Survival of the Fittest: Natural Selection Explained

If an organism survives but never has any offspring, then its traits die with it. If it reproduces successfully, then its genetic "fitness" is high because its traits continue in the next generation.

If a population produces many more offspring than the environment can support, then there will be a struggle for resources. If there is a struggle, then only the best-suited individuals will survive.

If a scientist observed that finches had different beaks suited for different food sources and concluded that the environment "selects" the best traits, then that person is Charles Darwin.

If an organism has a trait that helps it find food or avoid predators, then it has a higher chance of staying alive. If it stays alive, then it can pass those helpful traits to the next generation.

If we find older fossils that look different from modern animals but share similar features, then we can see a path of change. If this path exists in the rock layers, then the fossil record supports evolution.

If a trait makes an animal easier for predators to see, then that animal is likely to die before reproducing. If the animal dies early, then it cannot pass that trait on, causing the trait to eventually disappear.

If a small, slow animal is better at hiding and has 10 babies while a big, fast animal is easily seen and has 0 babies, then the small one is "fitter." If "fitness" is about passing on genes, then the best-adjusted parents win.

If the trees became dark with soot, then light-colored moths were easily eaten by birds. If dark moths survived and reproduced more, then the population shifted to be mostly dark through natural selection.

If Darwin's theory relies on variations that are already there, then it is a process of selection. If Lamarck's theory relies on animals stretching or changing themselves, then it is a process of "acquiring" traits.

If an organism needs a new trait to survive, it cannot just "decide" to have it. If an accidental change in DNA (a mutation) creates a new trait, then natural selection can decide if that trait is helpful or not.

If mutations are random, then the starting variations are accidental. However, if the environment consistently saves the "best" traits and kills the "worst" ones, then the results of selection are non-random and predictable.

If evolution requires many generations of reproduction and death to shift a population's traits, then it is a slow process. If large animals have long lives, then significant changes take thousands or millions of years.

If a trait is "acquired" (like a scar or a tan), then it does not change the DNA in the sperm or egg. If the DNA doesn't change, then the trait cannot be passed to the next generation through natural selection.

If resources are limited and there are too many individuals, then they must compete to stay alive and have babies. If they compete for food, water, space, and mates, then those are the drivers of selection.

If evolution is the change in the frequency of traits in a group, then it cannot happen to one animal. If it takes many generations of births and deaths to change a group, then only populations can evolve.

If every member of a species was exactly the same, then no individual would have an advantage over another. If there are differences (variations), then the environment can favor one over the other.

If Darwin observed variation, inheritance, overproduction, and limited resources, then he had the evidence for natural selection; however, he did not believe animals could change their own DNA by "wanting" it.

If a trait is helpful in the desert but deadly in the rainforest, then the surroundings dictate survival. If the surroundings dictate survival, then the environment is the selective pressure.

If a farmer only breeds the largest cows to get more milk, then a human is doing the "selecting." If a human is in control of the process, then it is artificial selection.

If a polar bear's white fur helps it hide in the snow to hunt, then that trait provides a survival benefit. If a trait provides a benefit for a specific environment, then it is an adaptation.