June 19, 2007
Evolution-1: The power of natural selection
We are rapidly approaching 2009, a year that marks a major scientific milestone that is going to be commemorated worldwide. It is both the 150th anniversary of the publication of the landmark book On the Origin of Species that outlined the theory of evolution by natural selection, and the 200th anniversary of the birth of its author Charles Darwin.
Darwin's theory represents arguably one of the most, if not the most, profound scientific advances of all time, ranking well up with those scientific revolutions associated with the names of Copernicus, Newton, and Einstein. And yet it is widely misunderstood, or more appropriately, under-understood because most discussions of it remain on too high a level of generality, enabling critics to make statements about the theory that are not valid but yet seem plausible.
In order to create a better awareness of what the theory involves, today I will begin an occasional series of posts that looks at the details of the theory, including the mathematics that underlies it and which was developed later by people like J. B. S. Haldane, Sewall Wright, and R. A. Fisher.
One of the most common misconceptions about evolution by natural selection is that it works purely by chance. After erroneously assuming that notion, people then look around them, see the wonderful complexity of nature, and conclude that this simply could not have occurred by chance and that therefore this points to the existence of a designer who must be god. This is exactly the explicit argument of intelligent design creationists, but also the implicit argument of some people who want to somehow find evidence for the necessity of god's existence.
It seems as if no amount of reiteration (by those who have studied the theory of evolution) that this basic assumption of chance is not true, seems to have any effect. I recently had a correspondence with someone who, despite my repeatedly pointing out that chance was not the sole driver of natural selection, kept saying things like "How can you think all this came about by chance?"
Now chance does play a role in the way that genetic changes occur, externally from the occurrence of mutations due to things like ultraviolet radiation, and internally in the way that genetic shuffling occurs in the copying of the genetic information during reproduction. You cannot be sure, for example, what genetic features you will inherit from your mother and what from your father. But these chance variations are then acted upon by selection forces that are the very opposite of chance in that they pick out only those varieties that are beneficial for future propagation. This is a highly directed process that acts without an intelligent director and it is these selection forces that are behind the complexity of the systems that have evolved.
In response to the "evolution is just chance and is very unlikely to produce complexity" argument, those who understand the theory of evolution sometimes argue in its defense that the theory is just as good at producing complex things as any conscious designer. But such people are really selling the theory short. In actual fact, the theory of evolution by natural selection produces results that are often much better than those produced by conscious design.
A wonderful example that illustrates this point is given by biologist Steve Jones, as recounted in his book Almost Like a Whale: The Origin of Species Updated (1999) (Chapter IV, Natural Selection). (Thanks to Heidi Cool for alerting me to the podcast of a talk by Jones which is where I first heard this story.)
I once worked for a year or so, for what seemed good reasons at the time, as a fitter's mate in a soap factory on the Wirral Peninsula, Liverpool's Left Bank. It was a formative episode, and was also, by chance, my first exposure to the theory of evolution.
To make soap powder, a liquid is blown through a nozzle. As it streams out, the pressure drops and a cloud of particles forms. These fall into a tank and after some clandestine coloration and perfumery are packaged and sold. In my day, thirty years ago, the spray came through a simple pipe that narrowed from one end to the other. It did its job quite well, but had problems with changes in the size of the grains, liquid spilling through or − worst of all − blockages in the tube.
Those problems have been solved. The success is in the nozzle. What used to be a simple pipe has become an intricate duct, longer than before, with many constrictions and chambers. The liquid follows a complex path before it sprays from the hole. Each type of powder has its own nozzle design, which does the job with great efficiency.
What caused such progress? Soap companies hire plenty of scientists, who have long studied what happens when a liquid sprays out to become a powder. The problem is too hard to allow even the finest engineers to do what enjoy the most, to explore the question with mathematics and design the best solution. Because that failed, they tried another approach. It was the key to evolution, design without a designer: the preservation of favourable variations and the rejection of those injurious. It was, in other words, natural selection.
The engineers used the idea that moulds life itself: descent with modification. Take a nozzle that works quite well and make copies, each changed at random. Test them for how well they make powder. Then, impose a struggle for existence by insisting that not all can survive. Many of the altered devices are no better (or worse) than the parental form. They are discarded, but the few able to do a superior job are allowed to reproduce and are copied − but again not perfectly. As generations pass there emerges, as if by magic, a new and efficient pipe of complex and unexpected shape.
Natural selection is a machine that makes almost impossible things.
In other words, by mindlessly applying an algorithm based on the principle of natural selection, they were able to come up with a complex design for a superior spray nozzle that was inconceivable to the scientists trying to design one using engineering and science principles.
Believers in a god-like designer might argue that what natural selection did here was outperform mere mortal designers and that god, being a perfect designer, would be able to come up with a better design. But that argument doesn't work that well, either, as I will discuss in the next posting in this series.