Darwin's Theory Of Natural Selection

4 Answers

mwestwood's profile pic

mwestwood | College Teacher | (Level 3) Distinguished Educator

Posted on

After intensive observations and study, English naturalist and biologist Charles Darwin argued that environmental pressures, such as changes in climate, the presence of predators, and competition for food or mates lead to the survival of those better adapted. As the weaker and less adaptable die out, the species changes. This is natural selection.

While on his five-year voyage on the HMS Beagle, Darwin visited the Galapagos Islands. One of his important observations was that of the marine iguanas, who were the only aquatic lizards of their species. The amazing adaptation of these iguanas to their environment convinced Darwin of his theory of natural selection. These "imps of darkness" that Darwin described are unique. Because of this uniqueness, Darwin became convinced that they had adapted to their present conditions which are so different from those on the other side of the island where more typical iguanas live.  

The marine lizards live on a side of the island that has a much different environment from the other side. These iguanas differ from others in several ways. One distinction is that they are dark gray and black in order to better absorb the heat from the sun. Because of their coloring, they can retain enough warmth to swim in the cold waters. Also, their claws and legs are much stronger than those of other iguanas so that they can hang on to rocks when the waves crash upon them. In addition, their long limbs and flattened tails help the lizards to swim well in the water. Their noses have become flattened and much shorter than others of their species. These flattened noses allow the marine iguanas to bite and eat the seaweed on the rocks more easily. 

Unique to only this one side of the Galapagos Islands, the marine iguanas demonstrate natural selection. Those who have had longer legs, longer claws, and flattened noses have survived and reproduced, thus altering the species. 

 

Sources:
krishna-agrawala's profile pic

krishna-agrawala | College Teacher | (Level 3) Valedictorian

Posted on

Darwin Theory of natural selection was proposed by Charles Darwin in 1858. Darwin believed all plants and animals had evolved from a few common ancestors by means of natural selection. Plants and animals produce many offspring, but some of the young die before they can become parents. According to Darwin's theory, natural selection determines which members of a species die prematurely and which ones survive and reproduce.

All living things must compete for a limited supply of food, water, space, and other necessities. The individual plants and animals whose variations are best adapted to conditions have an advantage in this struggle. These organisms, on average, tend to leave a larger number of offspring than other members of their group. As a result, the proportion of the group sharing the traits of the best-adapted organisms increases from generation to generation. Scientists use the term fitness to refer to the ability of an organism to reproduce. For this reason, natural selection is often called the "survival of the fittest."

For natural selection to operate, two biological conditions must be met. First, the individuals of a population must differ in their hereditary characteristics. Human beings, for example, vary in almost every aspect of their appearance, including height, weight, and eye colour. People also differ in less-obvious features, such as brain size, thickness of bones, and amount of fat in the blood. These differences have some genetic basis.

The second requirement for natural selection is that some of the inherited differences must affect chances for survival and reproduction. When this occurs, the fittest individuals will pass on more copies of their genes to future generations than will other individuals. Over time, a species accumulates genes that increase its ability to survive and reproduce in its environment.

There are several types of natural selection. They include (1) directional selection, (2) stabilizing selection, and (3) sexual selection.

Directional selection produces new features that help a species adapt to its environment. This type of selection is what most people think of as natural selection.

Stabilizing selection occurs if a species is already well adapted to its environment. In such cases, the individuals with average characteristics leave the most offspring, and individuals that differ most from the average leave fewest. Unlike directional selection, stabilizing selection eliminates extreme characteristics, reducing the amount of variation in a population. Stabilizing selection may actually be the most common type of natural selection.

Sexual selection occurs primarily among animals. Adults of many species prefer mates who display certain behaviors or have certain external features. Sexual selection explains, for example, why males of many bird species have more colorful feathers than the females.

kumarankush's profile pic

kumarankush | Student, Undergraduate | (Level 1) eNoter

Posted on

Sir,


With all due respect, can you answer my one simple question? what exactly is nature?

I believe if you find the answer to it, then I believe, you'll know what exactly is a misnomer and what's not.


Have a great time!

truetrini's profile pic

truetrini | College Teacher | (Level 1) eNoter

Posted on

Survival of the Fittest is a misnomer, a very misleading misnomer at that.

This term fails to adequately describe what happens in nature.

 

There is not always a "fittest" type.  There may be several different organisms that are equally fit for different reasons.  They may be suited to different facets of the environment. One is not going to replace the other becasue each has its proper place in the environment.


It is not just a matter of survival.  Natural selection is a difference in reproductive success that involves both the ability to survive until the reproductive age  and then the ability to reproduce.

The very idea of survival of the fittest is unfortunate becasue it has been viewed as some universal unconditioned truth, but it is an empty statement for those who say that the fittest are those who survive and there is no real predictive content to the notion of natural selection.

That is simply false.