What Is A "Species?"

Submitted by: LordJim 1 month ago in Science

It may be time to reconsider.

An excerpt from Discovery Magazine: When it comes to species, says biological anthropologist Rebecca Ackermann, “forget everything you learned in high school.”

The classic textbook definition, known as the biological species concept, is a group of organisms that only produce fertile offspring with one another. By this rule, domesticated dogs are a single species — whether dachshund or Great Dane — but a donkey and a horse are not.

Ackermann, a professor at South Africa’s University of Cape Town, favors a different definition that’s not dependent on successful sex: a group of organisms sharing a mix of anatomical, behavioral and genetic traits that distinguishes them from other groups. But, she adds, “Many, many evolutionary biologists I know often avoid the word species entirely.”

That’s because the evolutionary tree is tangled, and many organisms on diverging branches can still interbreed. “Canids have, pigs have, mice have. You name it, and it has,” says University of Georgia evolutionary biologist Michael Arnold. “There’s a hybrid under every bush.”

That includes our ancestors. Genetic evidence has shown that ancient Homo sapiens interbred with Neanderthals and their eastern cousins, Denisovans, several times from 100,000 to 40,000 years ago. Neanderthals and Denisovans mated with each other, and Denisovans hooked up with a distant lineage, not yet known from fossils, that may have been closer to the earlier Homo erectus.

In recent ancient DNA studies, almost “every time a new individual is sequenced from the human fossil record,” says Ackermann, “there’s some new piece of evidence for gene flow.”

Interbreeding may have been a common theme in human evolution, but it’s difficult to understand today, when ours is the only Homo species left. To better grasp our past, anthropologists like Ackermann have begun researching other animals that mate across classic biological species lines.

There is one major problem with the biological species concept: It can’t be applied to organisms that reproduce asexually, which includes most microbes. The sex requirement also poses a challenge for extinct animals because paleontologists can’t tell just by looking at two similar fossils if the creatures could mate. Excluding extinct and asexual organisms means the biological species concept does not work for the vast majority of life that has existed.

Nevertheless, biologists long championed the definition, in part because it fit the prevailing image of evolution as a branching tree, in which a single ancestral species diverges into distinct lineages of descendant species.

“That was a classical idea,” says Arnold. Instead, he says, we need to recognize that as descendants branch off, “genes are still being exchanged, even though we call them different species.”

Interbreeding has now been detected in 10 percent of animal species and 25 percent of primates, including ongoing crosses between such distant relatives as gelada and baboon monkeys, whose last common ancestor lived about 4 million years ago.
There are 19 comments:
Male 121
sigh. populist crap. species is also based on behavior and/or other triggers that prevent mating as well as geographic separation.

Ligers have been around for hundreds of years. But in their natural environment a tiger and a lion will never mate.  Only when both are in captivity.

If a male bird learns the wrong birdsong he will never mate. 

The have known for many decades, long before I got my degree in biology in 1983, that a greater then 0.5% genetic difference results in a mule.  And 1% and greater (if memory serves) results in no fertilization.
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Male 9,498
I really wish people wouldn't get sidetracked on the What's a Species? issue. The philosophical and linguistic difficulties surrounding the concept by no means make evolution less certain. Evolution is, by definition, a gradual process, in many instances occurring over a timeframe of millions or even tens of millions of years. Philosophically, it is always difficult to delineate when something that is continually changing in incremental degrees becomes something else. The fact that evolutionary changes occur on a timescale most humans have an impossible time grasping makes the situation that more complex.

Let's use an example more suitable to the human lifespan.

Are these two cars the same car?





It depends on how you use language and how you want to define "the same car." They are both Toyota Corollas (1969 and 2018). Are they the same species? Or would you say the differences in horsepower and handling and technology are so great there's no way they can be considered the same?

If they're different cars, at what point did the 2018-type Toyota Corolla split off from the 1969-type Toyota Corolla?
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Male 1,094
squrlz4ever I'm not sure using cars is the best way for you to make a point for evolution.  The two cars were separate creations, created by a common creator (humankind).  They use the same parts (or methods and concepts), but they're simply different.    Yet one did not literally evolve from the other.

But I agree with you, getting sidetracked on the issue of what a species is does nothing any good.
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Male 4,484
squrlz4ever All I know is that I love my Corolla!
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Male 1,094
I love this: "Ackermann, a professor at South Africa’s University of Cape Town, favors a different definition"

That's exactly the problem...  different  scientists can't even agree on a definition.  Communication only works if we're using the same definitions.  We can't just decide on our own, or what we want a word to mean.
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Male 274
cjeffblanchr that's why there is a discussion. They are not saying species do not exist, or that the notion is useless; they are refining it so that it can be applied more broadly and with greater certainty (I.e. their mention of organisms that reproduce asexually).
It's the difference between expecting all dogs to be copies of the archetypal dog and acknowledging that a species encompasses a spectrum of organisms that have a shared ancestry (to within a given specificity; which is why we also have genus, clade, etc...)
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Male 1,094
elgabalo My point is that the word species is just a definition, a way to classify entities, and that definition does not mean the same thing to everyone.  You can't have a discussion unless people agree on the definition (I'm talking about a discussion on evolution in general, not a discussion on what 'species' should mean).
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Male 9,342
cjeffblanchr   You can't have a discussion unless people agree on the definition 

You can have a discussion about the definition. Which is what this is.
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Male 1,094
LordJim I don't disagree that is what this is.  I just think it is nonsensical to keep trying to redefine a word just because someone wants it to mean something else.
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Male 274
cjeffblanchr but it does, there are clearly defined and easily accessible resources with which to find these definitions. (And then there are even more, still easily accessible, resources that delve into the complexity surrounding the issue).
None are based on "common sense"; science has no place for common sense.
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Male 1,094
elgabalo I think that's what I mean... There are already clearly defined definitions, yet from time to time, someone comes around and decides they don't like that particular definition, so they decide to define it their own way.  Science cannot be stationary and unchanging by its very nature, but at a given time, we have to be using the same definition of a word to have meaningful discourse.  If you and I are talking about an apple, but I really mean a banana, but decide to call it an apple, then we're going to run into problems communicating.

I get that in part this article is a discussion about how species should be defined, but it is also displaying the point that I'm trying to make.  It is only necessary to redefine it because scientists are not using the same definition to define what a species is.

However we define it, it is still just a word to describe how we wish to classify organisms.  That can and obviously does change.  In Biblical times, bats were classified as birds.  By modern definitions that is wrong, but that doesn't mean that the scriptures were wrong--it just means they classified differently than we do.  (Yes, now I'm crossing topics of our discussions).  We run into the same problem in modern times if we are not using the same definition for terms such as Species.

See, it is because of this (not this article alone, but because I see this differing uses a lot in scientific circles) that I feel justified in thinking of animals as 'kinds' rather than species.  Yes, this is injecting my religious beliefs into a scientific topic, but to me, they are not all that far apart.  But saying Kinds is really no different than another way of saying species, especially when there is no absolute definition for species.  It doesn't change or help anything, though, because as you said, it is a rather complicated issue. 

To me, Kinds is best defined as a group of organisms with similar traits--both physical and genetically--that are capable of reproducing.  We would expect because of natural selection and adaptation that over time things would become quite complicated.  Correct me if I'm wrong, but I think that some breeds of dogs are in fact not capable of breeding with others.   This is certainly true with some species--there has just been enough change within them that separate branches cannot reproduce.

But this is not to say that I accept evolution in the sense of one species being able to change, even given enough time, into a totally different type of animal (such as monkeys to men).  I absolutely accept natural selection and adaptation, as these are observable facts.  We do see these in nature.  But beyond that, it is all speculation.  Common traits, even genetically, does not prove evolution.  It is evidence for a theory, yes, but not proof.  It is likewise evidence for a common creator.

It is for discussions like this that I think we need an absolute definition of a word like  species.
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Male 274
elgabalo I think I meant to say that the definitions are clearly defined and the resources are easily available. I don't know what a clearly defined resource is in this context.
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Male 18,342
The evolution diagrams are always supposed to be a bit fuzzy, not clearly delineated. 

The definition of a species in common zoological use may describe unique physical characteristics, but you can't go around testing animals by getting them to fuck other species. I've even seen a Slovenian breed with a cheeto and all it took was the offer of money.
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Male 274
The coolest part is that we're finding evidence of unknown hominid ancestors in the genes of a number of human populations.
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Male 45,617
There's a brand new species . Not newly discovered, newly evolved and scientists are quite giddy about it.  For the first time they get to see the early generations and such.

It's a new species of finch on the Galapagos Islands


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Male 5,277
Gerry1of1 Cool Gerry, thanks!
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Male 18,342
Neandertal Lives Matter
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Male 900
Draculya Not Denisovans, though - eff those guys.
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Male 1,873
faustsshadow we probably did.  Think about most males you know, then remove hundreds of thousands of years of civilization.  yep, wed've hit it.
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