WEBVTT 00:00:00.000 --> 00:00:14.000 (Music) 00:00:14.000 --> 00:00:17.000 The Five Fingers of Evolution. 00:00:17.000 --> 00:00:20.000 A thorough understanding of biology requires 00:00:20.000 --> 00:00:22.000 a thorough understanding of the process of evolution. 00:00:22.000 --> 00:00:26.000 Most people are familiar with the process of natural selection. 00:00:26.000 --> 00:00:30.000 However, this is just one of five processes that can result in evolution. 00:00:30.000 --> 00:00:33.000 Before we discuss all five of these processes, 00:00:33.000 --> 00:00:35.000 we should define evolution. 00:00:35.000 --> 00:00:38.000 Evolution is simply change in the gene pool over time. 00:00:38.000 --> 00:00:42.000 But what is a gene pool? And for that matter, what is a gene? 00:00:42.000 --> 00:00:45.000 Before spending any more time on genetics, 00:00:45.000 --> 00:00:47.000 let us begin with a story. 00:00:47.000 --> 00:00:52.000 Imagine that a boat capsizes, and 10 survivors swim to shore on a deserted island. 00:00:52.000 --> 00:00:57.000 They are never rescued, and they form a new population that exists for thousands of years. 00:00:57.000 --> 00:01:00.000 Strangely enough, five of the survivors have red hair. 00:01:00.000 --> 00:01:05.000 Red hair is created when a person inherits two copies of the red gene from their parents. 00:01:05.000 --> 00:01:08.000 If you only have one copy of the gene, you won't have red hair. 00:01:08.000 --> 00:01:10.000 To make this easier, we will assume 00:01:10.000 --> 00:01:14.000 that the five non-redheads are not carriers of the gene. 00:01:14.000 --> 00:01:16.000 The initial frequency of the red hair gene 00:01:16.000 --> 00:01:20.000 is therefore 50 percent, or 10 of 20 total genes. 00:01:20.000 --> 00:01:22.000 These genes are the gene pool. 00:01:22.000 --> 00:01:25.000 The 20 different genes are like cards in a deck 00:01:25.000 --> 00:01:28.000 that keep getting reshuffled with each new generation. 00:01:28.000 --> 00:01:32.000 Sex is simply a reshuffling of the genetic deck. 00:01:32.000 --> 00:01:36.000 The cards are reshuffled and passed to the next generation; 00:01:36.000 --> 00:01:39.000 the deck remains the same, 50 percent red. 00:01:39.000 --> 00:01:43.000 The genes are reshuffled and passed to the next generation; 00:01:43.000 --> 00:01:47.000 the gene pool remains the same, 50 percent red. 00:01:47.000 --> 00:01:50.000 Even though the population may grow in size over time, 00:01:50.000 --> 00:01:53.000 the frequency should stay at about 50 percent. 00:01:53.000 --> 00:01:56.000 If this frequency ever varies, then evolution has occurred. 00:01:56.000 --> 00:02:00.000 Evolution is simply change in the gene pool over time. 00:02:00.000 --> 00:02:02.000 Think about it in terms of the cards. 00:02:02.000 --> 00:02:05.000 If the frequency of the cards in the deck ever changes, 00:02:05.000 --> 00:02:07.000 evolution has occurred. 00:02:07.000 --> 00:02:10.000 There are five processes that can cause the frequency to change. 00:02:10.000 --> 00:02:15.000 To remember these processes, we will use the fingers on your hands, 00:02:15.000 --> 00:02:17.000 starting from the little finger and moving to the thumb. 00:02:17.000 --> 00:02:21.000 The little finger should remind you that the population can shrink. 00:02:21.000 --> 00:02:24.000 If the population shrinks, then chance can take over. 00:02:24.000 --> 00:02:28.000 For example, if only four individuals survive an epidemic, 00:02:28.000 --> 00:02:31.000 then their genes will represent the new gene pool. 00:02:31.000 --> 00:02:33.000 The next finger is the ring finger. 00:02:33.000 --> 00:02:38.000 This finger should remind you of mating, because a ring represents a couple. 00:02:38.000 --> 00:02:41.000 If individuals choose a mate based on their appearance or location, 00:02:41.000 --> 00:02:43.000 the frequency may change. 00:02:43.000 --> 00:02:47.000 If redheaded individuals only mate with redheaded individuals, 00:02:47.000 --> 00:02:49.000 they could eventually form a new population. 00:02:49.000 --> 00:02:52.000 If no one ever mates with redheaded individuals, 00:02:52.000 --> 00:02:54.000 these genes could decrease. 00:02:54.000 --> 00:02:55.000 The next finger is the middle finger. 00:02:55.000 --> 00:02:59.000 The M in the middle finger should remind you of the M in the word "mutation." 00:02:59.000 --> 00:03:03.000 If a new gene is added through mutation, it can affect the frequency. 00:03:03.000 --> 00:03:07.000 Imagine a gene mutation creates a new color of hair. 00:03:07.000 --> 00:03:10.000 This would obviously change the frequency in the gene pool. 00:03:10.000 --> 00:03:12.000 The pointer finger should remind you of movement. 00:03:12.000 --> 00:03:16.000 If new individuals flow into an area, or immigrate, 00:03:16.000 --> 00:03:17.000 the frequency will change. 00:03:17.000 --> 00:03:20.000 If individuals flow out of an area, or emigrate, 00:03:20.000 --> 00:03:22.000 then the frequency will change. 00:03:22.000 --> 00:03:25.000 In science, we refer to this movement as gene flow. 00:03:25.000 --> 00:03:30.000 All four of the processes represented by our fingers can cause evolution. 00:03:30.000 --> 00:03:34.000 Small population size, non-random mating, 00:03:34.000 --> 00:03:37.000 mutations and gene flow. 00:03:37.000 --> 00:03:39.000 However, none of them lead to adaptation. 00:03:39.000 --> 00:03:41.000 Natural selection is the only process 00:03:41.000 --> 00:03:45.000 that creates organisms better adapted to their local environment. 00:03:45.000 --> 00:03:48.000 I use the thumb to remember this process. 00:03:48.000 --> 00:03:52.000 Nature votes thumbs up for adaptations that will do well in their environment, 00:03:52.000 --> 00:03:55.000 and thumbs down to adaptations that will do poorly. 00:03:55.000 --> 00:03:59.000 The genes for individuals that are not adapted for their environment 00:03:59.000 --> 00:04:02.000 will gradually be replaced by those that are better adapted. 00:04:02.000 --> 00:04:05.000 Red hair is an example of one of these adaptations. 00:04:05.000 --> 00:04:08.000 Red hair is an advantage in the northern climates, 00:04:08.000 --> 00:04:12.000 because the fair skin allowed ancestors to absorb more light 00:04:12.000 --> 00:04:15.000 and synthesize more vitamin D. Thumbs up! 00:04:15.000 --> 00:04:19.000 However, this was a disadvantage in the more southern climates, 00:04:19.000 --> 00:04:23.000 where increased UV radiation led to cancer and decreased fertility. 00:04:23.000 --> 00:04:25.000 Thumbs down! 00:04:25.000 --> 00:04:29.000 Even the thumb itself is an adaptation formed through the process of natural selection. 00:04:29.000 --> 00:04:34.000 The evolution that we have described is referred to as microevolution, 00:04:34.000 --> 00:04:36.000 because it refers to a small change. 00:04:36.000 --> 00:04:38.000 However, this form of evolution may 00:04:38.000 --> 00:04:41.000 eventually lead to macroevolution, or speciation. 00:04:41.000 --> 00:04:46.000 Every organism on the planet shares ancestry with a single common ancestor. 00:04:46.000 --> 00:04:49.000 All living organisms on the planet are connected back in time 00:04:49.000 --> 00:04:52.000 through the process of evolution. 00:04:52.000 --> 00:04:53.000 Take a look at your own hand. 00:04:53.000 --> 00:04:58.000 It's an engineering masterpiece that was created by the five processes I just described, 00:04:58.000 --> 00:05:00.000 over millions and millions of years. 00:05:00.000 --> 00:05:04.000 Can you recall the five main causes of evolution from memory? 00:05:04.000 --> 00:05:07.000 If you can't, hit rewind and watch that part again. 00:05:07.000 --> 00:05:18.138 But if you can, give yourself or your neighbor a big five-fingered high five.