|
Register | Sign In |
|
QuickSearch
EvC Forum active members: 65 (9162 total) |
| |
popoi | |
Total: 915,817 Year: 3,074/9,624 Month: 919/1,588 Week: 102/223 Day: 13/17 Hour: 0/0 |
Thread ▼ Details |
|
Thread Info
|
|
|
Author | Topic: Evolution of Humans even more complex than thought | |||||||||||||||||||
DBlevins Member (Idle past 3776 days) Posts: 652 From: Puyallup, WA. Joined: |
The evolution of human morphology had generally been thought to be one that was more straightforward, with the more gracile forms replacing the more robust forms, such as Neanderthals and the recently discovered Denisovians (with little to no hybridization). Re-analysis of the Iwo Eleru cranium along with other fossils found in the Congo, appears to indicate a more complex picture of human evolution, with archaic features retained among populations living more recently than previously believed.
Additional link to BBC News report for a quick review of the paper.
|
|||||||||||||||||||
Percy Member Posts: 22392 From: New Hampshire Joined: Member Rating: 5.3 |
Discoverers of new hominin fossils are a notoriously self-promoting group, often claiming their find is a direct human ancestor, and the most important one, too, so it's refreshing to see a group announce a discovery confirming what has actually been long believed by less attention-seeking hominin researchers, that despite the claims of all the extravagant self-promoters in the human origins field, our ancestry is likely a very complex bush. The new discovery may indicate that human evolution is more complex than we had evidence for, but not more complex than we thought.
--Percy
|
|||||||||||||||||||
DBlevins Member (Idle past 3776 days) Posts: 652 From: Puyallup, WA. Joined: |
It seemed to me that the dominant thoughts about Human evolution were that it was much more 'linear' and it hasn't been until recently that studies have shed some more light onto the complexity of our lineage. Certainly the biggest objection I had had with the identification of some individual hominin fossils as separate species has been the geologically recent bottleneck effect on our variation, which to my mind created a more narrow interpretation of what constituted H. Sapiens. With the inclusion of these recents finds, others in West Africa and the recent findings concerning hybridization among Neanderthals and Denisovians, it appears that there is a stronger multi-regional facet to the OOA hypothesis.
|
|||||||||||||||||||
RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi DBlevins, thanks.
The skull was compared with a modern and an 140,000 year old skull, all Homo sapiens, The older skull is comparable to the two Homo sapiens idaltu skulls found in Ethiopia that are ~160,000 years old. http://www.berkeley.edu/.../releases/2003/06/11_idaltu.shtml Interestingly, there is a link at the bottom of your page to discusses another pair of skull from Ethiopia that are now considered older than idaltu -- 196,000 years: BBC NEWS | Science/Nature | Age of ancient humans reassessed
quote: Again showing variation in the population. Enjoy.by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
|
|||||||||||||||||||
RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi again DBlevins,
It seemed to me that the dominant thoughts about Human evolution were that it was much more 'linear' and it hasn't been until recently that studies have shed some more light onto the complexity of our lineage. People like to think of species as linear, however when you look at subspecies and variations between populations, it is self evident (imho) that a bushier arrangement is appropriate, maybe even more of a weave when subspecies interbreed and produce hybrids. Personally I think there will always be an impetus to branch away from the parent lineage, particularly when new eco-systems are involved that cause variation on the selection process. Until such branching reaches speciation, the picture will be shrubby rather than linear.
Certainly the biggest objection I had had with the identification of some individual hominin fossils as separate species has been the geologically recent bottleneck effect on our variation, which to my mind created a more narrow interpretation of what constituted H. Sapiens. Because it happened during the time H.sapiens was already established as a species. Don't know how it affected the H.neanders (anyone know?) ...
With the inclusion of these recents finds, others in West Africa and the recent findings concerning hybridization among Neanderthals and Denisovians, it appears that there is a stronger multi-regional facet to the OOA hypothesis. Be careful here. Multi-regional, IIRC, was originally about H.sapiens arising independently in several locations (an aspect I have always had trouble with -- such a scenario should result in different species or subspecies not the same one), whereas what we have here is some rather limited hybridization between hominid populations. I would expect that many hybrid offspring may have been infertile, thus reducing the impact of such individuals on the overall populations. After all some mules are fertile and can produce offspring with horses and donkeys. Mule - Wikipedia
quote: So I would not be surprised to see similar small numbers of offspring from hybrids when the genetic divergence had almost reached isolation levels. Enjoyby our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
|
|||||||||||||||||||
DBlevins Member (Idle past 3776 days) Posts: 652 From: Puyallup, WA. Joined: |
People like to think of species as linear, however when you look at subspecies and variations between populations, it is self evident (imho) that a bushier arrangement is appropriate, maybe even more of a weave when subspecies interbreed and produce hybrids. I should have been more clear, but I was speaking of the literature and instruction. H. sapiens evolution was considered to be more 'linear' in the sense that it was thought that we evolved from one species, which evolved from a previous one, and so on. Few were advocating either hybridization or a multi-regional type gene flow. It has been a fairly recent development that hybridization and gene flow has been found to have occured during our evolution, and this recent paper helps 'bush' out our evolution from the stricter linear one.
Because it happened during the time H.sapiens was already established as a species. Don't know how it affected the H.neanders (anyone know?) ... Again, I should have been clearer. I used to be of the impression that the relatively small amount of morphological variation in humans today, was due to the recent development bottleneck. The greater variation in the DNA of previous populations (before the bottleneck) would have been reflected in their greater morphological variation as compared to us today, and these populations should have been thought of as belonging in our species.
Be careful here. Multi-regional, IIRC, was originally about H.sapiens arising independently in several locations (an aspect I have always had trouble with -- such a scenario should result in different species or subspecies not the same one) Which is NOT what I was taught in College, even in 1988. My understanding, and the textbook from that time that I still have, states that the Multiregional hypothesis posits that enough gene flow occured to allow the populations to evolve together, and NOT that they evolved independently.
I would expect that many hybrid offspring may have been infertile, thus reducing the impact of such individuals on the overall populations. After all some mules are fertile and can produce offspring with horses and donkeys. As far as H. sapiens is concerned, certainly that is a possibility, but I should point out an example that fits a bit closer to home, so to speak. From a 2001 article by Clifford Jolly:
Another source of phylogenetic uncertainty is the possibility of gene-flow by occasional hybridization between hominins belonging to ecologically and adaptively distinct species or even genera. Although the evidence is unsatisfactorily sparse, it suggests that among catarrhines generally, regardless of major chromosomal rearrangements, intersterility is roughly proportional to time since cladogenetic separation. On a papionin analogy, especially the crossability of Papio hamadryas with Macaca mulatta and Theropithecus gelada, crossing between extant hominine genera is unlikely to produce viable and fertile offspring, but any hominine species whose ancestries diverged less than 4 ma previously may well have been able to produce hybrid offspring that could, by backcrossing, introduce alien genes with the potential of spreading if advantageous. Selection against maladaptive traits would maintain adaptive complexes against occasional genetic infiltration, and the latter does not justify reducing the hybridizing forms to a conspecific or congeneric rank. Whether reticulation could explain apparent parallels in hominin dentition and brain size is uncertain, pending genetic investigation of these apparently complex traits. (my bold)
|
|||||||||||||||||||
RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi again DBlevins,
Which is NOT what I was taught in College, even in 1988. My understanding, and the textbook from that time that I still have, states that the Multiregional hypothesis posits that enough gene flow occured to allow the populations to evolve together, and NOT that they evolved independently. But that would still have problems generating a homogeneous species, rather than isolated subspecies or varieties that have a low or little interest in cross-mating. Personally, I just don't see it as one big hybrid zone. Now I could be wrong, and this may be the best explanation for races (which are essentially varieties) that I've seen. I look at the Greenish Warbler for an example of how I see it operating: Greenish warblers
quote:
There is a map of gene flow in human populations that looks similar to the Greenish Warbler in spreading out into different ecologies. Tracing Human History Through Genetic Mutations
quote: This image shows an OOA pattern for the main gene flow and diversification. It doesn't address the possibility that some of those genetic variations come from hybridization with other hominids.
Again, I should have been clearer. I used to be of the impression that the relatively small amount of morphological variation in humans today, was due to the recent development bottleneck. There is some evidence of this:
BBC - 404: Not Found
Go to the link near the bottom for
quote: And then page down to
quote: There is more information there about the possible causes. Enjoy.by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
|
|
|
Do Nothing Button
Copyright 2001-2023 by EvC Forum, All Rights Reserved
Version 4.2
Innovative software from Qwixotic © 2024