Extinction or Evolution?

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Discussion by: KrustyG

I apologize if this seems naive, but I was asked a question that appears to me to be kinda deep, but might just turn out to be a detail about terminology.

I had been discussing evolution with my son when he raised the question, did the common ancestor of humans and chimps and bonobos "really go extinct"?  I immediately understood his query, though he further clarified it by adding "…like the dodos did."  And I had to say, technically, "I don't know!"

Clearly, that common ancestor (or any of our evolutionary ancestors for that matter) is extinct in the sense that there are no longer living creatures of that species in existence today.  But did they technically "go extinct"?  It seems to me they survived – I'm living proof!

When I think of the tree or bush of life, I think of that common ancestor as a branching point, with humans evolving along one branch, and chimps and bonobos along another (perhaps I've got the ordering messed up or simplified, you get my point) – the species didn't die out per se, it diverged and evolved along different paths.  But when I think of the dodo, it's the end of a twig.  That's it, lopped off, no more of them, no more of their genes being directly passed on, the end of the line – it didn't evolve, it was snuffed out.  

The extinction of the dodo seems like a very different kind of thing than the extinction of a species with evolutionary descendants.  Our ancestors' genes are still "with us", the dodo left no ancestors, so they are not.  Extinction seems like a negative thing, like a failure to adapt to changing environment or to succumb to a given evolutionary pressure.  But our ancestors didn't succumb, they succeeded, and their descendants evolved and adapted and continue to successfully reproduce and thrive.  Am I just dealing with a terminological distinction for which there is a simple, technical nomenclature?  Are there really different words for these seemingly different things?  (If so please tell me!)  Perhaps it's as simple as 'evolution' versus 'extinction'?  Should we just say that whereas the dodo truly went "extinct", our ancestor species actually "evolved" (and maybe it's wrong to say they went extinct at all)?  Or is the difference more elusive than that…

I started rereading bits of The Selfish Gene and The Extended Phenotype for some guidance.  OK, I realized this tree image is perhaps too linear, and it might even be a tad group- or species-selectionist.  The gene-tree picture would be much more complicated, with gene lines looping in and out of organisms, like strands woven through individuals, through species.  And as the genes flow through time, species would look more like fluid rivers than solid tree trunks. And then the whole thing gets even more complex when extended phenotypic effects are introduced, with rivulets spilling over banks affecting other rivers' gene-flows!  That's one messy tree!

From this I envision (though am by no means certain) that from a gene's point of view, there might not be much difference at all between these seemingly very different types of species-level extinction.  (I don't know if the following points are in fact true of the dodo specifically, but) assuming that most of the genes of the dodo continue to exist in its cousin species (albeit in different configurations), then the gene lines passing through the dodo river might not look significantly different in (mathematical) character from the gene lines going through the river that was our common ancestor with chimps and bonobos.  From the gene point of view, the extinctions of individual species aren't necessarily causally connected to the ends of gene lines (any more than they are connected to the deaths of individuals), and so might not appear to be significant events in the 'life' of a gene at all, let alone appearing to be significantly different events.  (Barring mass extinctions, of course.)  That is, if bonobos and chimps share 99% of their DNA, then 99% of the genes don't care and don't even notice if one of those species goes extinct, for they continue into future generations via the genes in the successful cousin anyway.  The death of any one species doesn't really impact gene lines any more significantly than the death of an individual impacts the continuation of a species.

So back to my original query, is there really a difference between the two types of extinction? — is this just a species-centric way of asking a question that doesn't really have meaning at the gene-selection level of evolution?  Or am I just being misled by the group-selectionist fallacy instilled by the image of the tree?

It's been two weeks now, I still haven't answered my son.

28 COMMENTS

  1. Members of a species can breed fertile offspring with other members of the same species. Let’s say for some reason two populations become geographically separated, and become so different, they could no longer breed with each other. We now have two different species.
    There might be three species altogether, the original, branch A and branch B. When all animals capable with breeding with the original population are gone, we say it is extinct, even though many of its genes live on in branch A and B.

    It is quite amazing how many genes you share with nematode worms. Sharing genes is not a meaningful way to measure extinction.

  2. Clearly, that common ancestor (or any of our evolutionary ancestors for that matter) is extinct in the sense that there are no longer living creatures of that species in existence today. But did they technically “go extinct”? It seems to me they survived – I’m living proof!

    On the tree of life, parts which continue to grow and morph into new variations (with or without branching) are descendants of ancient ancestors. http://www.wellcometreeoflife.org/interactive/

    Branches which come to a dead-end show extinction of that particular species – although others of its relatives may live on.

    Phylogenetic tree diagrams show the ancestral origins of particular groupings (Animals, fungi, plants etc) or species of life forms.

  3. The issue has to be approached from the right perspective. You have two different lenses. The first is contemporary organisms and extinction. The Dodo went extinct at a point in time. It was no longer contemporary to its “peer” organisms — gone.

    The second lens is temporal. The bonobo – chimp common ancestor did not go extinct in contemporary terms, but rather, it went extinct is temporal terms. It is no longer here because it branched and changed.

    Here is a metaphor. Sanskrit (the language) is like the dodo. It is a “dead” language. Latin is like the bonobo – chimp common ancestor because it has given rise to all these other languages and even though it is no longer spoken, it is still present.

    Now,this is a bad metaphor for many many reasons. So I’ll try again….

    The many god system of religion employed by the ancient greeks is like the dodo… gone. Christianity is like the bonobo-chimp ancestor, the original has been usurped and bastardized out of recognition, but there are 40,000 or so offshoots…

    I don’t really like either of the metaphors and want to delete them, but I’d like to keep them published to see if other contributors can fix them for me.

    • In reply to #4 by crookedshoes:

      The issue has to be approached from the right perspective. You have two different lenses. The first is contemporary organisms and extinction. The Dodo went extinct at a point in time. It was no longer contemporary to its “peer” organisms — gone.

      The second lens is temporal. The bonobo – chimp…

      I’m not sure that Sanskrit could be compared to the Dodo ( I’m still trying to figure out the comparisons ), but I think using the development of languages is a really good metaphor to use when trying to illustrate evolution of living things.

      Sanskrit is the indoeuropean language that gradually evolved into modern European languages. A change of pronunciation here and meaning there (eg “g” and “c” or “t” and “d” ) and within a relatively short space of time they become mutually unintelligible. Languages faced physical barriers like the Carpathian Mountains and changed depending on the route they took. Russian has elements in common with Italian and German though they seem so different. US English is only slightly different to UK English so they haven’t completely divided in a way that would make them a different “species”.

      To my way of thinking, people who have great difficulty coming to grips with the reality of evolution by natural selection would benefit by looking at the similar process playied out in the area of language development.

      • The thing is, I knew when I was writing it that the language metaphor is a good one and I tried to pick one (like in my uninformed mind) sanskrit that I figured died. But, the metaphor breaks down because sanskrit did NOT go by way of the dodo, but rather (I think) all languages go by way of the bonobo-chimp ancestor….. ie, all languages lead to new languages. So, i tried to pick one that seemed to be a “dead end”… But, your greater knowledge on the subject shows why my metaphor (at least half of it) —- stinks.

        But, I do agree wholeheartedly with you that language development and history of language provides an excellent parallel to evolution.

        How was my religion metaphor???? Even worse, I am sure.

        In reply to #5 by Nitya:

        In reply to #4 by crookedshoes:

        The issue has to be approached from the right perspective. You have two different lenses. The first is contemporary organisms and extinction. The Dodo went extinct at a point in time. It was no longer contemporary to its “peer” organisms — gone.

        The second lens…

        • In reply to #6 by crookedshoes:

          The thing is, I knew when I was writing it that the language metaphor is a good one and I tried to pick one (like in my uninformed mind) sanskrit that I figured died. But, the metaphor breaks down because sanskrit did NOT go by way of the dodo, but rather (I think) all languages go by way of the bo…

          I think you’ve delivered a killer blow by bringing in the evolution of religion! I can’t detect any elements of Zeus worship carrying through to more ‘evolved’ types! Maybe I’m just not looking hard enough. I think you could comfortably draw a parallel of Zeus and his team with that of the dodo. Any systems that involve change and replication could fit the bill as an illustration when you think about it.

          When it comes to the evolution in the automotive industry, as expressed by Alan4Discussion, I tell my kids that the automatic gear change is more highly evolved than their manual types. They refuse to believe me and prefer their primitive cars.

          • In reply to #8 by Nitya:

            In reply to #6 by crookedshoes:

            I don’t know of any remnants of Zeus worship but we are now about five weeks from the big Saturnalia version 2. In April next year, Oestre’s rituals get their annual eggy outing. For that matter, in two day’s time Tiw is remembered, then in three Woden, four days’ Thor gets a look in (in more Romanised parts of Europe I think it’s the Gods Mars, Mercury etc).

          • In reply to #13 by steve_hopker:

            In reply to #8 by Nitya:

            In reply to #6 by crookedshoes:

            I don’t know of any remnants of Zeus worship but we are now about five weeks from the big Saturnalia version 2. In April next year, Oestre’s rituals get their annual eggy outing. For that matter, in two day’s time Tiw is remembered, then in…

            Ha ha! Touché !

        • In reply to #6 by crookedshoes:

          crookedshoes, your language analogy is perfectly fine. Languages can indeed die. When the last speaker dies, the language dies too. While it’s true that Sanskrit and Latin didn’t die because they evolved into ‘sub-species’ which are still spoken today, there are plenty of other languages that simply ran out of speakers. In fact there is a linguistic ‘extinction event’ going on right now because so many smaller tribal languages are losing ground to larger regional languages (English, Spanish, Indonesian, etc). This Wikipedia page lists several languages that have recently become extinct or are down to a single speaker.

          • Thank you for the clarification. I know the evolution side of the metaphor, but as you see, my knowledge of the linguistic side of it is pretty limited. One of the reasons i like it here is the diverse knowledge base possessed by the users. I lean on it often. This is the perfect example.

            In reply to #21 by Aquitania:

            In reply to #6 by crookedshoes:

            crookedshoes, your language analogy is perfectly fine. Languages can indeed die. When the last speaker dies, the language dies too. While it’s true that Sanskrit and Latin didn’t die because they evolved into ‘sub-species’ which are still spoken today, there are plen…

      • In reply to #5 by Nitya:

        In reply to #4 by crookedshoes:

        Sanskrit is the indoeuropean language that gradually evolved into modern European languages.

        Not quite.The common ancestor of the European languages is Proto-Indo-European. Sanskrit is a descendant of P-I-E, as are its younger sisters Greek and Latin. It´s still not a bad analogy: Sanskrit went extinct but some of its genes can still be traced in modern European languages, Latin evolved into the Romance languages, and Greek is still with us, it just adapted.
        >

        • In reply to #9 by Brian Fieldhouse:

          In reply to #5 by Nitya:

          In reply to #4 by crookedshoes:

          Sanskrit is the indoeuropean language that gradually evolved into modern European languages.

          Not quite.The common ancestor of the European languages is Proto-Indo-European. Sanskrit is a descendant of P-I-E, as are its younger sisters Greek…

          Thank you. This is what happens when you depend on a rather unreliable memory and don’t bother to check it first. I’m duly chastened.

    • In reply to #4 by crookedshoes:

      The second lens is temporal. The bonobo – chimp common ancestor did not go extinct in contemporary terms, but rather, it went extinct is temporal terms. It is no longer here because it branched and changed.

      Another analogy would be manufactures up-grading models over the years.

      The first of a new model car may be a three-speed automatic. The next year a four-speed diesel model with new upholstery and a better music system is introduced …. Then an estate version with roof bars, a six-speed manual gearbox, and reversing camera etc …. Next a soft-top sports model … . Mechanical evolutionary designs by modification!
      (..and all those veteran and vintage extinct models.)

  4. You (the OP) are correct — if there are decendents, then the species did not go extinct.

    Even if the descendents are radically different so as to be a distinct species from their ancestors, the one thing to consider is that as you trace back, there is not good place to put a “line” where one species starts and its predecessor species ends. There is no “end” to the ancestor species and beginning to the descendent species.

    It is possible that a species splits and one branch remains mostly the same while the other becomes quite different and the branch that stayed mostly the same might die out and go extinct. And if that branch was so similar to the ancestor species that we would consider them the same, then in some sense we might think of the ancestor species having gone extinct, but clearly the ancestors of a living species did not go extinct.

  5. I think there is a quantitative difference between species extinction and the fate of common ancestors. As you say, extinction is a bit like a tree losing a twig, but the the common ancestor is more like a twig growing into two surviving branches.

    Admittedly genes are more complex than twigs. Only half of my deceased father’s genes were passed to me. Different halves of his genes went to my two brothers but it seems very possible that some of his genes were never passed on. But maybe only 20% of his genes have not been inherited, compared to 100% of any dodo’s genes.

    Yet it would be more usual to say that my father had died, rather than become extinct. The same applies to the common ancestor of humans and bonobos.

  6. Well it is possible to say that your forbearers did go extinct. I’m sure much of the reproduction that took place was from similar species yet significantly different. Surely our evolution is owed to hybrids as well.

    • In reply to #16 by Pauly01:

      Well it is possible to say that your forbearers did go extinct. I’m sure much of the reproduction that took place was from similar species yet significantly different. Surely our evolution is owed to hybrids as well.

      No, it isn’t possible to say that your forebears went extinct, because extinction is specifically death without issue. If your forebears went extinct, it wouldn’t be possible for them to be your forebears and, by corollary, for you to exist.

      A semantic point, but an important one, and the source of some confusion.

  7. The answer is ‘no’.

    A thought experiment:

    Suppose that, at some time in the future, two populations of humans exist. They become reproductively isolated to the point that there is a genetic divergence (speciation). Which of the two populations will have the right to be called ‘human’?

    This is a simplification, of course, since ‘human’ is not a robust specific classification, but the point is, I hope, reasonably clear. Humans will not have become extinct, they will simply have diverged.

    This is precisely the issue that cladistics is designed to deal with. Every clade consists of a species and all its descendants. Thus, we are apes, we are monkeys, etc. AronRa summed it up beautifully in his ‘Turns Out, We Did Come From Monkeys’ video:

    http://www.youtube.com/watch?v=4A-dMqEbSk8

    On the subject of extinction generally, I like to make the point that extinction IS evolution, specifically a case of macroevolution, so loathed by the cretinist.

    Evolution is defined as variation in the frequencies of alleles, where an allele is a specific iteration of a given gene. Microevolution is defined as variations in the frequencies of alleles below species level, in a population of organisms. Macroevolution is defined as variations in the frequencies of alleles at or above species level, or in populations of populations. The easiest way to think about this is that evolutionary biologists study frequencies of alleles that are shared between two species so, for example, there are many genes that are shared between humans and chimpanzees, which is to say that humans and chimps carry exactly the same version of the gene.

    Another useful example is extinction, in which the frequency of all alleles in a species go from some to none.

    What the creationist is actually talking about here is something that would falsify evolutionary theory wholesale, namely a cat giving birth to a dog. This, of course, doesn’t happen. What does happen, though, is speciation, and in fact there is a beautiful example of extinction and speciation in a single event, namely an extinction event in a ring species. If a selection of sub-species in the middle of the ring go extinct, by a bolide impact, for example, and the remaining subspecies are no longer reproductively compatible, then we have an extinction event that is also a speciation event, both of which are correctly defined as macroevolution.

    Hope this helps.

  8. when taking individual organisms into account, virtually everything goes extinct. the ancestors of the great apes did not all go extinct but take any two (say humans and chimps) and there is a male ancestor and a female ancestor on each side who had many siblings and many cousins and even more peers that we would describe as being of the same species. Other than those 2 males and 2 females, the rest are extinct so yes, the species that you evolved from are to all intents and purposes extinct.

    of course it’s more complex in reality. those t males and 2 females never met, probably existed hundreds of thousands of years apart and there was no day when the chimp/human ancestors said “right let’s split into 2 groups and never interbreed” because it’s likely the true seperation took millions of years.

    taking the question genetically and it becomes far more complex. there’s no way of knowing which genes are extinct but all the genes replicating today have survived (albeit with shuffling and mutations) for 3.5 billion years and most of the genes in those extinct human/ape ancestors are still around today

  9. The OP question is largely a question of defining terms.
    The phenotype expression of species at a point on the time-line no longer exists, so along with the dead-end branches of the phylogenetic tree, could be said to be “extinct”. What is actually “extinct”, is a collection of its genes :- genes which are constantly being made extinct or disabled by natural selection as new ones take over in the gene-pool.
    (This is of course, a far from clear process, as some genes are recessive or switched off, so it may be only their expression, which is temporarily extinct – with later “throw-backs” still possible!)

  10. You did not mention the child’s age for which you are trying to formulate an answer. Most humans cannot imagine a time when they did not exist nor imagine a time when they will not exist – we possess the knowledge but not the imagination. So to a young growing mind these may seem to be ancestors who were here yesterday, but not here today. Not understanding the time element; thinking in billions, millions and thousands of years can baffle the best of us. Also we “share a common ancestor” and how much we share would be more technical than my uneducated mind can understand. A species would be extinct at the point in time it had no means of reproducing itself and our common ancestors are as extinct as the Dodo Bird. One thing is positive, science itself evolves and today’s conclusions may change as research progresses. I commend you for trying to find a truthful answer and your son for asking a perplexing question.

  11. The problem you face lies in the word extinction. The dodo was extinct by us but the common ancestor of humans and apes went extinct throughout time. The difference is in fact that you find genes of the common ancestor in apes and in humans whereas you will never find genes of dodos again in any other creature. The dodo will never become a common ancestor of other species, whereas humans and apes might become that for both of us are still here.
    But for the fact that there is no more living copy of the common ancestors of humans and apes and no more living copy of the dodo, both species are extinct.

  12. The problem you face lies in the word extinction. The dodo was extinct by us but the common ancestor of humans and apes went extinct throughout time. The difference is in fact that you find genes of the common ancestor in apes and in humans whereas you will never find genes of dodos again in any other creature. The dodo will never become a common ancestor of other species, whereas humans and apes might become that for both of us are still here.
    But for the fact that there is no more living copy of the common ancestors of humans and apes and no more living copy of the dodo, both species are extinct.

  13. Professor Dawkins points out in Chapter 7 of “The Greatest Show on Earth”, pp 190-200, that the concept of species only makes sense if all the ancestral forms connecting two individuals together have died, because each of them was the same species as its parents, all the way back to the most recent common ancestor. Jared Diamond, in “The Rise and Fall of the Third Chimpanzee”, argues that Homo and Pan are more closely related than the two species of gibbon that are put in one genus, so the chimpanzees ought to be Homo troglodytes and Homo paniscus;

  14. crookedshoes wrote, “I think you’ve delivered a killer blow by bringing in the evolution of religion! I can’t detect any elements of Zeus worship carrying through to more ‘evolved’ types!”

    I can’t think of a Zeus element either, but the fourth gospel has several “competitive” stories showing Jesus emulating Greek gods: Hermes, walking on water; Bacchus, turning water into wine; Hercules, going to the underworld and returning.

  15. To answer your question in very understanable form for you son: Think about cars … why we do not see first automobiles ie. from 1900s roaming in our streets? The answer is … well, we see them everyday! Except they are nowdays under brands like Ferrari, Lamborghini, Skoda, Volkswagen, GM etc. The first autmobiles are technically(design and specifications) not here anymore … but they are NOT extinct! They LIVE IN those brands … they transformed! In every Lamborghini ‘there is’ a car from 1900s! And the same goes for our evolution! We dont see our ancestors … our ancestors live in us … WE ARE OUR ANCESTORS!
    Hope i helped.

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