Can we see natural selection occurring?String94 - 6 Answers
There are many well documented cases of natural selection which are currently occurring. One of the earliest that I can remember reading about is the case of the Peppered moth. This medium sized moth is common across the Northern hemisphere where it exists in two color forms, a light colored white with black specks moth, and a dark gray and black moth. Before the Industrial revolution in Europe, the white form made up some 98% of the population with dark individuals being rare.
The white moths would rest on the trunks of trees during the day and these trees commonly had light colored, lichen covered bark. Birds which fed on the moths could easily find any dark individuals on the light bark so nature selected against them and kept their numbers low. Then the industrial revolution happened and smoke belching factories became numerous along with coal burning machinery. All the pollution caused the lichens to die and the trees to develop darker colored bark.
By the late 1800's the population of the peppered moth had totally turned around with the dark individuals making up some 95% of it. Now the white moths stood out on the dark tree trunks, to be found and eaten by birds. Natural selection again decided which individuals would survive longer and thus would pass on their genes more often.
Other examples of natural selection at work would include, drug resistant bacteria, herbicide resistant weeds, rattlesnakes that never develop rattles, nylon eating bacteria, and pesticide resistant insects. There are pigweeds that have developed a resistance to roundup herbicide, fleas that can resist insecticides, and bacteria that can eat nylon, a substance that didn't even exist until after the 1940's. Adapt or die is the rule of nature.
Natural selection occurs from small genetic mutations over several generations. In modern society it would be very hard to find a natural example of natural selection in action. Mostly since we are not constantly seeing animals in their natural habitat.
If you want a few examples of natural selection that are observable we must turn to science. Rats have a relatively short breeding period, so scientists can induce a mutation and breed rats quickly to see how there genome mutates. For example scientist removed a particular chromosome from twenty or rats and began breeding them. Then they bred the children and the children's children. They did this for ten generations to see how the future generations would respond to the chromosome omission. They discovered the later generations had mutated and regained this particular chromosome.
Since natural selection involves changes occurring over generations it is difficult to see in a short time. Dog breeders have managed to "create" new dog species by choosing certain characteristics they preferred. This is not exactly natural in that the breeder is doing the choosing rather than Mother Nature, but over a few generations they have succeeded. Darwin used the beak of the finch, a bird common to the Galapagos Islands to describe how, depending on the particular island they were living on and the types of flowers growing on trees on those islands, the beaks changed by natural selection. Scientists in the laboratory can use bacterial cultures placed in differing environments to grow quite different subspecies overnight. This is a kind of natural selection, although the scientist plays the role of Mother Nature....
Have you caught a cold or flu this season?
Generally speaking once a specific strain of the cold passes through a group that group is immune to that bacteria. Therefor every season a new strain will circulate. This is caused by natural selection limiting the spread of the strain that has fewer susceptible hosts.
This also effects antibiotics. When an organism takes antibiotics all susceptible bacteria are effected. Yet they figure 1/9,000,000,000 bacteria will be immune to every antibiotic. While you may think one out of 9 billion is low odds, an infection requires billions of bacteria to effect the host organism. Therefore they naturally select for bacteria that are immune to the antibiotic.
We can see unnatural selection occurring. That is much faster. People breed certain animals together and after a few generations you can see the results. They have done that a lot with dogs. In nature you can see the results of natural selection but you can't see it occurring because it takes way too long.
Look at different animals in the wild and the different environments they live in. There are lots of animals that adapted to thrive in a specific environment. The ones that are best suited to survive and reproduce live and have babies. They pass on their traits. The other ones perish. So their traits are not passed on.
Natural selection occurs all around us, constantly.
For example, animal breeders use it to steer breeds towards certain desirable characteristics or even to create new breeds from scratch.
In the wild, animals adapt to their surroundings all the time. If a given trait makes it slightly more likely for a given animal to survive and procreate, then those traits will become more common over time.