".

 

[bobze]

It occurs to me that evolution is not what we should be talking about. Evolution is fact. We see it happen all the time.

The thing that is in question is natural selection - what drives the evolution of critters.

eg. We know that there are finches on Galapagos that have evolved specialized beaks. The question is not whether they have evolved them over time, the question is what forces led to the variation.

Is it, indeed, that for example, ones who ate certain types of berries and who had longer beaks were able to take advantage of a food source and thus proliferate, eventually out-breeding other, more general types?

The mechanism by which an entire population changes, and the mechanism by which new species diverge from old ones - these are the things hotly contested.

Dave,


That's a great point, One I tried to make at the beginning of my post, but you certainly put it more clearly here.

Evolution has the misfortune of sharing that name of the theory, with the natural phenomena it explains. Evolutionary theory is really a catch-all for all the smaller, no less important, theories and hypotheses which explain the phenomena (fact, if you will) of evolution.

This I suspect, causes a great deal of confusion amongst lay-folk or anyone not particularly educated in biology. When biologists are "arguing about evolutionary theory" they aren't arguing something so exciting as, whether or not it occurred --Normally something much more mundane like, which selective pressure influenced such-and-such structure's evolutionary development more.


To this end then, one can easily see that "evolutionary theory" is falsifiable, at least the different theories and hypotheses referred to under "evolutionary theory" (sometimes retermed the "modern synthesis", which avoids some of the name commonality confusion).

The real chance to "falsify" evolution (the idea or phenomena) came from Watson and Crick's great discovery back in the 50s, that of the structure of DNA (arguably the most pertinent to human kind scientific discovery thus far).

Had it played out differently (with DNA, genes, mutations etc), Darwin's idea (descent with modification) may have went the way of the dodo. Rather than that, the molecular biology revolution cemented in fact, evolution.

It again plays to the old Englishman's genius. For in Darwin's day when he postulated Natural selection (a theory), the fact that theory explained, was not yet even a "fact". He really was one of the most perceptive or lucky scientists in history.

Anyway (sorry for the tangent ) where I was going with this is; You are exactly right.

Evolution is a fact and we use different theories to explain it; Natural selection, sexual selection, artificial selection, cladogenesis, sympatric speciation, etc. And those are all falsifiable.

 

[bobze]

bobze:
Thanks for those links, John Endler's guppy experiment is fascinating.

Now I take back what I said before. I think that my mistake was that I failed to recognize a distinction similar but not identical to the one that DaveC426913 pointed out. I was looking at evolution as more of an historical question, i.e are all the organisms we see today byproducts of natural selection as explained by evolution. And while this is also possible to prove, it's much harder to experiment with than sciences like physics because we're pretty much limited to natural experiments where we're not in control or even aware of all the factors. But the theory "organisms evolve through natural selection and that could conceivably account for life on Earth" can be tested with definitive experiments.
In addition, I think that I was a little fixated on evidence from fossils and, as I said before, nothing guarantees that we find what we're looking for. On the other hand, homology might be a better approach to this kind of experiment.

Even though this is a minor issue in comparison, I think that part of the problem was that in the book I was reading [in one of the first posts I said which one] the author repeatedly said things like "evolution predicts that fossil A will be found and we really found it" which in my opinion isn't entirely honest. Because like I said, sometimes biologists search for certain fossils without actually find them and this poses no problem for evolution. So I think that if the author wanted to give examples of fulfilled predictions he should have chosen examples similar to the ones posted in this thread.

Right and that is a cultural bias we've inherited from teachers and scientists who grew up without molecular biology. I've been saying for the past decade we really need to get away from teaching evolution through fossils.

There's no point. They don't make or break evolution, even without fossils, the evidence from molecular biology, genetics, EvoDevo, etc would still be overwhelming. Fossil evidence (sorry to any paleontologists reading along, I don't mean to piss you off ) really is the weakest and least convincing evidence that exists for the different parts of evolutionary theory.

 

[Ken Natton]

sorry to any paleontologists reading along, I don't mean to piss you off

I don’t think palaeontologists will be pissed off with you. They might have been if there was a grain of truth in what you say, but there isn’t. Elsewhere, I have seen the matter of evidence for and against evolution compared with the situation of a criminal trial. Always, the most powerful evidence in a trial is evidence that is corroborated by two independent witnesses. Palaeontology and microbiology each offer powerful evidence in their own right. It is when that evidence corroborates that it really becomes unanswerable.