taxonomy it's the science of classifying
living things that sounds exciting today
will basically be learning the Dewey
Decimal System of evolution it's like
filing must be on the edge of your seat
okay shut up when it comes down to it
this science doesn't just categorize
organisms when you look a little deeper
you realize it's telling the story of
all life on Earth and it's a pretty good
story
every living thing on this planet is
related to every other living thing if
you go far enough back we all have a
common ancestor an organism that both
you and I are descended from or
something that a starfish and a blue
whale are both descended from or even
weirder that an oak tree and a salmon
are both descended from that organism
lived he lived very long ago but it was
here and I dig that the trick of
taxonomy is basically figuring out where
all those branches of the evolutionary
tree are and finding some convenient
labels to help us understand all of
these remarkable interrelationships
let's be clear though taxonomy isn't
about describing life in all of its
ridiculous details mostly about helping
humans understand it because it's way
too complicated without structure to get
that structure biologists use the
taxonomic system to classify all the
organisms on the earth it's sometimes
called the phylogenetic tree or the Tree
of Life and it illustrates the
evolutionary relationships between all
living species so there are about two
million known species but there could be
anywhere from five million to a hundred
million species scientists really have
no freaking idea new species keep
getting discovered all the time and the
more organisms we have to keep track of
the more complex the phylogenetic tree
becomes so there's not always a
consensus about how to classify this
stuff there's a lot of gray area in the
natural world actually let me rephrase
that the natural world is one giant gray
area sometimes it's just hard to know
where to put a certain group of
organisms and eventually the group gets
so big the classification system has to
be messed with to make room for it so
the system isn't perfect but it's good
enough that we've been using it for
around 250 years what's that do you
spell a biography coming on
carl linnaeus was a Swede born in 1707
and early in his career as a botanist he
realized that the botanical nomenclature
of 18th century Europe was well just
crap for instance in his day the formal
name of a tomato plant was solanum
Calais and now mayor Basya Phyllis
Bennis insists receiveth simplicity sona
has actually said once I shudder at the
site of most botanical names given by
modern authorities not only did the
sloppiness bother him he saw a whole
sugar storm blowing in because new
plants were still being discovered in
Europe but that was nothing compared to
the crazy stuff that was coming from the
new world
Linnaeus saw that pretty soon naming
conventions were just going to collapse
under all these new things to name and
then what so Linnaeus famously started
off by naming himself he came from a
peasant family and at that time surnames
were just for rich people so when Carl
went to college they asked him for his
surname and he just made one up Linnaeus
after the linden trees that grew on his
family's homestead Linnaeus got a
medical degree and became a professor at
Uppsala University where he devoted
himself to the study of nomenclature he
had a students go to places and bring
back specimens for him to study and
categorize method he eventually adopted
was based on morphology or physical form
and structure this wasn't necessarily a
new idea back then people grouped
organisms by analogous or homo platic
traits structures that appear similar
but actually come from completely
independent origins by this definition
birds would be more closely related to
butterflies than to reptiles because
both birds and butterflies can fly
Linnaeus had a good mind for this stuff
and turned it to have a real knack for
choosing actual homologous traits for
his classification system traits that
stem from a common evolutionary ancestor
Linnaeus of course didn't know jack
about evolution
Darwin wouldn't come around for another
100 plus years but he intuited that some
traits were more important than others
for instance he was struck by the fact
that reproductive apparatus seemed to be
a good way of classifying plants he also
caused a bit of a scandal by classifying
class Mammalia based on the female
abilities to produce milk from their
nipples because Ben and I was pretty
racy stuff back then in his lifetime
Linnaeus catalogue roughly seven
thousand seven hundred plants in four
thousand four hundred animals
he published his classifications in a
catalog called Systema naturae which by
the time he wrote its twelfth edition
was 2,300 pages long in the meantime
Linnaeus actually adopted a personal
motto
God created Linnaeus organized although
taxonomy has come a long way since
Linnaeus we still use a bunch of the
conventions that he invented for
instance we still arrange things into
taxa or groups of organisms and we still
use the same tax as Linnaeus kingdom
phylum class order family genus and
species we also still use Linnaeus
convention of binomial nomenclature
using a unique two-part name for every
species the genus and its species name
in Latin or sort of Latin ish practice
actually started back in the Middle Ages
when educated people were expected to
know Latin we know a lot less Latin now
but we know a lot more about evolution
which Linnaeus didn't and we have
technologies like genetic testing to
classify relationships between organisms
and yet we still use Linnaeus's
morphology based system because genetic
evidence generally agrees with
classifications that are made based on
structure and form however because there
was a lot of life that Linnaeus had no
idea about
we had to stick a new taxa above
Linnaeus's kingdom we call it domain and
it's as broad as you can get the domains
are bacteria archaea and Eukarya the
bacteria in the archaea are prokaryotes
meaning that their genetic material goes
commando with no nucleus to enclose it
while the Eukarya make up all of the
life-forms with a nucleus and include
pretty much all of the life that you
think of his life and quite a lot of the
life that you don't think about it all
it might seem like since all macroscopic
life only gets one domain it's kind of
silly to give prokaryotes too and for a
long time we didn't we didn't divide
them up into different domains they hung
out together in a single domain called
Manero but it later became clear that
bacteria which lived pretty much
everywhere on earth including inside of
you when deep in the Earth's crust and
archaea which are even more Hardy than
bacteria have distinct evolutionary
histories archaea being more closely
related to eukaryotes and yes thus me
and you they have totally different cell
membranes and the enzymes that they used
to make RNA their RNA polymerase is much
more like ours
under the domain Eukarya which is by far
the most interesting and even
occasionally adorable domain we have
Kingdom's Protista fungi Plantae and
Animalia now scientists have settled on
these four for now but these are
categories that are a human creation but
there are good reasons for that human
creation the unscientific truth is that
we looked at life and divided it up
based on what we saw so we were like
well protists are single-celled
organisms so they're very different from
the rest of the domain and plants get
their energy from the Sun and fungi look
and act very different from plants and
animals and you know we already know
what animals are so they have to get
their own Kingdom and those scientists
are sometimes loath to admit it that
system of just looking and dividing
things up actually worked pretty well
for us not perfectly but pretty well but
there's a reason why this worked so well
evolutionarily there are actual
categories each of these kingdoms is a
huge branch in the tree of life at each
branch an evolutionary change occurred
that was so massively helpful that it
spawned a vast diversity of descendants
plants or plant a are the autotrophs of
the domain Eukarya
autotrophs meaning that they can feed
themselves through photosynthesis of
course there's cellulose based cell
walls and chloroplasts giving them a
distinct difference from all other
multicellular life there are two other
sorts of troughs
there's the heterotrophs which get their
energy by eating other organisms and the
chemo troughs which are weird and crazy
and only show up in bacteria and archaea
and they get their energy from chemicals
now the kingdom Protista is weird
because it contains both autotrophs and
heterotrophs some protists can
photosynthesize while others eat living
things throat ists are basically a bunch
of weird eukaryotic single-celled
organisms that may or may not be
evolutionarily related to each other
scientists are still trying to figure it
out some are plant like like algae some
are more animal-like like amoebas and
some are fungus like like slime molds
protists are one of those gray areas I
was telling you about so don't be
surprised if by the time you're teaching
this to your biology students there are
more than four kingdoms in Eukarya fungi
which are you know the fungus is they
include mushrooms and smuts and puff
balls and truffles and molds and yeasts
and they're pretty cool because they
have cell walls like plants but instead
of being made of cellulose there may
of another carbohydrate called chitin
which is also what the beak of a giant
squid is made of or the exoskeleton of a
beetle because fungi are heterotrophs
like animals they have these sort of
digestive enzymes that break down their
food and get reabsorbed but they can't
move so they don't require a stomach for
digestion they just grow on top of
whatever it is they're digesting and
digested right where it is - super
convenient and finally we have kingdom
Animalia which is the lovely kingdom
that we find ourselves and 100% of
adorable organisms in animals are
multicellular always we are
heterotrophic so we spend a lot of time
hunting down food because we can't make
it ourselves
and almost all of us can move at least
during some stage of our life sites and
most of us develop either two or three
germ layers during embryonic development
wait for it unless you're a sponge so
like I said we use this taxonomic system
to describe the common ancestry and
evolutionary history of an organism
looking at the phylogenetic tree you can
tell that humans are more closely
related to mice and we are to fish and
more closely related to fish than we are
to fruit flies so how about we pick an
organism we follow it all the way
through the taxa from Kingdom to species
just to see how it works I know let's
pick this kitty because I know she'd
like it right yet so kitties have cells
that have nuclei and membrane surrounded
organelles and they're multicellular and
heterotrophic and have three germ layers
of cells when they're embryos so they're
in the kingdom Animalia and they have a
spinal cord running down their backs
protected by vertebra and discs in
between them and they have a tail that
doesn't have a butthole at the end of it
like a worm which I'm really glad about
and that puts her in the phylum Chordata
kitty clearly does not like this so I'm
going to put her down now
and the kitty lactates gives birth to
young like a cow instead of laying eggs
like a chicken and they have fur and
three special tiny bones in their ears
that only mammals have so they're in the
class Mammalia so she's more closely
related to cow than to chicken good to
know and like a bunch of other placental
mammals that eat meat like weasels the
mustelids and dogs the canines kitties
are in the order Carnivora and they're
the cat family felidae whose members
have live bodies and roundish heads and
except for cheetahs retractable claws
and their littler than tigers and
Panthers which puts them in the genus
felis and then at the level of the
species the descriptions get pretty dang
detailed so let's just say that you know
what a cat is so the species name is
caddis now look at that
felis catus noogie I could have that
holding course stitched onto a pillow
for usually wine and you'll be killed
thank you for watching our taxidermy
issue no I mean taxonomy episode of
crash course biology we hope that you
learned something thanks to everybody
who helped put this episode together if
you have any questions for us please
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comments below
and we will get to them hopefully very
quickly I will see you next time