Species

Dec 2017
312
Regnum Teutonicum
I wanted to discuss the concept of species. It has become clear that species doesn’t exist in reality. It is only a concept in the human mind (of course it is the best we have so far, so we have to continue working with it). Long gone are the days of the definition if organisms can produce (fertile) offspring, then they belong to the same species. Some interesting examples are:

Horses and donkeys
Horses and donkeys can have offspring. The offspring are not fertile.
One species or two?

Lions and tigers
Lions and tigers can have offspring. Male offspring are not fertile. Female offspring are fertile.
One species or two?

Brown bears and polar bears
Brown bears and polar bears can have fertile offspring. Some brown bears are genetically closer to polar bears than to the other brown bears (polar bears are inside brown bears).
One species or two?

Modern humans and neanderthals
Modern humans and neanderthals could have fertile offspring. Most genetic material from neanderthals is slowly squeezed out of modern humans, but there is a lot of genetic material which is favorable for survival, so it is increased and modern human genetic material is squeezed out.
One species or two?

Gulls/warblers
In europe you have the herring gull. If you follow it to the west to north america its wing colour gets darker and darker and somewhere in asia it is almost black. If you follow it to europe you have the lesser black-backed gull. In europe the herring gull and the lesser black-backed gull can’t have offspring, but nevertheless if you go into the other direction you end up with the other one.
Another example is the greenish warbler, where there are two "subspecies“ in the eastern tibetan plateau that can’t have offspring, but if you follow one around the himalaya (connected by other "subspecies“ which can have fertile offspring), you end up with the other one.
One species or two?

Edible frogs
The edible frog is a "hybrid“ between the pool frog and the marsh frog. Normal edible frogs can’t have offspring with other edible frogs, but they can if one parent is a marsh frog or a pool frog. So normally one would expect that edible frogs vanish, were there are no pool or marsh frogs. But this isn’t the case. There are some edible frogs which are triploid, which means they have the full genetic information of one of their "parent species" in them. An those frogs can reproduce with the other edible frogs.
One species or two or three?

Amazon mollys
Amazon mollys are sexual parasites. Only females are known. To produce offspring they need semen of male sailfin mollys, broadspotted mollys or atlantic mollys (maybe also common molly) to reproduce. But the offspring are amazon mollys, the genetic material of the males isn’t used. They only need the semen to start the development of the ovule.
One species or two or four or five?

Chronospecies
If a type of organism lives a long time, what if the first ones can’t have fertile offspring with the last ones, if they magically met each other?
One species or two?

Mitochondrions
Mitochondrions were organisms, that sometime went into symbiosis with another organism. Now they are just organelles of another organism. And this organism can't live without the mitochondrion. (See endosymbiontic theory)
One species or two?
 

Jake10

Ad Honoris
Oct 2010
11,960
Canada
Well, since horses, zebras and donkeys had a common ancestor, then it appears they have evolved to the point of no longer being compatible with one another. The same can be said for lions and tigers. So, the concept of species refers to the point at which organisms from the same background change to a point at which compatibility is no longer possible. This means that time will, eventually, result in mutations and adaptations which will introduce new species to the planet, which should apply to humans as well.
 

Naomasa298

Forum Staff
Apr 2010
35,367
T'Republic of Yorkshire
I wanted to discuss the concept of species. It has become clear that species doesn’t exist in reality. It is only a concept in the human mind (of course it is the best we have so far, so we have to continue working with it). Long gone are the days of the definition if organisms can produce (fertile) offspring, then they belong to the same species. Some interesting examples are:

Horses and donkeys
Horses and donkeys can have offspring. The offspring are not fertile.
One species or two?

Lions and tigers
Lions and tigers can have offspring. Male offspring are not fertile. Female offspring are fertile.
One species or two?

Brown bears and polar bears
Brown bears and polar bears can have fertile offspring. Some brown bears are genetically closer to polar bears than to the other brown bears (polar bears are inside brown bears).
One species or two?

Modern humans and neanderthals
Modern humans and neanderthals could have fertile offspring. Most genetic material from neanderthals is slowly squeezed out of modern humans, but there is a lot of genetic material which is favorable for survival, so it is increased and modern human genetic material is squeezed out.
One species or two?

Gulls/warblers
In europe you have the herring gull. If you follow it to the west to north america its wing colour gets darker and darker and somewhere in asia it is almost black. If you follow it to europe you have the lesser black-backed gull. In europe the herring gull and the lesser black-backed gull can’t have offspring, but nevertheless if you go into the other direction you end up with the other one.
Another example is the greenish warbler, where there are two "subspecies“ in the eastern tibetan plateau that can’t have offspring, but if you follow one around the himalaya (connected by other "subspecies“ which can have fertile offspring), you end up with the other one.
One species or two?

Edible frogs
The edible frog is a "hybrid“ between the pool frog and the marsh frog. Normal edible frogs can’t have offspring with other edible frogs, but they can if one parent is a marsh frog or a pool frog. So normally one would expect that edible frogs vanish, were there are no pool or marsh frogs. But this isn’t the case. There are some edible frogs which are triploid, which means they have the full genetic information of one of their "parent species" in them. An those frogs can reproduce with the other edible frogs.
One species or two or three?

Amazon mollys
Amazon mollys are sexual parasites. Only females are known. To produce offspring they need semen of male sailfin mollys, broadspotted mollys or atlantic mollys (maybe also common molly) to reproduce. But the offspring are amazon mollys, the genetic material of the males isn’t used. They only need the semen to start the development of the ovule.
One species or two or four or five?

Chronospecies
If a type of organism lives a long time, what if the first ones can’t have fertile offspring with the last ones, if they magically met each other?
One species or two?

Mitochondrions
Mitochondrions were organisms, that sometime went into symbiosis with another organism. Now they are just organelles of another organism. And this organism can't live without the mitochondrion. (See endosymbiontic theory)
One species or two?
https://en.wikipedia.org/wiki/Genus

https://en.wikipedia.org/wiki/Species
 

fascinating

Ad Honorem
Dec 2011
2,403
I wanted to discuss the concept of species. It has become clear that species doesn’t exist in reality. It is only a concept in the human mind (of course it is the best we have so far, so we have to continue working with it). Long gone are the days of the definition if organisms can produce (fertile) offspring, then they belong to the same species.
I don't know if I agree that the concept of species doesn't exist in reality. I thought that if two animals can mate and produce viable offspring, then they should be the same species. "Viable" means offspring that can themselves produce offspring. On that basis, horses and donkeys are separate species.
 
Dec 2017
312
Regnum Teutonicum
... I thought that if two animals can mate and produce viable offspring, then they should be the same species. "Viable" means offspring that can themselves produce offspring. On that basis, horses and donkeys are separate species.
It is not that easy. Polar bears and brown bears can produce viable offsprings. With your definition they are not different species, but polar bears are a subspecies of brown bears.

Also, how do you explain the greenish warblers with this definition of species:

Subspecies A - subspecies B - subspecies C - subscpecies D

B can have fertile offspring with A and C, C with B and D and so on, but D can't directly have viable offspring with A. Nevertheless they could have viable offspring over several generations via B and C.
 

Asherman

Forum Staff
May 2013
3,410
Albuquerque, NM
You may find more informed answers on sites where Biologists congregate, than in a room filled with Historians.
 
Jan 2018
1,609
China (Hong Kong SAR)
Well, you can't mate an ant with a horse, so that is where we could draw our intuition for the traditional species definition. For, if the offspring is not fertile and thus there is no continuation, how could we even denote the existence of a new species? And, if it is (fertile), why should they be defined to be of a different species?

Definitions utilizing polypeptide combinations ("DNA", though calling it "DNA" is horrifically disrespectful of its first principles, doesn't jive with mathematical biology) will be much, much clearer in the future as more mathematicians enter biology. You'll love this OP, that the species definition is not going to be dropped anytime soon because there are very strong intuitive bases for it, it's just going to be refined.
 
Last edited:
Jan 2018
1,609
China (Hong Kong SAR)
Subspecies A - subspecies B - subspecies C - subscpecies D

B can have fertile offspring with A and C, C with B and D and so on, but D can't directly have viable offspring with A. Nevertheless they could have viable offspring over several generations via B and C.
How you describe it, they call this process evolution. Of course, it would be a tree instead of just A to B to C and whatever. And over time, the speciation becomes more concrete. Homo Sapiens supposedly bred with Neanderthals, which is not a surprising claim, but they both have many common ancestors which they cannot breed with, including a multicellular "organism" that started everything, the number of species for which they cannot breed with continues up to the mammals and so on. Hence why the definition of a species won't be dropped so easily. Of course, modern definitions are being refined.

e.g.

etc.

You can obviously see the closeness of the Sapiens to the Neanderthals.
 
Last edited:

AlpinLuke

Forum Staff
Oct 2011
27,206
Italy, Lago Maggiore
As usual, we follow conventions, since our mind needs “stable data” to reason. We need definitions to deal with “entities” of any kind and we love to categorize.

There are different conventions defining the species and this means that the word can indicate different things.

Generally it’s the biological meaning of the word to be the most used and diffused around.

The convention states that a species is based on common near ancestors and reproductive isolation. This means that:

* Going backwards through time a species exists until it’s recognizable;
* It’s not enough that a horse an a donkey have an offspring: such a offspring has to be fertile without generational limitation.
* Furthermore … the hybridization has to happen in nature [not planned or caused by humans]. So that if humans find a way to make horses and donkeys have a fertile offspring without generational limitation … horses and donkeys keep on being different species. Even If they are of the same genus [Equus].
 

Dreamhunter

Ad Honorem
Jun 2012
7,486
Malaysia
Was Neanderthal a distinct species, i.e. Homo neanderthalensis, or a sub-species of Homo sapiens, i.e. Homo sapiens neanderthalensis?