Tuesday, September 8, 2015

How Does Evolution Explain Design? Part 3: Does Natural Selection Make an Increase in Complexity Inevitable?

Guest Post by Andrew Rogers

In his book, Did Darwin Write the Origin Backwards?, Philosopher of biology Elliott Sober makes an argument for why natural selection will inevitably lead to an increase in complexity.

Sober says that, “Complexity increases from life’s beginning because of the initial conditions, not the laws. This is analogous to the random walk depicted in figure 1.1. A marker on a line changes position because of a coin toss. If the coin lands heads, you move the marker one space to the right; if the coin lands tails, you move the marker one space to the left. These are the rules of change unless the marker happens to be at the left-most or the right-most points. If the coin lands tails when the marker is at the extreme left, you simply toss again. Suppose the game begins with the marker placed at the left-most point on the line. Where will the marker be after five or fifty or five hundred coin tosses? Probably not at square one. Even if selection is indifferent to simplicity versus complexity, evolution by natural selection can still be expected to manifest a net increase in complexity.” (Sober 2011, p. 17).

Is this really analogous to natural selection. There are two assumptions in Sober’s analogy that bother me:

Assumption 1: If an organism goes below the level of complexity required for evolution then it gets to “flip again.”

Assumption 2: The odds of a mutation leading to an increase of complexity are the same as the odds of a mutation leading to a decrease in complexity.

In regards to Assumption 1, it seems that if an organism has to deal with a mutation that pushes it below the level of complexity required for evolution, then that organism would simply die out without any offspring. This is definitely not the same as getting to flip another coin until it gets an increase in complexity.

So that part of the analogy should be changed to “If the coin lands tails when the marker is at the extreme left, you simply toss again die and leave no offspring!” Even with this change it could be argued that with enough life forms and enough offspring there will be an inevitable increase in complexity.

This brings me to Assumption 2. Is the probability of a mutation increasing complexity really the same as the probability of a mutation decreasing complexity? This seems unlikely if the mutations are random. If I randomly start hitting my keyboard without looking is it more likely to decrease or increase the complexity of this paper?


Looks like a decrease in complexity to me and I would bet good money that the vast majority of random keyboard smacks would likewise decrease complexity.

To be clear, my argument is not that there wasn’t an increase of complexity throughout evolutionary history—I’m pretty sure there was. And my argument is not that God must have intervened in order for this increase in complexity to occur—I’m pretty sure it could have happened without God intervening. My argument is that the mechanism of natural selection alone does not entail an inevitable increase in complexity (or even a high probability of an increase in complexity). 

No comments:

Post a Comment