April 17, 2024

Your great exponential grandfather

P.Z. Myers and I first became acquainted with each other many years ago through a Usenet group called Talk.Origins.  My wife suggested that a couple of those all-but-forgotten articles should be revived and posted on my blog.  OK honey, whatever you say.  One of the two I would like to show is from the 4th of July 2002 that was awarded Post-of-the-Month.  Amusingly, my wife  found out after reading the post  that it had already been referenced just last year, right here on FtB, byStephen ” DarkSyde” Andrew of Zingularity, another Talk.Origins alumnus.  His article looks pretty good and even has an updated follow-up.   Here is the [edited/updated] original.


A few days ago, “Joe Cool”, [email address withheld] wrote the following;

>man, if you want to believe your great^100 grandpa was a rock, be my

>guest…but it’s STUPID!

Well yes, that would be pretty stupid. Clearly you don’t have an adequate grasp of either the actual concept of evolutionary ancestry or of the significant time factors involved. I think you need a whole lot more zeros as well as a more realistic ultimate original entity.

I figure at 20 years per generation, 100 generations of grandfathers would equate to twenty centuries. That means the grandpa you’re talking about was a contemporary of rabbi Yeshua bar Yosseff just 2,000 years ago. Not quite an adequate evolutionary time-scale and certainly far from the mark when talking about the origin of life on Earth. But even 100 years ago, 16 years per generation was more the norm, as it was with my grandparents and many of their ancestors. That would have put your great^100 grandpa in the time of another wildly exaggerated hero, King Arthur, the other “once and future king” in about the 5th century of the common era.

Increasing the multiple, your great^1,000 grandpa would have had even shorter generation gaps, being about 14 or 15 years apart on average. He would have been a Paleolithic nomad in about 13,000 BCE, just shortly before the foundation of the most ancient cities like Jericho and Damascus. He still would have been fully human and already a member of the only surviving human species, Homo sapiens.

Your great^10,000 grandpa would have been everyone else’s great grandpa too. (Everyone alive today that is) He would still have been definitely human and visibly different from his Neanderthal neighbors. Whether he would be considered Homo sapiens yet 140,000 years ago or still classified as Homo antecessor or heidelbergensis doesn’t really matter. All are still obviously people, albeit primitive.

Your great^100,000 grandpa might now be called Homo ergaster or erectus having lived some 1.3 million years ago. And his great^10,000 grandfathers would have been called Homo habilis or maybe rudolfensis. Any or all of them would have appeared to be a bit more ape-like than the most monkey-faced modern guy, but he still would have been definitely human, especially when compared to the other fully bipedal apes that were wandering around a million-and-a-half to a couple million years ago. If you were to put your erectine or habiline grandpa on a crowded pew in your church, he would have looked like an ape-man. But if you saw him amongst his natural neighbors, the paranthropines, you would have seen him as nothing less than a man. However, the generations would be shorter, now being something like 13 or 12 years apart on average.

Your great^1 million grandpa on the other hand is quite a leap away from Homo erectus. A lot can happen in 900,000 generations and the world was much different 10 million years ago. There were no definite humans yet, but there were other hominids even though none of them could walk on two legs for very long. There were creatures similar to modern gorillas, chimpanzees and orangutans, but they were different than the ones we have today. One of the orangutan relatives for example stood as much as 8 feet tall. The space between generations would have been only eight to ten years, and much less as time goes on in reverse.

At six or seven years between generations, your great^10 million grandpa would have been barely recognizable as a primate, looking almost as much like a squirrel-like sort of thing. He might have witnessed the demise of the dinosaurs, or he would have grown up in the harsh wasteland that was the wake of the KT impact for so many years. Now the generation gap really begins to close. For most of the Mesozoic era and a long time before that, the age difference between father and son would only be about a year.

Your great^100 million grandpa was a shrew-like mammal darting through the Jurassic underbrush 170 million years ago. The amniotic sacs his great^10,000 grandchildren were born in didn’t have quite the same integrity that his great^10,000 grandfather’s birth-sacs had. Although leathery and easily torn, they would still have been considered egg “shells” much like some snakes are born in today. This grandpa would have already been mammalian, but not yet placental.

Your great^1 billion grandpa would have lived under water along with everything else, including trilobites and some really alien beasties a few hundred million years ago, and at least a couple hundred million years before the first dinosaur. The generation gap is now a monthly rather than yearly division. But for most of the last half-billion years of our genealogy, that wasn’t the case. In 400 million years, your ancestors went from toothy swimming worms like conodonts and pikia and became crossopterygian fish and then tetrapoidal amphibians, synapsid “reptiles”, and even amniotic proto-mammalian cynodonts. But the generations before that were far less interesting.

The world of your great^10 billion grandfather wasn’t much different than that which was already described, although there were a lot fewer trilobites then. He wasn’t even a swimming worm yet. He would have been more like a roundworm, if he would have been considered a worm at all. He may have looked more like a jellyfish with a sense of direction. Before that, he may have been something even simpler, like a microbial sponge-nymph, but still definitely a metazoic animal, even if he wasn’t really a “he” in the sense of discernable gender anymore.

Your great^100 billion grand-whatever ancestor may not have even been an animal yet, but a kind of slime-mould, which is still a eukaryotic organism.

Your great^1 trillion ancestor would have been bacteria and your great^10 trillion ancestor would have been bacterial too, although we are no longer talking about anything recognizable as an exclusively evolutionary phylogeny. Instead your genealogy would be completely befuddled by an intractable mash-up of horizontal gene transfer and endosymbiosis, not really an ancestry at all.

Your great^100 trillion -um- predecessor may have been an even simpler replicative protein in an inhospitable world unrecognizable as Earth.  Now we’re no longer talking about evolution or endosymbiosis, but abiogenesis, another wholly different string of processes.  In any case, none of your lineage would ever have been rocks. Rocks tend not to reproduce for some reason and therefore cannot evolve.



I know elements of this tend to be confusing for a lot of people.  A decade ago, some of it confused me too.  So I intend to flesh out species-level classifications from a paleontological perspective in an up-coming lecture, either in Houston or at LSU, but neither date has yet been set.

37 thoughts on “Your great exponential grandfather

  1. Nice. I’m so glad you reposted this, because I didn’t see it the first time around, and it’s awesome. It’s a great way to make sense of the depth of evolutionary time.

  2. You’ve become an insprired teacher, aronra. I look forward to your articles and videos, and cheerfully direct people to them when I’m asked questions about evolution and science.

  3. Tangential:

    It seems as though everyone calculates generation lengths as though only firstborn children leave descendants. That’s pretty obviously an over-simplification, but how much difference does it make to generation lengths in hominids, apes, or earlier primates?

    I assume that any answer to this would involve guesswork, but it still seems worth trying. Otherwise we are implicitly assuming either that our average great-n-thousand grandmother had triplets or quadruplets, or that the death rate before sexual maturity from all causes, including hunger, predation, and disease, is effectively zero.

  4. This can’t possibly be true since the universe is only 6000 years old and all life was created in a single day. I have it on good authority from an old book of fables. I like the way the post handled this story, certainly shorter but not quite as interesting as Ancestor’s Tale. Abiogenesis is too big a word for Joe Cool and his co-fools to know.

  5. I’ve been a big fan of your on YouTube and am glad you have a space here at FTB. I am also glad you don’t post all that often, because I simply would not be able to keep up with it what with all my other obligations in life.

    However, if you do come to do a talk at LSU please make sure and put it as a separate post here on FTB as I would very much like to attend and hopefully meet you as well. I am in medical school down here in New Orleans and an avid commentar and occasional author at Science Based Medicine and Neurologica (well, I’ve never posted there but I do comment a lot).

    I also have a young man who is a freethinker and came under my tutelage as a result of my med school volunteer activities who is trapped in a community where he cannot come out as atheist nor talk about his love of science and evolution all that much who I would advice to come to your talk as well.

    Hopefully it happens.

    Best wishes and keep up the phenomenal work.

  6. Great post.

    The one tiny thing I’d criticise is the generation length for humans. You seem to have gone for the length of time to birth of first born. It might be better to go for length of time to birth of middle child. Going back through generations, there’s no guarantee that your ancestors were all firstborn, although going forwards it’s possible to count like that.

    For the past 400 years, at least, the average generation gap has been more than 30 years, not 20. Going back 10 generations from my middle child (born 1992), we get to ancestors born from 1630 to 1710. Say, 1670. That’s about 32 years per generation.

    Considering that modern human females are fertile from (approximately) 16 to 48, an average generation gap of 32 years is not surprising.

    1. Second this.

      I’d like to add, though, that two other effects (beyond length of time to first born != length of time to average child) might shift generation length upwards.

      One is the downward trend in the age of menarche, due to better nutrition it seems. So even if it’s true that women e.g. in the 17th century typically had their first child within a two or three years after it became physically possible, that may still have been closer to 20 than to 15. You’ll find a ton of papers on this through http://scholar.google.at/scholar?q=menarche+20th+century&btnG=&hl=de&as_sdt=0%2C5 – some claiming a decrease of as much as 2-3 months per decade over the 19th and earlier parts of the 20th centuries.

      Another possible confound is a positive effect on survival rates from older siblings reported in some of the anthropological literature in contemporary “primitive” societies. This implies that the average age at the time of birth of the mother of a person who lived to become your great^x-grandparent is higher even than the average age of the mother at the birth of a child, any child. You can start here: http://scholar.google.at/scholar?start=10&q=effect+of+siblings+on+survival+rates+allomothering&hl=de&as_sdt=0 or specific reviews here http://mitpdev.mit.edu/library/books/mitpress/0262033488/cache/chap2.pdf and here http://eprints.lse.ac.uk/21225/1/Who_keeps_children_alive_(LSERO).pdf

      On the other hand, many (most?) women did not survive till the end of their child-bearing age – maternal childbed mortality was rampant before modern medicine – so the average age at the birth of a child shouldn’t be asssumed as ((age at menarche)+(age at menopause))/2 but rather substantially below that even before we take into account declining fertility.

  7. Tangential humor

    Before that, he may have been something even simpler, like a microbial sponge-nymph…

    Now, I totally want to get into some kind of slanging match so that I can pronounce “Your grandma was a microbial sponge-nymph!”

  8. ” jellyfish with a sense of direction ” sounds like a great band name, as does “microbial sponge-nymph”. The latter is probably a bit sexier though.

  9. A well-versed takedown of a creationist strawman- precisely what I have come to know you for! 🙂

    My only comment is that a person with only a passing understanding of evolution might read this as a promulgation of the idea of direct ancestry, rather than the branching, nested hierarchies that are the cladograms of life.

  10. As Paul Durrant’s comment notes, your generation times appear to be way off. I’m eleven generations separated from my ancestor Constance Hopkins (born in 1606), giving an average generation time of 34 years.

    A Google search of the terms [average generation time humans] led me to this paper, “Generation time and effective population size in Polar Eskimos”: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2602656/ which reports a generation time of 27 years (maternal) to 32 years (paternal).

    You also state the generation time for an ancestor creature “similar to modern gorillas, chimpanzees and orangutans” as having a generation time of “only eight to ten years”. In contrast, the paper I just linked reports: “Next, we constructed the life tables for two wild chimpanzee populations and calculated the generation time. The maternal generation time is estimated to be 24 years in the Mahale population and 19 years in the Taï population.”

    Sorry, I don’t read your blog, I saw this post because Anne Hanna linked to it. It’s a cool idea for a thought experiment, but I was disappointed to see you making confident statements (as if they were fact) for numbers you seem to have very little support for. It’s frustrating behavior to deal with in any discussion, and especially so in scientific ones. Paying attention to evidence for things — distinguishing between guesswork and fact — is one important distinction between science and religion. But it’s an old post, you might’ve written it differently if you wrote it now.

    1. You wrote, ” Paying attention to evidence for things — distinguishing between guesswork and fact — is one important distinction between science and religion.”

      I agree with this statement, but your criticism is mostly based on guesswork. Had you done an exhaustive review of the relevant peer-reviewed literature, then you you could make “confident statements (as if they were fact) for numbers you seem to have very little support for” (Your support being a 10 minute Google search?)

      Perhaps a more thoughtful way to relay your criticism without violating your own premise of stating assertions as though they are facts, would be to ask Aronra if he’d being willing to share his research on how he calculated generations. Then you could offer your brief review as a hypothesis that his own calculations may not have been as precise as needed.

      1. Oh, and my accusation that you were doing guesswork of your own–I only meant that it appeared that you were “guessing” that Aronra did not have any research to back up his generational timeline calculations. I don’t know if you are right or not, but until Aronra tells us or until you have completed an exhaustive review of all relevant literature, it would appear that you are merely guessing.

      2. I have to admit, what you’ve written looks like an allergic reaction to any sort of criticism. I don’t have a lot of time these days, so I can’t continue a pointless protracted argument.

        Regarding your “10 minute Google search” criticism: because of my work (in whole genome interpretations), I’ve become an unusually efficient reader of scientific papers.

        The word “exhaustive” is an ill-defined criterion. (One translation attempt: “More than what you did already, because I don’t like your conclusion”?) The number in the literature I found was in close agreement with numbers from my own data and Paul Durrant’s; I had three consistent datapoints and concluded no further literature review was necessary. More extensive review would be warranted if sources disagreed.

        Indeed, I was *guessing*, and my language was consistent with this: I did not make a factual assertion, I stated that Aron Ra *seemed to* have no support for the generation time numbers. There is evidence supporting that suspicion — I find consistent numbers from three different sources (two family histories and the paper I cited: 32, 34, and 27-32), and these significantly differ from numbers given by Aron Ra (20 and 16).

        I do not believe my criticism was thoughtless, just not as polite as you might have wanted. I did try to temper it: the idea for the analysis is nice, and the post might’ve been written differently if it were written today.

        1. You ignored my point entirely. You wrote, “I was disappointed to see you making confident statements (as if they were fact) for numbers you seem to have very little support for.”

          You make the claim that Aronra “seem[s] to have very little support for” his numbers on calculating generations. My only criticism for you at that your limited search (even if you do have 3 points of data) does NOT validate your claim, it merely suggests you have a point worth considering. Indeed, you provided more data the Aronra to substantiate your point of view. However, you would either have to ASK him for his data which is simple enough or do an “exhaustive” review that would be exceedingly difficult, but it would then support your claim that he “seem[s] to have very little support.”

          I am by no means allergic to criticism, I depended on criticism to refine my views. I even appreciate your own critique of me, though I found it thin-skinned. I was simply trying to present a way for you to enhance your ability to discuss this issue in a meaningful way.

        2. I lied there, you didn’t ignore my point. I re-read the whole discussion, and I get your point. Your language was precise enough and ultimately I agree with you that it would have been good for Aronra to cite his data for his numbers. And I don’t think your criticism was thoughtless. I should have just wrote from the beginning, “Rather that speculating on whether or not Aronra can or cannot support his math; let’s ask him, “Can your provide us with the rationale and research your used to base your argument?”

          I apologize for the tit-for-tat nature of this discussion.

          1. Sorry I didn’t follow-up here for a while. Thanks for your second response, I appreciate it. Aron Ra never did respond, it seems.

            He wouldn’t be alone in erring with too short generation assumptions, although his numbers look more extreme than the error made by phylogeneticists / evolutionary scientists:


            (A coincidentally-timed news item.)

            In science we often need guesswork, but we need to be clear about when such guesses are being made (vs. based on evidence). I may have come off as unduly harsh because I’m sensitive to flaws in scientific reasoning: I’ve had to deal with inaccuracies or exaggerations in peer-reviewed literature while doing whole genome interpretations.

      3. I think the bottom line of Mad’s complaint here is that while the piece is good as an order of magnitude/back of the envelope type exposition of the depth of evolutionary time, it would be even better if the specific numbers used were carefully sourced and references provided, in order to make it as scientifically accurate as possible. I imagine that’s probably also a hell of a lot more work, but if Aron ends up making more extensive use of this piece in the future, it might be worth doing.

        1. Agreed, and well-said. I love blogging and the exchange of ideas, but it is so easy to misread/misinterpret that it is sometimes comical. I frequently have to remind myself of that cartoon that says, “Are you coming to bed?” “I can’t. Someone on the internet is wrong!”

  11. Some commenters are disputing the times between generations, but if the number of offspring are factored in, given the differences in siblings, variability in generations would seemingly be greater than what is predicted by looking at only the first born. I have a brother who is athletic, I’m a klutz. I have a brother who is well spoken and extroverted, I’m a somewhat tongue tied introvert. Another brother had a fantastic memory, I’m sort of pedestrian in that area. All this variability in one generation.

  12. Well, the Bible says your great^200 grandfather was some clay, so I guess the difference between science and religion’s view of origins is just degree and moistness.

  13. “Rocks tend not to reproduce for some reason and therefore cannot evolve.”

    Oh yeah mister smarty science pants? Then explain how my pet rock wound up with googly eyes and a tail. Or are you saying that that was “Intelligent Design”?

    (Also, if you throw it hard enough you can induce mitosis in most rocks. Though it seems to be an entirely degenerative process which leaves the “species” of rock totally extinct after just a few generations.)

    ((Holy crap! I didn’t intend to write this much, this was intended entirely as a gag comment, but after that last parenthetical statement a childhood full of elementary school geology came rushing back to me. I was reminded of the “life-cycle” of rocks. From Igneous to Sedimentary to Metamorphic and all points between. Rocks have a pretty exciting “sex” life on a geologic time scale. It seems that when you measure years in the billions that even non living things tend to change quite drastically from their initial state. Who knows? It’s possible, or even probable, that some of the minerals necessary for early abiogenesis were a product of that simple rock melting down. So your Grandfather^a-gajillion is totally a rock! Not only that but, barring panspermia, if you go back far enough all of the ingredients of life were just molten minerals that cooled into rocks. Also, even if you invoke panspermia, that “seeded” life had to come from somewhere and if we are assuming abiogenesis as the origin of life, then even if it didn’t quite happen that way on earth then wherever that life did come from it probably started out as a rock. Since I’m going way too Meta with this already I might as well just end this with “We are all made of stars.”))

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