Question for evolutionary anthropologists regarding speciation?

[Danevan]

Hello, just joined the site because have been watching the new Brian Cox series and it reignited a problem that I have had understanding an anthropological concept for some time.

 

Some background; I am a veterinary scientist, I remember doing some work at uni on speciation in orang-utans. It was fascinating and what I remember from it was the discussion of the point at which speciation occurs. People have done research into the number of genetic differences between the two major subtypes. Even though when kept together the two still seem perfectly able to breed and produce viable off spring, their differences on a genetic level are greater than between some different species of apes.

 

The upshot was that my understanding has always been that if individuals can mate and produce viable offspring then they are, by the most popularly accepted definition of the same species. So, even though lions and tigers, horses and donkeys can reproduce, as the off spring are nearly always sterile, they are not of the same species.

 

I love watching documentaries on human evolution and I have trouble understanding how the same principle is applied to hominids. Recently I have seen several programs talking about the fact that it is now accepted that early homo sapiens interbred with Neanderthals, to the extent that perhaps between 10-15% of some human genomes could be 'neanderthal'. So, if that's right and homo-sapiens and Neanderthals were breeding and those off-spring were going on to contribute significantly to the human genome, surely they were the same species? However most authors insist they were a different species.

 

I also saw a commentator recently discussing the recent allocation of what had been previously thought of as the same species into different species based on phenotypic variations such as dental variations or mandible shape. Yet I look at dogs and the variety of phenotypic examples, all from the same 'species' who are perfectly able to reproduce effectively.

 

So, is there a broadly used definition of species amongst the early hominids that explains why different s, which existed alongside homo-sapiens could have contributed to our dna? Obviously there are any number of different species further up the tree that have contributed their dna to what eventually became modern humans but would not have been able to inter-breed with them. But isn't anyone who could breed with homo-sapiens, by definition homosapien?

 

I'd be happy to follow up any useful links if you have them,

Cheers in advance

[mistermack]

The word "species" regularly causes this problem. It's not an exact definition, it's a word that just gives an indication of the relationship between discreet populations. A similar situation exists for brown bears. We say that Russian brown bears are the same species as American ones, even though they never interbreed. They are close enough to interbreed readily, if they ever did meet.

The same seems to apply to modern humans and Neanderthals. They could readily interbreed, but were separated by distance for many tens, or even hundreds of thousands of years.

You could call them the same species, and you wouldn't be wrong or right. You would just be outside of the current way of looking at them.

 

Incidentally, with bears, even the Polar Bear has been known to mate with Browns, on very rare occasions. But they don't normally, even where they meet. So maybe they are a different species.

BUT, I seem to remember that Polar Bears are found to be closer to Grizzlies genetically, than some Asian Brown Bears.

So it's a very fuzzy subject.

[CharonY]

The species concept is indeed a fuzzy one and even the criterion of successful interbreeding is not quite as simple as it seems. Specifically to hybrids I'd like to add this: while there are fertility issues, ligers, for example are not always sterile. Others, such as the Beefalo are actually fertile. And the situations is even more complicated once we move to plant species.

 

Looking at neanderthals one has to note there is data suggesting that male hybrids were most likely sterile, as DNA analyses showed a dearth of neanderthal genes on the X-chromosome.

[Strange]

This page has good overview of the issues re defining species

http://www.talkorigins.org/faqs/faq-speciation.html

Edited January 31, 2017 by Strange

[mistermack]

Looking at neanderthals one has to note there is data suggesting that male hybrids were most likely sterile, as DNA analyses showed a dearth of neanderthal genes on the X-chromosome.

Could it also be that there was sexual selection going on, and that female modern humans were not inclined to mate with Neanderthals or hybrids, whereas males were not so fussy?

[delboy]

There is a similar situation with the carrion crow and the hooded crow. They used to be considered subspecies because they are perfectly capable if interbreeding. But they are now classified as two separate species because they only interbreed in the limited geographical area where they overlap.

 

If it was purely behavioural/cultural differences that stopped sapiens and neanderthals interbreeding, they would be considered separate species by most definitions. But if the barriers were overcome interbreeding was obviously possible.

[mistermack]

I've been fascinated by the hooded/carrion crows for ages.

 

I've come to the conclusion that (guessing) neither the hoodie, nor the carrion, knows what it is.

If a hoodie were brought up in a purely carrion crow area, it would think that it was a carrion crow, and try to find a carrion crow mate.

But the carrion crows would reject it, because it LOOKS different to all the other crows that they see.

And vice versa with the carrion crow brought up in a purely hoodie area.

 

Only in the margin, where the ratio is about fifty fifty, do you get interbreeding, with confusion as to what they are.

But if a hybrid strays from the marginal area, it won't find a mate.

Going by that theory, if you dyed the feathers of a hoodie, and released it in a carrion crow area, it would have no trouble finding a mate. But it's chicks would struggle, if they inherited the hood.

[SamCogar]

Danevan, I can easily understand your confusion most every time you hear or read the term “Homo sapien” but it is only partly or 50% your fault for not understanding what the author was referring to …… and 50% fault of the author for not knowing what the ell they were actually talking about.

 

The term “Homo sapiens” actually defines a species within the genus Homo …… which is in the Family Hominidae. And humans are a sub-species within the Homo sapiens species and they are CORRECTLY referred to as …… Homo sapiens sapiens .

So Danevan, whenever you hear, read or encounter the term “Homo sapiens”, ….. you should STOP right there and ask yourself, ……. “Just exactly which one of the ‘sapiens’ is he/she talking about?”

 

And don’t be believe everything you read or hear without reasoning out its content ...... and the following should help cure your confusion, to wit:

 

The binomial name Homo sapiens was coined by Carl Linnaeus (1758). The Latin noun homō (genitive hominis) means "man, human being".

 

Subspecies of H. sapiens include Homo sapiens idaltu and the only extant subspecies, Homo sapiens sapiens. Some sources show Neanderthals (Homo neanderthalensis) as a subspecies (Homo sapiens neanderthalensis). Similarly, the discovered specimens of the Homo rhodesiensis species have been classified by some as a subspecies (Homo sapiens rhodesiensis), but these last two subspecies classifications are not widely accepted by scientists.
Read more @ https://en.wikipedia.org/wiki/Homo_sapiens

 

 

And Danevan, the actual fossil lineage for humans (Homo sapiens sapiens.) on the "Homo Ancestral Tree" has not yet been determined ........ simply because no fossil evidence has been found to confirm said lineage.

 

[StringJunky]

The species concept is indeed a fuzzy one and even the criterion of successful interbreeding is not quite as simple as it seems. Specifically to hybrids I'd like to add this: while there are fertility issues, ligers, for example are not always sterile. Others, such as the Beefalo are actually fertile. And the situations is even more complicated once we move to plant species.

 

Looking at neanderthals one has to note there is data suggesting that male hybrids were most likely sterile, as DNA analyses showed a dearth of neanderthal genes on the X-chromosome.

Evolution is not linear, is it, within a population. There will be individuals at different evolutionary stages within it.

Edited February 10, 2017 by StringJunky

[Delta1212]

Evolution is not linear, is it, within a population. There will be individuals at different evolutionary stages within it.

I'm not even sure describing the diversity of a population as being different evolutionary stages is really even the right way to talk about it.

[CharonY]

As a matter of fact, "stages" is not really a good way to look at it.

[SamCogar]

Evolution is not linear, is it, within a population. There will be individuals at different evolutionary stages within it.

 

Correct, evolution is NOT linear within a population, it is random. And then again, “yes” it is linear within said population.

 

It is random, because the gene mutation(s) within an individual’s DNA are random occurrences (copying mistakes). And if that individual with said “mutated” gene survive to procreate, then that can result in “descent with modification” of said individual’s offspring(s) …… which said evolutionary change or “mutation” then remains “linear” within the procreating decedents.