Evolution  (Page 5/9)

In addition, consideration of these processes in the real world leads to a better understanding of the questions in the introduction to this chapter. As you can see, the process of evolution is NOT random; the interaction of the organism and its environment leads to selection, and selection, by the very nature of the word, is not random. Just as an animal breeder chooses specific individuals as the parents of the next generation, the process of natural selection chooses specific individuals as the parents of the next generation, leading to evolution of the population. There are some important differences, however. In artificial selection, the breeder has a goal (e.g. to get a goat that produces more milk), and designs the breeding program with that goal in mind. In natural selection, there is no ultimate goal, and no plan; organisms are selected for their adaptation in a particular environment, which can (and often does) change. The process is unguided, in the sense that there is no goal in mind, but unguided is not the same thing as random.

Secondly, careful consideration of this process also disproves the notion that evolution equals progress toward a “better” organism. An organism that is better adapted to one environment can be very ill-adapted if the environment changes. In that situation, a “worse” organism, one that is rare in the first environment, is now the “better” one in the new environment. That is not progress, it is just change. In fact, some organisms become so well-adapted to their environments that they lose some of the complex structures or pathways that their ancestors had. Cave fish have no eyes, even though their ancestors did. Whales have no legs, even though their ancestors did. Some parasites, living in a rich sea of nutrients, have lost organelles such as mitochondria, even though their ancestors had those organelles and all of the metabolic pathways associated with them. These highly-adapted organisms are actually less complex than the ancestors from which they evolved. Evolution clearly is not a synonym for progress!

Finally, it should be clear that evolution is a change at the level of the population, and not at the level of the organism. Natural selection acts on organisms, but the result of selection is seen in the next generation. And this change is usually very gradual; there is no need to invoke absurd situations where a cat gives birth to a dog, or vice-versa.

Darwin correctly pointed out the analogies between this process of natural selection and artificial selection, the well-known process that animal breeders used to select for interesting or useful variants in animal species. In other words, natural processes can generate the diversity we find in the natural world if all of those conditions are true, and if there is sufficient time to produce many generations. You will learn more in the studio exercises about how even small differences in reproductive success can, over time, lead to large changes in the characteristics of organisms in a population. Small changes (one or two genes in organisms that still are members of the same species) are sometimes described as micro-evolution . Larger changes that result in different species, for example, are described as macro-evolution . This is an artificial distinction, actually. Macro-evolution is merely micro-evolution that has proceeded for a longer time. For a clever graphical illustration of that, see figure 2 below.