The Origin of Copulation

The subject of sex can be challenging to write about, but when it’s in the news it can’t be avoided. We shall endeavor to maintain our customary high standards throughout this post.

The topic is sometimes raised by creationists, who assert that sex couldn’t have evolved. The first time we ran across that argument was at the Jack Chick website — see Jack Chick: Sex Is Evolution’s Nightmare. Then the same line was echoed by Answers in Genesis (AIG). Our post about that one was Answers in Genesis: Sex Didn’t Evolve. Here’s a quote from the AIG article:

Sexual reproduction is only possible when both sexes have fully functional reproductive organs at the same time. … How is it then possible that such different and complex organs, which fit one another in every morphological and physiological detail, could have evolved suddenly?

Now we’ve found an article at PhysOrg that, ah … touches on the subject: Sex? It all started 385 million years ago (w/ Video). As that title suggests, there’s a video you can watch if you click over to their article. Your Curmudgeon hasn’t seen it, so proceed at your own risk. Anyway, here are some excerpts from the article, with a bit of bold font added for emphasis:

It may not have been love as we know it, but around 385 million years ago, our very distant ancestors — armoured fish called placoderms — developed the art of intercourse. So suggest a team of evolutionary scientists, who point to the fossil of a placoderm species blessed with the name of Microbrachius dicki.

There’s some information about them at Wikipedia: Microbrachius, which briefly mentions the latest findings, but we’ll stay with PhysOrg. Let’s read on:

Measuring about eight centimetres (four inches) in length, M. dicki lived in habitats in modern-day Scotland — where the first specimen was found in 1888 — and in Estonia and China. Placoderms have previously been found to be the most primitive jawed animal — the earliest known vertebrate forerunner of humans.

Then it gets interesting:

But they now have an even more honoured place in the book of life.

Oh dear, here it comes:

Microbrachius is the first known species to copulate in order to carry out internal fertilisation, according to a paper published on Sunday in the journal Nature.

Here’s a link to that paper: Copulation in antiarch placoderms and the origin of gnathostome internal fertilization. PhysOrg continues:

Male fish had bony, L-shaped genital limbs called claspers which transferred sperm into the female, a more effective way of reproduction compared to spawning in the water, the study says. The females, for their part, developed small, paired bones with which they locked the male organs in place in order to copulate.

Egad, this is terribly graphic! Here’s more:

“‘Microbrachius’ means little arms, but scientists have been baffled for centuries by what these bony paired arms were actually there for,” said John Long, a professor of palaeontology at Flinders University in Adelaide, Australia. “We’ve solved this great mystery because they were there for mating, so that the male could position his claspers into the female genital area.”

Ah, the mystery has been solved. Moving along:

Covered with thick, bony plates covering the head and trunk, placoderms ruled the world’s oceans, rivers and lakes for around 70 million years. They were then were wiped out around 360 million years ago in a mysterious mass extinction.

Well, they had a good long run. Another excerpt:

The critters handed on features such as jaws, teeth and paired limbs that are seen today in reptiles, birds and mammals, including humans. If the new study is right, the “claspers,” over hundreds of millions of years, evolved into the penis.

There’s more in the PhysOrg article. They actually describe how the, ah, deed was done. We’ll let you discover that for yourself. It’s going to be interesting to see what the creationists say about this — other than I ain’t no kin to no placoderm! Maybe they won’t say anything at all.

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31 responses to “The Origin of Copulation

  1. Christine Janis

    “If the new study is right, the “claspers,” over hundreds of millions of years, evolved into the penis.”

    Er — no. Sorry about that. The penis is basically an internal organ (not something appended to the hind legs) that is not present in any bony fish or amphibian, and is of sufficiently different morphology among the major groups of amniotes (mammals, turtles, (most) lepidosaurs, and archosaurs) to imply independent evolution in these groups (plus is absent in the tuatara, basal member of the lepidosaurs).

    But there’s popular reporting for you. I bet the authors explained copiously to the press that placoderm pelvic claspers weren’t the same thing as the human penis at all.

  2. Christine Janis says: “The penis is basically an internal organ …”

    Actually — no, never mind.

  3. Christine Janis

    Yeah, yeah — primates are unusual in having a pendulous penis, rather than one that is usually retracted. Just think of a horse peeing and you’ll see what I mean. (I think it’s all because the primate body wall is higher up than in most mammals —- no space to retract it into.)

  4. Jim Thomerson

    It is interesting that most modern birds have lost the penis and depend on a “cloacal kiss” for sperm transfer.

  5. Christine, I get your point. This must explain how I had my cat Holly for two years without discovering that she is really Buddy Holly.

  6. Christine Janis, at least one of the journalists whose accounts I read (don’t remember which one–sorry) did acknowledge that placoderm claspers did not evolve into the modern penis, and stressed that internal fertilization in more recent lines of animals evolved independently.

  7. Did the male M. dicki pick up his mate at a sandbar? And then take her to the seabed? One thing for sure, though — they didn’t enjoy a smoke afterwards (although it’s said they drank like fish).

  8. retiredsciguy says: “Did the male M. dicki pick up his mate at a sandbar?”

    As an M. dicki would say: Get a grip on yourself.

  9. It’s likely that there was sexual reproduction before placoderms started getting it on. Consider spiders: males spiders have specialized appendages called pedipalps for depositing sperm
    http://en.wikipedia.org/wiki/Spider_anatomy#Reproductive_system

    Spiders are believed to have evolved in the Devonian period, (410 – 360 million years ago).

  10. Christine Janis

    @ Retired prof. Yes, I would have bet my house on this! “Scientific” reporters are often impossible to dissuade of nutty ideas —– for example, they cannot understand that an animal that is extinct wasn’t the “ancestor” of something around today — they see evolution as a strictly linear ladder of progress (much of what creationists claim to be “evolutionary science” is actually what is misstated by science reporters).

    @ Hideo Gump. The issue isn’t sexual reproduction in general (or even internal fertilization), it’s internal fertlization within our own lineage. I think that most eukaryotes have some form of sexual reproduction

  11. Diogenes Lamp

    So Christine, what did our penis (and clitoris) evolve from? And what is our most distant relative that has a penis (and clitoris) homologous to ours?

    I mean I know some penises are not really penises, same function but not a homologous structure, like the large penises on the duck and the barnacle, and sea cucumbers IIRC. So I’m excluding those.

    But I’m wondering jiw far out the homology goes. E.g. hyenas have a disgusting reproductive apparatus that I believe is homologous to ours, but monotremes just have a cloaca and I guess no penis. So is our penis (and clitoris) specific just to placental mammals? Or within the placentals, and if so, where did it evolve? Or in the common ancestor of placentals and marsupials, but not monotremes? I’m sexually confused.

  12. Diogenes Lamp

    And what anatomical structure were our penis (and clitoris) before they became what they are? Almost every anatomical structure used to be something else.

  13. Diogenes Lamp confesses: “I’m sexually confused.”

    That explains your politics.

  14. “Sexual reproduction is only possible when both sexes have fully functional reproductive organs at the same time. … How is it then possible that such different and complex organs, which fit one another in every morphological and physiological detail, could have evolved suddenly”

    Whether you’re a “Rhoid” or an evolutionist 70 million years doesn’t seem so sudden to me. I would also think that AIG would be more concerned with where the knowledge of what to do with those suddenly evolved organs came from. I wish I owned an entire orchard of apple trees like that. Mikes “Hard” Cider indeed. And my only other question is being a guy of small stature at just over 5 ft. 5in. tall is that 8cm average length or girth. :-))

  15. Christine Janis

    Monotremes certainly have a penis (google “echidna penis” for a laugh), but it’s kept retracted within the cloaca most of the time and, unlike that of marsupials and placentals (but like all other amniotes) it is not used for urination, just sperm transmission.

    The four major groups of amniotes (see below) seem to have had an independent evolution of a penis. It may have evolved from cloacal folds (like one sees in some salamanders, and also in birds).

    INTEG. AND COMP. BIOL., 42:216–221 (2002)
    The Functional Morphology of Penile Erection: Tissue Designs for
    Increasing and Maintaining Stiffness
    D. A. KELLY

    Inflatable penises have evolved independently at least four times in amniotes, specifically in mammals, turtles, squamates, and the archosaurs. Males in these lineages therefore share the functional problem of building a penis out of soft and flexible tissues that can increase its flexural stiffness and resist bending during copulation. Research on penile erectile tissues in mammals and turtles shows that these two taxa have convergently evolved an axial orthogonal array of collagen fibers to reinforce the penis during
    erection and copulation; in both lineages, the collagen fibers in the array are crimped and folded in the flaccid penis. Collagen fiber straightening during erection increases the stiffness of the tissue and allows changes in penile radius that increase its second moment of area: both of these changes increase the flexural stiffness of the penis as a whole. And once erect, axial orthogonal arrays have the highest flexural stiffness of any fiber arrangement. The high degree of anatomical convergence (to the level of microanatomical features) within mammals and turtles suggests that the stiffness requirements for copulation produce an extremely restrictive selective regime in organisms that evolve inflatable penises.

  16. @Christine. You wrote “. The issue isn’t sexual reproduction in general…”
    That may be your issue, but notice the very first sentence of the quote from the AIG article: “”Sexual reproduction is only possible when both sexes have fully functional reproductive organs at the same time.”

    My point is that organs which permit copulation (as performed by mammals) could have evolved from more primitive organs of reproduction. Spiders are but one example of species with more primitive reproductive organs. Happy now? 🙂

  17. Christine Janis

    Seeing as spider taxonomy is largely based on the very intricate different “lock and key” mechanisms of the genitalia, I would say that their reproductive organs are anything but primitive. And, of course, irrelevant to the issue of the evolution of reproductive organs in vertebrates. You seem to be arguing via a type of “scala naturae” mode.

    And, of course, “reproductive organs” don’t necessarily mean structures that can be homologized (or even analogized) to a human penis, used for internal fertilization (rather than for reproduction in general). Unicellular eukaryotes have sexual reproduction, and one would be hard pressed to find a penis there.

  18. Fascinating Christine, thank you for the reference. But:

    Inflatable penises have evolved independently at least four times in amniotes, specifically in mammals, turtles, squamates, and the archosaurs.

    Did they forget about ducks?

    Wikipedia: Among bird species with a penis are paleognathes (tinamous and ratites),[3] Anatidae (ducks, geese and swans),[4] and a very few other species (including flamingoes[citation needed] and chickens[5]). A bird penis is different in structure from mammal penises, being an erectile expansion of the cloacal wall and being erected by lymph, not blood.[5] It is usually partially feathered and in some species features spines and brush-like filaments, and in flaccid state curls up inside the cloaca. The Argentine Blue-bill has the largest penis in relation to body size of all vertebrates; while usually about half the body size (20 cm), a specimen with a penis 42.5 cm long is documented.

  19. Christine Janis

    “Did they forget about ducks?”

    Nope: ducks are archosaurs. (So are crocoducks)

  20. 42CM?!! Wheretf was I when they were passing those out to birds of all things? HALF MY BODY LENGTH? I’d settle for 20 cm. I can’t afford new pants anyway.

  21. @Christine: You wrote, “You seem to be arguing via a type of “scala naturae” mode.” No, that is not at all what I am arguing (and that’s certainly not what I think). (BTW, I am neither a biologist nor an academic, so I’m neither attacking nor defending anyone’s professional reputation here). All I’m saying is that if a given creature has or had organ X, there is a high probability that one (or both) of its parents had organ X….
    as did its grandparents, great-grandparents, etc. (but with decreasing probability the further back one looks). That, and I believe that natural selection may, over time, favor offspring who have organ X, or have certain sizes/shapes/colors etc. of organ X. AFAIK this conforms to generally accepted scientific ideas about evolution.

    You also wrote, ‘they [‘Scientific” reporters] see evolution as a strictly linear ladder of progress.’ I don’t doubt that many folks (reporters or not) may have this misconception. But I doubt that you’ll find that view among the regulars in this forum.

    Finally, you wrote, ‘they cannot understand that an animal that is extinct wasn’t the “ancestor” of something around today.’ Could you clarify what you mean? Can we agree that Neanderthals are extinct? According to the good folks at 23AndMe, I have a smidge of Neanderthal DNA. So I believe I would be correct in saying that the now extinct Neanderthals are part of my ancestry.

    As I said, I’m neither a biologist nor an academic. I participate in these discussions for fun, and for occasional “enlightenment”. Emphasis on light 🙂

  22. winewithcats

    Has no one at AIG ever tried Tequila?

  23. only if snake water counts.

  24. Ceteris Paribus

    PhysOrg says:

    The females, for their part, developed small, paired bones with which they locked the male organs in place in order to copulate.

    Sounds kind of kinky for the ID to do that. But I suppose the ID hadn’t yet gotten around to designing ropes and hand cuffs.

  25. Doctor Stochastic

    But why did The Designer think it a good idea to run a sewer pipe through a recreational area?

  26. Christine Janis

    “But why did The Designer think it a good idea to run a sewer pipe through a recreational area?”

    Because there are only two major body outlets/inlets. You might as well ask “why did the Designer think it a good idea to run the snot disposal through the eating area”.

  27. Diogenes Lamp

    Christine, that’s a bug, not a feature.

  28. Christine Janis

    Not so sure. Bilaterians all have a “through gut”, which does the job of intake and outlet, but a possible bonus is that there are not too many entry points for pathogens. How would one evolve (rather than design) other points of entry and exit? Not so tough in the head area, where we have the remnants of gill slits in development (so can have things like the spiracle = eustachian tube + middle ear as an alternative route), but how would a completely separate exit at the nether end evolve?

    I say prove of evolution rather than “intelligent” design.

  29. ” Why resort to contrivance, where power is omnipotent? Contrivance, by its very definition and nature, is the refuge of imperfection. To have recourse to expedients, implies difficulty, impediment, restraint, defect of power.”
    William Paley, Natural Theology page 39

    To be fair, Paley raises this question only to state his answer to it. I am quoting him not by way of suggesting that he agreed. Here is, in brief, Paley’s answer:

    “…God prescribes limits to his power, that … God thereby exhibits demonstrations of his wisdom.” Page 41

    I recommend that one read the whole context.

  30. Sorry, that should be “exhibit”, not “exhibits”.