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1 .Listen to part of a lecture in a zoology class
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2 .(female professor) Until recently, our main approach to classifying organisms into groups, their species, genus had been to classify them according to their similar physical features.
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3 .These classifications have helped us understand how organisms are related in terms of their evolution.
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4 .Of course, recent breakthroughs in DNA analysis have given us new information about many organisms, causing us to go back and reclassify them.
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5 .But here\'s an interesting case where DNA analysis actually supported some previous classifications.
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6 .Okay, our story starts with Vladimir Nabokov. (male student) Nabokov? The author from Russia?
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7 .(female professor) Yes. Most of us know him for his fiction that made him famous in the 1950s, right?
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8 .But little did you know, he also did extensive work as a taxonomist. In particular, Nabokov specialized in classifying species of butterflies.
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9 .Well, in 1945, he wrote an extensive research paper, and that paper contained a radical hypothesis about a new way to classify a group of South American butterflies and its evolutionary origins.
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10 .The group of butterflies is called Polyommatus blues, or blues for short.
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11 .So, why radical? Well, blues have been studied for centuries, but there are over 400 species classified as blues, and they can be found in most of the northern regions of the world, but also from central Mexico to most of South America.
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12 .So, their evolutionary relationships were far from understood. And where did they originate? Nobody knew.
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13 .But in his paper, Nabokov proposed a new classification scheme for blues, and a very specific hypothesis for the evolution of North and South American blues that they all evolved from Asian ancestors.
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14 .This kind of detailed analysis simply was unheard of among experts at that time.
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15 .(male student) But how would blues have gotten to the Americas all the way from Asia?
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16 .(female professor) Let\'s look at a world map. Okay. Nabokov believed that the ancestor of blues had migrated from Asia into Alaska, crossing what\'s now the Bering Strait, which was a solid landmass at the time.
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17 .And this happened in five separate colonizing waves with a very specific timeline. The first wave took place about 11 million years ago.
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18 .After reaching Alaska, this first group of blues slowly dispersed in North America and southwards down into South America, evolving into the South American species we find there today. They subsequently died out completely in North America.
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19 .After that, between 9 and 1 million years ago, 4 other distinct colonies originating in Asia, occurred in succession again, at very specific times.
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20 .Each colonization produced a new and distinct group of blues, each evolving from the ancestors that made the trip.
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21 .And each of these distinct groups remained in the northern regions after crossing the Bering Strait, evolving into the species we find throughout much of North America today.
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22 .Some hypotheses, but guess what? The scientific community just dismissed Nabokov’s ideas, mainly because he had no formal scientific training.
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23 .But fast forward to today. Recently, another butterfly expert Naomi Pierce. That\'s P-I-E-R-C-E, Pierce.
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24 .She read Nabokov’s paper and she became so intrigued with his hypothesis that she decided to test it out.
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25 .So, she and her team did extensive work extracting and analyzing the DNA of a wide range of Asian and American blues species to determine their relationships.
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26 .And they concluded from their analysis that not only were Nabokov’s classifications right, but that American blues could be traced back to a single common Asian ancestor.
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27 .(male student) Wow! Was Nabokov right about the timing of the migrations?
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28 .(female professor) He was! And how did they show this?
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29 .Well, temperatures have fallen in the Bering Strait region over the last 11 million years, right?
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30 .So, they looked at exactly when the temperatures fell and by how much during this period of time, then they studied the temperature tolerances and distribution of existing blues.
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31 .This allowed them to estimate the temperature tolerances of blues ancestors.
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32 .And they concluded that as the temperatures in the area surrounding the Bering Strait dropped, each new colonizing species had been more tolerant to the cold, allowing them to make the trip across the Bering Strait.
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33 .(male student) Oh, and the first group that thrived in warmer climates dispersed southward as temperatures dropped.
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34 .(female professor) Right. Whereas the subsequent groups could tolerate the northern climates.
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35 .So, they evolved into the species we find in the northern areas of the Americas today.
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