Tree of life
Taxonomy and the Tree of Life The science of taxonomy and where humans fit into the tree of life
⇐ Use this menu to view and help create subtitles for this video in many different languages.
You'll probably want to hide YouTube's captions if using these subtitles.
- This right here is a picture of Carl Linnaeus,
- and I'm sure I'm mispronouncing the word.
- And he's a Swedish gentleman who lived in the 1700's.
- And he's known as the Father of Modern Taxonomy.
- And the word taxonomy,
- if you just split it up into it's original root,
- it really is the science of really classifying things.
- But when people talk about taxonomy,
- in this particular in Carl Linnaeus' case,
- they're talking about the classification of living things.
- So, classifying... classifying, organisms.
- And his real innovation, before he came about,
- people realized that you had species of animals
- that lions had certain properties that made them all lions,
- and they could interbreed and things like that
- monkey or chimpanzees would all interbreed
- and that would be a separate species
- and that polar bears were a separate species,
- and that humans were a separate species.
- But what he really brought to the table, is he decided,
- well "Let me just not just group animals into species,
- maybe I can group species into, into other categories
- and that's where we get the genus from...
- You group similar species into a genus.
- And then he went even beyond that,
- because even the idea of grouping things into a genus
- dated back to the Ancient Greeks.
- He said, "Well, why don't I group similar genuses together,
- into orders, orders together into classes,
- and then classes together into kingdoms.
- So, really, what he did is, he said,
- Well, maybe I can classify, I can create a tree.
- I can create a tree of life.
- I can create a structure so we can really see
- how far apart any two organisms are.
- And that's really why he's the Father of Modern Taxonomy.
- And he did not have many tools.
- All he could do was look at the powers,
- his powers of observation.
- He said: OK, those kinds of animals,
- they have fur, or they reproduce in this way,
- or they lay eggs, or they don't lay eggs,
- or they have spinal columns,
- or they don't have spinal columns.
- So that's the best that he could do,
- when he did his taxonomy.
- But since then, there's obviously been tons of innovations
- and how we perceive animals
- or the natural world, and our tools for studying them.
- So one thing that he did not know about is evolution.
- This idea of common ancestry
- and between our understandings of evolution
- and our ability to look back at the fossil record,
- that helps us get more precise at figuring out
- which animals are related to which.
- We can see: do they have a common ancestor,
- more recent, or further back?
- And what even Charles Darwin didn't have,
- which we now use as a tool in taxonomy,
- is the genetic evidence.
- So now we don't even have to rely on the fossil record,
- we can look at the DNA of two species that exist today
- and see how similar is the DNA,
- and that tells us how recently they branched apart
- if we were able to find it in the fossil record
- or how recently in the past
- did these two species become two different species.
- Now with that said, I do want to make this clear.
- This is something, you know, I always have a little bit
- It was fuzzy to me the first time I was exploring the idea of taxonomy.
- It's that taxonomy is as much an art as it's a science.
- Today, even to these days people are debating about
- the best way to classify things.
- And what you're pay attention to
- and DNA has been the best tool so far
- in giving us a more systematic, a more analytic way
- of deciding how close two animals are,
- but to a large degree a lot of these categories.
- Deciding where to divide along
- kingdom, phylum, class, order, family, tribe
- these're somewhat arbitrary
- these're just based on early taxonomists, including Carl Linnaeus
- and saying "Oh this looks like a grouping right over here."
- But they could have grouped on a broader level or at a deeper level
- so this things right over here are somewhat arbitrary. Aaah...
- A more analytic way is just to see
- how much DNA you have in common
- and then you just use that as a measure of
- how far apart two animals are.
- Or really I should say two species are,
- because this taxonomy doesn't know
- it doesn't apply just to animals,
- it applies to plants and bacteria,
- and Archaea and all sorts of things,
- so it's actually a broader thing that just animals.
- Now with that out of the way
- what I'd thought would be fun
- just so that we could really get a sense of
- where modern taxonomy is,
- where the field that was essentially fathered by Carl Linnaeus,
- where it is now?
- how we,... And use that to figure out
- where we humans fit into the big picture.
- And obviously I'm drawing
- just a small fraction of the universe of the organisms
- that we even know about right now,
- but at least it frames the picture
- in terms of something we understand,
- in particular: us, in particular humans.
- Now our species, we call ourselves humans,
- but we are really Homo sapiens
- and the sapiens is the species part
- and then Homo is the genus.
- What I'm doing right over here is I'm saying:
- Well, if Homo is the genus,
- what other species were inside of Homo?
- and the reality is, or as least as far as we know,
- there are no living species inside of Homo
- that we've probably killed them all of
- or did or maybe we interbred with them somehow.
- which might have argued that
- maybe they weren't different species,
- but more likely they were competing in the same ecosystems,
- and they became endangered species very quickly
- when they competed with our ancestors,
- but the most recent other species within the genus
- that we know about are the Neanderthals
- and the formal word, the formal, the formal term
- for their species is Neanderthalensis.
- Now if we go further up the tree of life, further up the taxonomy,
- and you'll sometimes see tribe dimension, sometimes you won't,
- and we tend to get a little more granular
- the closer we get to humans
- when we go further away in the tree of life
- we get a little bit less granular sometimes,
- but that's not always the case, as well.
- You go a little bit further up and you get to Hominini,
- and I'm sure I am mispronouncing some of this, as well,
- but another species that is in Hominini that is not in Homo,
- and I'm definitely not listing all of them
- and that's why I'm showing all of these other branches,
- all of these other branches over here,
- is what we call the common chimpanzee
- and their species name is, their genus is Pan
- and their species is Troglodytes.
- So you'd refer to them as Pan troglodytes.
- And that's also another convention
- that Carl Linnaeus came up with,
- is that you refer to a particular species by its genus
- and then its species, and you capitalize the genus
- and you lower-case the species.
- We are Homo sapiens, this is Homo neanderthalensis,
- this is Pan troglodytes,
- or often referred to as chimpanzees.
- Now, if you go up one higher level of broadness
- on this tree of life, you then get to the family
- and we are in the family Hominidae, Hominidae
- and I'm sure I'm mispronouncing it once again.
- But just to give you an example,
- so everything I listed so far,
- everything I've talked about so far are within this family.
- And to show you an animal that is not in this family
- you just have to look at the gorilla.
- And you could call it the Gorillini, the Gorillini
- Gorillini gorilla, or G. gorilla,
- that's its actual species name.
- And this family right over here
- sometimes the common term is the great apes,
- the great apes.
- Now you go one further level, and this is;
- the whole reason why I'm doing this,
- and I am not by any means,
- am I being exhaustive about the other species
- that are in that family but that are not in our tribe,
- I'm just trying to get a picture of,
- as we get further and further out,
- as we get further out of our tribe, our family, our order,
- we're getting to things where the common ancestor with human
- goes further and further back in time,
- the genetic similarities become more and more different,
- and even just the physical differences
- if we look at it in a very superficial level,
- become more, and more, and more different.
- So you get to even a broader category,
- this is where you get to the primates
- and this is probably something that
- you might be somewhat familiar with.
- And the term primates is general,
- these animals that look like
- they either live in trees or rain forests,
- or they're descendant of things that live in trees
- or they have these things that they can grasp things with.
- They're good at climbing broadly, not all of them are.
- Humans are probably the worst primates
- when it comes to climbing, or one of the worst.
- But that's the general classification that we...
- that's what we generally think of
- when we think of a primates.
- And if we think of a primate that is not a great ape,
- you just have to think of a baboon.
- So this right here is a baboon.
- It is a primate, but it is not a great ape.
- It is probably descendant.
- Some baboons actually don't live in trees,
- but all of them are probably descendant
- from things that first live in trees and
- that's why their hands and their feet look the way they do.
- Now you get into an even broader level of classification.
- You get to the mammals, and once again,
- probably something you're used to thinking about,
- mammals are air-breathing animals.
- They tend to have fur or hair.
- They tend to provide some form of milk for their young.
- They have active memory glands.
- There're other things we can talk about what makes mammals.
- I am not going into the rigorous definition.
- But just to give you an example of a mammal that is not a primate,
- I can show you a polar bear right over here.
- This is a mammal, mammal that is not a primate.
- I can do other thing. I can show you a tiger
- or I can show you a giraffe or a horse.
- By no stretch of the imagination, am I being comprehensive.
- Let's keep getting broader. Now let's go to the class.
- Or we are already at the class Mammalia.
- Now let's go to the Phylum.
- And Phylum...we are humans.
- All mammals we are in the Phylum Chordates.
- And Chordates we are actually in the sub Phylum,
- which I didn't write here vertebrate,
- which means we have a vertebra.
- We have a spinal column with a spinal chordate.
- Chordates are a little more general.
- Chordate is a Phylum where kind of the arrangement
- where the mouth is, where the digestive organs,
- where the anus is, where the spinal column is,
- where the brains, where the eyes, where the mouth.
- They are kind of all in the same place.
- If you think about it, everything I listed here,
- kind of has the same general structure.
- You have a spinal column.
- You have a brain.
- You have a mouth.
- And the mouth leads to some type of digestive column.
- In the end of it, you have an anus over there.
- You have eyes in front of the brain.
- So this is the general way.
- I am not being very rigorous here.
- It's how you describe a Chordate.
- To show a Chordate that is not a mammal,
- you just have to think about fish or sharks.
- So this right over here,
- this right over here is a non mammal Chordate.
- This is a great white shark over here.
- Let's go even broader.
- You'll see, now we are getting to things
- that are very very not human like.
- So you go one step broader.
- Now we are at Animalia, the kingdom of animals.
- This is the broadest definition
- or the broadest category that Carl Linnaeus thought about.
- Actually he did go into trees as well.
- When you think about kingdom of animals,
- you think of things that aren't Chordates.
- You start going into things like insects
- You start going into things like jellyfish.
- If you go even broader,
- now we are talking about the domain.
- You go into Eukarya.
- So these are all organisms that have cells.
- Inside those cells, they have complex structures.
- So if you are Eukarya,
- you have cells with complex structures.
- If you are Prokarya,
- you don't have complex structures inside your cells.
- But other Eukarya that are not animals,
- include things like plants.
- Obviously I am giving no justice
- to this whole branch of the tree of life.
- It can be just as rich
- or richer than everything I have drawn over here.
- This is just a small fraction of the entire tree of life.
- Let's go even broader than that.
- So if you go even broader than that,
- You say what's a kind of life form that isn't Eukarya?
- That wouldn't have these more complex cell structures,
- that is, the mitochondria in the cells, the cell nucleus-es.
- Then you just have to think about something like bacteria.
- If you want to go even broader,
- there are things like viruses that
- you can even debate whether they really even are life,
- because they are dependent on other life forms
- for their actual reproduction.
- But they do have genetic materials like everything else.
- That to me is kind of a mind blowing idea.
- As different as a plant is,
- look at house plants that are in your house right now,
- or the tree when you walk home,
- or bacteria or this jellyfish,
- there is the commonality that we all have DNA.
- That DNA for the most part
- replicates in a very very very similar way.
- So it's actually crazy that we are actually even all related.
- We even do have a common ancestor,
- or some of these things.
- That even begs the question:
- what are about things like viruses?
- Anyway I'll leave you here.
- I really just want to let you know that
- make sure you realize that
- it's definitely worth studying,
- because we understand
- where we fit in the universe of living things.
- But I also want to let you know that
- it is a little bit of an art on where you decide
- where to make these classifications,
- where you decide to focus on,
- what you want to focus on,
- you know, what properties,
- how they reproduce
- or how they feed their their young
- or can they move around
- or what they breed whatever, things like that.
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
|
Have something that's not a question about this content? |
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
abuse
- disrespectful or offensive
- an advertisement
not helpful
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
wrong category
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site
Share a tip
Suggest a fix
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.