Back in episode 118, we discussed some of the flaws in probabilistic arguments against evolution: the claims that advanced forms of life are so improbable that the math simply disallows the possibility that it could have evolved. And we do have to admit, looking at some basic components of the human body, like our rather complex eye, it does seem unlikely that such a feature could just show up by random chance. These kind of arguments continue to show up again and again in popular literature, but they demonstrate a basic misunderstanding of some of the key concepts of evolution and of probability. Recently I’ve been reading another great book by Richard Dawkins, “Climbing Mount Improbable”, that addresses this argument in more detail, so I thought it might be worth revisiting these ideas in this podcast.
Dawkins introduces a central metaphor, Mount Improbable, a huge mountain that represents the pinnacle (as we see it) of human evolution. Suppose you are approaching the mountain, and in front of you see a sheer cliff, with the peak a mile above. You might wonder: how could anyone ever get to the top of this mountain? It’s likely you would judge the task impossible, and turn around and go home rather than attempting it.
But suppose the opposite site of the mountain looks completely different. There is a gentle slope, leading upwards from the seashore, where you travel hundreds of miles horizontally to get to that one mile elevation. While it would take a lot of time, gradually walking up such a slope is not impossible at all: at any given moment, you are comfortably rising a barely perceptible amount, and getting closer and closer to the peak. Eventually you will reach it, having taken a lot of time but not encountered any other difficulty. From the cliff, you might stare down at the foolish tourists below as they gape at your amazing mountain climbing feat.
Essentially, evolution is like this long journey up the mountain. Evolution’s critics are right that a mutation that suddenly creates a major new feature in an animal is nearly impossible— but biologists don’t claim that that’s what happens anyway. The classic complaint is that a sudden mutation creating a humanlike eye in an eyeless creature would be equivalent to a tornado blowing through a junkyard and suddenly creating a Boeing 747 airplane. However, the role of random mutation in the evolutionary process is that of creating tiny incremental improvements: whenever a small genetic change makes a creature more likely to reproduce, that change will gradually become more and more prevalent in its species’ gene pool. The gradual, incremental effect of all these changes, each one of which is a tiny improvement on the previous creature, is what causes evolution. The sum total of such gradual improvements leads eventually to what appear to be extremely complex features.
Now, you might say that this all sounds great, but doesn’t explain the “irreducibly complex” features of the human body, like the eye. Half an eye, or a small piece of an eye, is certainly useless, so how can an eye gradually develop? How can it be possible that a series of incremental improvements leads from no eye to a human eye? Dawkins actually goes into detail on this particular example, since it comes up so often. The basic point is that there is indeed a set of gradual stages that can be observed in the development of the eye, if you look closely at a wide variety of primitive creatures. The idea that the eye is irreducibly complex is simply an assumption, a knee-jerk reaction that overlooks the details discovered by centuries of scientific study.
The first stage in eye development is light-sensitive spots, a relatively simple feature to randomly appear. Since many primitive forms of life get their energy from sunlight, this is pretty basic— some form of interaction with light is almost inherent to the concept of life on Earth. Once you have a light-sensitive spot, you can detect a looming predator nearby… but you can do it even better if that spot is slightly indented, so you can get a basic idea of the direction light is reflected from, by seeing which of your light-sensitive cells in the indented spot get activated. Developing such an indentation in a spot on the body is another relatively simple mutation to arise randomly.
Once you have an indented light-sensitive spot, there are a few simple types of mutations that would improve it. Increasing the number of individual light-sensitive cells will increase your accuracy, so the natural selection will move in this direction. Also, deepening the indentation, and partially closing the top like a pinhole camera, are also simple improvements that can increase visual precision. And once you have such an indented region full of light-sensitive spots, some kind of fluid over them would both help focus light and provide some degree of protection— so mutations that create such fluid, or a membrane covering that eventually fills with fluid, would be very useful. And so on. I won’t go into all the details here, but you can find a lot more information in the book. The key point is that there really is a gradual, slow path up Mount Improbable leading from simple light-sensitive spots to a modern eye.
So, if you’re interested in biology and mathematics, but left uneasy by the implication in many poorly-written textbooks that impossibly unlikely random genetic mutations are required for advanced life to evolve, I would highly recommend Dawkins’ book. The concept that evolution claims a tornado through a graveyard created a 747 is a fundamental misunderstanding of how probability fits into the theory. Dawkins makes a very strong case that the impossibly looming probabilistic cliffs of evolution have gentle, highly probable slopes lurking just out of sight on the other side.
And this has been your Math Mutation for today.