The theory of evolution was developed by
Charles Darwin [sticks his tongue out,says "bleh."] and published in his
book "On the Origin of Species."
He explained that natural selection is a
process behind evolution. Charles Darwin
developed his theories after his
adventures upon the HMS Beagle. In his
travels, he observed that creatures found
on the islands he visited were similar
to ones found in the mainland, but
appeared to be slightly different. It
wasn't until he returned home that he
came to the conclusion that species are
specially modified to their environments,
and that's why they differ.
He developed four conditions explaining
why this happens. Darwin's theory of
natural selection by descent with
modification is testable and observable
fact. [Thud]  Experiments have been conducted in
the wild and in labs Let's dive deeper
into Darwin's four conditions.
[Sound of Darwin walking in. Darwin mutters.]
Condition number one: Individuals within a
population differ.
There are features that differ within populations of the
same animal. In our case, the feature that
varies between our giraffes is neck
length. [Blinking sound.] Some giraffes were born with long necks [Blink.],
Some were born with short necks. [Blink.]
Condition number two: The differences are, at least in part, passed from parents to offspring. [Darwin mutters.]
Darwin's descent with modification is
the idea that offspring are fairly
similar to their parents with some
genetic differences.
Condition number three: Some individuals are more
successful at surviving and reproducing
than others. [Blink.] In the case of our giraffes,
the long neck individual did not acquire
its neck by stretching to grab the leaves. [Munching sounds.] Instead, individuals within the population
were born with the neck length that was longer than others. [Continued munching sounds.]
[Blink.] Because a longer neck allowed them to reach the food that was otherwise unattainable,
it gave them an advantage.  
 [Munching.]
Condition number four: The successful  individuals succeed because of variant traits they have inherited,
and will pass on to their offspring. [Blink; Darwin mutters.] Giraffes with the longer-neck advantage
are in better health and able to pass this feature to their offspring. [Munch.]
Because this trait is more successful than
shorter necks, more individuals in the
population have it. [Munching continues.]
Over time, this process can result
in populations that specialized for
particular environments, and may
eventually result in emergence of new
species. In other words, natural selection
is an important process, though not the
only process, by which evolution takes
place within a population of organisms. [Munch.]
Let's review. Individuals within a population differ.
The differences are at least, in part, passed from parents to offspring.
Some individuals are more successful at surviving and reproducing than others.
[Darwin speaks] Excuse me. [Sound of Darwin walking backward.]
The successful individuals succeed
because of variant traits they have
inherited, and will pass on to their
offspring.
That's all for now. Thanks for watching! [Blinking sound; Darwin mutters.]
