Wednesday, June 16, 2010

Evolving Thoughts on Homology



Accompanying the above intriguing illustration, John Wilkins has written a really good essay on the concept of homology, which we are taught (and go on to teach) as a really basic concept in evolution, but has surprising ambiguities and potential circularities (not unlike a few other evolutionary terms I can think of). John very helpfully traces some of the history of the term, and how its application has evolved as we've become better at building and testing phylogenies as hypotheses of evolutionary relationships. I have to agree with him when he says:
The notion of homology is complex, and as we recently saw when I asked about the use in mathematics, it has a slew of other meanings, but the one that seems to me to be consistent across all uses is this: a homology is a mapping or “agreement” of parts of organisms with other parts of organisms. A mapping relation is not a similarity, and it is not the explanation of the relation (such as evolutionary common ancestors, which are proposed to explain the homology). It is an identity relation: this is the same as that. The identity may be an identity of place, of sequence, of developmental process, or just of a shared name, but what it is not is similarity or common ancestry. Similarity may be how we identify homology (and what kinds of similarity depends on what we use), and common ancestry may be how we explain homology, but in both cases homology is the relation itself.
You know you'll be reading the rest of that essay for sure if you are in my class the next time I teach Evolution!

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Sunday, June 13, 2010

Just how big are your cells? - an interactive infographic

Hat-tip: @younglandis who tweeted yesterday about this fun interactive illustration.

...and note that Posterous' game attempt at capturing the infographic didn't quite catch all of the interactive elements (try the slider under the picture), so you really should click on the image to visit the original page if you want to see and play with this, and read more about it!

Posted via web from a leaf warbler's gleanings

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How I ended up here...

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Thursday, June 10, 2010

Biology Overload in the latest Scientia Pro Publica

I know I'm not always diligent about noting blog carnivals here, even when my postings are part of a carnival! Can't promise I'll be consistent about that in the future either. But if you are looking for some good science writing to read this summer, you could do worse than reading the weekly roundup in the Scientia Pro Publica carnival, which I have hosted in the past, and try to contribute to when I can. You'll find this week's edition, which came out on June 7, at The Dichotomous Trekkie 2.0, with an overload of biological posts! What fun! And it even includes my recent rant about evolution not being a ladder. So what are you waiting for? Go visit the carnival now!

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Wednesday, June 2, 2010

Repeat after me: Evolution is NOT A LADDER and does not lead to any pinnacles!!!!

ResearchBlogging.orgI am more than a little irritated.

This is not how I normally feel after listening to one of my favorite podcastlets "Our Ocean World" broadcast on the local public radio station most mornings.

As a landlubber biologist, I love learning about the fascinating and often bizarre creatures in the ocean, and therefore really enjoy this brief dose of news from the biggest biome on earth. Especially because it typically comes on when I'm dropping my daughter off at school in the mornings, giving us something wonderful to share.

But today's segment (which came on just after I dropped the kiddo off - sorry I was unusually early!) on Tuna, titled Big Fish, Big Sea, really pushed some sensitive buttons. It could be that I had just finished grading finals for my Evolution class, and was particularly touchy about evolutionary misinterpretations. But no, this particular gaffe came from a Stanford Professor of Marine Sciences, no less, and is therefore even less acceptable for being broadcast on the radio!! 

Professor Barbara Block, the tuna expert featured in today's podcast, described these no doubt remarkable fish as being at the top of a bleeping "evolutionary ladder"!! She also said Tuna were "more evolved" than other fish! And that they were on a "pinnacle of evolution"!!!#$*!!!  

More than once! (I checked. I hadn't misheard).

And here I thought we had buried that damned metaphor of evolution being a ladder for good! Heck, I try to bury it ritually for my students every semester in all of my classes, starting with Intro Bio. Yet it keeps rising, like a zombie, even from the mouths of accomplished biologists!! What's it going to take to purge this metaphor entirely from our vocabulary, folks?!

And while on the subject, let's also be clear that no species is "more evolved" than any other. How could they be? If you accept the evidence that we all come from one common ancestor, that the tree of life has one common origin, then every living species has been subjected to the vicissitudes of life on this planet for the same overall length of time, no?! We may have taken different, often surprising and bizarre, twisting branching paths on this journey, but we've all (except those branches that went extinct along the way) traveled the same length of time, have we not? How can any one of us, bacterium to tuna, virus to human to dolphins who say thanks for all the fish, then claim to be "more evolved" than any other species?

Granted there are local peaks and valleys in the fitness landscape for any species, and natural selection may be constantly trying to push us onto the nearest one - but there are no lofty "pinnacles" that we can be proud of conquering! If anything, given the dynamic nature of our world and the new curveballs nature keeps throwing at us, being stuck on any tall pinnacle could lead to the worst sort of evolutionary dead-end. We're probably far better off wandering around local peaks and remaining capable of even drifting across the fitness landscape. Definitely don't want to be stuck on any too tall peak, thank you very much! In fact, as my friend Andrew Jones just reminded meall species evolve to extinction!

Although, now that I think about it, perhaps most other species on this planet, our fellow travelers in the evolutionary journey, are hoping that we humans have reached exactly such a pinnacle, and are, even more hopefully, about to fall off our lofty perch for good. Perhaps from these new ecofriendly smokes.

Meanwhile, repeat after me (especially if you are a biologist):

Evolution, in fact, is best described as a TREE:



And remember, the only thing we are all definitely evolving towards is EXTINCTION!


Thank you!!

Reference:
Andrew R. Jones (2009). The next mass extinction: Human evolution or human eradication? Journal of Cosmology, 2, 316-333

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