Natural Selection
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Darwin's main idea of his evolutionary theory was without doubt his postulates about Natural Selection. Even if Darwin himself did not do so, most texts dealing with his theory, often break down parts of the biologist's introduction of Origin of Species into the four following postulates (the illustration on the left should help to better understand the four points):
1. Individuals within a species are variable
Just looking at the people around you is enough to demonstrate that humans are variable. The
same can be said for almost any other type of organisms that reproduce, apart from those
which reproduce clonally.
2. Some of an individual's variations are passed onto its offspring
Most children look similar to their parents. That is because they inherit a set of
genes material from them. However, not all variations are always passed on to offspring. For
example, if an organism acquires a trait during its lifetime, this trait is not passed on to its
offspring. To make this point clearer: Imagine a lizard loses its tail to a predator, but it survives
and still reproduces. Then the lizard's offspring will not be tailless, because it still carries and
passes on its genes required to develop a tail.
3. More offspring are produced than survive
This postulate can best be understood when taking a specific example into consideration: a single female of the ocean sunfish (Mola mola) may
produce about 300 million eggs. If one Mola mola produces that many eggs, the question arises why the oceans are not filled with an
overabundance of sunfish. The reason for that is that most of the eggs and the juvenile fish are consumed by predators or do not
survive due to some other reason. Just a few live long enough to actually reproduce.
4. Those offspring that survive and reproduce have inherited a variation that gives them an advantage
Seeing any documentation about wildlife shows quite quickly that predators like lions target rather young and weak members of a herd. That means
the healthier and stronger and faster you are, the more likely you are to being avoided targeted by a predator or to survive an attack. This means, if
the advantage that helps an organism to survive is controlled by its genes, and if it then survives and reproduces, it probably passes those genes,
and with it the advantage, on to its offspring. Here it comes to a process between the different individuals which Darwin described as a
"struggle for existence", a phrase which often comes to one's mind when thinking of Darwin.
Wanting to understand Darwin's main contribution to evolutionary theory, it is highly important to comprehend those basic principles of Natural Selection. The following video also tries to explain the essentials of Darwin's theory. The four principles are ordered and broken down a little bit differently than I have done above, but the assumptions are very much the same. Maybe it helps to further understand the main idea of Natural Selection:
1. Individuals within a species are variable
Just looking at the people around you is enough to demonstrate that humans are variable. The
same can be said for almost any other type of organisms that reproduce, apart from those
which reproduce clonally.
2. Some of an individual's variations are passed onto its offspring
Most children look similar to their parents. That is because they inherit a set of
genes material from them. However, not all variations are always passed on to offspring. For
example, if an organism acquires a trait during its lifetime, this trait is not passed on to its
offspring. To make this point clearer: Imagine a lizard loses its tail to a predator, but it survives
and still reproduces. Then the lizard's offspring will not be tailless, because it still carries and
passes on its genes required to develop a tail.
3. More offspring are produced than survive
This postulate can best be understood when taking a specific example into consideration: a single female of the ocean sunfish (Mola mola) may
produce about 300 million eggs. If one Mola mola produces that many eggs, the question arises why the oceans are not filled with an
overabundance of sunfish. The reason for that is that most of the eggs and the juvenile fish are consumed by predators or do not
survive due to some other reason. Just a few live long enough to actually reproduce.
4. Those offspring that survive and reproduce have inherited a variation that gives them an advantage
Seeing any documentation about wildlife shows quite quickly that predators like lions target rather young and weak members of a herd. That means
the healthier and stronger and faster you are, the more likely you are to being avoided targeted by a predator or to survive an attack. This means, if
the advantage that helps an organism to survive is controlled by its genes, and if it then survives and reproduces, it probably passes those genes,
and with it the advantage, on to its offspring. Here it comes to a process between the different individuals which Darwin described as a
"struggle for existence", a phrase which often comes to one's mind when thinking of Darwin.
Wanting to understand Darwin's main contribution to evolutionary theory, it is highly important to comprehend those basic principles of Natural Selection. The following video also tries to explain the essentials of Darwin's theory. The four principles are ordered and broken down a little bit differently than I have done above, but the assumptions are very much the same. Maybe it helps to further understand the main idea of Natural Selection:
