Evolution is brutal

In AI yesterday, I began describing genetic algorithms, a.k.a. evolutionary programming. I thought it important to get the essence of Darwinian evolution on the record too: descent with modification plus selective survival. I find that even among people who are generally supportive of evolution, and science in general, there is a lot of misunderstanding about how it works.

By watching the reactions on my students' faces, I began to realize how brutal the whole thing sounds. Evolution has an enormous death toll. Lots of critters must die in order for the average fitness of the population to increase. This carnage, resulting from competition for scarce resources, is not optional; it's essential.

It sounds all the more sinister when I mention that we will impersonate gods by applying our own selection criteria to the population. This isn't natural selection, it's artificial. You get to live and reproduce because you came closer to solving my problem than your peers did. In contrast, natural selection seems like a harmless truism: those who are good at surviving and reproducing are more likely to survive and reproduce.

Again, I tried to make the lecture more interactive with props. And nothing represents the concept of chance better than dice. Ideally, for an in-class demonstration, I'd like to leave nothing to chance. But in this case, I gave the dice to my students, put the success of my demo in the hands of Fortuna, and thus demonstrated my own ‘faith’ in the evolutionary process.

We ran through a simulation on the board, where I wrote 6 random 6-bit strings, and computed their fitness as solutions to a 0-1 knapsack problem with 6 elements. As my students passed and rolled the dice, we went through tournament selections, cross-overs, mutations, etc. The average fitness score of our offspring were clearly increasing compared to their parents. And I thanked Fortuna when, on the final roll of the die, a mutation flipped precisely the right bit to produce the optimal solution to the problem. (If that didn't happen, I'd either have to go on to a 3rd generation, or be content with demonstrating just an increased average and max fitness.)

©20022015 Christopher League