What is a Species? Nobody Knows!

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well hi there this is a tiger and this

is a tiger and this is a tiger and this

is a tiger and this is a tiger and this

is a tiger and this is a tiger and this

is a tiger and this is not a tiger and

neither is this are all of these the

same species

or many species if there are many

species how many species which ones are

the same and which ones are different

and what is a species anyway that last

question seems like an easy one I think

that if you ask moderately informed

people the majority will tell you that a

species is defined as a group of

organisms that can breed with one

another and produce viable offspring

that themselves can reproduce and this

is a great definition it's

straightforward coherent and intuitive

as always like And subscribe and we hope

to see you real

soon but wait this tiger the the first

one we saw is a wild tiger from

Southeast Asia and this tiger is a

captive tiger in North America they will

never encounter one another let alone

breed are they the same species or

different species this tiger is extinct

as is this one probably we do have a

whole video about that one but are they

the same species as this tiger or a

different species this is a tiger

whiptail and this closely related lizard

is a New Mexico whiptail it's a female

you can tell that it's a female because

the females have stripes like this one

and the males don't exist that's right

the entire species is female they

reproduce asexually via parthenogenesis

which means that none of them breed with

one another is each

individual therefore a separate species

this is a tiger salamander and this

salamander is an entina and so is this

and so is this and so is this you might

notice that there is some pretty great

variation in inas now here's the crazy

thing tinas live at relatively high

elevations but not extreme elevations as

a result 19 populations are found in the

mountains that encircle California's

Central Valley all together these 19

populations form kind of a horseshoe

around the valley they don't form a

complete circle because the mountains on

one side are just a little bit too tall

for them now here's the thing each

population is capable of breeding and

producing viable offspring that

themselves can reproduce with the

neighboring population so it is possible

for beans from one end of the Horseshoe

to make their way all the way to the

other end of the Horseshoe but

individuals from one end can't reproduce

with individuals from the other end so

are they one species or many species if

many how many and why and this is a lion

it can breed with a tiger and produce a

viable Offspring called a liger or a

taigon depending on who was the lady and

who was the fella well these lion tiger

hybrids are viable and that they can

survive just fine but they're sterile

usually at least males are females can

potentially reproduce with a male lion

or a male tiger so are lions and

tigers the same species or different

species hopefully by now you are no

longer as confident that you know what a

species is as are the moderately

informed and you have entered the

uncomfortably uncertain position of the

highly informed because as comfortable

as it is to divide life into discrete

boxes called species it turns out that

life is an everchanging Continuum and

finding a way to divide continuous data

into discrete categories is not always

easy to do in an objective and intuitive

manner but we're going to try anyway so

now that we've lost all sight of what a

species might

be let's talk about what a species might

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the species concept that we discussed

earlier the top answer in Family Feud is

called the biological species concept

like all species Concepts it has

strengths and weaknesses species

Concepts that have no strengths are

called garbage ideas not species

Concepts and if we had one with no

weaknesses we would call it the species

concept but there are enough weaknesses

with the biological species concept for

us to recognize that it's difficult to

apply objectively in some instances like

with lions and tigers tigers in

different places or with the salamanders

and downright impossible in others like

with fossils and asexual lineages so

while it can work certainly doesn't

always work and that is why it isn't the

species concept so what are the other

ones what are their strengths and

weaknesses let's talk about the most

frequently used species Concepts and if

you still haven't found one that you

like maybe we'll revisit this topic in

the future and let's start with another

one that is fairly straightforward the

morphological species concept do you

remember that fossil tiger well if you

do you might recall that I have no idea

if it could breed with any of the other

Tigers the lion the Jaguar or anything

else alive today heck I wouldn't even

know if two identical fossil tigers

found at the same place at the same time

with a bunch of babies could breed with

one another I could find two skeletons

in the act of mating and I wouldn't know

if they were able to produce viable

fertile offspring but I could carefully

study their skeletons and determine if

there are significant differences

between them are their skeletons

significantly different from those of

modern tigers or any other living

organism if they aren't meaningfully

different I can conclude that they're

the same species based upon the

morphological species concept that two

organisms are the same species if they

share many unique features and do not

differ significantly from one another

and this species concept has many

strengths it's broadly applicable much

more broadly applicable even than the

biological species concept I don't need

to know anything about reproduction it

works on asexual lineages extinct

organisms really anything I can observe

alive or dead it's basically the gold

standard of paleontology where

morphological features may be all that

we have and yet it's just about as

intuitive as the biological species

concept

but it isn't the species concept it has

many shortcomings for example look at

these two gorillas they have many

similarities but they aren't identical

so how different is two different seems

pretty subjective I mean who's making

making that call would you agree with

their standard and if the two

morphologies are significantly different

what's causing that difference these two

grasshoppers are the same species but

they don't look the same and why do they

not look the same because one of them

grew up in close proximity to other

Grasshoppers and the other did not these

grasshoppers have little hairs that if

bumped above a certain frequency caused

them to mol into longdistance flying

locusts instead of a grasshopper that

tends to stay prettyy much in one place

they will differ in coloration Wing

shape and size muscle composition fat

storage as well as Behavior but not

because their genes are different but

because their environment was different

triggering a different set of genes to

be activated this is called phenotypic

plasticity two grasshoppers with the

same genetics can develop to totally

different morphologies and their

morphology will not play a significant

role in determining which morphology

their offspring present and don't get me

started on green anacondas as we will

discuss next week in our featurelength

documentary about all of the boa species

we just discovered a new species of

green anaconda but the reason that we

didn't realized that there were two

species of green anacondas sooner was

because

morphologically the two species are

nearly identical it wasn't Until We

examined their DNA that we learned that

the two species are reproductive

isolated from one another and highly

different genetically but

morphologically that's not the case

these two butterflies look identical too

they live in the same place but they

never mate why because under ultraviolet

light they look nothing alike and the

butterflies can see that but it took us

centuries to notice other nearly

identical organisms may not mate because

they use different pheromones or calls

or other things that are difficult or

impossible to observe morphologically

not to mention convergent evolution

where two highly unrelated organisms may

end up with a nearly identical

morphology and gosh look at these two

animals one is twice the size of the

other with a very different skull

morphology but they're both gorillas

just different Sexes this is called

sexual dimorphism which by the

morphological species concept could

easily cause us to assign each sex

erroneously to a different species so

it's not perfect okay I'm going to

preface this next one by telling you

that my Master's research was in

evolutionary ecology so I'm a published

ecologist but the ecological species

concept is in my opinion the most

garbage of the four most widely used

species Concepts I should also tell you

that ecology meetings make me question

my reason for being and evolution

meetings remind me exactly why I love

biology so much but the ecological

species concept considers organisms to

be the same species if they utilize the

same basic set of resources in the

environment the same ecological niche

which is historically the only correct

pronunciation of the word niche in

English and it's certainly a correct

English pronunciation today but the

ecological species concept defines a

species essentially by its Niche and the

adaptations that it has to utilize those

resources which is really about all that

keeps the II from being a woodpecker

according to the ecological species

concept and it also kind of plays into

this stereotype about ecologists that if

you go on a walk with an ecologist and

point to a plant and ask what it is

they'll say looks like a C4 grass

ecologists don't care what an organism

is they just care what it does in the

environment they don't care that new

world and old world vultures are not

closely related they perform the same

basic function in the environment so

they're the same thing and if an

organism's place in the Ecology of a

region is all that you care to know

about it then the ecological species

concept works just fine it works for any

organism about which you have

considerable ecological data but if you

care about almost anything else then

you're going to need a different species

concept not to mention other weaknesses

such as the fact that no two niches are

exactly the same and how similar is

similar enough what if the environment

changes and their Niche with it what

about generalists that lack a highly

specialized Niche what if you don't know

too much about its exact Niche and more

there's more but right now I want to

talk about my personal favorite species

concept and don't act too surprised the

philogenetic species concept because I

think that when we're talking about a

species we're talking about a group of

organisms with a unique recent

evolutionary history and philogenetic

Analysis unlike ecological analysis

teaches us a tremendous amount about

organisms that we didn't know when we

classified them it is Mass massively

predictive unlike basically all other

organizational systems that we have ever

devised for organisms for example I

could find an organism that has never

been seen by anyone before if I had

nothing but a genetic sample I could

determine its likely location in the

philogyny of living organisms it could

even be the case that I've never even

seen this organism myself and I have no

preconceived notions about what it is

like what it looks like or how it acts

but now all of a sudden because of phog

gentics I know that it's more closely

related to will than it is to Jason

knowing nothing more than that about it

but given what you know about Will and

Jason and their position in the

philogyny of life I bet that you can

make all sorts of accurate predictions

about this previously unknown organism

so philogenetic analysis rocks but how

do I use it to Define a species well in

a nutshell a philogenetic species is a

group of organisms that share unique

common ancestry and are genetically

similar within predetermined thresholds

as to insinuate recent if not current

gene flow is occurring within the group

but not with other groups basically each

tip of a philogyny is a unique species

at least if you include all of their

close relatives on that philogyny now if

you ask me the biggest downside to the

philogenetic species concept is simply

that philogyny is somewhat foreign to

most people the same people that

understand reproductive isolation unique

morphology and ecological niches may not

really understand what phog gentics is

how it works or why it's so powerful of

course my solution to this problem is

just to try my darnest to explain

phylogenetics to the world but it has a

ton of strengths for one thing it can be

applied based on any source of data that

can be used to generate a philogyny this

includes fossils morphology and

molecular analysis and often a

combination of these distinct sources of

data it works for living organisms

extinct organisms sexually reproducing

organisms and asexually reproducing

organisms the horizontal Gene transfer

in bacteria can throw a wrench and

things and it's far more objective and

free of bias than any other species

Concepts that we've discussed as long as

you clearly State your thresholds for

what constitutes a unique species any

researcher can evaluate your data set

and draw the same conclusions it isn't

based on what features the researcher

deems to be important but on actual

evolutionary history and diversification

from other groups because at the end of

the day species are a real thing and

phylogenetics is the best system we've

yet derived from modeling the real

relationships and history of organisms

on this planet that said it isn't

without it shortcomings for one thing it

generally requires large amounts of data

that can be expensive to collect and

difficult to analyze and while it is

super effective for organisms for which

we have extensive morphological and

genetic data it can be much harder to

apply to organisms known only from

limited and often incomplete fossil

evidence and knowing exactly where to

draw the line between species that can

still be difficult it's easy to

oversplit groups or have disagreements

about how much difference is Meaningful

and

so you may walk away from this video

still

wondering what's a

species and that's okay cuz nobody

really knows sorry as always like And

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you to all of these people a video like

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two skeletons in the act of mating and I

wouldn't know if they were able to

produce viable fertile offspring

thank you CL

yes these are just the most broadly used

if they come from the same

kind that well that would be a big one

there you go that's uh baraminology is

what that's called baram baramin bman

baraminology and uh I can discuss that

one I understand that way better than

most creationists do okay I really do

like like you know people all the time

are asking for a definition of what a

created kind is I'm glad you asked this

question because this is a this is this

makes your patreon extra's video totally

worth

it one day yeah just don't suck it up

too much it'll go straight in your LS

yeah flies out and you then you'll cough

it up and you won't have a meal

yeah such a disaster

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