Natural selection

Natural selection is the gradual process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution. The term "natural selection" was popularized by Charles Darwin who intended it to be compared with artificial selection, now more commonly referred to as selective breeding.

Examples:

1. Humans

Are humans still evolving? The simple answer is yes, even if the changes are not obvious. Experts believe that about 9 percent of our genes are undergoing rapid evolution as we speak. The genes most affected by natural selection are those involving the immune system, sexual reproduction and sensory perception.

Lactose intolerance is one example of natural selection. We are the only species that doesn't become lactose intolerant as we grow up. According to experts, this seemed to have happened when cattle became domesticated in Europe centuries ago. Another example is the sickle hemoglobin gene, which occurs in people who live in certain regions of Africa and other areas where malaria is endemic. This gene mutation makes people who have it more resistant to malaria. While they can still contract the disease, they are less likely to die from it. The mutation probably happened over hundreds of generations as a result of the constant exposure to malaria and people contracting and surviving it

2. Lizards

A number of studies have been done on lizards to determine natural selection. One experiment temporarily eliminated the lizards' natural predators from a particular area, and then scientists observed what impact that had on the lizards. The surprising find was that it's not so much the predators that influence the death or survival of certain lizards. Instead, the smaller lizards were more likely to die off anyway despite the lack of natural predators, because the larger, stronger lizards in the area still had better access to food. The lizards with the longest legs were able to climb better, escape the ground when floods or storms came, and reach food that wasn't available down below.

3. Nylon-eating Bacteria

Since nylon wasn't invented until the 1940s, bacteria that can eat nylon can be nothing but new. The bacterium Pseudomonas is able to metabolize nylon thanks to certain enzymes it has. However, a surprising thing happens when you take a non-nylon eating variety of this bacterium and place it in an environment where the only type of food available is nylon. Every single time the experiment was tried, the bacteria would evolve until it was able to consume nylon. This is a very simple example of natural selection, where the most basic forms of life can adapt to whatever food the environment offers.

• Regressive Evolution: the disappearance of traits that were once useful but now obsolete. One example is the existence of eyes on Mexican cavefish, a species found in subterranean caves. Because of the caves' perpetual darkness, eyes became no longer necessary and eventually fish were born without them. Cave-dwelling fish have also lost their pigmentation and have become nearly transparent, since they no longer need camouflage because of the lack of natural predators

4. Deer Mouse

Nebraska's Sand Hills is home to a deer mouse that's one of the quickest-evolving examples of natural selection in animals. The deer mouse is normally dark brown, which is a good color for mice living in the woods and surrounding areas, since it allows them to hide better and avoid predators. The deer mouse that lives in the Sand Hills, however, has evolved into a much lighter, sand-like color. Without this change, the deer mouse would be easily spotted by predators against the area's light terrain. Just one single gene had to change for the mouse's coat to become lighter. What's even more impressive? The change took only about 8,000 years, which is the equivalent to seconds in the evolutionary scale 

5. Warrior Ants

The warrior ants in Africa are probably one of the most impressive examples of adaptation. Within any single colony, ants emit a chemical signal that lets the others know they all belong to the same compound. Or, put more simply, a signal that says "Don't attack me, we're all family." However, warrior ants have learned how to imitate the signal from a different colony. So if a group of warrior ants attacks a colony, they will be able to imitate that colony's signal. As a result, the workers in the colony will continue on, now under the direction of new masters, without ever realizing an invasion has taken place.

6. Peacocks

The more impressive the tail of a male peacock, the higher its chances of finding a mate. Female peacocks choose mates based on the color of the feathers and the overall physical prowess of the animal. According to experts, the brightness of the plumage might signal to females that the animal has high-quality genes. This would make him ideal for reproduction and to ensure the survival of the offspring, so they're chosen first when it's time to mate. In reality, not all males have bright, large tails, and this was especially true a few thousand years ago. And because females kept choosing the brightest males as partners, the ones without the impressive tails were less likely to mate and reproduce. As a result, their numbers diminished from one generation to the next, making them rare today.