November 20, 2021 | David F. Coppedge

Evolutionary Fitness Is Not Measurable

The central concept of natural selection cannot
be measured. This means it has no scientific value.


How do you measure fitness? If you are an athlete, you can measure it in muscle, speed and endurance, or good vital signs. This is not what Darwinians mean by fitness. When they speak of “survival of the fittest” (a phrase coined by Herbert Spencer but adopted by Charles Darwin in later editions of the Origin as the phrase best capturing his meaning of natural selection), evolutionists mean lots of things: ability to bear the most offspring, survive predation, outcompete others, evade extinction, or whatever. But to measure something, it needs units. How is fitness to be measured? What are the units? Physicists have degrees Kelvin, ergs and Joules of energy and Faradays of electricity, but do 100 Spencers on a Haeckl-o-meter equal 10 Darwins of fitness?

Laypeople tend to think of the “fittest” as the biggest, fastest or greatest: the Lion King image. One problem with the term is that it can mean opposite things in practice. For instance, a sloth is fit because it continues to bear young, even though it is extremely sluggish. A predator is fit, but so is its prey. And is a fly that lays thousands of viable eggs more fit than a rhinoceros that bears one young every few years? There are other problems. Does the term refer to an individual or to a population – or to a subset of the population? Does it refer to an individual or to its parts? I.e., are a few female eggs more fit than millions of male sperm cells destined to perish without passing on their genes? And when is fitness to be determined: at birth, at maturity, or at death? Is short-term fitness different from long-term fitness? How many generations must be followed to get a grasp on reproductive success?

Fitness an Undefined Term

The term “fitness” becomes nebulous when you try to pin it down. Five evolutionists attempted to nail this jello to the wall, and wrote up their results in a preprint on bioRxiv by Alif et al. that asked, “What is the best fitness measure in wild populations?” (One might wonder why this question is being asked 162 years after Darwin presented his theory to the world.)

Fitness is at the core of evolutionary theory, but it is difficult to measure accurately. One way to measure long-term fitness is by calculating the individual’s reproductive value, which represents the expected number of allele copies an individual passes on to distant future generations. However, this metric of fitness is scarcely used because the estimation of individual’s reproductive value requires long-term pedigree data, which is rarely available in wild populations where following individuals from birth to death is often impossible. Wild study systems therefore use short-term fitness metrics as proxies, such as the number of offspring produced.

Alif et al. went out to measure fitness in twenty years’ worth of data about a population of passerine birds. They used various proxy measurements of a well-studied species to predict “reproductive value” (as defined above), including “reproductive success, individual growth rate and de-lifed fitness as lifetime fitness measures, and as annual de-lifed fitness” (de-lifed referring to “individual offspring production and survival adjusted for population growth”). Unfortunately, none of these proxies worked particularly well.

We compared the power of these metrics to predict reproductive values and lineage survival to the end of the study period. The three short-term fitness proxies predict the reproductive values and lineage survival only when measured at the recruit stage. There were no significant differences between the different fitness proxies at the same offspring stages in predicting the reproductive values and lineage survival. Annual fitness at one year old predicted reproductive values equally well as lifetime de-lifed fitness. However, none of the short-term fitness proxies was strongly associated with the reproductive values. In summary, the commonly short-term fitness proxies capture long-term fitness with intermediate accuracy at best, if measured at recruitment stage [i.e., when able to produce at least one viable egg]. As lifetime fitness measured at recruit stage and annual fitness in the first year of life were the best proxies of long-term fitness, we encourage their future use.

Good luck with that. Without omniscience or the ability to follow every individual in a population for multiple generations in the wild, when each individual looks alike, and sequence their genomes on top of that, one could not even measure the proxies, let alone the fitness. Imagine trying that with ants. Maybe some proxies could be measured for this species of bird, but how sure are they that each individual of the wild population was followed accurately over the study interval? Birds do fly away after all.

Inability to Generalize

Whatever success they feel they had measuring fitness, it must be noted, concerned only this species of bird. The authors admit that their results do not necessarily apply to all living things.

The concept of fitness is central to evolutionary theory. Natural selection maximises fitness, which is therefore a driving force of evolution as well as a measure of evolutionary success. One definition  of fitness is how good an individual is at spreading its genes into future generations, relative to all other individuals in the population. A universal definition of fitness in mathematical terms that applies to all population structures and dynamics is however not agreed on.

Remember that this statement comes over 162 years after evolutionists began talking about fitness. If you cannot define something, how can you measure it? And if you can’t measure it, is it really scientific? These and many other evolutionists estimate this nebulous “fitness” concept using proxies, but the proxies are nebulous, too, because they depend on other subjective measures.

The two most commonly used individual fitness proxies are lifetime reproductive success (LRS) and individual growth rate (IGR). Both count the number of offspring produced in the individual’s lifetime, but IGR gives more weight to offspring produced at a younger age, therefore results differ. As a consequence, different fitness proxies do not necessarily correlate well and more research is needed to determine which is the most appropriate measures of fitness. Choosing the appropriate fitness proxy is therefore an important consideration when designing a study.

Exceptions Outweigh Rules

To see the subjectivity of fitness thinking, consider measuring the fitness of individual human beings with these proxies. Which individual is more fit: a drunk and his mistress who have 14 children who all grow up poor and drop out of society on drugs and abortions, or a Chinese official with one child who influences the government to lift the one-child policy, thereby leading to a dramatic population increase in the country? According to the proxies, the first individual would be the fittest! Which bird is more fit: one that lays ten eggs that produce chicks that each lay one egg on an island with high predation, or one “founder” bird lays two eggs on a deserted island without predators that leads to an explosion of population for that species? If the scientist only measured fitness using the proxies, the first individual would be the fittest.

With animals, even a “fit” individual is vulnerable to accidents of nature, such as floods or earthquakes that could lead to the death of its entire progeny. How many “fittest” dinosaurs perished in the mass extinction? So were the butterflies more “fit” than the dinosaurs, because they survived? Too bad for those mighty dinosaurs. Darwinian theory works in strange ways. Solomon lamented, “Again I saw that under the sun the race is not to the swift, nor the battle to the strong, nor bread to the wise, nor riches to the intelligent, nor favor to those with knowledge, but time and chance happen to them all” (Ecclesiastes 9:11). That’s the “stuff happens” law for beings “under the sun” when divine providence is left out of the equation (cf. Solomon’s conclusion in chapter 12).

Defining Truisms

The authors claim that some short-term fitness proxies predict long-term fitness more reliably than others, and should be used in future studies. But what the above drawbacks and limitations imply is that there is no way to reliably predict the fitness of an individual or brood when measured in terms of reproductive success. There is only retrodiction, or hindsight. If fitness can only be measured in hindsight, though, then every species alive is fit, because it survived. Fitness, therefore, collapses into a tautology: if it survives, it is fit. Which are fit? Those that survive. Worms that survived the alleged asteroid impact were more “fit” than T. rex. The usefulness of an undefined, unmeasurable term that can produce outcomes like this seems dubious. Fitness means anything that an evolutionist wants it to mean. (See “Fitness for Dummies,” 19 June 2014.)

Cartoon on article website perpetuates known myths about human progress.

Another Tautology with Dark Implications

Embedded within the Darwinian “fitness” concept is the myth of progress. Why? Because Darwinians believe humans evolved from bacteria. That requires vast amounts of new genetic information to emerge. Darwin’s mechanism of natural selection—semantically equivalent to survival of the fittest—is purported to be the engine of innovation. Chance variations produce increases in complexity over time, we are told. Evolutionists will often challenge this assertion, saying that decreases in complexity are also examples of evolution (see 25 Oct 2021), but they’ll never get eyes and wings that way. There had to be variation, and some variations had to be more “fit” than others.

More sinister in the myth of progress are the implications for human society. For evolution to work, some individuals must be ranked lower on the fitness scale. And they were: the dark history of scientific racism is a blotch on history (see 9 June 2020).

That motivation behind scientific racism: is it dead? In, Bob Yirka wrote about “Evidence found of genetic evolution in Europeans over past several thousand years.” Noticeable at the top of the article is a depiction of the myth of progress: a silhouetted version of the discredited “March of Man” icon. By implication, some humans are becoming more fit by evolution. Maybe it’s the Europeans again! Perish the racist thought. What, then, does he mean by “evidence of natural selection” in European genomes?

Surprisingly, Yirka does not use the term “fitness” in the article. He refers to a team of evolutionary biologists publishing in Nature Human Behavior who used divination on the genes of living and dead Europeans. They supposedly found genes that were under “selection pressure” –

In looking at the data, the researchers found evolution at work in 755 genes related to the traits they had selected over the past 2,000 to 3,000 years—and they included skin pigmentation, dietary traits and body measurements. All three traits were found to be under near constant selection pressure, leading to near constant changes to the genome.

Nothing in the brief article states that Europeans are “better” or more “fit” than non-Europeans. (These days, they had better not say such things in public like their forerunners used to.) But watch out. The article ends with, “The research team acknowledges that their results are still preliminary as more detailed work is needed.” They can always pass the Buck v Bell to futureware providers. Science marches on.

A more accurate march of human evolution. Note: first figure at left is mythical. Second from right is typical of the American population. So in Darwinian terms, they are the fittest; they continue to survive past reproductive age.

Searches for differences in “fitness” between people groups did not end well last time. Fitness as Darwinians conceive of it is not only a vacuous, undefinable, indistinct, subjective, unscientific term. It is also pregnant with evil.

We do, however, encourage and promote individual physical fitness, which is measurable and beneficial. “Glorify God in your body,” our Maker advised (I Corinthians 6:20).






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