Wednesday, March 30, 2011

Evolution, Environment and the Red Queen

So, the original prompting for this blog came from my friend, Daniel, who has recently started his own blog to explain economics, which you can find here. He challenged me to do the same and to answer questions that normal people have about paleontology but don't know anyone to ask.

I prompted him to give me such a question, believing people didn't wonder things like that. And so:

"Evolution seems more intuitive to me if you call it an environmental process rather than a biological one (ie, as environment in a location changes the things that CAN will change as well). Is it safe to think that or is there a snag there? Why do we learn about evolution in biology class, not in earth science?" - Daniel (Edited for typographical issues)

Well, Dan, that's a heck of a question! You don't know it, but that question touches on a lot of issues in biology.

The simple answer is that, no, evolution is not better attributed to environments rather than biological entities (organisms, however we should define them). We discuss evolution in biology because evolution is largely a feature of life.

I think it's important to consider what 'evolution' means, as there tends to be confusion about that. Evolution, the term, just means change (literally 'unfolding', 'unrolling' according to Wikipedia). Note that we can refer to evolution in things that are certainly not alive (minerals and economic markets are common examples), but let's just focus on the living. Generally when we want to discuss evolution in biology (as opposed to evolution of non-living things, like minerals), we define it as change in inherited characteristics. A dog that loses its leg did not 'evolve' because that change cannot be inherited.

So, in your changing environment context, the really interesting process is how organisms living in that environment evolve inheritable changes (or fail to change). Biologists are ultimately interested in how that process works, which is essentially a biotic process (although understanding how the physical environment is changing is also pretty important!) Also, we see lots of evolutionary change which can't be tied to any particular observation of environmental change, which further muddies an argument for evolution as an environmental process (although, as I get into below, defining 'environment' is difficult).

Now, let's just take a step back so I can explain how your question touches on some hot topics. So, I'm pretty sure you are using environment to mean physical environment, but actually, it's pretty damn hard to seperate physical factors of the environment (like climate, sunlight and altitude) from environmental aspects which are functions of other organisms (like how much predation there is or how much competition there is for some required resource). Organisms live in environments that are constantly changing due to both biotic and abiotic factors, and seperating those can be pretty difficult. One school of thought says they are fundamentally unseperatable, particularly when you consider organisms that greatly alter the physical aspects of their environment (like beavers, ants, many plants) which we call ecosystem engineers.

The important thing to remember is that the environment is always changing. Even if all the physical components were held constant, an organism would be living in a world full of other evolving organisms. To survive, organisms (and populations, and lineages) need to constantly evolve to keep up. This concept was introduced by Leigh Van Valen as the Red Queen Hypothesis (in reference to the Red Queen in Through the Looking Glass). Although some interpret Red Queen as the supremacy of biotic factors in influencing evolution over abiotic, Leigh was actually trying to include both. (This interpretation has led to the formulation of the "Court Jester" hypothesis, as a counter to the supposedly biotic-focused Red Queen, where ecological communities are relatively static until perturbed by sudden large-scale environmental change.)

So, to sum up:
We tend to define evolution as the process by which organisms evolve inheritable traits. Physical change in the environment does not always cause evolutionary change, and evolutionary change is not always caused by changes in the physical environment. Thus, they are treated as separate but interconnected processes.

In addition, scientists have found it difficult to always divide the physical (abiotic) components of the environment from the biotic components, such as competition and predation. Thus, it may be more right to consider study of the environment as partly biological. Understanding the interplay between the (perhaps constantly changing) environment and evolution is a primary question of evolutionary biology.

Why "Nemagraptus gracilis"?

Hello all,
I'm David Bapst, a graduate student at the University of Chicago. I'm starting this blog to answer some questions my friends have about paleontology. I'll probably also bring up more advanced topics in phylogenetic comparative methods and functional morphology, as they relate to paleobiology and topics connected to graptolite studies. Finally, I may occassionally use this to discuss a matter involving independent roleplaying game design, which is a minor hobby of mine (my main hobby being my work).

But you might ask: why name my blog after a graptolite species?

First of all, Nemagraptus gracilis is the most beautiful graptolite, in my opinion. I've made a nice little figure of it, to the right, which I've also made the background. You've gotta admit, it's a nice little shape.

Second of all, Nemagraptus represents much of what is interesting about graptoloid morphology and function. Nemagraptus regains a multi-branched form, having evolved from two-branched Dicellograptus-like ancestors, but does so via a novel constructional modification ('cladia'). Nemagraptus's form makes it instantly recognizable, which is probably also why it is a major index fossil. There may also be some Cyrtograptus species in the Silurian which converge on a Nemagraptus form (Mitchell, 1990). Work by Fortey and Bell (1987) also suggested that is form would be optimal for feeding efficiency. Its spiral form has also been of interest to those curious about graptoloid hydrodynamics (Rigby and Rickards, 1989). These connections to functional research make it a good emblem for my research into graptoloid function.

Note that Nemagraptus is also relatively well-understood in terms of its phylogenetic relationship. This is another key connection to my researching involving the phylogeny of graptoloids. Note that I also picked a branching graptolite: just like a phylogenetic tree.