Sunday, April 4, 2010
(Picture from here.)
I talk a lot about evolution. I think a lot about evolution. Other folks think about philosophy and art, engineering and science, love and marriage-- I think about these, too. Sure. But I spend a lot of time thinking about evolution. I even wrote a small play about it. (See here.)
As I said a while back (here) evolution is hard to understand. It doesn't help that evolution affects us, as well. We like to think of ourselves as above the rest of the world. Apart from it. Evolution kicks that idea right to the curb. Whatever we are, wherever we came from, evolution brought us here.
A few years ago I wrote a long trilogy of essays on religion and evolution (here, here and here) which I will not bore you with today. But I do want to dwell on how we got where we are. There's a lot of interesting information that has come out in the last few years.
So: I'm going to talk about human evolution and bring it back to science fiction at the end. This is going to be a meandering trip.
Let's start by looking at a cladogram. (Picture from here.) These show the ancestral relationships between organisms. The basis for a cladogram can be anything-- DNA similarity, morphological similarity, etc. What's important is the grouping characteristics and the relationship of the groups across time. The first cladogram is one showing the evolution of mammals. Often, the end point is the subject matter for the investigation and the result is the form as is shown.
At left is a cladogram of human evolution based. (See here.) It's a common enough derivation. Pongo (orangutans) come off the mainline first, followed by gorillas, followed by the split between humans and chimps.
Any evolutionary understanding of human beings has to account for these relationships, either as they stand or some other, similar relationship between the living great apes.
We have a lot of special characteristics: upright posture, hands and feet, our brain, invisible ovulation and regular menstruation, lack of hair, etc. The latter don't fossilize but are just as important to our nature as the former.
So: what's been going on in human evolution?
Let's go bottom up and start with bipedalism.
The discussion that's been going on for a long time is whether or not we came down from the trees or up from the ground. The "down from the trees" hypothesis suggest we developed the precursors of bipedalism as tree dwellers and came down to walk when the trees disappeared when our area in Africa went from forest to savannah. The reasoning derives from chimps which have a pelvis that actively discourages upright posture and forces the legs of the chimp out to the side. By the time Lucy came along, the pelvis had rotated so that back so that she could stand upright, her legs directly beneath her. (See here.) For selection to occur, this had to be present in the population before bipedalism in order to select for bipedalism. An interesting erosion in the orangutan pelvis is similar to what might have occurred that pre-Lucy ancestor. Hence, when the ape came down from the trees was predisposed to walk upright. Selection then had an opportunity to operate.
The "up from the ground" hypothesis has our own closest relatives going for it: both gorillas and chimpanzees are essentially ground walkers. If they're our closest relatives, it's reasonable to suppose that our ancestors were more like them. However, that would suggest that gorillas, chimps and humans were all knuckle walkers back in the day. New evidence (see here) suggests that in fact chimp knuckle walking and gorilla knuckle walking are not the same thing at all but evolved separately. This takes history right off the table and forces us to look at the evidence differently.
It's clear which side I fall on.
Which brings us to hands and feet.
Just this year, an interesting article came out about human feet. (See here.) As one would expect, bipedalism frees the hands to be used independent of motion. This opens all sorts of opportunities to select for hand use: tools, manipulation, scratching, etc. We can, therefore, consider bipedalism required to make humans a tool using animal.
Even so, we have spectacular hands, able to play the piano or perform complex surgery. Remember how evolution works: predisposition presents the opportunity for selection.
It turns out that the hands and feet developed together. As evolutionary pressure was brought to bear on foot development, there was a knock on effect on hand development. Think about your foot: big toe, more or less uniform toes, all in the same plane. Think about your hand: more or less uniform fingers, stubby but thick thumb, more or less in the same plane.
It turns out that development of hands and feet share a lot of the same body plan genetics. So, as we were developing good feet we got a predisposition to usable hands.
Which brings us to our brains.
Again, we have to look for a predisposition in our ancestors.
Well, it turns out our primate ancestors had a predisposition for "higher" thought long before the great apes.
Rhesus monkeys are old world monkeys. This puts them into the half of all monkey species that include human beings. Any trait we share has a significant probability of being a common trait we inherited from a common ancestor. This is, of course, not a certainty. (See knuckle walking above.) But it's a reasonable bet.
Researchers in Germany have been studying how Rhesus monkeys apply greater than/less than rules-- in effect, a form of higher mathematics. (See here.) They decided to not only investigate how well the monkeys did, but by using fMRI they wanted to see if the reasoning originated in the same region of the brain as human beings. To make a long story short: it did.
This makes sense. Evolution is changing the expression of things for which the rudiments and predispositions exist. Bipedalism, hands and feet are physical things with physical expressions. We should expect evolution to show up changes and differences there. The brain is another physical organ. Why should we expect evolution in the brain to be any different? So, if we have a mathematical ability, we should expect to find something common to it in a cousin species the same way we would expect to find hands and feet, eyes and ears.
And we see it in ourselves.
Reading is biologically recent-- at best, a few thousand years old. An article in Scientific American last October described some research regarding Broca's Area in the human brain. Broca's Area is highly involved in language processing. (See here.) Broca's area also exists in the great apes, though it is not involved in language processing since they have no language. (See here.) It turns out the Broca's Area is tightly coupled with reading. fMRI studies reveal that reading is processed similarly to spoken language. We were predisposed to read by our ability to speak.
(A similar experiment, published in 2007, showed similar results for Chinese, a more pictographic language. I was surprised by a paper I found from 2008 (see here) that suggests that Chinese is processed similarly to English. Ain't science wonderful?)
What we should expect, then, from evolution is that human beings exists in a biological context. We have relatives that look like us and act like us. We can determine specializations that are unique to us but they derive from common characteristics.
Therefore, when we write about humans (or any biological organism such as aliens) they must exist in a biological context. They came from somewhere. They're going somewhere. Who they are is the cumulative result of all of the decisions their ancestors made over the last few million years.
If we write about dragons and magic, (to my mind) they must exist in their real world. Dinosaurs had to manage their weight; so do dragons. Pterodactyls, beetles and birds have to work within aerodynamics; so do fairies and hippogriffs. Humans, chimpanzees and gorillas had to work with the biological materials at hand; so do elves and dwarfs.
To me, this is inescapable reality.
Wall of Idiots
Florida Senate race
Links of Interest
Images from Mars
What is light?
Toads detect earthquakes
Victorian sexual scholarship
Disguising a litter box
DIY tips for kids
Snow day projects