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The Five Fingers of Evolution.

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A thorough understanding of biology

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requires a thorough understanding
of the process of evolution.

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Most people are familiar
with the process of natural selection.

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However, this is just one
of five processes

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that can result in evolution.

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Before we discuss
all five of these processes,

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we should define evolution.

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Evolution is simply change
in the gene pool over time.

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But what is a gene pool?

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And for that matter, what is a gene?

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Before spending any more time on genetics,

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let us begin with a story.

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Imagine that a boat capsizes,

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and 10 survivors
swim to shore on a deserted island.

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They are never rescued,

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and they form a new population
that exists for thousands of years.

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Strangely enough,
five of the survivors have red hair.

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Red hair is created
when a person inherits two copies

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of the red gene from their parents.

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If you only have one copy of the gene,
you won't have red hair.

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To make this easier, we will assume

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that the five non-redheads
are not carriers of the gene.

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The initial frequency of the red-hair gene
is therefore 50 percent,

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or 10 of 20 total genes.

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These genes are the gene pool.

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The 20 different genes
are like cards in a deck

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that keep getting reshuffled
with each new generation.

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Sex is simply a reshuffling
of the genetic deck.

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The cards are reshuffled
and passed to the next generation;

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the deck remains the same, 50 percent red.

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The genes are reshuffled
and passed to the next generation;

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the gene pool remains
the same, 50 percent red.

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Even though the population
may grow in size over time,

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the frequency should stay
at about 50 percent.

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If this frequency ever varies,
then evolution has occurred.

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Evolution is simply change
in the gene pool over time.

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Think about it in terms of the cards.

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If the frequency of the cards
in the deck ever changes,

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evolution has occurred.

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There are five processes
that can cause the frequency to change.

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To remember these processes,
we will use the fingers on your hands,

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starting from the little finger
and moving to the thumb.

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The little finger should remind you
that the population can shrink.

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If the population shrinks,
then chance can take over.

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For example, if only four
individuals survive an epidemic,

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then their genes will represent
the new gene pool.

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The next finger is the ring finger.

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This finger should remind you of mating,
because a ring represents a couple.

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If individuals choose a mate
based on their appearance or location,

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the frequency may change.

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If redheaded individuals only mate
with redheaded individuals,

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they could eventually
form a new population.

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If no one ever mates
with redheaded individuals,

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these genes could decrease.

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The next finger is the middle finger.

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The M in the middle finger should remind
you of the M in the word "mutation."

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If a new gene is added through mutation,
it can affect the frequency.

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Imagine a gene mutation
creates a new color of hair.

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This would obviously change
the frequency in the gene pool.

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The pointer finger
should remind you of movement.

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If new individuals
flow into an area, or immigrate,

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the frequency will change.

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If individuals flow out
of an area, or emigrate,

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then the frequency will change.

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In science, we refer to this
movement as gene flow.

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All four of the processes represented
by our fingers can cause evolution.

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Small population size, non-random mating,

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mutations and gene flow.

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However, none of them lead to adaptation.

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Natural selection is the only process

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that creates organisms
better adapted to their local environment.

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I use the thumb to remember this process.

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Nature votes thumbs up for adaptations
that will do well in their environment,

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and thumbs down to adaptations
that will do poorly.

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The genes for individuals
that are not adapted for their environment

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will gradually be replaced
by those that are better adapted.

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Red hair is an example
of one of these adaptations.

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Red hair is an advantage
in the northern climates,

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because the fair skin
allowed ancestors to absorb more light

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and synthesize more vitamin D.

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Thumbs up!

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However, this was a disadvantage
in the more southern climates,

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where increased UV radiation
led to cancer and decreased fertility.

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Thumbs down!

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Even the thumb itself is an adaptation

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formed through the process
of natural selection.

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The evolution that we have described
is referred to as microevolution,

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because it refers to a small change.

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However, this form of evolution

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may eventually lead
to macroevolution, or speciation.

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Every organism on the planet shares
ancestry with a single common ancestor.

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All living organisms on the planet
are connected back in time

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through the process of evolution.

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Take a look at your own hand.

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It's an engineering masterpiece

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that was created by the five
processes I just described,

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over millions and millions of years.

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Can you recall the five main
causes of evolution from memory?

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If you can't, hit rewind
and watch that part again.

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But if you can,

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give yourself or your neighbor
a big five-fingered high five.