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Author | Topic: One evolving species vs speciation. | |||||||||||||||||||||||
jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
I see a lot of discussion here at EvC that seems to revolve around looking at critters two different ways. I believe an example can be seen in this post.
As an admittedly somewhat uneducated lay person looking at a great big pile of data and trying to make some sense out of it, it appears to me that when we look at the fossil record we see two different things going on. The first is that critters evolve, and over periods of time separated sufficiently from one another there will be enough of a difference between two critters to call them different species. However, if we could look at all the intervening steps, it would likely be difficult to tell much difference between adjacent critters. This is due to the selective filtering of traits across a population. Gradually some trait is added or subtracted from the population as a whole. In that case, it is only when looking at samples separated by long periods of time that the changes are significant enough to say, "These are different species." A second method is one species splitting into two species. The most common example of this is when a population becomes geographically separated into two or more isolated groups. In this case each group evolves slightly differently and we find a point in the record where we see two or more related yet unique species, both existing concurrently. In the former case we see but one species at any given point in the record, but multiple species when examined over longer periods of time, each species occupying an ordered position along the timeline. In the later we see one species at one point in the timeline but multiple species at a more recent point. (It can also go in reverse where we see a division and then one or more of the daughter populations disappearing) When it comes to humans, it seems to me that when looking forward down the path of Human evolution, we will only see the former until we leave earth and colonize other worlds or possibly (and I give this a very low probability) unless there is a major catastrophic event. Is there a reasonable scenario for Humans to become split and isolated over a period of time long enough to result in two separate species other than our moving off world? Edited by jar, : fix awkward sentence Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
Is there a catastrophe you can imagine that would keep the populations separated long enough for speciation to occur?
Would some other factors need to be thrown in such as increased radiation levels? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
It doesn't have to be an extraterrestrial "dinosaur killer" of course, or a global nuclear war. A nice airborne hypervirus could theoretically do the trick. The key is time IMHO. Could even a hypervirus keep populations apart long enough for speciation? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
Another factor that might be important when we consider H. sapiens is that our species seems to have something of a wanderlust. IOW, given that it appears there have been at least one and possibly two "out of Africa" migrations in our lineage, it strikes me as entirely possible that there wouldn't be sufficient time to allow isolation and natural selection to "do their thing" before gene flow between catastrophically isolated populations is re-established. Exactly. And we also have evidence that isolation of even tens of thousands of years is simply not enough; consider the dispersal of humans and the lack of "ring species".
The science here seems to be pretty soft, if you ask me. I'm not sure how realistic any of the above might be when you look at our species. It just might be that the only realistic scenario for human speciation would be the one where utterly different selection pressures operate on a totally or mostly isolated population for a really really long time (i.e., the "other planet" scenario). Agreed. Unless we incorporate some additional factors, I see no other possibilities. If though we reduced the ozone layer at the same time, so that we could incorporate isolation with increased radiation, then I think a likely scenario might be imagined. Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
So, to head back towards the question from the OP...
Is there a reasonable scenario for Humans to become split and isolated over a period of time long enough to result in two separate species other than our moving off world? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
But since we have examples of atleast two such scenarios, the original dispersal and whatever events led to the bottlenecks seen in the genetic record that did not lead to speciation, how reasonable is that?
The second consideration is that even in such a scenario, today there is the knowledge that there are other humans in other areas that would help drive attempts at travel. Edited by jar, : appalin spallin Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
Hoot Mon writes: Now I'm wondering if humans would even need to become split and isolated in order to speciate. Are you talking about what I described in the first example in the OP?
jar writes: The first is that critters evolve, and over periods of time separated sufficiently from one another there will be enough of a difference between two critters to call them different species. However, if we could look at all the intervening steps, it would likely be difficult to tell much difference between adjacent critters. This is due to the selective filtering of traits across a population. Gradually some trait is added or subtracted from the population as a whole. In that case, it is only when looking at samples separated by long periods of time that the changes are significant enough to say, "These are different species." Hoot Mon writes: Maybe our own genetic engineering will be how we eventually speciate. I can certainly see the technical possibility of something like that happening, either from the rich choosing some particular trait or from some despotic power imposing some trait. Speciation as policy or fad. Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
Folk, the thread is on Human speciation, not mosquitos.
Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
If you insist, then I insist that my scenario is pretty much the best one right now. Kill off 90% of the population of Earth. With the remaining 10%, kill off some more. Then split them in 2 groups. Keep them seperate in two entirely different environments for hundreds of thousands of years. Except your scenario contains no model or mechanism to keep the populations separated. Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
As you and WK both pointed out, it's a question of time. I agree with WK's speculation that re-acquiring technology from a "stone-age" start point might not take long enough for speciation to occur. Our species seems to have an amazing dispersal ability. Agreed. Re-Acquiring technology would certainly proceed faster than the initial acquisition, unless intentionally limited. So it looks like realistically, moving off planet will almost certainly lead to speciation simply because unless some major breakthrough is found, the separation will be very longterm. This would be less likely if the expansion was intrasolar, almost assured if it was extrasolar. Human speciation (into two concurrent species) seems unlikely. That leaves one possibility, and that is intentional speciation. How likely is that? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
Now THERE'S an interesting speculation. I assume you mean through genetic engineering of some kind? Homo superior has long been a favorite speculation of sci-fi authors. Or equally likely. Homo inferior. I can see three likely scenarios, Wealth, Despot, Religion. There might be others. Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
One question, even if we should leave earth, what might lead to speciation in an intra-solar colonization scenario?
The only one I have been able to think of would be if once one or more colonies were established, something happened (catastrophe or Chinese Great Withdrawal scenario) on the earth. Can anyone suggest anything else? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
In the example in Message 39 it would simply be natural speciation.
For example, considering intra-solar colonization, the separation would be on the order of going to a new country during the age of sail. Habitable planets in this solar system are all within a few months travel from each other. However, for many centuries even if they were self-sufficient, it is unlikely they would have the resources to build space craft independently. If if something happened on Earth that stopped space travel, either a catastrophe or some political decision as happened in China and led to their Great Withdrawal, is it likely the different human populations in the colonies would remain isolated long enough for speciation to happen? Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
This thread is on the issue of whether speciation of humans is likely and under what conditions.
Aslan is not a Tame Lion
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jar Member (Idle past 393 days) Posts: 34026 From: Texas!! Joined: |
What you have described seems more along the lines of lactose tolerance vs lactose intolerance. You have shown no model for why the two populations either could not mate or would not mate.
In order for human speciation to occur we would need isolation over an extended period. We know for a fact that historically, even human populations that have been separated for tens of thousands of years have not speciated. So what conditions might we reasonably see that would lead to humans evolving into two or more species? Aslan is not a Tame Lion
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