Thursday, November 27, 2008

The end of the long road. A new beginning.

Friday, 21 November, 2008, I successfully defended my doctoral thesis: "Endocranial Morphology and Phylogeny of Palaeozoic Gnathostomes". I'm no longer a student, I'm now a doctor of philosophy. It's a strange feeling being done, but now you know a bit about why I've been conspicuously absent from posting much in the past year. I've had a lot to do!

My next stop will be a postdoctoral fellowship at the Museum für Naturkunde in Berlin. Hopefully, I'll be able to pick up more blogging in the next few weeks. But first, I think I'm going to have a little holiday. Maybe somewhere sunnier than Sweden, for a change...
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Wednesday, October 08, 2008

Friday, September 19, 2008

Homology: what's evolution got to do with it?

British palaeontologist Colin Patterson became an unwitting friend of creationism during his career. That misbegotten legacy continues to this day, in misquotations that continue to pop up in creationist literature. Patterson has been widely cited by creationists as some sort of closet creationist who though evolution was a speculative farce. Unfortunately, what has become lost in the maelstrom of attack and counter-attack in the world of creation/evolution apologetics are lessons for both evolutionists and creationists.

If anybody was a skeptic, Patterson was. In the forward to his posthumous second edition of his textbook Evolution, two of his close colleagues wrote: "His favourite critical internalised question was 'how do we know that?': to which he often got the answer 'authority or tradition'--something he respected only after he had explored the evidence for himself". He was notorious for a need to figure things out for himself and endeavoured like no other to never let preconceptions get in the way. Indeed, based on anecdotes of people who knew him, I have learned that "how do you know that?" was not merely internalised, but frequently vocalised in a deep Oxford English from the back of the room.

As a result of Patterson's take-no-prisoners approach to belief and science, he became the champion of some unpopular ideas. Patterson questioned every authority and, in the end, challenged (and I believe overturned) some deeply held beliefs about evolution. More importantly, he overturned some ideas about how we know what we know about evolution. For instance, even as a palaeontologist, he argued strongly that fossils themselves play little (if any) role in the establishment of species relationships. That belief emerged from beliefs about fossils revealing ancestor-descendent relationships, and from prior commitments about transformation.

This is where the creationist and evolutionist misunderstandings commence. Patterson argued that evolutionary theory had no role to play in systematics. To creationists, this is touted as evidence that the theory of evolution has no practical applications and is, indeed, unnecessary in biology. To evolutionists, this is often either ignored, disagreed with, or misunderstood.

But what Patterson showed was that a lot of the pre-Darwinian basis for evolutionary theory had been co-opted or subsumed into evolutionary theory. Ideas that had a pre-evolutionary basis had become drenched in evolutionary pre-conceptions and language. Homology, for instance, had become (and still is for most): shared similarity due to common ancestry. However, if homology is explained by common ancestry, then what is the basis for the inference of common ancestry? Well, as it turns out, homology! Patterson recognized the problem and iterated a definition of homology that took into account the way in which homologies define nested groupings. That is, homology is the relation that defines the ranks in a nested hierarchy.

Homologies are homologies because they define nested groups. They are sets of characters that fall into a series of congruent groupings. Similarity alone isn't enough to justify statements of homology, otherwise, we have no way to distinguish convergence from homology. Many will cite examples such as bird, bad, and pterosaur wings as examples where "fundamental differences" allow us to distinguish homology from non-homology.

But, the reality is that we already know these structures are non-homologous because they appear in distantly related groups. We know they're not homologous because of the distribution of other characters which act as a test of homology. If there were ample character evidence that birds, pterosaurs, and bats were all a tightly related group, we might then explain the differences as specializations of a common ancestral wing. The test, ultimately, is whether these taxa share other important characters in common.

The consequence of Patterson's definition of homology--the relation that defines a monophyletic group--is that evolutionary preconceptions are not necessary. Many evolutionists are uncomfortable with this. There is a sort of pluralistic approach (what I call a 'holistic' approach) to homology assessment that many biologists subscribe to. People argue that as many lines of evidence as possible should be considered. I agree, but the question is, through what filter do we analyze this evidence? Patterson would have answered: "tradition, authority, convenience, or assumptions about evolution". There is actually no need to be uncomfortable with Patterson's approach, which I'm surprised has not become more widely embraced.

The problem, as others had pointed out before Patterson, was that we need a knowledge of phylogeny (or interrelationships) in order to know anything about evolutionary history. In order to make generalizations about how evolution works, we need to know the pattern of descent. However, if our assumptions about evolution feed into our inferences about the pattern of descent, these assumptions become untestable. As a result, Patterson argued that our beliefs about evolution played no role in systematics. It was the task of systematists to uncover the patterns that exist in nature which we choose to explain by evolution and common descent. Patterson's rejection of the role of evolutionary theory in systematics was an attempt to keep the enterprise from decaying into circular argumentation.

So, the lesson for evolutionists should be kept in mind as we are deep into a new age in comparative biology. Genes and proteins can now be sequenced, we can map gene expression to embryos, and study the fate of populations of cells in developing embryos. We must ask ourselves: what beliefs about evolution that we developed before these wonderful advances have we carried with us to the present? And for each of these beliefs have we asked: how do we know that?.
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Thursday, September 18, 2008

Open thread: are genes really a guide to homology?

I have been putting this question to some of my colleagues:

What is the value of gene expression data in determining homology of morphological features?

Are genes really important in determining if two structures in two different animals are homologous? If so, why? If not, then what does really matter?

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Sunday, July 20, 2008

"It will have been more than worth it"

A nice article in the National Post about the fallout from the rumours that Stephen Hawking might move to the Perimiter Institute in Canada. It winds its way to a nice conclusion about the value of supporting basic research and the careers of promising youn scientists. Although it's clearly written by somebody with some first-hand (or otherwise close) experience with science and academia, I can't find the name of the author on the piece.
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Thursday, March 06, 2008

Reader comments: Learning about evolution

A question in the comments prompted me to give a response up here:
[I]s there anyway I could learn about evolution without having an upper level education in biology and whatnot, (I'm a senior in High School)?
Yes! The "catch" (if there is one) is that you will develop an upper level education in biology on the way. You just have to do a lot of reading. Thankfully, there are a number of good books out there that can introduce you to the topic. It is, however, a good idea to have a basic familiarity with biology, particularly genetics and a bit of molecular biology. But, to begin with, the material covered in a high school biology class (or equivalent level of textbook) is a good start. It's important to know, for instance, what an allele is, or the base-pairing of DNA. Also, it's important to understand the relationship between DNA and proteins.

The study of evolution is pretty varied. We can break it down into two major parts:

1) The study of the mechanisms and principles that cause evolutionary change
2) The history of life: the historical record and inferred pattern of changes/transformation

It's important to understand both of these things and they will come from different sources. For instance, basic texts on evolution are pretty weak on paleontology. But paleontology texts will be pretty weak on aspects of evolutionary mechanisms. They're needed to complement each other.

The most important thing, beyond anything, is to understand the evidence for any proposition about evolution. Always ask if the evidence is convincing. If so, why? If not, why not?

Some book recommendations:

A few lay-reader type of books that are really good:

Weiner, J. 1995. The Beak of the Finch. Vintage.

Carroll, S.B. 2005. Endless Forms Most Beautiful. Norton.

Zimmer, C. 1998. At the Water's Edge. Free Press.

Texts on biology and evolutionary biology are always a good and obvious place to start. But my preferred way to do things is to get some basic knowledge set up and start looking at evidence (that's how I learn). Books of any type, age, or scope on zoology, botany, anatomy, palaeontology, are very good because they're extremely visual and give you an understanding of the diversity of living form. If you're a very visual learning, as I am, then these can really be helpful. But they're also useful because a lot of texts on evolution or biology talk about things as though they're somewhat divorced from the actual organism to which they might be relevant. A good background in zoology, botany, as well as palaeontology will be extremely helpful.

The short answer is: yes, there are a lot of readily available resources for self-educating in evolutionary biology. Have fun!
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Wednesday, March 05, 2008

Define evolution in one sentence!

Here's my stab at the challenge:
Evolution is the accumulation of changes over generations in a self-replicating system caused by heritable biases in the probability of self-replication.

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Monday, March 03, 2008

Sunday, March 02, 2008

Being wrong for all the right reasons.

Just a bit of a ramble with some totally unresearched ideas here. Well, not totally unresearched, but impressions and the like, but without explicit references.

Working with fossils can be as frustrating as it is rewarding. It's a lot of fun, but each fossil only tells you so little. In fact, a fossil might be said to really tell you nothing. By themselves, fossils are dry bones, unanimated. Everything we know about fossils depends on our interpretations of them. This seems a little nihilistic, not to mention ripe for creationist misquotation. I'll warn now that there is nothing of use to the creationist here. I'm not talking about the big picture about evolution. I'm talking about the finer points. The crossed t's and dotted i's. Creationists might claim that there are no transitional fossils and try to use my words as a way of showing that even I, the palaeontology graduate student, thinks there's a problem. However, I'm not only predicating this post on the reality that there are many transitional fossils, but that our human frailties might even be preventing us from recognizing more transitional fossils than we have. I believe that we can cut the story of early vertebrate evolution even more finely than most palaeontologists are willing to admit.

When studying the fossil record, we need to recognize patterns. Humans recognizing patterns is tricky business -- we're pattern-seeking animals. We see shapes in the clouds or in random scattering of pebbles in a riverbed. We are often very prone to error, as our common sense thinking can fail us when more arcane matters are in question. We have confirmation bias, where we easily remember the confirming instances for our pet hypothesis but ignore, discard, reject, or rationalise any contradictory observations.

But this is why we have science. The idealised scientist aims to eliminate bias, tries to suspend wishful thinking, and (most importantly) challenges conventional wisdom and common sense thinking. The greatest discoveries in science were not the confirmations of things we already believed, but the revelation the startling facts that were totally inaccessible to our naked perceptions--often demonstrating how wrong we actually were.

There is apparently a world that exists independently of our ability to perceive it. And so, there are necessarily truths about the world that we may not be comfortable with. The point is that science can only tell us something new if it doesn't exist to support those comforting narratives we tell ourselves about how the world works. It is an "unnatural way of thinking" as the embryologist Lewis Wolpert put it:
[T]o do science it is necessary to be rigorous and to break out of many of the modes of thought imposed by the natural thinking associated with ‘common sense’. p. xiii-xiv. Wolpert, L. 1993. The Unnatural Nature of Science. Faber & Faber, Ltd. London
What Wolpert is saying is that science is almost like an affront to a very sacred sense of understanding the world: common sense. It forces us to think in ways that sometimes feel counterproductive, uncomfortable, and even revealing conclusions that do not look like they make sense. The conclusions might be very difficult (or even impossible) to understand.

Palaeontology has, for a long time, been a discipline of narratives. Stories, of whatever sort, tied to fossils in order to explain the patterns observed. The tradition has often been one of very elegant, if not fanciful, speculation that has, in some way, been tied to peculiar observations about fossils. No one can count the speculative hypotheses on dinosaur behaviour, for instance. Some have proven more testable than others, of course. The stories of evolutionary relationships between fossil species, as well as between fossil and living species, were at one time unverfiable just-so stories. At least this was the case in terms of their expression as narratives. We understood two things to be related because they bore homologous structures, but we also knew two things to be homologous because they were borne in related creatures. The cladistic revolution changed that and allowed us to express homology in terms of the nested distribution of similarities. It be came an explicit way of uncovering the patterns in our observations about fossils.

Palaeontology is still experiencing its growing pains in becoming a mature, accountable, rigorous science. The tools, like cladistics and related methods, are there and so is the ambition to use them. However, the steps towards Wolpert's vision of a science are not complete.

Cladistics, when treated with care and in an honest attempt to eliminate your bias, can be very helpful. However, it can just as easily be used to come up with a tree that makes you feel comfortable. It's just an algorithm. You can shove whatever you want in to make whatever you want happen. The point is what the algorithm does, and the logic behind choosing to apply it.

I won't go into the details of it, because I don't think that's what this rant is about. The point is that it acts like a filter for our observations. We can record apparent similarities between a bunch of fossil, or living, or fossil and living things and interpret, in our own minds, what that means. Or, we can subject it to a particular type of analysis that might not give us what our brain tells us it should be. What it will (hopefully) give us is a result of the kind we want, based on logical principles that we have worked out beforehand. These arguments are, themselves, worked out based on some general principles.

Methods like cladistics might not give us the right result. Methods will, at one time or another and however frequently or infrequently fail. Usually for some reason (the method is bad, we used it improperly, or just pure randomness).

The point, interestingly, isn't even about the right answer. It's actually about the wrong answer. We can and will be wrong when trying to explain the world. But we can be wrong for two reasons: the right reasons and the wrong reasons. It's like anything else, you can have all the calculations and the protocols and experimental controls right, and still Nature can throw you a curveball. Or it can be impossible to collect all the neccessary data, or simply impossible to know how much to collect. Nevertheless, we have to try. This can lead to us being wrong, but we will be wrong at no fault of our own. Alternatively, we can be too caught up with getting a result -- especially the result we want. This leads to us being wrong for all the wrong reasons.

So, for those of us working with fossils, I think we can be wrong for the righ reasons and wrong for the wrong reasons. I think honest attempts to challenge received wisdom, to upset old taxonomies, and question the authority of old is a good thing. It may lead us to stronger hypotheses, if not simply to a more honest evaluation of our data. It might be that we simply don't have the evidence to say all the things we're saying. We might, for the time being, only have the evidence for a very coarse picture of interrelationships of some fossil organisms. But the more we strive for a result, and the more we strive for a result that makes us feel comfortable, the farther our thinking get from Wolpert's description of true scientific thinking.
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