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Stated Clearly presents:
What is Natural Selection?
Natural selection is one of several key concepts
contained within the theory of evolution.
To understand exactly what natural selection is and
why it's so important
let's first take a quick look at two other evolutionary concepts:
Descent with Modification
and the overarching idea
of Common Descent.
Descent with Modification
is the observable fact
that when parents have children, those children often look and behave slightly
different than their parents,
and slightly different than each other.
They descend from their parents with modifications.
The differences found in offspring
are partially due to random genetic mutations.
Common Descent
is the idea that all life on Earth is related.
We descended from a common ancestor.
through the gradual process of descent with modification over many many
generations,
a single original species is thought to have given rise to all the life we see
today.
the common descent of all life on earth is not a directly observable fact.
We have no way of going back in time to watch it happen.
Instead,
Common Descent as a conclusion based on a massive collection of observable facts.
Facts found independently in the study of fossils
genetics
comparative anatomy
mathematics
biochemistry
and species distribution.
Because the evidence for common descent is so overwhelming,
the concept has been around since ancient times.
In the past however, it was rejected by many philosophers and scientists for one
main reason:
You cannot get order and complexity from random chaos alone.
The bodies and behaviors of living things
are extremely complex and orderly.
Descent with Modification
simply produces random variation.
All through history
no one could explain how complex life arose from simple life through random
variation,
until Charles Darwin discovered Natural Selection.
Charles Darwin, who lived from 1809 to 1882
was a naturalist:
someone who studies nature.
At the start of his career
he traveled the world by ship,
collecting and documenting plants and animals.
During his travels,
Darwin became very interested in the idea of common descent.
He noticed that islands contain species of plants and animals unique to those
islands,
they can't be found anyplace else on earth,
but they often look and behave surprisingly similar to creatures found on
nearby continents.
Tortoises on the Galapagos islands
can be distinguished from those of Africa,
meanwhile,
with the exception of size,
they're almost identical to a species found nearby in South America.
Darwin believed the similarities could be best explained through Common Descent.
Long ago a tortoise from the mainland may have drifted to the islands,
possibly on a raft of storm debris,
and once arriving,
laid her eggs.
Random changes caused by Descent with Modification over thousands of years,
eventually transformed the island creatures and the mainland creatures so
much, that they could no longer be considered the same species.
This idea made good sense to Darwin
except for one thing:
the island creatures he found were not just randomly different from their mainland
cousins,
they were specially adapted for island life.
the Galapagos
is a collection of 18 main islands, many of which are home to tortoises.
The larger islands have lots of grass and vegetation.
Tortoises there grow extra heavy
and have dome like shells.
Some of the smaller islands have very little grass,
forcing the tortoises to feed on island cactus.
the best cactus pads grown the tops of these plants.
Fortunately,
tortoises on these islands are equipped with expanded front legs and saddle like
shells
allowing them to stretch their necks extra long to reach their food.
It's almost as if these island creatures
have been perfectly sculpted to survive within their unique environments.
How did this sculpting take place?
Random Descent with modification alone
could never do such a thing.
Darwin drew upon his knowledge of selective breeding
to answer this question.
For thousands of years,
farmers have been taking wild plants and animals,
and through the process of selective breeding,
have sculpted the original wild forms
into new domestic forms,
much better suited for human use and consumption.
The process is slow but simple
if a single plant produces a hundred seeds,
most will grow to be nearly identical to the parent plant.
A few however, will be slightly different.
Some variations are undesirable:
smaller size,
bitter taste,
vulnerability to disease and so on.
Other variations are highly valued!
Thicker sweeter leaves for example.
If a farmer only allows the best plants to reproduce and creates seeds for the
next crop,
small positive changes will
add up over multiple generations,
eventually producing a
dramatically superior vegetable.
You might be surprised to hear that broccoli
cauliflower, kale,
brussels sprouts,
and cabbages, are all just different breeds of a single type of weed
commonly found along the shores of the English Channel.
The evolution of this original plant
into all the varieties we see today
was carefully guided by different farmers around the world,
who simply selected for different traits.
It's important to note,
that the farmer doesn't actually create anything.
Random Descent with Modification creates new traits.
The farmer simply chooses which of those new creations are allowed to reproduce,
and which
are not.
Darwin proposed that nature itself
is also capable of selection.
It may not have an intelligent brain like a farmer,
but nature is an extremely dangerous place in which to live.
There are germs which can kill you.
Animals that can eat you. You could die of heat exhaustion.
You could die of exposure to the cold.
When parents produce a variety of offspring,
nature,
simply by being difficult to survive in, decides which of those variations get to
live in reproduce,
and which do not.
Over multiple generations,
creatures became more and more fit for survival and reproduction within their
specific environments.
Darwin called this process Natural
Selection.
Since Darwin first put forth his idea in the mid 1800s
Natural Selection has been studied and witnessed
numerous times in nature and in the science lab.
What started out as a mere idea is now officially
an observable fact!
Darwin's discovery has greatly expanded our understanding of the natural world
it has lead to amazing new breakthroughs,
and it finally allowed scientists
to seriously consider the idea of Common Descent.
So to sum things up,
What exactly is natural selection?
Natural Selection
is the process by which random evolutionary changes are selected for by
nature
in a consistent
orderly
non random way.
Through the process of descent with modification, new traits are randomly
produced.
Nature then carefully decides which of those new traits to keep.
Positive changes add up over multiple generations,
negative traits are quickly discarded.
Through this simple
ongoing process,
nature,
even though it may not have a thinking mind,
is capable of producing incredibly complex
and beautiful creations.
I'm Jon Perry,
and that's Natural Selection stated clearly!
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