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Biology: Classifying Evolution Products - Taxonomy


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About this Lesson

  • Type: Video Tutorial
  • Length: 10:13
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 109 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: The Evolution of Life on Earth (34 lessons, $64.35)
Biology: Classifying Earth's Organisms (4 lessons, $8.91)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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If I were plopped down in the middle of this planet and were looking around and had to talk to you about the incredible diversity of life on this planet, I'd have a real problem because you and I wouldn't speak the same language. And as I look at all the products of evolution all around me, I say, "Wow! Now that we know a little bit about their evolution..." And you know, I want to stress even though a student might be completely overwhelmed about how much we know about evolution, the more we know, the more we realize we don't know, which is a good thing. It gives us something to do. And so the point is that what do we do with these products of evolution, and what do we do with the extinct members of our planet that we've lost along the way, and how do we refer to them, and most importantly, how do we put them together in some coherent group? Which brings us to a fascinating field of biology called "systematics."
What systematists do is they study the diversity of life forms. This is the study of diversity. In their study of diversity, and diversity can be anything from their evolutionary history to their genetic--to their DNA, to their anatomy. Get the idea? There is a branch of systematics called "taxonomy." The taxonomists literally take this information and come up with a classification scheme. I want you to understand something. Taxonomy is based on systematics, and systematics isn't just based on what does something look like. Evolutionary history is really what it ends up being a lot about.
So we get to this idea of taxonomical hierarchies. I like the word "hierarchies" in here because it gives you this idea of a cascade, of a branching tree, of an idea where there is one thing that leads to another, which leads to another. Like the analogy of a company, there's the CEO and then there's the vice president, and then there are people under them, and it's the same kind of branching tree idea. Indeed, taxonomy works the same way.
Let me tell you a little history. As we began the study of systematics in the 20^th Century--well, we've been studying systematics literally since the days of Linneaus. He didn't realize it, but in his comparative anatomies he was literally studying what was known of systems. It wasn't a whole lot of stuff, but nevertheless, he set us up with a classification scheme we're still using. As we learn more and more about these things, we got to the 1950's and there was a lot of documentation happening and this whole branch of taxonomy was kind of stalled. And then, in the 1960's big things started to happen. You know what those were. Molecular genetics was one of them. A literal explosion in our knowledge of molecular genetics. It was incredible. And so there were two new approaches. We'll start with the first one--phenetics.
When I think of phenetics... What does it mean? It means phenotype. That's where the word "phen" comes from. Phenotypes--physical traits. What pheneticists did is they were literally data driven. Let's take a group of organisms and just crunch into computers the number of similarities. Let's not worry about evolutionary lineage yet. Forget about evolutionary lineage. Let's just base it completely on anatomical similarities and not even wonder about function. If it's got a wing, it's got a wing. I don't want to hear if it's an insect wing or a bird's wing. If it has a wing, it has a wing. What that particular idea was after a while the things that weren't necessarily related, like an insect's wing and a bird's wing, would therefore kind of fall by the wayside because they would be small divergences in the unbelievable quantity of data that would be established. And this whole idea of data-driven taxonomy was a very good idea because it really set us up for the second system, which is not only collecting anatomical similarities, and not only crunching numbers, but to look at other things, too.
And so we come to the next field called "cladistics." Now, cladistics draws upon this idea of numbers, and draws upon comparisons, but I want you to understand there are some limitations to that, too, and that's one of the reasons why cladistics is literally what we think of today as phylogeny, as the system we use today.
I'll give you a good example of why using number crunching by itself can be dangerous. Ready? We use a kind of a rule of thumb, and the rule of thumb is this--and now I'm getting into DNA. If two creatures have about 95 to 96 percent DNA homology, a rule of thumb is they're in the same species. Think about it. If you share 96 percent of your DNA with something, you're pretty darned similar, aren't you? Well, that's great except--human and chimps--98.4 percent of your DNA is identical to a chimp's by DNA homology. That's by hybridization. You're not even in the same genus as a chimp.
So you see, this whole idea of number crunching is good, but it's a tool, and it's not the be all and end all. So let's talk about what we do in cladistics. In cladistics, which, in essence, is what you and I will refer to as phylogenetics. This whole idea of phylogeny--don't lose track of where I'm going here--phylogeny, we're going to use some of the genetic mechanisms to establish cladistics, but generally in speaking, which people talk about cladistics, this is the way to do it. Here's what happens. What we do is we consider clades, which, in essence, are evolutionary branches. You've heard the term "cladograms." Cladograms are branching trees. So when a phylogeny is established, it ends up looking like a tree. It ends up looking something like this. Take a look at this particular phylogeny that was established by DNA and protein comparisons, and indeed, to a point, anatomical similarity.
First of all, let's look at the idea of the branching tree. So we have an ancestral carnivore down here, and what we have next is this idea of a branch. The key I want to show you here is--look at this branch right here and these two creatures, the raccoon and the lesser panda. They, by DNA homology and protein homology, and anatomical comparisons, are put on this branch, while the rest of this particular group is put out on another branch of the tree. Now, picture this as a tree. So what we have is this branching thing. This would be the trunk, and notice what we have here is time. On the y-axis we have time, and so therefore we're looking here, at least on this particular one, at when the divergences occurred. This is important to understand in a cladogram. What's coming next is--picture it like a tree. And so you have a trunk, and then you have branches, and then off of the branches you have branches, and eventually you get to the point where at the very little twiglets at the end, you have what's alive today. That is what a Phylogenetic tree is supposed to be all about.
Well, there's a lot more to this story, and you know, the bottom line is this. When we start to look at the diversity, the nice part about this is we can take one branch off that tree and work on it once we know where it branched off. And then, as we learn more and more, we can take one of the twigs off that branch and start dividing that up. And so it becomes, again, a work in progress, which eventually gives us this idea, and that's why we entitled this lesson this way, of a taxonomical hierarchy. This is very cool stuff.
The Evolution of Life on Earth
Classifying Earth's Organisms
Classifying the Products of Evolution: Taxonomy Page [2 of 2]

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