Evolution: Could speciation in humans happen by choice?

[edpell]

I think "physics" forum is not the place to find a discussion on evolution. I am hoping someone can point me to a place where evolution is discussed. Let me be clear I do not want a discussion of whither evolution is real. I am looking for a group of people ALL of who accept evolution to discuss the fine points of evolution. Thanks.

 

[Greg Bernhardt]

I think "physics" forum is not the place to find a discussion on evolution. I am hoping someone can point me to a place where evolution is discussed. Let me be clear I do not want a discussion of whither evolution is real. I am looking for a group of people ALL of who accept evolution to discuss the fine points of evolution. Thanks.

That is this place. We have biologists here. Ask away.

 

[edpell]

Thanks, OK. Usually speciation happens by geographic isolation of a sub group. Could speciation in humans happen by choice? That is by ideological choice to breed only with fellow members of the sub group. I guess the sub group ideology could be anything, a physical trait, a psychological trait, a political position, etc..

 

[CraigDxHypo]

Can speciation in nonhumans happen by choice?

Could speciation in humans happen by choice?

I find this a complicated question because of its use of the term “choice” qualified by “human”, which in the context I read it is a psychological and philosophical one.

The question seems easier when applied to nonhuman species, such as those in the cat family. For example, in captivity, the 4 main species of the panthera genus (lion, tiger, jaguar, leopard) can be cross-bred easily, producing offspring that are not obviously less fit than their parents, being fertile and in some cases larger and stronger than either parent, but occur rarely, possibly never, in the wild, even when the species’ habitats overlap. In the wild, these species, which are capable of cross breeding, “chose” not to. They don’t cross socialize, either.

The panthera species’ last common ancestor is believed to have lived about 6,370,000 years ago, showing that these species “speciated”. In some cases, geographic separation was likely the dominant factor in this, but assuming their habitats overlapped as they do today, “choice” was arguably a factor, also.

The last common ancestor of the species of the hominidae family (great apes, including humans) is believed to have lived 4,000,000 to 8,000,000 years ago. Perhaps “choice” was a factor in this speciation.

That is by ideological choice to breed only with fellow members of the sub group. I guess the sub group ideology could be anything, a physical trait, a psychological trait, a political position, etc..

Speciation in animals like cats and humans takes many 100,000s of years. I find it hard to imagine an ideological prohibition agains interracial breeding persisting that long. I don’t think there’s sound historically evidence that large populations of humans ever obeying such a prohibition – best current genetic data and analysis suggests to me that humans have never heeded “racial boundaries”, only geographical barriers. Whatever factors allow living panthera species to do so, and allowed hominidae species to do so 4,000,000 to 8,000,000 years ago, don’t appear to be present or effective in humans.

 

[256bits]

Thanks, OK. Usually speciation happens by geographic isolation of a sub group. Could speciation in humans happen by choice? That is by ideological choice to breed only with fellow members of the sub group. I guess the sub group ideology could be anything, a physical trait, a psychological trait, a political position, etc..

Does your question entail the DNA testing of the fetus or embryo and aborting if not to the parents liking? What if a particular trait became all the rage for a group of parents? If the offspring continued testing for the trait? Baring legalities, in a short term would not such choice result in said trait then becoming dominant?

 

[Borek]

I think the idea is unlikely - but not for biological reasons, but for socio-political ones. For the speciation you would need to wait for at least tens of generations, it seems quite unlikely that any group that is not geographically separated would be capable of maintaining their genetic isolation for long enough.

To some extent it was already tried in the past, in Egyptian pharaoh dynasties, but the group was too small so they suffered from the unwelcomed consequences of the interbreeding.

Also see http://news.usc.edu/52998/the-secret-life-of-fruit-flies/ - I guess social niche construction (SNC) is a nice term that can help in further research.

 

[Ygggdrasil]

Who's to say this didn't happen in the past? Extinct hominid subspecies such as Neanderthals and Denisovans are known to have lived in the same areas as modern humans and there is evidence for limited cross-breeding with these populations. However, they are quite morphologically and genetically distinct from modern humans. Perhaps "speciation by choice" is one reason why they were able to exist as separate species from modern humans.

 

[edpell]

Craig, thanks for the thought provoking reply. I am confused. I thought the definition of different species was two groups that can not breed and produce fertile offspring. You say all panthera can breed and produce fertile offspring. Does this make them sub-species rather than species? Is there a biology term for sub-species? Is this common, the ability to successfully breed between two groups that are commonly called species?

Your example answers my question if simple panthera can do it clearly hominids can do it. Curious this is never considered in early homo evolution, Australopithecus to Heidelbergensis.

 

[Borek]

Who's to say this didn't happen in the past? Extinct hominid subspecies such as Neanderthals and Denisovans are known to have lived in the same areas as modern humans and there is evidence for limited cross-breeding with these populations. However, they are quite morphologically and genetically distinct from modern humans. Perhaps "speciation by choice" is one reason why they were able to exist as separate species from modern humans.

Interesting point. It doesn't make me convinced though - they already started as separate subspecies.

Do we know for how long they coexisted? (I don't mean in general, I mean in a single place, occupying the same area.)

 

[ModusPwnd]

I guess that genetic engineering, cyborg cybernetics and general trans-humanism are too speculative for this forum and thread? I see all these as viable means of human speciation. But this is somewhere between accepted science and speculation.

 

[Monique]

I wonder if there are human syndromes with abnormal chromosomes that could be considered as the start of a new species? That the chromosomes would be unable to pair with an average human, but they would be able to with someone with the same chromosomal organization?

 

[Borek]

Craig, thanks for the thought provoking reply. I am confused. I thought the definition of different species was two groups that can not breed and produce fertile offspring.

As far as I am aware there is no definition of species that would work with everything nature throws at us. She is just way too creative for our attempts at classifying everything.

 

[Ygggdrasil]

Interesting point. It doesn't make me convinced though - they already started as separate subspecies.

Do we know for how long they coexisted? (I don't mean in general, I mean in a single place, occupying the same area.)

Yes, speciation could have originated from a different event such as geographic isolation, but mate choice may have played a role in maintaining the species boundary when the ancestors of modern humans spread from Africa into Neanderthal territories. It is uncertain how long they co-existed in the same regions (Wikipedia suggest several thousand years), so you are correct that we can only speculate about the role of mate choice in maintaining the species boundary.

I wonder to what extent interbreeding with modern humans contributed to the disappearance of Neanderthals. Researchers studying Darwin's finches in the Galapagos have noticed that certain species seem to be disappearing, but surprisingly these species aren't disappearing due to extinction: they're disappearing because they're hybridizing with other finch species. The process is essentially speciation in reverse where two seemingly separate species (or subspecies) mix together to form one species. Perhaps someone with a better knowledge of human evolution could shed some light on whether this hypothesis is a possible explanation for the extinction of Neanderthals.

 

[thorium1010]

two articles in phys.org regarding neanderthals -

http://phys.org/news/2014-05-dna-interaction-neanderthals-humans.html

http://phys.org/news/2014-04-neandertal-inferiority-early-modern-humans.html

 

[CharlesAZorn]

I celebrate all scientists discussing all sciences. Inter-disciplines will make our future. I dig physicist/biologists hybrids and I recommend interbreeding.

My answer is yes.

It comes down to the term. Speciation (Sad that the spell checker is not familiar with the word). And what circumstances allow it to happen. Not really a philosophical question because choice and free-will diversions are not relevant thought experiments here. It is the practical, specific idea of choice. One of biological opportunity to choose.

Choice is of available reproductive vectors (even those that might not lead to offspring, think a sexy sheep or a coconut on a deserted island... bad choices if trying to pass on genes but a cute primate...) and where we CHOOSE to put our efforts to procreate or specifically not.

Prejudice, geographic distance, and isolation, all can happen by choice or appear to circumscribe difference that allows divergent genetics that WILL eventually differ enough as to not enable reproduction. Bigotry and natural separation provide distance that leads to difference. If either involves a choice, given sufficient time, speciation happens.

We have plenty of examples of intermediary and newly differentiated species. Btw presently EVERY species is highly evolved and is a transitional, but at different points of divergence, convergence, or relative stability. Theoretically, highly isolated modern humans with sufficient time will be speciated. Should be calculable but the wild cards are, among other factors, complexity of base genome, relative to differing gestation periods (I use this in class as a referent) and closeness of Phylogeny (degree of match).

Another question would be is human perception (of difference) a choice, and of species that we now know are likely capable of choice, do (or what) circumstances allow them to do so? Domestication, selective breeding and caging do not typically allow choice even when capable. Neither does grand geographic separations nor entrenched ethnocentrism...

A few useful links for discussion and elucidation:

Speciation:
http://www.bbc.co.uk/bitesize/higher/biology/genetics_adaptation/natural_selection/revision/2/
http://www.tutorvista.com/content/biology/biology-iii/organic-evolution/speciation.php
http://en.wikipedia.org/wiki/Speciation

Phylogeny or Phylogenetics
http://www.nymphalidae.net/Phylogeny/Phylogeny.htm
http://arthropods.eugenes.org/species/
http://en.wikipedia.org/wiki/Phylogenetics
And to help us learn whilst chuckling:
http://vserver1.cscs.lsa.umich.edu/~crshalizi/weblog/477.html

 

[CraigDxHypo]

Definitions of "species", hybrids and hybrid speciation

I thought the definition of different species was two groups that can not breed and produce fertile offspring.

That definition, which has come to be known as the biological species concept (BSC), and associated with Ernst Mayr’s 1942 book Systematics and the Origin of Species, from the Viewpoint of a Zoologist, is a common and popular one, but I’d argue must be taken as general guidance rather than an absolute rule. A more general definition of “species” is “a useful category of biological organisms based on observed traits”, though this definition is to general to be very useful without additions. My point is that the consensus definition of a species is more a question of utility than of objective qualities, with different kinds of biologist finding it useful to defined species in different ways.

You say all panthera can breed and produce fertile offspring. Does this make them sub-species rather than species?

It’s interesting to see how Mayr, who was aware of this, resolved this apparent conflict between the BSC and captive breeding of different cat species. His response was that captive breeding removed reproductive barriers that occurred in the wild, so really wasn’t good data for forming biological concepts.

A problem with this response is that intra-genus cross-species breeding does occur in nature. A recent example is the confirmed cross-breeding of Ursus maritimus (polar bears) and U. arctos (grizzly bears), to produce “grolar bears” which appears to be becoming more common due to climate-change induced changes in polar bear behavior.

Is there a biology term for sub-species?

Yes, the one you use, sub-species. This is a case of the general scientific principle that if a term is useful in a well-defined context, people should be free to use it.

Is this common, the ability to successfully breed between two groups that are commonly called species?

Yes and no. The general term for it is hybridization. When it results in the formation of a distinct species, it’s termed hybrid speciation. hybrid speciation is “fairly common” in the plant kingdom, in the animal kingdom occurs “mostly” in insects, and less common among larger animals.

Hybrid speciation describes a speciation event, so arguably only occurs when a viable wild population of cross-breeds occurs. By this definition, ligers and tigons don’t pass, as they’re known only in captivity, while time will tell if grolar bears form a distinct population worthy of official recognition as a species. Canis rufus (red wolves) is accepted as distinct hybrid species of C. latrans (coyotes) and C. lupus (gray wolves). That speciation is believed to have occurred about 150,000 years ago. At least one dolphin species is believed to be a hybrid.

Our growing ability to quickly and inexpensively analyze DNA has greatly helped our understanding of hydrid speciation.

Your example answers my question if simple panthera can do it clearly hominids can do it. Curious this is never considered in early homo evolution, Australopithecus to Heidelbergensis.

Curiouser still, there are a few examples of captive cross-breeding within the wider hominidae family, of Chimpanzees and Bonobos (http://www.macroevolution.net/bonobo-chimpanzee-hybrids.html[/url ).

Curious to the point of weird, there’s no scientific consensus that humans can’t be cross-bred with other hominidae species, though chromosome differences suggest that such hybrids would likely be infertile. This wikipedia article is one of many entries into this weird science realm.

 

[Pythagorean]

The process is essentially speciation in reverse where two seemingly separate species (or subspecies) mix together to form one species.

I've always wondered why there's never convergence of the branches on the evolutionary tree to represent this.

 

[CharlesAZorn]

Homo Sapians, are continuing on one branch (for now). We only recently gathered more evidence to clarify that some ancestors crossed paths with Neanderthals (http://en.wikipedia.org/wiki/Neanderthal).

This evidence speaks to the "when" question and "to whom", not "if." Those who do not understand that the if is Yes are denialists. I digress.

It seems more of a question of opportunity and continuity of lines than relation. Still all could mix genes whither Neanderthals are referred to as Homo sapiens neanderthalensis or just Homo Neanderthalensis. It is not a question of better or worse because we could go back to any moment of branching (differentiation) and look at connected land masses, migration, love or war etc. that caused our ancestors to get busy with phylogenically similar, long-lost cousins and when it stopped (separated enough to cause a branching).

Homology is about continuity of diverging earlier lines and Analogy is about convergent lines with apparent traits that were not inherited.

The classic prejudicial trait for discussions that I use in class are Neanderthalensis-like, cranial ridges (a surface or phylogenic trait) used erroneously and prejudicially by popular culture and bigots alike. Observable traits are only the tip of the iceberg. Our genes being similar enough to allow procreation would be a rather grand or deep example of a non-surface trait (urp... THE example of all traits). The capacity to yield offspring is indisputable (i.e. babies). Genomes are as indisputable as pregnancy. Distorted to suggest inferiority (although we all have cranial ridges), only Europeans have residual Neanderthalensis genes. Evidentially we all emerged from the continent of Africa but evidently only some crossed paths with our estranged Neandethalensis cousins. The evidence amounts.

Who knew before science? Our getting busy ancestors in the moment.

Therefore convergence is not seen on branches because it takes science to return to those moments when we waved goodbye to our cousins eons (eras) ago.

(Lots of fun reading and clarification in this thread!)

I would like to hear more from Evolutionary Biologists on these issues.

 

[edwardr]

It certainly *could* happen, but it's much easier in theory than in the real world. The group(s) would need to be sufficiently isolated to minimize gene flow to a non-existent or bare level, and this would need to continue for tens of thousands, perhaps millions of years. And at what point would they become a sub-species? Or an entirely new species? That's a fuzzy boundary. It is possible the group's appearance could become markedly different despite sharing much genetic material. Consider, for example, the physical variation between human populations despite such little genetic variation.

Embracing the biological species concept, this theoretical group would be classified as another species when the potential for interbreeding becomes impractical or otherwise impossible. Considering that the myriad of cultural and physical variance between human populations doesn't really serve as a barrier today (or in modern history), this new species would probably need to be quite different to reach that point.

There would be challenges associated with this. For example, have a look at some of the research on genetic disorders within the Amish community:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3077314/

The path to speciation is not pretty.