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  • The Five Fingers of Evolution.

  • A thorough understanding of biology requires

  • a thorough understanding of the process of evolution.

  • Most people are familiar with the process of natural selection.

  • However, this is just one of five processes that can result in evolution.

  • Before we discuss all five of these processes,

  • we should define evolution.

  • Evolution is simply change in the gene pool over time.

  • But what is a gene pool? And for that matter, what is a gene?

  • Before spending any more time on genetics,

  • let us begin with a story.

  • Imagine that a boat capsizes, and 10 survivors swim to shore on a deserted island.

  • They are never rescued, and they form a new population that exists for thousands of years.

  • Strangely enough, five of the survivors have red hair.

  • Red hair is created when a person inherits two copies of the red gene from their parents.

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

  • To make this easier, we will assume

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

  • The initial frequency of the red hair gene

  • is therefore 50 percent, or 10 of 20 total genes.

  • These genes are the gene pool.

  • The 20 different genes are like cards in a deck

  • that keep getting reshuffled with each new generation.

  • Sex is simply a reshuffling of the genetic deck.

  • The cards are reshuffled and passed to the next generation;

  • the deck remains the same, 50 percent red.

  • The genes are reshuffled and passed to the next generation;

  • the gene pool remains the same, 50 percent red.

  • Even though the population may grow in size over time,

  • the frequency should stay at about 50 percent.

  • If this frequency ever varies, then evolution has occurred.

  • Evolution is simply change in the gene pool over time.

  • Think about it in terms of the cards.

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

  • evolution has occurred.

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

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

  • starting from the little finger and moving to the thumb.

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

  • If the population shrinks, then chance can take over.

  • For example, if only four individuals survive an epidemic,

  • then their genes will represent the new gene pool.

  • The next finger is the ring finger.

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

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

  • the frequency may change.

  • If redheaded individuals only mate with redheaded individuals,

  • they could eventually form a new population.

  • If no one ever mates with redheaded individuals,

  • these genes could decrease.

  • The next finger is the middle finger.

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

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

  • Imagine a gene mutation creates a new color of hair.

  • This would obviously change the frequency in the gene pool.

  • The pointer finger should remind you of movement.

  • If new individuals flow into an area, or immigrate,

  • the frequency will change.

  • If individuals flow out of an area, or emigrate,

  • then the frequency will change.

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

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

  • Small population size, non-random mating,

  • mutations and gene flow.

  • However, none of them lead to adaptation.

  • Natural selection is the only process

  • that creates organisms better adapted to their local environment.

  • I use the thumb to remember this process.

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

  • and thumbs down to adaptations that will do poorly.

  • The genes for individuals that are not adapted for their environment

  • will gradually be replaced by those that are better adapted.

  • Red hair is an example of one of these adaptations.

  • Red hair is an advantage in the northern climates,

  • because the fair skin allowed ancestors to absorb more light

  • and synthesize more vitamin D. Thumbs up!

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

  • where increased UV radiation led to cancer and decreased fertility.

  • Thumbs down!

  • Even the thumb itself is an adaptation formed through the process of natural selection.

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

  • because it refers to a small change.

  • However, this form of evolution may

  • eventually lead to macroevolution, or speciation.

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

  • All living organisms on the planet are connected back in time

  • through the process of evolution.

  • Take a look at your own hand.

  • It's an engineering masterpiece that was created by the five processes I just described,

  • over millions and millions of years.

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

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

  • But if you can, give yourself or your neighbor a big five-fingered high five.

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B1 TED-Ed gene evolution frequency finger red hair

【TED-Ed】Five Fingers of Evolution - Paul Andersen

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    Calvin Chen posted on 2012/12/17
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