Natural Selection Examples

Natural selection, a theory created by the famous Charles Darwin, is a process of evolution that results in the ratio of genes being adjusted from generation to generation based on "fitness" or how well that gene helps an organism survive until it can pass on its genes through reproduction.

In order for natural selection to take place there must be genetic diversity. This means that organisms must have different genes from one another. They can share some of the same genes, but they must have somewhat different combinations of genes.

Another factor that must be present, along with heredity of genes, is having some genes that make it more likely for an organism to survive. For example, maybe one member of a population has better eyesight than the rest, or maybe a few individuals have a better sense of smell than the others.

When these factors combine, the result is a difference in survival rates of the individuals within a species. A difference in survival rate means that some individuals will live long enough to reproduce and pass on their genes to the next level while other individuals may not live long enough to pass on their genes to the next generation.

The genes that help an individual survive long enough to reproduce will then be passed on to the next generation while genes that make it harder for an individual to survive will most likely not be passed on to the next generation.

The end result is the best of the best genes being passed on to the next generation; survival of the fittest!

Camouflage is a protective feature that has evolved over the years and is a great example of natural selection.

How did camouflage evolve?

If a predator is searching for prey then it makes sense that the animals that are easiest to see will be spotted and eaten first, correct? This means that the animals that are hardest to see will have a better chance of surviving and reproducing. These hard to see animals will pass their genes on to the next generation while the easy to see animals won't pass their genes on to the next generation because they were eaten!

From generation to generation, the animals that are hardest to see will survive more than animals that are easy to see and the ratio of those hard to see animals will increase over time. The animals that blend in the best will survive and be able to pass their genes on, then the animals in the next generation will consist of the hardest to see out of the hardest to see; the best of the best!

Prey animals that don't have good camouflage will be "weeded out" by natural selection. This effect keeps getting stronger and stronger as the term claims, "survival of the fittest."

The Great White shark is appropriately named with its huge white belly, and it is no coincidence that sharks have developed this color pattern over the years.

Why did sharks evolve blue or gray tops with white bellies?

To understand this example of natural selection you must picture yourself being inside the ocean. If you are under water and you look up towards the surface you will see a bright blue or clear-ish surface with the bright sun. However, when you look down towards the sea floor you will be looking into the dark blue color of the deep sea.

It is no coincidence that sharks have a color pattern that makes them blend in. When you look at a shark from above, its dark blue or gray topside will blend in with the background of the deep and dark blue sea. When you look at a shark from below, its white belly will blend in with the bright colored surface waters along with the sun!

This coloration evolved due to the sharks blending in with these two different backgrounds. The theory is that sharks blending in with the dark blues of the deep sea are difficult to spot from above and therefore their prey would not see them coming, and as a result those sharks would feed more often due to a higher rate of successful hunting. The same goes for blending in with the bright surface waters.

The evolution of antibiotic resistant bacteria is one of the best examples of natural selection because the process takes place much quicker than the evolution of larger animals due to the rapid reproduction of bacteria. Effects and changes can be seen sooner since bacteria can go through several generations in just a single day where as some animals take over 10 years for just one generation!

How do antibiotic resistant bacteria evolve?

The process is quite simple. Say you have an infection and you are prescribed a treatment program consisting of antibiotics. You take the pills and they kill off most of the bacteria to the point where you are feeling better so you stop taking the antibiotics. However, not 100% of the bacteria was killed, in fact, maybe some of the bacteria had genes that made them somewhat resistant to the medication, or in other words, maybe some of the bacteria was "tought" than the rest.

Those "tougher" bacteria were the only ones that survived, which means they will now reproduce and create a new population full of bacteria very similar to themselves; tough bacteria!

Now you have a brand new population of bacteria and they have those same "tought" genes which means they are going to be harder to kill, and therefore more resistant to antibiotics. That effect continues from generation to generation until they become so resistant that some medications may be rendered useless!

The evolution of pesticide resistant insects is very similar to the process of evolution of antibiotic resistant bacteria.

The theory is that when insects are sprayed with a pesticide it will kill all of the insects that are vulnerable or greatly affected by the chemicals. However, due to genetic diversity or variation, there may potentially be a few insects that are not affected too severely by the pesticide and may survive the encounter.

Since all of the insects that were severely affected by the pesticides have now died, that means that the surviving insects are somewhat resistant to the pesticide and will reproduce. Their reproduction will establish a new population consisting of insects that share the gene that allows them to survive contact with those otherwise harmful chemicals.

The result is pesticide resistant insects! In order to kill the pesticide resistant insects you must create a new pesticide. Which leads us to the "Red Queen Hypothesis" in which there is a constant evolution of predator and prey driven by the need to keep up with eachother's new evolutionary adaptations.

The Red Queen Hypothesis refers to the idea that predators and prey are constantly taking part in an evolutionary race in order to keep up with eachother's new adaptations.

A great example of the Red Queen Hypothesis can be seen in pesticide resistant insects. We kill insects with a pesticide until they become resistant to that pesticide. Since they have become resistant to that pesticide we must develop a new pesticide. Then the bugs will eventually become resistant to that chemical and we will have to create a new one. The process goes on and on as we battle back and forth.

Another example can be seen with camouflage and eyesight. If a prey develops exceptional camouflage then only predators with good eyesight may be able to spot the prey. As a result, the predators will evolve better eyesight over the generations. Then, since the predators evolve better eyesight and can see their camouflaged prey more easily, the prey will then continue to evolve better camouflage in response to the improved eyes of their predators.

It is a constant evolutionary battle between predator and prey with each side continuously evolving some kind of adaptation to stay ahead of the other.