Why Darwin Matters_ The Case Against Intelligent Design - Michael Shermer [8]
B. In a natural environment, however, population numbers must stabilize at a certain level. The population cannot increase to infinity—the earth is just not big enough.
C. Therefore, there must be a “struggle for existence.” Not all of the organisms produced can survive.
D. There is variation in every species.
E. Therefore, in the struggle for existence, those individuals with variations that are better adapted to the environment leave behind more offspring than individuals that are less well adapted. This is known as differential reproductive success.
As Darwin said, “as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life.”13
The process of natural selection, when carried out over countless generations, gradually leads varieties of species to develop into new species. Darwin explained:
It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were.14
The time frame is long and the changes from generation to generation are subtle. This may be one of the most important and difficult points to grasp about the theory of evolution. It is tempting to see species as they exist today as a living monument to evolution, to condense evolution into the incorrect but provocative shorthand that humans descended from chimpanzees—a shorthand that undercuts the facts of evolution.
Natural selection is the process of organisms struggling to survive and reproduce, with the result of propagating their genes into the next generation. As such, it operates primarily at the local level. The Oxford evolutionary biologist Richard Dawkins elegantly described the process as “random mutation plus non-random cumulative selection,”15 emphasizing the non-random. Evolution is not the equivalent of a warehouse full of parts randomly assorting themselves into a jumbo jet, as the creationists like to argue. If evolution were truly random there would be no biological jumbo jets. Genetic mutations and the mixing of parental genes in offspring may be random, but the selection of genes through the survival of their hosts is anything but random. Out of this process of self-organized directional selection emerge complexity and diversity.
Natural selection is a description of a process, not a force. No one is “selecting” organisms for survival or extinction, in the benign sense of dog breeders selecting for desirable traits in show breeds, or in the malignant sense of Nazis selecting prisoners at Auschwitz-Birkenau. Natural selection, and thus evolution, is unconscious and nonprescient—it cannot look forward to anticipate what changes are going to be needed for survival. The evolutionary watchmaker is blind, says Dawkins, pace Paley.
By way of example, once when my young daughter asked how evolution works, I used the polar bear as an example of a “transitional species” between land mammals and marine mammals, because although they are land mammals they spend so much time in the water that they have acquired many adaptations to an aquatic life. But this is not correct. It implies that polar bears are on their way (in transition) to becoming marine mammals. They aren’t. Polar bears are not “becoming” anything. Polar bears are well adapted for their lifestyle. That’s all. If global warming continues, perhaps polar bears will adapt to a full-time