Sunday, March 21, 2010
(Tree of life graphic here.)
I talk about evolution a lot. If you read by regular blog, it comes up regularly in both text and links. Sometimes I talk about it with respect to religion but not always.
As an SF writer, I think about evolution all the time. To me, it's not just where the rubber meets the road, it's the road, the tires and most of the automobile.
For example, I saw Cameron's Avatar a few weeks back. I knew immediately that the aliens (the Na'vi) were not native to the planet.
Why? You might ask.
Because the wild life had six limbs and the Na'vi had four. Because the wild life had two pairs of eyes and the Na'vi have one-- like humans. Look at chimps, gorillas, horses, giraffes, lions, tigers and bears: all have the same tetrapod form, four limbs, two eyes, head in the right place. Because we all evolved from the same ancestor. When you leave that tetrapod form you make a huge jump to jelly fish, cray fish and flies. Very different animals. The Na'vi had very little resemblance to any of the other wild life. Therefore, either they were a unique species either in adaptation or heritage or they weren't from around here. I vote for the latter.
Evolution is important. But understanding evolution is very, very hard.
The problem comes not from evolution, of course. But our inability to encompass it. The principles of evolution aren't hard to grasp and are not original in evolution at all. They derive from Adam Smith's ideas of capitalism. You remember capitalism, don't you?
In a nutshell, Adam Smith's idea was that in a free marketplace competition would drive goods and services. Charles Darwin read this and applied it to biology. He realized that individual members of species competed against members of their own species and against other species for resources. Innovation was the currency of competition between them. The field of play was reproductive success. Most of us have some kind of understanding of capitalism and this sort of evolution-lite. But, like in capitalism, things get interesting when you get into the details.
The first problem in evolution is sheer scale. Every organism competes for resources of some kind or another. Pick up a handful of soil and all of the trillion organisms there are competing against one another and, likely, you for air, food, water and space.
Scaling up to all of the organisms of the planet and the task of figuring out the webs of competition is daunting. Scaling backwards in time to figure the nature of these webs in the past makes your brain hurt.
So we do what humans always do when faced with an intractable problem: we subdivide the problem to get to a manageable scale and abstract the problem so we can glean operating principles.
It turns out living organisms do something similar.
First, organisms subdivide their resources into niches where they specialize. They no longer have to defend the entire landscape of resources; just their own area. Niches are interesting in that the narrower the niche is the less stable it is. In addition, niches can overlap. For example, cats (felidae) are obligate carnivores-- they must eat meat. They are specialized for individual hunting. Dogs (canidae) are also obligate carnivores but are specialized for pack hunting. There are pros and cons for both. Individual hunting puts all of the burden on the individual animal but the needs are no more or less than that of the individual animal. Pack hunting shares the burden and risk but a pack eats much more than an individual animal. Pack hunters need a large territory or a broader range of food stuffs they're willing to eat. The niches of the two animals overlap.
In contrast, consider the koala that is not only an obligate herbivore but is also is specialized to a single sort of leaves: eucalyptus. The koala has little competition from other animals but is totally dependent on the stability of eucalyptus species over time.
Human capitalist mechanisms are similar: we have vertical markets and horizontal markets. Vertical markets are analogous to specialized animals like the koala-- they specialize in a narrow band of services or products. Horizontal are broader niches more similar to cats and dogs.
In evolution, one of the interesting aspects is determining the actual nature of competition and innovation. We think we know what competition is-- "nature red in tooth and claw" and like images. However, think back to human beings. Without a doubt, our single best skill, the absolutely most fundamental talent by which we define ourselves is our ability to cooperate with other humans. It is the most basic means by which humans have covered and conquered the globe. So, in our case, did we become who we are by competing to be the best at cooperation?
Such conundrums abound in evolution. For example, it has been shown that bacteria have exchanged DNA across "species" boundaries. (See here.) Clearly, if bacteria evolve (which we know they do), evolution must have favored this process.
Another truly odd way of looking at evolution is what I've started calling recursive adaptation. Nobody else is using this in biology yet so if you hear it elsewhere, you heard it here first.
Some time back, you might have heard of Walter Gehring's work on the eyeless gene in fruit flies. Essentially, eyeless is a gene that turns on and off the creation of eyes. By turning on the gene in different places you can make a fruit fly with eyes on its legs, abdomen, wings, etc. Where it gets truly crazy is you can take the same eyeless gene from a fruit fly, implant that gene in a developing frog and get frog eyes in the leg, abdomen, etc. This gene has been termed a "master control gene" in that it acts as a switch to create a major structure.
I read this and thought wait a minute: this is an evolutionary mechanism. This is a mechanism to facilitate innovation. It is the evolution of evolution. I.e., it is a mechanism allows direct genetic selection of structures. For example, it creates a situation where a single mutation could remove eyes in the equation-- creating a situation where the absence or presence of eyes are a selection criteria. Think eyeless cave fish. Think eyeless crayfish. It's a means by which eyes can be reintroduced after they've been lost. (Think snakes.)
So that has to be included in the evolutionary bag of tricks.
And then, there are transposons.
Transposons are sequences of DNA that can move around the genome. Since location is one of the means by which DNA is actually expressed, transposons are one more mechanism of creating novel combinations in the genome-- presenting the opportunity for those combinations to be selected.
And that's just the genetic component of evolution. What about epigenetics, inherited traits outside the genome or how physical conditions of one generation affect inheritance in the next?
More on that another time.
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