Natural selection depends on the environment. Traits that are helpful in one environment will not be helpful in all. Here are some examples of natural selection:
In a habitat there are red bugs and green bugs. The birds prefer the taste of the red bugs, so soon there are many green bugs and few red bugs. The green bugs reproduce and make more green bugs and eventually there are no more red bugs.
In an ecosystem, some giraffes have long necks and others have short ones. If something caused low-lying shrubs to die out, the giraffes with short necks would not get enough food. After a few generations, all the giraffes would have long necks.
A species of rats live in a certain type of tree with the branches evenly spaced. Smaller rats could not reach from branch to branch and larger rats would break the branches and fall. Soon, all rats were just the right size for the tree branches.
Deer mice that migrated to the sand hills of Nebraska changed from dark brown to light brown to better hide from predators in the sand.
Galapagos finches all have different types of beaks. During drought, the finches with the larger beaks survived better than those with smaller beaks. During rainy times, more small seeds were produced and the finches with smaller beaks fared better.
In one ecosystem, lizards that had long legs could climb better to avoid floods and reach food.
Insects become resistant to pesticides very quickly, sometime in one generation. If an insect is resistant to the chemical, most of the offspring will also be resistant. Considering that insect generations can be a matter of weeks, insects in an area can become immune to a chemical within months.
The bacterium Pseudomonas metabolizes nylon; but, when a certain type of this bacterium that did not eat nylon was placed in an environment where nylon was the only food, the bacterium evolved until it ate the nylon.
Peacock females pick their mate according to the male's tail. The ones with the largest and brightest tails mate more often. Today, males that do not have bright feathers are very rare.
The peppered moth used to be a light color with black spots. When the atmosphere in London became filled with soot because of the Industrial Revolution, the white trees became darker and light colored moths were eaten by birds more readily. Within months, moths became darker and lighter moths were rare. After the Industrial Revolution, light colored moths were found in greater numbers.
Rat snakes are all very similar except in coloring. Some are striped and some are green, black, and orange. This is due to living in many different types of terrain and adapting to the environment.
Warrior ants have a chemical signal that tells other ants in the family not to attack. Some have adapted and learned to imitate the chemical signal from other colonies so they can invade and take over another colony and the workers will never know.
Sharks are colored white on the underside and blue or gray on the top. This is their camouflage as the top blends with the water color to someone looking down into the water and the bottom blends with the light coming through the water from above.
Bacteria have become resistant to antibiotics and this can happen very quickly, since bacteria can produce several generations within one day. The strongest bacteria are the last to die and the antibiotics sometimes do not kill all of them.
The field mustard plant survived a drought in southern California because of genetic changes that made it produce flowers earlier. Plants that survive a drought have to have a short growing season and the field mustard evolved quickly.
Because of its long body, the moray eel's mouth did not produce enough suction to catch prey; so, it adapted and grew a second set of jaws and teeth.
Humans have evolved and are still evolving. There are people more resistant to malaria that live in Africa.
Humans don't all become lactose intolerant as some species do. This is thought to be because of the domestication of cattle.
Early humans survived because of a certain hand shape that could either toss a spear or throw a rock the best.
In the 18th century, researchers found in an island community where there was a genetic disposition to mate earlier and have larger families. Over 140 years, the age at first reproduction dropped from 26 to 22 and this was due to natural selection.
