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Evolution and natural selection review

Key terms

EvolutionThe process by which modern organisms have descended from ancient organisms over time
Common ancestorAn ancestor shared by two or more descendant species
Natural selectionEvolutionary mechanism in which individuals that are better suited to their environment survive and reproduce most successfully
VariationDifference between traits in individuals of the same species
AdaptationA trait that improves an organism's ability to survive and reproduce in an environment
FitnessThe ability of an organism to survive and reproduce
Artificial selectionSelective breeding of organisms to promote the appearance of desirable traits in offspring
Genetic driftA mechanism of evolution in which allele frequencies of a population change over generations due to chance

Darwin's theory of evolution

Charles Darwin developed a theory of evolution to explain the unity and diversity of life, based on the idea of shared common ancestors.

Natural selection

Darwin's theory was based on the mechanism of natural selection, which explains how populations can evolve in such a way that they become better suited to their environments over time.
Light colored mice are more easily seen by predators and are therefore preyed upon more. Dark mice are better adapted to their environment and better able to survive and reproduce.
Natural selection acting on mice population over time.
Individuals have variations within their heritable traits. Some variations make an individual better suited to survive and reproduce in their environment.
If this continues over generations, these favorable adaptations (the heritable features that aid survival and reproduction) will become more and more common in the population.
The population will not only evolve (change in its genetic makeup and inherited traits), but will evolve in such a way that it becomes adapted, or better-suited, to its environment.

Artificial selection

There are other types of selection, in addition to natural selection, that are out there in the world.
Artificial selection, also called "selective breeding”, is where humans select for desirable traits in agricultural products or animals, rather than leaving the species to evolve and change gradually without human interference, like in natural selection.
A timeline showing how dogs became domesticated over a long period of time due to artificial selection.
Dog breeding is a perfect example of how humans select for desirable or fashionable traits. Breeders deliberately mate parents with the hope of producing offspring with specific traits (such as color, size, ear shape, snout length, and so on).

Common mistakes and misconceptions

  • Evolution is not the same as adaptation or natural selection. Natural selection is a mechanism, or cause, of evolution. Adaptations are physical or behavioral traits that make an organism better suited to its environment.
  • Heritable variation comes from random mutations. Random mutations are the initial cause of new heritable traits. For example, a rabbit can't choose to have a different fur color. Rather, a genetic mutation causes a difference in fur color, which may help that rabbit hide better in its environment.
  • Natural selection acts on existing heritable variation. Natural selection needs some starting material, and that starting material is heritable variation. For natural selection to act on a feature, there must already be variation, and that variation must be able to be passed on to offspring.
  • Natural selection depends on the environment. Natural selection doesn't favor traits that are somehow inherently superior. Instead, it favors traits that are beneficial in a specific environment. Traits that are helpful in one environment might actually be harmful in another.

Want to join the conversation?

  • piceratops seedling style avatar for user msarcenom0001
    What is the difference between natural and artificial selection
    (5 votes)
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  • aqualine tree style avatar for user Goody Doogy
    Hi, I'm not sure whether I'm correct or not.
    This page gives the meaning of natural selection as an *"Evolutionary mechanism in which individuals that are better suited to their environment survive and reproduce most successfully".*

    So in this case, doesn't it mean that natural selection doesn't have to lead to evolution. For example, people (in a population) living in a harsh condition should exercise to be stronger in order to fit the environment. However, their strength can not be inherited (their offsprings don't descend from them).

    Therefore, in my opinion, the definition of natural selection and evolution should involve genetic matters. Otherwise, it is not reasonable to say that natural selection is the cause of evolution.
    (4 votes)
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    • male robot donald style avatar for user Tybalt
      For your specific case, natural selection can still be genetic. Yes, you can't always pass down behaviors. However, there still are genes that influence muscle function and how easy it is to exercise. For instance, ALS, the disease that rendered Stephen Hawking unable to move much of his body, is hypothesized to be partially genetic. Plus, there are genes that influence muscle strength, and "strongman" genes do exist. Even if behaviors will not be passed down, those with genes that promote muscle strength will survive and would be more likely to pass them down. They will build more strength faster, and will thus be more fit. There are so many genes in just a single organism alone, and only now are scientists discovering what all of them do. Thus, for a characteristic, it is likely that it may be genetically inherited (what degree the gene influences the characteristic, though, is still up for debate).

      However, you are somewhat correct on your statement regarding natural selection being the cause of evolution: it is not the sole cause of it. There is also genetic drift and random mutations, which do not relate to the survival of the fittest.

      Does this help?
      (4 votes)
  • male robot hal style avatar for user Bojeram
    Is evolution why humans are the apex predators in every enviorment or is it that we have the most advanced brain?
    (3 votes)
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  • leaf red style avatar for user oogie boogie
    What is the difference between evolution and adaptation?
    (3 votes)
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  • blobby green style avatar for user Chris
    Mass extinctions pretty much always have a dramatic effect on life on Earth. A good example of this is the asteroid that killed off the dinosaurs. If that event had never happened, there might still be dinosaurs around, which would be kind of terrifying.

    So yeah, mass extinctions definitely impact what happens later on.
    (4 votes)
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  • blobby green style avatar for user mresetich
    what is the meaning of natural selection
    (4 votes)
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  • blobby green style avatar for user 43790
    How does natural variation affect evolution?
    (3 votes)
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    • aqualine ultimate style avatar for user Ant
      Natural variation in a species affects evolution because when there is only one type of variation of a species, natural selection would be more difficult. If there was no natural variation, and some of the organisms survive and reproduce, since they have the same characteristics and no different variation in DNA the offspring would have the same characteristics as the parents.

      So, in order for a species to evolve, only those that are stronger and better than the others can survive.
      In conclusion, natural variation affects evolution because the more variation there is in a species, the more results in future generations. Sometimes, it does not matter though. Even if an organism had the same DNA as another, the better one (the one who gets the food, survives from predators, and gets enough necessities) will pass its "strength" to their offspring.
      (2 votes)
  • blobby green style avatar for user 201145839
    What if the species dies before natural selection takes place?
    (3 votes)
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  • duskpin sapling style avatar for user i.m.riggs
    What if there was a big mass extinction? Would the Earth still be the same before the mass extinction? Would you please explain this? Thank You!
    (3 votes)
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  • mr pink red style avatar for user Isabella Escobar
    how natural selection affects evolution?
    (2 votes)
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    • aqualine tree style avatar for user Prisha B
      If an organism has a mutation that increases its chances of survival, it's more likely to reproduce and have offspring with that mutation. Organisms that fail to survive, obviously, will not pass on their traits. Whether or not an organism survives to reproduce depends on their surrounding environment. This is natural selection. Over time, that mutation can develop into a distinguishable adaptation and/or become more pronounced in a species since it increases the chances of survival. Sometimes many mutations over many, many, many years can result in an entirely different species or type of species.
      (4 votes)