Why do we consider Neanderthals a different species than humans?

[Aidyan]

According to wiki "Neanderthals are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago." But according to wiki again: "A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction." Sounds to me a contradiction. Since we know that we mated with Neanderthals that produced offspring we should assume that they were not a different species than us. Why can't we say that Neanderthals were just homo sapiens with a slightly different anatomy (that, after all, one finds also among present humans)?

 

[anuttarasammyak]

Since we know that we mated with Neanderthals that produced offspring

As a layman I would like to know how scholars conclude it.

 

[jim mcnamara]

You are making a logical step one too far, IMO.

No. Species are arbitrary. Just because you can think of something as one thing does not make it so.
Modern Asian humans have Denisovan genes, modern European humans have Neanderthal genes, African humans have neither. This breaks the Linnean species definition.

Species exist mostly in the human mind. We use the concept as a useful tool to sort out diversity in living things. There is no universal law of nature to dictate species.

https://en.wikipedia.org/wiki/Carl_Linnaeus
Carl von Linne (Linnaeus) created the rules for binomial nomenclature.

At a graduate level, you learn that just because you can place something in a taxonomic cubbyhole for convenience does not always relate to what really happens in Nature.
Why? How about examples:

Examples: Quasipecies concept

Viruses are awful fits taxonomically, so we had to break the "rules" to make classification more useful and not confuse everyone, so we label them as a quasispecies and then we resort to this kind of thing:

https://www.avma.org/sites/default/files/2020-02/AVMA-Detailed-Coronoavirus-Taxonomy-2020-02-03.pdf

Virus do not reproduce like most plants and animals - they hijack cell machinery to churn out lots more virions. And a lot of these new virions are not identical, about 5% of the new virions Covid spewed out have one or more mutations. Which breaks that chart's usefulness long term. The Omicron variant is an example of this.

How bad is this? Well, fairly awful for people who feel they must use things like that chart in the link above.
This is closer to reality (Omicron is the five red dots way out on the right):
https://nextstrain.org/ncov/open/global

Take home point:
But nobody actually uses binomial nomenclature for Covid.

Plants do not play the species name game either. Plants have to have an even number of chromosomes sets to produce healthy viable seeds or spores. That number has to match from the male to female sources.

So, how about a plant species that is not a species by the interbreeding definition?
Switchgrass (we still use Panicum virgatum as a species name). It violates lots of taxonomic rules.

The plant is clump of stems, florists dry it and use it sometimes in making floral display. Pretty.
But one clump can be 8, 10, or 20 completely non-interbreeding "things", since we do not call them separate species. We cannot tell them apart without using a microscope, taking samples at just the right time of year and counting chromosomes. Otherwise the plant stems in your clump are indistinguishable.

They do not interbreed very well. But we cannot tell them apart to know who mates with whom.

Humans have two chromosome sets, think of the sets as "ploids". We write 2n to mean two sets, or diploid.
Can you count in Latin and Greek...? 2n=diploid, 3n=triploid, 4n=tetraploid... and so on.

Switchgrass clumps do not play fair. A stem can be one of several possible ploids. So pollen from one stem may not be able to fertilize an adjacent stem's female flower.

A lot of plants, especially cultivated ones, have extra sets of chromosomes. Because more sets increase the size of the fruiting body or seed: modern wheat=6n, strawberries=8n. Humans played with this fact as you can see. So switchgrass is not the only plant to do this. Some ferns are like 50n and more.

Bottom line - living things are not always a perfect fit for the species definition. Humans, ancient or modern, are living things. Do not overthink the use of a definition from 1761.

 

[DaveC426913]

As a layman I would like to know how scholars conclude it.

By sequencing our own genes and finding Neanderthal genes mixed in.

 

[BillTre]

By sequencing our own genes and finding Neanderthal genes mixed in.

To do this, the Neanderthal and Denisovan genomes had previously been recovered from fossil finds. The Denisovan genome was known before more than a little pinkie bone and tooth was known of their structure.

 

[Aidyan]

Bottom line - living things are not always a perfect fit for the species definition. Humans, ancient or modern, are living things. Do not overthink the use of a definition from 1761.

Ok. So, the concept of "species" is a very questionable one that has not a scientific and clear-cut correspondence in the real living world.

But then why are we making the distinction between homo sapiens and home Neanderthalensis in the first place? It is said that "compared with modern humans, Neanderthals had a more robust build and proportionally shorter limbs." I guess you could find lots of "robust build" with shorter than average limbs in present humans as well. Then that neanderthals had larger eyes and a protruded skull. But its build is most similar to that of Inuit and Siberian Yupkis among modern humans and that the braincase volume was "within the range of the values for modern humans." From the descriptions and the pictorial reconstructions, there seems to be some morphological difference, but not really that much (e.g. https://en.wikipedia.org/wiki/Neanderthal#/media/File:Reconstruction_of_Neanderthal_woman.jpg). Moreover, we know they buried their dead and had some form of primitive art. There are lots of other differences but then, in the wiki text, you will find the attached words "similar to those of modern humans" at least eight times. The question is if this is enough to differentiate them from homo sapiens? Is this difference greater than that we can find nowadays, say between the Aborigine and a European population? It still remains obscure to me the technical reason why nowadays we describe them (Neanderthals) as clearly other than us (homo sapiens)?

 

[jim mcnamara]

You are worried about why somebody made a decision about species 160 years ago.
I cannot help you there. And. "We", meaning many biology nerds, do not consider Neanderthal as a separate species. Most popular literature seems to use terms like sub-species, if that makes you feel better.

If you gave one of our ancestors a thorough cleaning, modern clothing, and then put him/her on the midtown bus nobody would notice. Just hope that nobody would try to talk to our impostor.

[opinion]
I think that the zeitgeist of the times in 1860's was anthropocentric thinking:
H. sapiens was the very, very best nature could ever possibly do. Anything else is inferior by definition.

So you have to denigrate the position of a fossil species in the H. sapiens hierarchy clade since they cannot possibly be H. Sapiens. Ergo, they are inferior. So name 'em something else.
[/opinion]
FWIW:
This worldview is patently obvious in Gary Larson comics. He makes cave men out to be dull thuds. And we think it is funny.
I don't usually link to comics but this is useful here I think:
https://www.thefarside.com/

 

[jim mcnamara]

FWIW - some neanderthal fossils have brain volumes on a par with extant humans. Seems the Genus Homo lost measurable 6ground in the brain size department about 3000 years ago.

Discussion here (popular science):
http://www.sci-news.com/othersciences/anthropology/human-brain-size-10198.html

 

[PeroK]

My mother disliked the term Neanderthal being used pejoratively and used to write to newspapers and television stations to complain on their behalf.

 

[Rive]

So, the concept of "species" is a very questionable one that has not a scientific and clear-cut correspondence in the real living world.

More like real living word (biology) has no interest in clear-cut scientific approach.

Take it like this: to do some useful work with species science needed some artificial guideline about differentiating them.
But once the useful work took momentum exceptions and special cases started to pop up, along with discoveries of hereditary mistakes.
The old guidelines are still mostly useful (within their original usage), but since it become a progress and evolution of a sort, there may be confusion and fuzzy cases (and to be honest, Neanderthals are just an insignificant example for that).

As of now, 'Neanderthals' is kind of a title, and if anyone wish to discuss them then it's useful, regardless if it's taken as the name of a specie or sub-specie or population or buckets of sad bones.

 

[BillTre]

Just to add to all this:

In most cases, reproductive isolation will be a good argument for a new species, but not always:

This group of sub-species can interbreed among each other, going from eschscholtzii on the southern coast and looping (clockwise) around the central valley, until you get to croceater, which can not interbreed with eschscholtzii where they contact.
It just is what it is.

Different species concepts are a more useful fit to certain sets of organisms than others.
Differences in reproductive methods and how inheritance is transmitted can be important.

Some groups of species can undergo extensive horizontal gene exchange (prokaryotes), others not (vertebrates).

Some can form new reproductively isolated groups by crossing with a different species (some sunflowers). New individuals can be added to the new breeding group by repeated breeding between the original two species.

Its a hard concept to nail down.

 

[pinball1970]

According to wiki "Neanderthals are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago." But according to wiki again: "A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction." Sounds to me a contradiction. Since we know that we mated with Neanderthals that produced offspring we should assume that they were not a different species than us. Why can't we say that Neanderthals were just homo sapiens with a slightly different anatomy (that, after all, one finds also among present humans)?

I cannot add to the biology, the other posters have outlined that.
There is interesting history regarding palaeoanthropology and some of the naming/species debates.
Easy reading is Richard Leakey. Origin of human kind. Chris Stringer is another, The origin of our species. Some interesting technical things on dating too. (Fossils)

 

[DaveC426913]

I cannot add to the biology, the other posters have outlined that.
There is interesting history regarding palaeoanthropology and some of the naming/species debates.
Easy reading is Richard Leakey. Origin of human kind. Chris Stringer is another, The origin of our species. Some interesting technical things on dating too. (Fossils)

Surely, there are no actual fossils in the world of palaeoanthropology.

 

[pinball1970]

Surely, there are no actual fossils in the world of palaeoanthropology.

Not sure. Lucy is about 3 million? All actual bones?
Ardi a bit older described as 'fossils.'
https://en.wikipedia.org/wiki/Ardipithecus

 

[DaveC426913]

Not sure. Lucy is about 3 million? All actual bones?
Ardi a bit older described as 'fossils.'
https://en.wikipedia.org/wiki/Ardipithecus

Right.
Wiki calls them fossils.

I'll see myself out.

 

[pinball1970]

Right.
Wiki calls them fossilized bone.

I'll see myself out.

No you're right actually. I do not think they are true fossils Dave. Let me look!

 

[pinball1970]

Right.
Wiki calls them fossils.

I'll see myself out.

This is where wiki falls down a little bit.
'This correction of the initial allocation of the fossil record was based on the argument that Ardipithecus kadabba had more "primitive" features than other Ardipithecus fossils. Ardipithecus kadabba thus also has a greater similarity with the genera Sahelanthropus and Orrorin. These statements were based on additional bone finds that came to light in November 2002 and were dated at 5.8 to 5.6 million years.'

So are they actual bones? I think Lucy and Turkana were. @DaveC426913

 

[BillTre]

Traditionally, "fossils" have usually referred to bones with some of their chemicals replaced by chemicals from their geological setting.
However, there are other "fossils" that are imprints (footprints and other impressions), so not a strict interpretation.

Once fossilized, are they still bones?
To most people yes, but not all apparently.

Almost anything biological known from the geological past would be based on either buried remains dug up or found in some other way, or now-a-days by molecular methods, which still rely on digging up old stuff containing DNA.

DNA containing materials have probably not had their chemicals substituted as in the traditionally described fossillization process. So, not a fossil? Could also be not-a-bone, if it was from some other tissue.

These seem to be semantic issues to me.

 

[jim mcnamara]

The term fossil meaning turned to rock, is another example of nature not exactly fitting a definition:
Some examples:
https://www.penn.museum/sites/expedition/frozen-mummies-of-the-andes/
Mummies (Andean and Egyptian for example) are another type of really old remains.

Bog men --- Great photo:
https://www.smithsonianmag.com/science-nature/europe-bog-bodies-reveal-secrets-180962770/

Amber insects -- we often use the term fossilized for amber insects.

 

[Bandersnatch]

The term fossil meaning turned to rock, is another example of nature not exactly fitting a definition:

And when Aerosmith does a gig these days, we call them living fossils. But it doesn't mean they're rock men. Oh, wait...

I'll see myself out.

 

[jim mcnamara]

@Phil Core We need a reference for that statement...