Were there multiple lineages from primate to human?

I’m responding to the original post without more than the briefest skim of the intervening comments, which is always a bit dangerous. If I’m off the mark, please disregard.

I went to your link from edge.org to see the context of Nowak’s comments, which I’ll copy here.

Important steps in evolution are robust. Multi-cellularity evolved at least ten times. There are several independent origins of eusociality. There were a number of lineages leading from primates to humans. If our ancestors would not have evolved language, somebody else would have.

If I could venture to interpret this paragraph, it seems what he meant was, “There are a number of primate lineages in the hominid group that were similar to but different from homo sapiens. If our ancestors had not evolved language, somebody else would have.” At least, that’s how I read it, and it seems consistent with the overall point of his paragraph about convergent evolution.

Does that help answer your question at all?

@AMWolfe:

He said, “were a number of lineages”, thus that multiple lineages existed; your interpretation is that they could have, leaving open that they may or may not have existed. Maybe he wrote inexactly, but that’s why I raised the question. As I read the posts above, the evidence supports only one.

I treated his point about language as separate. I’m dubious that humans complex level of language displaced other species’ development of relatively simpler languages, so I don’t know why other species did not much develop languages except for reasons independent of humans’ having done so. But that’s a topic not on point in this thread.

I suppose it’s possible that one primate species evolved into humanity and then killed off other primate species’ human offspring, so that if the first had not come into being another would have and then would have developed complex language, but the notion of killing off probably has no evidence now.

@Nick

Hi Nick,

I appreciate the effort and detail in your response and understand your reasoning. I however, am part of the “hard sciences” and in that context, if I put forward any serious model dealing with complex schemes, and argue that it lacks predictive capabilities because of the difficulties inherent in such a model, my model would be rejected by my peers. They (and I would agree) would simply say, you should not put forward work on such a model, as it is grounded on an inadequate theoretical understanding.

I will add that even if we take out the inability to make any prediction regarding the appearance of new species in any future (even if they fail to survive for a lengthy period), the thinking within the model related to past events and rise of new species would be suspect - even though a rational may be provided for the results of the modelling.

Thanks for your response.

@Nick

I understand what you are saying here… But in the Primate world… if you are going to discuss MULTIPLE lineages for HUMANS … I don’t think you can go particularly far. Here’s what I mean:

Do we think Humans could still reproduce with the Human/Gorilla common ancestor, if such a thing were to still be alive? Does anyone think the Human/Gorilla common ancestor would even be compatible with Homo Erectus?

I’m very very skeptical.

I just don’t think speaking about multiple Human lineages WITHIN the Primate family is a productive topic.

In contrast, thinking about multiple lineages WITHIN THE HUMAN family … (say, "Adam descendant groups vs. non-Adam descendant groups) is much more intersting.

@GJDS: For research, yes, you’re right, it would be rejected especially for immediate consensus and for crediting whoever came up with it even when a subsequent peer-reviewed study is partly grounded on it, but unless there’s a viable alternative explanation it would normally be on track for acceptance sooner or later, so questions are whether it’s logical and satisfies Occam’s razor and other tests; and there’s still room for intellectual experimentation, which scientists and other scholars often use for developing investigations and methods. That’s as far as my ideas can go, at least for now. I wasn’t proposing a specific model, just a reason for there being one; and, as noted, there could be multiple models until we know enough to rule all but one out. One debate about string physics, at least as of a few years ago, is on the lack of empirical confirmation (one critic said the physics Nobel Prize is not awarded without that), but at least the many highly-respected string-supportive physicists have somewhere to look to get that evidence, if it’s possible; the same principle applies for other disciplines.

@gbrooks9: No, I don’t think today’s human could reproduce even with the primate of 4.3 million years ago, because humans have evolved. (Empirically testing that probably won’t be possible for some years to come; we’d need to find enough DNA or chromosomes to be sure of identifying and combining the rare nondegraded parts and even then we’d have to ask whether what we found would recreate a primate with which a human of that time could healthily have reproduced.) I don’t know the speed of evolution such that even early humans could no longer have reproduced with those primates, although I guess it’s more than a couple of generations. I agree that humans eventually split into multiple lineages, maybe during their first generation, but I think there was one and only one “Adam” unless evolution in one sex happened more than once, and the consensus seems to be that it did not (much like where you said “I just don’t think speaking about multiple Human lineages WITHIN the Primate family is a productive topic”, other than that I think it productive to think about it even when concluding against a multiple there), thus only one “Adam” existed. (In other words, you referred to “non-Adam descendant groups” but apparently there weren’t any.) Add “Eve” and that “Adam” and “Eve” may never have met, there would be at most two human lineages, one traceable to “Eve” and one traceable to “Adam”, and if those two folks did meet maybe there was only one lineage, but not three or more, and that count continues through today. Counting more than that is based solely on later divisions within humanity, an importantly interesting topic but not the one I originally wondered about here, because of that quotation at the top.

The point I was hoping to get to relates to the title of this thread: “Multiple lineages FROM Primate TO Human” ???

This is a terrible abuse of the idea of Evolution. Evolution is not a MERGER of diverse lineages of life. It is quite the opposite.

Evolution frequently creates multiple DIVERGENCES …

No, I was not going in that direction at any time. I was wondering whether three humans evolved directly from nonhumans and the answer appears to be negative. Two, yes, one of each sex; three or more, no.

I recognized divergences, specifically up to two. After that, humans diverged from each other, although probably not to a degree we’d recognize as divergence into separate species.

I did not think a human is a primate made by committee. I did not think several primates got together in any way other than the ordinary sexual way to form a human. No, I was relying on traditional views of evolution to ask how many times it happened (and that was two, evidently).

I hope this clears things up.

You could edit the title of the thread… so that it read something more like this:

“How many dead-end humanid lineages were there?”

Or do you have a choice of words that better fits your thoughts?

I would not advocate that scientist cease to speculate, hypothesise and experiment according to their respective theoretical/paradigm settings - far from it. However, I and perhaps other scientists would object to speculation presented as confirmed hypothesis, or extend such speculation into other areas such as theology.

If I understand correctly what you are suggesting, this is not correct. Populations evolve - humans “became human” incrementally, over time, as the average characteristics of our lineage shifted to what we consider human. It’s like asking who the first two speakers of modern English were.

@gbrooks9: That’s a quite different question than I was asking or that (as far as I recall) got answered. This topic’s title was virtually extracted from the statement by a Harvard biology professor and it’s good enough for me. I’ll leave it as it is. Thanks.

@GJDS: We agree, except that I’d delete the “perhaps”.

@DennisVenema: I think I did leave plenty of room for uncertainty as to who among perhaps thousands of living beings were the particular ones who be called the first female human and the first male human, precisely because evolution is gradual and if we could time-travel to 4.3 million years ago we’d not be able to identify exactly between whom among certain individuals the dividing line between nonhuman and human lay. But that doesn’t change that, according to what was said above, the evidence is of only one lineage to male humanity and only one lineage to female humanity. If that’s incorrect and there’s evidence of two for either sex, where would I find out more about that? Granted that when the differences in a community are extremely tiny then multiple lineages of either sex are possible, I understand that we have no evidence of that, but evidence of only one lineage per sex. As to English, the comparison would be to a single first speaker, not two, as sex isn’t needed for a natural language’s evolution, but, likewise, I’m unaware that English evolved twice, more or less side by side, although if it did subsequent merger would be more feasible than in biology reproduction, as even today words are borrowed back and forth between idiolects.

How would any model deal with your idea? Just how would any scientific examination identify “average characteristics” and the required shifts in these? And how would a bottleneck serve such incremental changes which presumably require lengthy periods.

Using the analogy of language is simply incorrect.

Hi Nick,

I didn’t realize that you were the originator of this thread. I’ve now read it over in an attempt to see where you are coming from. You seem quite confused about how evolution works. Let me try help out:

[quote=“Nick, post:34, topic:4935”]
I think I did leave plenty of room for uncertainty as to who among perhaps thousands of living beings were the particular ones who be called the first female human and the first male human, precisely because evolution is gradual and if we could time-travel to 4.3 million years ago we’d not be able to identify exactly between whom among certain individuals the dividing line between nonhuman and human lay. [/quote]

Evolution is a population-level phenomenon - it doesn’t happen suddenly to individuals. There is no biological “first human” of either gender. There is a population of interbreeding hominins that never dips below about 10,000 (effective population size). Eventually we call this population “human” - but there is no clear means of demarcating when this transition took place biologically, since it takes place incrementally over time. Note well - everyone in this population is the same species. Similarly, there is no easy way to demarcate when the “first English speaker” comes on the scene. Languages, like populations, shift their average characteristics over time as a group of speakers.

“Mitochondrial Eve” and “Y chromosome Adam” merely happen to be everyone’s great-great…etc grandmother and grandfather. They were part of this population that never was smaller than 10,000. See here for more details if needed.

As for that statement by that professor - it’s his answer to “what he believes but cannot prove” as of 2005. He’s likely thinking that there was some interbreeding between humans and other hominins, such as Neanderthals (which later evidence bore out). We also interbred with Denisovans. You can read more about this here. In this sense, yes, there are multiple non-human lineages that were grafted into present-day humans - some modern day humans (including yours truly) have ancestors in other hominin species.

Every model out there already deals with exactly this issue - shifts in average characteristics within a population over time - because that is how evolution is known to work.

[quote=“GJDS, post:35, topic:4935, full:true”]

Just how would any scientific examination identify “average characteristics” and the required shifts in these? [/quote]

Evolution is all about measuring average characteristics of populations as they shift over time. Pick any trait of any population - if there is variation, you can describe this variation using statistics. Endocranial volume of hominin lineages over time would be one obvious example relevant to human ancestry.

[quote=“GJDS, post:35, topic:4935, full:true”]

And how would a bottleneck serve such incremental changes which presumably require lengthy periods. [/quote]

I’m not following you here. “Serve”? The “bottleneck” to 10,000 is just that - a bottleneck. It’s not thought to be especially important for our evolution. It merely reduces our genetic variation somewhat; more so for those who are not sub-Saharan Africans. But I don’t think I’m understanding your question here. Yes, incremental changes do require time to shift within populations - but when measured on geological timescales (i.e. using the fossil record) we can see “rapid” changes (i.e. on the order of tens to hundreds of thousands of years).

No, the language analogy is an excellent analogy for how populations shift their average characteristics over time. If you want to argue otherwise, you’ll have to make a case rather than just saying so.

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GJDS, as Casper and I have tried (in vain) to explain to you, the studies that look for the most recent common ancestor (MRCA) of humans (and postulates one within the last few thousand years) does not (and I repeat, does not) show that humans uniquely descend from that MRCA.

As a way of understanding this: my cousins and I share a MRCA in either of our common grandparents. But we, as a group, do not uniquely descend from them - we have many other ancestors. If we were to examine the genetic variation of me and my cousins, we would see the evidence that we descend from many ancestors, not merely our two MRCAs (our common grandparents). So too with humans as a whole. We may well have a MRCA in the last few thousand years - though those studies are models that, in my opinion, do not adequately address the fact that humans were widely dispersed into places like South America, Australia, and Micronesia several thousand years ago, but I digress.

I’m not meaning this rudely, but you simply do not understand those studies. Your other claims also reveal that you don’t have a working knowledge of how evolution studies, or population genetics, works. I’m not sure I can do better (on short notice) than what I’ve already written (at length) here at BioLogos, so I’ll refer you to that. Perhaps one of our more knowledgable commentators will have more time available to try and help you - if you are interested in being helped, that is.

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You seem to be confusing “making a challenging topic somewhat accessible to non-specialists while remaining true to the actual science” with “making nebulous generalizations.”

If you think I am in error on some technical matter, by all means, let’s have that discussion. You have not, however, pointed out where I am in error - except for your example above, which is based on your misunderstanding of MRCA studies. Do you have another example?

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Perhaps you might explain how these two sentences fit together then?

Let me see if I understand this correctly: you’re claiming that there is not good evidence for a link between genotype and phenotype? If this is what you are claiming, I’m frankly floored.

Yes, for neutral variation there won’t always be a connection - but in overall, genotype, through the process of development in a given environment, equals phenotype. This goes back all the way to Thomas Hunt Morgan in the 1910s, all the way through to the present day. You could do nothing but read papers that make this connection, convincingly, for the rest of your life and not run out of things to read - papers in Drosophila, c. elegans, mice, zebrafish, humans, etc etc.

Hopefully for the last time:

(a) various models have been mentioned, one of which accounts for the current population by assuming it commenced from a single male and female pair and a period of 6-10,000 years- and this model uses data that is historically accessible. I mentioned another model that commences with a bottleneck of a few thousand people and a time period of over 200,000 years. This shows different models produce different results, so how do we as scientists decide which is model is accurate, or which model is not accurate. I have answered this by showing you that models must be related to data as predictions, or be related to measurements - the best models do both.

(b) Both you and Casper failed to address this matter.

I am not producing sentences that you cannot fit together - you just make things up.

Your analogy with language is unsound - I have shown this by referring to languages that have undergone extensive changes, with languages that have not. You have failed to address this objection.

I think I have said all I need to.

And as we have pointed out to you many times, this is flat out wrong. The model does not commence with a single male and female pair. You are misunderstanding these studies. These studies look for evidence for a MRCA. That you cannot understand the difference indicates you do not understand the studies.

As Casper and I have explained to you, these studies are addressing completely different questions: one set is trying to determine Ne, the effective population size, of our lineage - which is about 10,000 individuals. The second set of studies is trying to estimate how recently modern humans share a common ancestor (i.e. find an MRCA for all humans). The MRCA, even if one is there within the last few thousand years, is one individual among the 10,000.

So, these studies are not addressing the same thing. Comparing these two groups of studies is thus comparing apples and oranges - or as Casper put it (perhaps in a European form of the idiom) comparing apples and pears. They are not addressing the same question.

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