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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[br]of the process of evolution.

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Most people are familiar[br]with the process of natural selection.

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However, this is just one[br]of five processes

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that can result in evolution.

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Before we discuss[br]all five of these processes,

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we should define evolution.

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Evolution is simply change[br]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[br]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[br]that exists for thousands of years.

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Strangely enough,[br]five of the survivors have red hair.

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Red hair is created[br]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,[br]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[br]are not carriers of the gene.

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The initial frequency of the red-hair gene[br]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[br]are like cards in a deck

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that keep getting reshuffled[br]with each new generation.

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Sex is simply a reshuffling[br]of the genetic deck.

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The cards are reshuffled[br]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[br]and passed to the next generation;

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the gene pool remains[br]the same, 50 percent red.

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Even though the population[br]may grow in size over time,

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the frequency should stay[br]at about 50 percent.

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If this frequency ever varies,[br]then evolution has occurred.

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Evolution is simply change[br]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[br]in the deck ever changes,

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evolution has occurred.

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

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

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starting from the little finger[br]and moving to the thumb.

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

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If the population shrinks,[br]then chance can take over.

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For example, if only four[br]individuals survive an epidemic,

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then their genes will represent[br]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,[br]because a ring represents a couple.

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

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the frequency may change.

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If redheaded individuals only mate[br]with redheaded individuals,

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they could eventually[br]form a new population.

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If no one ever mates[br]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[br]you of the M in the word "mutation."

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

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Imagine a gene mutation[br]creates a new color of hair.

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This would obviously change[br]the frequency in the gene pool.

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The pointer finger[br]should remind you of movement.

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If new individuals[br]flow into an area, or immigrate,

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the frequency will change.

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If individuals flow out[br]of an area, or emigrate,

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then the frequency will change.

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

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All four of the processes represented[br]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[br]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[br]that will do well in their environment,

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and thumbs down to adaptations[br]that will do poorly.

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The genes for individuals[br]that are not adapted for their environment

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will gradually be replaced[br]by those that are better adapted.

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Red hair is an example[br]of one of these adaptations.

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Red hair is an advantage[br]in the northern climates,

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because the fair skin[br]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[br]in the more southern climates,

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where increased UV radiation[br]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[br]of natural selection.

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The evolution that we have described[br]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[br]to macroevolution, or speciation.

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

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All living organisms on the planet[br]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[br]processes I just described,

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over millions and millions of years.

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

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

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But if you can,

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