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How Darwin's Observations Showed the Process of Natural Selection

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  • 0:02 What is Natural Selection?
  • 2:17 Observations
  • 4:43 Genetic Diversity
  • 6:25 Lesson Summary
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Lesson Transcript
Instructor: Jayne Yenko

Jayne has taught health/nutrition and education at the college level and has a master's degree in education.

In this lesson, we will learn about the observations that led to the development of Darwin's theory of natural selection. We'll explore how natural selection happens and how this brings about genetic diversity.

What is Natural Selection?

Survival of the fittest - sounds like a reality show on TV, doesn't it? It doesn't mean those who are the toughest, strongest, or fastest. Survival of the fittest actually refers to those who have the most reproductive fitness. Those who have certain genetic variations and live long enough to reproduce are those who are the fittest. These genetic variations are able to be passed on to the next generation and eventually these variations will become common within the population. This is the key to natural selection, Charles Darwin's most important contribution to science.

Natural selection, or survival of the fittest (the phrases can be used interchangeably), means that evolutionary change happens through the production of variations in each generation and the different rates of survival of individuals with different combinations of these variations. For example, running speed in rabbits is an inheritable trait, so there are faster and slower individual rabbits. In specific populations of rabbits, the slower ones are eaten by foxes, so their genes are not passed on.

Individuals who possess variations in their genetic code that increase their probability to survive will have more chances to reproduce and their offspring will benefit from the inheritable variations. Over time, these variations spread through the population, causing the population itself to change - that is evolve, or what Darwin referred to as descent with modification. Each generation is slightly different than the one before.

Darwin's trip onboard the H.M.S. Beagle during the 1830s gave him the opportunity to see evidence of natural selection, although he didn't realize it at the time. Once he was back home in England, analyzing his notes and specimens, he was able to make observations about natural selection and how it contributes to genetic diversity. Let's find out what those observations were.

Observations

The first observation is overproduction. This means all species produce more offspring than will survive to become adults. Think of all the thousands of fish eggs produced each year. This means populations of species should be getting larger all the time, but they aren't, because there are mechanisms in place to curb population explosions, such as competition for food, predation, and disease. From this, Darwin was able to make a deduction: there is a struggle for existence. Many of those fish eggs are food for predators, who would not survive without them.

Darwin's second observation was variation. This means members of the same species show variation in characteristics. For example, zebras show variation in pattern and color of their stripes. Goldfish have gold scales, orange scales, or brown scales, or a mixture of all three.

Variation applies to all traits, even those essential for the survival of the individual organism. An eagle depends on excellent eyesight to locate prey, but it can still be born shortsighted. This means that variations are random and are not specific to any favorable adaptation.

The next observation, selection , means organisms that survive are more likely to reproduce and pass on favorable adaptations to their offspring than those with unfavorable adaptations. For example, height is an inheritable characteristic, and for the giraffe, having long necks (which added to their height) was reproductively advantageous. The taller giraffes were able to reach leaves in tall trees, which kept them alive longer, and able to reproduce, making them more reproductively fit than shorter giraffes who couldn't reach those leaves and died without reproducing.

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