Were there multiple lineages from primate to human?

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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Likewise, a biological lineage may have allele exchange with other populations (or even other species).

If a population “continues with their language” are you saying that language will never change over time?

For example, Japanese is one of the more isolated languages, due to the period where Japan was largely culturally isolated from China and other neighbours. Japanese, however, changes considerably over this time period, as all languages do. Feel free to look it up.

@DennisVenema

Good description! The only notation I would add is that in this presumably seamless population over thousands or half a million years … if God wanted to identify the FIRST individual to qualify as a MORALLY RESPONSIBLE agent, it would certainly be consistent with our view of God to do so.

God, the author of morality, is in the driver seat on the topic of humans and morality.

As to the question of this FIRST MORAL HUMAN being the ancestor of all humanity … this kind of question has been pondered ever since the Bible tells the story that Cain moved away to marry and found a city. WHOM DID HE MARRY?

This is where I think Genesis loses its relevance. Is it trying to tell us a story about the man who is EVERYONE’s descendant?

Or is the Bible really telling us a story about the FIRST MORAL (or first Morally Responsible) Human? The FIRST is always important and memorable. People who then start trying to apply logic to Eve and Cain and all the rest … well, that’s pretty dubious in my view!

You are right. The Dutch version of the saying is “appels met peren vergelijken” and I translated it directly to English, wrongly.

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No worries, Casper - I can’t imagine having a technical conversation like this in another language!

Though apples and pears are much closer relatives than are apples and oranges. :slight_smile:

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Dennis, maybe we can reference an earlier post you wrote: Evolution Basics: Becoming Human, Part 1: Mitochondrial Eve and Y Chromosome Adam.

One can see similar things appearing in the Amish community with the currently prevalence of the surnames, “Miller”, “Stoltzfus”, “Yoder” and “Zook”. Family surnames were originally more equally distributed but not every family line produced men in the next generation. As a result, the number of surnames in the communities condensed to a few with high frequency. Eventually, only one surname will remain. This inevitable shift to fewer surnames occurs even while the population of Amish community hasn’t dropped a lot — Actually, I think their populations are increasing.

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Yes - the genetics can only illuminate the biology of the situation - which is why I am careful to use “biologically” when discussing human evolution over time. If God decided to single out an individual or couple for a special role, etc (as John Walton argues) that is not something science can detect.

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So what you’re saying is… between the English and Dutch versions of this expression, some things (“apples and”) stayed the same while other things changed radically (“oranges” vs. “pears”)?

Next thing you’ll be telling me this shift was just one of many small changes made by a whole population of speakers! :wink:

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Original poster here.

Any analogy can be problematic. If it’s disputed, try abstraction.

I leave theology to others.

@DennisVenema: I take your angle as correcting some of what I’ve said above, although I think we were closer than you thought. We agree, for example, that change was not sudden. Since everyone in the first 10,000 or more beings was human and change is incremental, then there’s no clear demarcation between them and the preceding number, perhaps 10,000, and with 10,000 as the minimum then some earlier beings may also have been human. I already acknowledged as much. I steered clear of what happened 200,000 years ago and the MRCA and asked instead about the beginning of all of humanity, 4.3 million years ago (i.e., the oldest or least recent common ancestry), and in that context I wrote of an in-between state for a time when nonhumans slowly evolved into humans; that roughly corresponds to what you wrote of hominins. It’s not likely that anyone in any lineage who first met the definition of “human” could have been identified as such at the time or distinguished from their nonhuman contemporaries and nonhuman parents (as opposed to great-. . .-grandparents, who are more easily distinguishable), because of the gradualness of evolution. There’s no nonarbitrary method of identifying the first humans (in any quantity) from their immediate ancestors, given as nonhumans. But that means that whoever we with hindsight were to deem the earliest humans would have been able to reproduce with the nonhumans who were less than a generation older (maybe a bit more), because the genetic similarity was so nearly complete that reproduction between what we might with hindsight only arbitrarily call separate species would have been possible. Pressures on a population could affect the offspring of a human mating with a nonhuman so as to create another nonhuman-to-human lineage within the same community; that is a correction from what I posited above and that is based on or extended from what I understand of what you wrote. I hope I haven’t misunderstood your summary.

However, the same seems likely to be true of, say, the evolutionary invention of eyes (not to mention whales, chameleons, et al.). Perhaps skin became sensitive to visible electromagnetic frequencies and transmitted what it sensed to the brain which applied it to further its owner’s survival; perhaps some areas of the skin became more light-sensitive than other areas of the same owner’s skin; perhaps a more-sensitive area developed means to protect itself leading eventually to eyelids; and so on. That, too, would have been gradual and the pressure leading to it would have been on a population, probably not 10,000 but probably more or less and probably not exactly one or exactly 40. Yet, as I understand this, scientists have identified 40 places on the evolutionary tree where eyes begin. I think what that means is that at each of the 40 a population of one species evolved eyes but reproduction (here assuming reproduction was sexual) between a light-sensitive individual and a light-insensitive individual could result in a light-insensitive individual who in turn might reproduce with a light-sensitive individual producing a light-sensitive descendant, resulting in two light-sensitive lineages for that species at one spot on the evolutionary tree, because the tree is shorthand for what we know and does not map every individual.

Assuming the same principles apply to all complex evolutionary steps, they’d also apply to humans, so if one early human male were to be identified as “Adam”, that would be arbitrary within a particular generation and community (bounded by available transportation, not necessarily on foot), as there could be other “Adam”-like humans, i.e., male humans born of nonhuman parents, but not enough evidence has been preserved to allow identifying a non-Adam human lineage. Absent that evidence, the shorthand is still useful, even as scholarly shorthand. Thus, as shorthand, there’s only one locus of nonhuman-to-human evolution: one locus defined as within an age range allowing members to reproduce with each other and with sufficient proximity to be considered for our purpose to contain one community.

It still appears that the first male humans did not have to come into existence at the same time or place as the first female humans, although humans of the two sexes would have had to meet in order to continue humanity by the time humans had evolved enough to prevent any more reproducing with nonhumans, and perhaps had to earlier.

Another argument favoring community reproduction rather than being by only two individuals starting humanity comes to mind, but it’s speculative: There’s a taboo now against relationships that result in inbreeding. I think some animals exhibit this, too. My speculation is that perhaps that taboo also existed 4-5 million years ago. If so, if conditions supported pro-human evolution then multiple evolution would have been likelier and many nonhumans might have given birth to humans, albeit only where and when those pro-human-evolution conditions prevailed and not elsewhere or at other times.

I gather that all of the other taxonomic categories of humans, such as Neandertal, evolved later and not directly from nonhumans, so they’re irrelevant to my question opening this topic.

That evidence does not support multiple evolution is something I got from, “while evolution can lead multiple times to similar solutions, this has not happened (yet?) for our own unique capacities”, according to this topic’s moderator, Casper_Hesp, and perhaps other passages, supra. But I acknowledge your point here.

It’s possible, I speculate, that our species has evolved in its few million years of existence. If we could clone and try to reproduce with a million-year-old human, we might be genetically different enough not to be able to reproduce. But we don’t notice that, although million-year-old DNA might exist and even be analyzable, if we haven’t seen evidence of branching of species from the modern human lineage. Branching is a strong reason to label separately.

@Argon: Family names are not as tightly bound to families as are genotypes. Family lineages sometimes change names and one family may have multiple sons. If you’re right about the future of the Amish, they may decide that differentiable names are important for family identity and social relationships and some families will either change family names or adopt another convention.

@AMWolfe: Linguistics is a different kind of field. Languages evolve, but some words are more stable than others. Place names, the name of an entire people who speaks a given language, and the words with the most frequency and distribution of use tend to be evolve more slowly or hardly at all. Written and spoken forms may evolve at different rates. Phrases and words may evolve at different rates.

@GJDS: Different disciplines may have different givens and different standards for sufficiency of evidence. Within a discipline, different groups of specialists can have different standards. At one time, two mathematicians disagreed on a point about infinity and one found himself unable to get his work published in the nation where they both lived, but eventually some of the work was published in another nation. While standards tend to converge, they don’t always, and good work may get done and recognized even without convergence.

@AMWolfe Evidently you need to spend a few more years studying linguistics…

@Nick There is this thing people do called ‘irony’…:grinning:

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