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The Elusive Idea of Biological Fitness

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[Originally published as The Fitness Illusion]

Many people have heard the phrase “survival of the fittest.”

Evolution depends on fitness as part of its model. Organisms that survive are characterized as “more fit,” and phrases like “natural selection fits animals for their environments” are regularly used. I’ve even used them myself.

But the question of “what is fitness?” is rarely asked.

Scientists appear to assume fitness always means the same thing when in reality they apply it quite differently. Today we will peel back the curtain a bit on how evolutionists misuse fitness to try to win arguments.

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If the Darwinist is teaching a class, fitness means differential reproductive success. In other words, in evolution classes, students are taught that fitness is measured by looking at the number of surviving offspring. The problem here is threefold.

  • Measuring fitness in this way is, in a sense, the ultimate rescuing device.
  • Evolutionists are highly inconsistent with their application of this definition.
  • Fitness must be measured at the organismal level, not the genetic level, but evolutionists almost always appeal to genetic fitness.

Evolutionists are not exactly noted for ideological or logical consistency, and in this instance, they have outdone themselves. Frequently, I hear evolutionists refer to mutations as “beneficial.” Problem is, most of the mutations they are talking about have absolutely nothing to do with reproduction and therefore do not increase fitness one iota. For example, the mutation that causes tetrachromatic vision has absolutely no reproductive advantage to the organism. Yet I’ve seen it classed as a fitness-increasing beneficial mutation.

Probably the best example of the confusion over fitness comes from the sickle-cell anemia mutation.

Sickle cell anemia is a disease caused by a mutation that controls the shape of red blood cells. When the mutation is present, the blood cells are warped in the shape of a sickle. This is bad because it significantly reduces the amount of oxygen the blood can carry.

People who have two alleles for sickle cells can be very badly debilitated by the disease. It can even be fatal. People with a single allele for the trait are termed carriers but are rarely affected. However, in some countries, particularly in West Africa, malaria is a great threat. People with sickle cell anemia are much less likely to get the malaria parasite, and carriers’ symptoms are generally much less than those that do not carry the trait. Thus evolutionists will sometimes argue that the sickle cell trait increases the fitness of those who carry it.

Notice what has been done here: the definition of fitness has been changed.

Instead of involving reproductive success, now the definition is purely survival related. Evolutionists do this regularly when beneficial mutations are in question. They claim that any situational benefit to organisms is a beneficial mutation, therefore increasing fitness, when what they need is an increase in reproductive fitness, which most supposed beneficial mutations are not.

Even if They Have Offspring…

Further, even if mutations increased reproductive success, this measurement of fitness is literally the definition of punting it down the road. The fitness of an organism can never be measured in an ultimate sense.

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Sure, the number of offspring it has can sometimes be measured, but from how fitness is defined, this is not ultimately enough. To determine how fit an organism is, you would need to determine the sum of all of its descendants for all time. After all, an organism may have thousands of offspring, but if all its offspring are sterile, then how reproductively fit was it? There is no way, of course, to measure the ultimate fitness of an organism. The fitness measurement of the next generation is a poor stand-in.

The problem with the appeal to fitness is that it is so often applied at the genetic level. The problem here is due to the multitude of genes that make up an organism. Very rarely can one gene control the reproductive success of an organism. Reproductive success happens at the organismal level, not the genetic level. Yet what is most often examined is the fitness effect of a gene.

The above-described issues point to fitness being something of an elusive idea that cannot be tied down. If fitness does not exist or is inappropriately defined, perhaps we need to re-examine our definitions of natural selection and beneficial mutations as well since these are so closely tied to the fitness idea. Regardless, the evolutionary story is just that; a story, one best consigned to the waste basket.

Written by Emory Moynagh

I graduated from Pensacola Christian College with a B.S. in Biology, then worked as a high school science teacher for two years before transitioning into a quality assurance role. I now do science and apologetics research. My personal interests in apologetics stem back to high school when I was introduced to the teachings of Ken Ham, ICR, CMI and others. This created a passion in me for Creation Science, the Bible, and all things science related. You can find my friends and me at In His

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