Evolutionary Fitness: Definition & Explanation

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  • 0:01 What Is Evolutionary Fitness?
  • 0:57 Survival of the Fit or…
  • 2:19 Survival of the Fit
  • 5:05 Thought Evolution
  • 5:59 Lesson Summary
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Lesson Transcript
Instructor: Devin Kowalczyk

Devin has taught psychology and has a master's degree in clinical forensic psychology. He is working on his PhD.

Why is 'Survival of the Fittest' wrong? What did Darwin actually say? Does your brain have anything that makes you a better hunter? This lesson will discuss evolutionary fitness, natural selection and how they might relate to the evolution of the human mind.

What Is Evolutionary Fitness?

Evolutionary Fitness is how well a species is able to reproduce in its environment. If they're no longer reproducing then they are no longer evolutionarily fit. For example, you did not ride a Tyrannosaurus rex to the store. Why not? They're all gone. In their environment they were extremely fit as they ate, reproduced, and continued their species on. But what most often stops evolutionary fitness, and your pet T. rex , is a shift in the environment.

Your pet T. rex died out because the environment could no longer support it. The sun was blotted out resulting in a massive decrease in the amount of plants, causing the oxygen level to drop so the environment could no longer support large creatures. The plants died because there was less sun, resulting in the bottom of the food chain shrinking. With fewer plants the large herbivores starved to death, and with no herbivores to eat the predators starved to death.

Survival of the Fit or the Fittest?

The well known term 'survival of the fittest' was not actually said by Charles Darwin. The phrase was actually coined by Herbert Spencer, who used it for Social Darwinism, a concept we will not be exploring here. Survival of the Fittest is actually impossible, because fittest implies an end. If the fittest critter existed it would be a massive predator that feared nothing and could not possibly mate, because by mixing its perfect genes, or internal blueprints, with anything it would then become less fit.

Charles Darwin is best known for his work on evolutionary theory. He was not, however, the first to propose an evolutionary theory. The first would be Anaximander of 600 BCE Ionia, who noticed human limbs and fish limbs bear a striking similarity, leading him to believe that land-based animals must have originated in the sea. Darwin described the two mechanisms of evolution in his book, On the Origin of Species.

Another researcher by the name of Alfred Wallace came to similar conclusions as Darwin. However, Darwin's ideas and writings were more thorough and published, resulting in the scientific community attributing the evolutionary mechanisms to him. Darwin and Wallace's evolutionary mechanisms actually support the idea of survival of the fit: those who are fit enough to reproduce will pass on their genes, and those that do not work will die out.

Survival of the Fit

Natural selection is the process by which the critter with the best adaptions survives long enough to reproduce. Let us take 200 people, and divide them into two groups. Each group of 100 is going to live on a different island for the next 100 years.

Island A is near the equator, which means it will get a lot of sunshine and will be very warm and very humid. This type of climate is very similar to what is seen in the Philippines. Because it is very warm, the vegetation tends to produce very little edible plant matter, and the animals tend to be very small. If there is very little food, the larger people will be hungry while the smaller people will be able to survive off the smaller food. In addition, the bright sun will give light-skinned people some nasty sunburn, while those with darker pigmentation in their skin will be better off. After 100 years the 100 people we put on Island A are now smaller and darker-skinned. This is seen in a person with Filipino heritage.

Island B will be nearer the Arctic Circle, with heavy cloud cover resulting in tougher vegetation, but larger sea animals that stay warm because of their blubber. To hunt big sea beasts like walruses you need big people who can hunt. In addition, because this island receives less light, people on this island will need lighter skin so they can more efficiently process sunlight into Vitamin D. After 100 years you will have large, pale-skinned people who look very Scandinavian. This is the process of natural selection; what works best in the environment will endure. Natural selection works by having traits that are useful continue on to the next generation and what does not work will be bred out.

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