How Did Our Ancestors Evolve?발음듣기
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How Did Our Ancestors Evolve?
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태국어 번역 1명 참여
출처 : 칸아카데미
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DAVID CHRISTIAN: Here we are in Ewha Womans University in Seoul, Korea, and we're talking about human ancestors, the ancestors of you and me.발음듣기
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Now, that ancestor probably lived about 1.5 billion years ago and was an early form of eukaryote, but you and chimps also share a common ancestor.발음듣기
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That ancestor lived much closer to today, a mere seven million years ago, which is just an eye blink in geological time.발음듣기
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Taxonomy is the branch of biology that classifies living organisms by their relationships to each other.발음듣기
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And what taxonomy does is create huge sort of trees of life, systems of classification that show the relationships between all living organisms.발음듣기
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Fossils can tell us a lot about what our ancestors looked like and how they changed over time, but fossils could also tell us a surprising amount about how they lived.발음듣기
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We can also use radiometric dating techniques to date fossils so we know when a particular organism lived.발음듣기
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Since the 1960s, biologists have discovered that genes... a lot of genes change quite randomly.발음듣기
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Now, what this means is by comparing the genes of two species, you can tell roughly when they shared a common ancestor.발음듣기
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So we can use genetic dating techniques to check out the evidence we get from fossils about dates.발음듣기
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Now, a third type of evidence comes from modern studies of primate societies, particularly the studies of great apes - of gorillas and chimps.발음듣기
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We're very close genetically to the great apes, but it's quite probable that our ancestors evolved more rapidly and changed more from the great apes.발음듣기
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So what this means is that by studying the societies - the social relationships of chimps and gorillas - we can learn a lot about how our ancestors probably lived.발음듣기
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To study the history of our species let's begin by going back 65 million years to the time when the dinosaurs were wiped out.발음듣기
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After a mass extinction event like this, evolution very often happens very, very fast indeed.발음듣기
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This is because the surviving species tend to experiment with all the new niches that are left empty by the removal of other species.발음듣기
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Now, we know that something like this happened because within ten million years of the disappearance of the dinosaurs, we find a whole range of new mammal species.발음듣기
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Now, if you've ever climbed trees, you'll know the sort of skills you need to climb them without falling out.발음듣기
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Now, this is partly to process all that visual information, but it's also partly because a lot of primates seem to have really liked fruit and fruit tend to be harder to find than leaves.발음듣기
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Somewhat confusingly, there's a family called the hominids, which is smaller, within the hominoid group.발음듣기
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The hominids include the great apes: orangutans, gorillas, two species of chimps, and you and me.발음듣기
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We're so similar to apes that even Linnaeus, the founder of modern taxonomy, reluctantly classified us humans with the great apes.발음듣기
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If you compare the genes of humans and chimps, you find that about 98% of those genes are identical, and that's why modern biologists are convinced that humans and chimps shared a common ancestor about seven million years ago.발음듣기
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One possibility is that our ancestors lived in Eastern Africa, which was drier, so there were grassy savanna lands rather than forests.발음듣기
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And also, bipedalism freed the hands to manipulate stones or perhaps even throw them at an enemy.발음듣기
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Now, after an evolutionary radiation, this sort of winnowing of species is fairly common as one species that can adapt better than the others becomes a sort of standard model and the others die out.발음듣기
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But it's also possible that our ancestors played a role in eliminating our evolutionary cousins.발음듣기
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One group of species or genus, as the biologists call it, was the Australopithecines or southern apes.발음듣기
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The Australopithecines flourished in Africa between about four million and one million years ago.발음듣기
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Best known of all the Australopithecines is Lucy, an individual whose remains were found in 1974 in the Hadar Valley in Ethiopia by an American paleontologist, Don Johanson.발음듣기
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Lucy had a brain about the size of a chimp's brain and stood about three and a half feet tall.발음듣기
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More similar to us is a species known as Homo habilis, which flourished between about 2.5 and 1.5 million years ago.발음듣기
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The first remains of a Homo habilis were found by the son of the paleontologist Louis Leakey in Olduvai Gorge in the Rift Valley in Africa.발음듣기
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Louis Leakey was absolutely convinced that a crucial, key component of being human was the ability to make tools.발음듣기
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So he immediately thought, "These are humans," and he classified them within the genus Homo using the Latin word for human.발음듣기
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Even more similar to us is another group of species known variously as Homo ergaster/erectus.발음듣기
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They had larger brains than Homo habilis, and they were almost as tall as us, and they traveled.발음듣기
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They made beautiful stone tools and they traveled into a wide variety of niches, different environments; and yet their stone tools hardly changed over a million years.발음듣기
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