Could a isolated group of humans evolve into a different species?

[Ebenezer]

Say a large group of humans for whatever reason were trapped underground and for say a few generations survived in total darkness would they in time evolve into a different species? I ask because I hear on an episode of The Black List how a group of fish trapped in a cave yet survived becoming completely different in the process. I don't know if it's true but still it makes me wonder. Now hypothetically speaking could something similar happen to a group of human beings?

[Robittybob1]

Say a large group of humans for whatever reason were trapped underground and for say a few generations survived in total darkness would they in time evolve into a different species? I ask because I hear on an episode of The Black List how a group of fish trapped in a cave yet survived becoming completely different in the process. I don't know if it's true but still it makes me wonder. Now hypothetically speaking could something similar happen to a group of human beings?

I think the answer to that is yes, for the environment that these trapped organisms survive in is sufficiently different to the rest of us open air dwellers. It would take a bit more than a few generations though, in my guess it would need something in the order of 2-3 million years (you can do the calculations as to how many generations that might be).

[Delta1212]

I think the answer to that is yes, for the environment that these trapped organisms survive in is sufficiently different to the rest of us open air dwellers. It would take a bit more than a few generations though, in my guess it would need something in the order of 2-3 million years (you can do the calculations as to how many generations that might be).

It wouldn't take nearly that long for some pronounced differences with the rest of the human population to present themselves, but yes, it would certainly be more than a few generations. Tens to hundreds of thousands of years at least, depending on how extreme the selection pressures were, with tens being very lowball and the differences unlikely to be particularly extreme within that timeframe.

[Robittybob1]

It wouldn't take nearly that long for some pronounced differences with the rest of the human population to present themselves, but yes, it would certainly be more than a few generations. Tens to hundreds of thousands of years at least, depending on how extreme the selection pressures were, with tens being very lowball and the differences unlikely to be particularly extreme within that timeframe.

In tens of thousands of years you would get a different breed or subspecies but to get a true genetic difference that stopped interbreeding (species) I thought it would take a lot longer, that is why I started thinking in terms of millions of years.

With genetic engineering you could speed this up of course.

[CharonY]

Why would you think that the timeline is in the millions of years? Split between H. heidelbergensis and H. sapiens was about 130k years ago. H. heidelbergensis was around for sure for about 600k years up to 1.3 mio years.

[Arete]

The time it takes for speciation to occur is a function of generation time and population size.

 

Following isolation, it takes approximately 4 x the effective population size generations to approach a new genetic equilibrium in a given population http://www.jstor.org/stable/2460440?seq=10#page_scan_tab_contentsprovided that population isn't exceptionally small and thus subject to founder effects.

 

So using a humans as an example, population with an effective size of 1000 would take 4000 generations (~80,000 years) to be genetically distinct from the population it split from. Obviously, factors like migration, population growth, etc will affect this very rough estimate.

[Greg H.]

And humans are, by and large a very bad example - we tend to overcome our selection pressures, for the most part, either through technology or through cooperation..

 

For example, in a low light environment, most animals would evolve better low light vision. Humans might do that, but only if there was no way for us to produce artificial light, and if the selection pressures for better low light vision kept enough people from reproducing for the low light vision to become dominant in the genome.

 

Stature is another area that could be impacted. For a given horizontal length, a tunnel that is shorter veritically will require less time and energy to build, which would favor smaller statured people. But would we bother to build tunnels shorter, or would we just build them the same height anyway -and if we did build them shorter, would that really provide any real selection pressure?

 

At this point in our history, the argument could be made that, outside of a massive global catatrophe, humans have effective removed themselves from the process of natural selection, with the possible exceptions of disease resistance and gentic anomolies.

[CharonY]

 

For example, in a low light environment, most animals would evolve better low light vision. Humans might do that, but only if there was no way for us to produce artificial light, and if the selection pressures for better low light vision kept enough people from reproducing for the low light vision to become dominant in the genome.

 

I would be careful with that statement. Selection would favor traits that that would be able to survive in low-light, but it does not necessarily mean that any species would would suddenly obtain low light vision. Using human eyes as an example it is possible that over generations we would lose cones in favor of the more sensitive cones, at least in some groups. Other organisms may respond similarly. Or reduce reliance on vision completely. Traits arise mostly randomly and are then selected for, they do not rise in response (which may not what you imply but could be interpreted as such).

[Greg H.]

 

I would be careful with that statement. Selection would favor traits that that would be able to survive in low-light, but it does not necessarily mean that any species would would suddenly obtain low light vision. Using human eyes as an example it is possible that over generations we would lose cones in favor of the more sensitive cones, at least in some groups. Other organisms may respond similarly. Or reduce reliance on vision completely. Traits arise mostly randomly and are then selected for, they do not rise in response (which may not what you imply but could be interpreted as such).

You are correct, of course (artificial genetic engineering not withstanding), and it was not my intention to imply that. I was trying to point out that, even if the mutation did occur (or already existed within the population), it may not necessarily matter in the seleciton process because of our species predaliction for using technology to overcome obstacles that might otherwise prevent us from passing on our genes..

[CharonY]

Yes, though to some extent various other species will also have more or less selective pressure in any given condition, although I agree that for the most part they will not be as versatile. However, there are very resilient species out there that would shrug off conditions for which humans would need quite a bit of technology just to survive. And obviously all bets are off once we get down to bacteria.

[Robittybob1]

Why would you think that the timeline is in the millions of years? Split between H. heidelbergensis and H. sapiens was about 130k years ago. H. heidelbergensis was around for sure for about 600k years up to 1.3 mio years.

I did follow this a bit earlier but forgetting it as quick, but you'd have to consider whether they were competing species (side by side) or serial species (one type evolving into another over time but not competing). Neanderthals were thought to have interbred with Homo Sapiens so they weren't fully speciated in a way. Well that is my off the cuff non-expert view for what it is worth.

[CharonY]

Neanderthals and modern humans (and Denisovans) are considered their descendants. But obviously the transition would be gradual with some gene flow in the early stages of separation.

To put into perspective, common ancestor of humans, gorillas and chimpanzees are estimated to be around 6-8 million years ago. So unless there are some things that I am unaware of (which is quite possible as this is not my specialty), the initial estimate seems a bit like a random guess.

Edited February 10, 2015 by CharonY