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Evidence for human evolution


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In reply to an earlier post on Jun 21, 2012, 6:10:33 PM PDT
Last edited by the author on Jun 21, 2012, 6:50:07 PM PDT
zato says:
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In reply to an earlier post on Jun 21, 2012, 6:16:52 PM PDT
zato says:
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In reply to an earlier post on Jun 21, 2012, 6:24:52 PM PDT
"Ok, Bill, so we are dealing with more than one lineage. So back to the OP: how do we know that there is more than one lineage? Or is it just speculation, a best guess?"

Phylogenetic systematics. It's a methodology that does not a priori assume evolution. Look it up,

In reply to an earlier post on Jun 21, 2012, 6:50:52 PM PDT
zato says:
I will. Thank you.

In reply to an earlier post on Jun 21, 2012, 7:16:25 PM PDT
Hi Christine. What makes you think that phylogenetic systematics does not assume evolution a priori?

In reply to an earlier post on Jun 21, 2012, 7:23:35 PM PDT
Because the idea is to enter various characters (morphological or molecular) into a matrix, and then an algorithm will sort them out as to plesoimorphic and synapomorphic and create the phylogeny independent of an a priori hypothesis.

Now, of course, in practice it's not that simple, and of course the selection and weighting of the characters may be biased by the a priori assumptions of the investigator. In that way, molecular data might be objective, but that then brings its own set of assumptions. I'm actually quite cynical about this, but I still think it has value if done by someone who knows what they're doing. And, it forces the author to produce a list of characters that can then be tested by other workers.

But, despite the inevitable imperfections of the process (as with all science) the goal is to produce a pattern independent of the evolutionary process, against which the process can be tested. It has lots of flaws, but it beats the grand old (white) man of science expressing their personal opinion as the word of authority.

In reply to an earlier post on Jun 21, 2012, 7:40:08 PM PDT
But it does assume that all the taxa are related as a result of evolution.

In reply to an earlier post on Jun 21, 2012, 8:29:32 PM PDT
Last edited by the author on Jun 21, 2012, 8:43:22 PM PDT
I am not a paleontologist or anthropologist, however it seems to me that the evidence of multiple lineages would include the presence of different species, perhaps in different places, at the same time. That is what is observed in the fossil record of hominids, isn't it?

Phylogenetic systematics tells us how the lineages are related, not whether they are different lineages or not.

In reply to an earlier post on Jun 22, 2012, 5:53:29 AM PDT
Not necessarily. The entire field of "transformed cladistics" in the 1980s was all about ordering organisms in nested hierarchies by the accumulation of synapomorphies. A phylogeny is simply a pattern, and if you are doing this by computer algorithm then the computer will sort out what is primitive and what is derived according to the distribution of characters.

I don't put absolute trust in all these methods, as do many, but the entire point of cladistics was to attempt to remove the evolutionary assumptions.

In reply to an earlier post on Jun 22, 2012, 5:57:23 AM PDT
"it seems to me that the evidence of multiple lineages would include the presence of different species, perhaps in different places, at the same time."

Yes. Just like we have multiple species of antelope living alongside each other in Africa today.

"Phylogenetic systematics tells us how the lineages are related, not whether they are different lineages or not. "

It does both. Within the African antelope there are a number of distinct lineages, formulated as tribes (e.g., Bovini, Tragelaphini, Alcelaphini, Hippotragini, etc.) Then, these different lineages can be sorted as to how they are related to each other. Bovini and Tragelaphini are related to each other (i.e. sister taxa), as are Alcelaphini and Hippotragini.

In reply to an earlier post on Jun 22, 2012, 6:16:26 AM PDT
Last edited by the author on Jun 22, 2012, 7:46:01 AM PDT
A nested hierarchy is simply a pattern, but to call it a phylogeny assumes that the pattern is the result of evolution.

In reply to an earlier post on Jun 22, 2012, 7:37:14 AM PDT
Last edited by the author on Jun 22, 2012, 11:22:32 AM PDT
Whether or not a phylogenetic analysis can be used to infer the number of lineages depends on how the data matrix is set up. If the OTUs (Operational Taxonomic Units, AKA the leaves on the tree) are taxa (i.e. not individuals but species or lineages), then the analysis can only tell you how these taxa are related. This is certainly true for modern "species tree" analyses using coalescent models and multiple gene trees. I recently did some of these myself. On the other hand, if OTUs are individuals, as is the case with phylogeographic analyses (I have also done a few of these recently), we might discover geographically isolated clades that suggest unique lineages. We might also find that individuals do not form monophyletic groups that are consistent with current taxonomy, which could suggest that the lineages (taxa) are not properly defined (although other interpretations are plausible, e.g. incomplete lineages sorting). If individuals of two previously described taxa are mixed within a well supported clade this might suggest that this is really only one lineage; however, it may also suggest recent hybridization. So I do agree that phylogenetic systematics can be used to help determine the number of lineages, however it depends on how the analysis is done and it is not necessarily true with all analyses.

With a few exceptions (see recent mitochondrial and nuclear DNA analyses of neanderthals by Paabo et al.), phylogenetic analyses of fossil hominids have a priori assumed (this assumption is reasonable and based on alpha taxonomy) that the described taxa are independent lineages, grouped these individuals a priori into their lineages, and then inferred the relationships between these lineages, not between individuals. If I am wrong about this please let me know.

I suppose that if two OTUs in the above analyses were sister taxa in a phylogeny and neither exhibited any autaopomorphies, then one might conclude that these are not different lineages. However, this begs the question of why the OTUs were previously diagnosed as different in the first place and whether those data were included in the phylogenetic analysis.

In reply to an earlier post on Jun 22, 2012, 3:22:09 PM PDT
Well, you clearly know more about me in this aspect, as my direct experience in systematics predated even PAUP. But I am not unfamiliar with the genre.

However, for hominid fossils (or, indeed almost every fossil lineage), where we don't have huge amounts of genetic data to play with, the analyses tend to be a little more simplistic. Morphology may be misleading, due to homoplasy, but at least there is some understanding of which features may be homoplastic, which is less true for genetic data.

I was defending phylogenetic systematics for the original notion that it could produce nested grouping independent of a specific (or indeed any) hypothesis of evolution. But that, of course, is somewhat ideological. Personally I think that the (moderated) subjective input from a scientist who understands the group in question is better than relying entirely on a sorting algorithm, but that's just me.

"(this assumption is reasonable and based on alpha taxonomy) that the described taxa are independent lineages, grouped these individuals a priori into their lineages, and then inferred the relationships between these lineages, not between individuals."

We are clearly using the term "lineage" in a different way here. You are using to mean a group of individuals that can be assigned into a single taxonomic grouping (i.e. a population or species). I mean a "lineage" to mean a sequence of related taxa. This may be the difference in word usage between your field and mine.

In reply to an earlier post on Jun 22, 2012, 5:55:59 PM PDT
I suspect you are correct. The term lineage is used rather differently in different fields of evolution. I mainly work in popgen and molecular phylogenetics. Cheers.

Posted on Jun 27, 2012, 12:03:27 PM PDT
zato,
If you want a good read on human evolution through all its stages try:

Lowly Origin: Where, When, and Why Our Ancestors First Stood Up

In reply to an earlier post on Jun 27, 2012, 12:12:26 PM PDT
Rev Otter says:
i think it's blindingly obvious that actually learning stuff is NOT what he wants. :)

In reply to an earlier post on Jun 27, 2012, 6:10:26 PM PDT
Banished says:
"it's that your past history makes myself and others who are familiar with your posts rather wary."

Once bitten, twice shy. I too immediately questioned the legitimacy of zato's question because of his past trolling.

In reply to an earlier post on Jun 27, 2012, 6:12:45 PM PDT
Banished says:
Nice post.

In reply to an earlier post on Jun 27, 2012, 9:29:59 PM PDT
Re OP: "How do we know that we aren't dealing with two or more chains of evolution, with all chains dying off except the one that evolved into the current human species?" Actually, the evidence is that there were in fact several chains, and H. sapiens is the only survivor of these -- probably having killed off at least some of the others.
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Discussion in:  Science forum
Participants:  17
Total posts:  69
Initial post:  Jun 13, 2012
Latest post:  Jun 27, 2012

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