Pharyngula

How we got here

It’s been 25 years since Gould’s Wonderful Life: The Burgess Shale and the Nature of History crystallized the debate over the importance of contingency in evolution, most famously illustrated by his metaphor of “replaying the tape of life”. If we could roll back the history of life on earth and restart it in the pre-Cambrian, would we see the same forms arise again? Would we have dinosaurs a few hundred million years later, and bipedal intelligent apes after a half billion years?

Gould’s answer was no — that the role of chance was too great, and because the forms of life do not represent optimum ideals built by perfectly plastic forms, but rather are kludges built atop limiting and enabling prior adaptations. Some people, like Simon Conway Morris, argue otherwise that there are ideal forms (including us bipedal anthropoids) upon which life will tend to converge. I favor Gould’s view rather strongly — it’s absurd to talk about evolution without an appreciation that all organisms are the product of history, and that what traits we have now are almost entirely contingent on what traits our ancestors had.

My favorite example of the error of limited thinking about adaptive ideal forms is a comparison of bony fish and squid. Both are fast swimming, active predators that are torpedo shaped in motion (physics constrains that!), but in detail everything is completely different. If the pre-Cambrian ancestor of all chordates were accidentally squashed, there is no reason to assume that the pre-Cambrian ancestor of all molluscs would then evolve a line of torpedo-shaped predators with brainy skull at the front and an undulating muscular body for propulsion. Why should they? They have a demonstrated capacity in our universe to evolve into torpedo-shaped predators with tentacles at the front and propulsion via a jet of water squirted out of a muscular mantle cavity.

The body plan of the ancestor dictates what capacities the descendant will have. There is no reason to assume that the world as we see it now was inevitable — that’s simply a failure of imagination and reason.

An article by Zach Zorich explores other examples of evolutionary contingency. Much of it is dedicated to that fascinatingly concrete example of actually being able to roll back the tape of life, the Lenski experiments, in which populations can be frozen and restarted at any time. In that case we seen on a molecular level that the evolution of specific biochemical problems is not inevitable at all, but depends entirely on the presence of prior mutations. History, and your parents, matter!

But I also like this example.

“Not everything is possible,” no matter the process, Wake explains. “Organisms evolve within the framework of their inherited traits.” Organisms can’t pass on mutations that kill them or prevent them from reproducing. In the case of Hydromantes salamanders, their ancestors had to overcome a serious limitation: To acquire their ballistic tongues they had to lose their lungs. That’s because their tongue partly derives from muscles that their predecessors instead used to pump air into the lungs. Now, that formerly small and weak muscle is much larger and stronger. It wraps like a spring around a tapered bone at the back of the mouth, and when the muscle squeezes, the bone generates the force that fires the tongue along with its bones out of the mouth. So, Hydromantes’ ancestor did not simply acquire a mutation and evolve a fast ballistic tongue. Instead, the adaptation followed a series of mutations that first enabled the creature to overcome its reliance on lungs for oxygen and buoyancy control. Each change was contingent on the one before it.

Chameleons, on the other hand, retain their lungs. Instead of re-tooling their lung anatomy, they have evolved a piece of collagen that allows them to catapult their tongues at prey. On the surface, salamander and chameleon tongues converge, but not upon closer inspection. It takes a chameleon 20 milliseconds to shoot its tongue at its prey, a positively glacial pace when compared to the Hydromantes’ five-millisecond firing time. Why are chameleons stuck hunting with such slow tongues? The answer is that they have encountered a kind of obstacle to convergent evolution. The chameleon’s tongue is fast enough to ensure their survival, but they lack the “framework of inherited traits” to evolve the salamanders’ deadlier ballistic anatomy. The chameleons have reached what biologists call an “adaptive peak.”

Before anyone says that ballistic tongues represent an example of convergence, too, I’ll agree…but with the caveat that this is an example of modifying extant traits in the tetrapod toolkit. Two vertebrates evolved ballistic tongues, because they share the trait of having tongues. Squid also have a high speed prey capture mechanism, only lacking tongues, they use a pair of arms.

As D’Arcy Wentworth Thompson put it, “Everything is the way it is because of how it got that way.” You can’t appreciate evolution unless you also recognize the path it takes…it’s all about the trajectory.

Comments

  1. #1 glenstein
    August 4, 2014

    Aren’t anteaters a pretty famous example of organisms converging upon an ideal form?

  2. #2 Bill
    August 4, 2014

    Wouldn’t you agree that the Conway Morris “ideal form” view is pretty well rejected by biologists in general?

  3. #3 Richard Dawkins
    August 6, 2014

    Why JESUS DIED ON THE CROSS
    It all started with lucifer aka satan
    who was so in love with himself he wanted more and more
    God already had made him second after christ
    but being second after christ drove him crazy
    he wanted moreee
    so he asked God to make him the equal of christ
    But God told him i cant do that
    God explained to him that their is a order to everything that he cant break
    lucifer was silent for a while and at first accepted Gods order
    but the more time passed on
    he convinced himself that he would rather die than remain second place for eternity
    so he chose in his own heart to rebel against God
    just because God wouldnt grant him equality with jesus
    he knew God would destroy him
    but out of anger against God he determined to take down as many angels as he could
    he determined to get back at God by convincing all of Gods other creations
    of Gods injustice
    so he began to play the victim in heaven
    he pretended like he cared for the angels and that he didnt wanth God to treat them unfairly
    he pretended that he was fighting for the rights of the angels
    and something happend
    the angels didnt know what side to chose
    lucifer aka satans biggest complaint against God was that he makes demmands from the angels
    but he is never welling to make a sacrfice
    satan said you give us all these laws to keep and we toil for you
    but you never do anything for anyone
    espically your son jesus
    DO YOU SEE WHERE THE SACRFICSE OF THE CROSS came into the picture
    1 third of the angels believed lucifer
    The lord jesus tried to convince satan to back down and in the beginning satan pretended to listen
    at one point satan knew he was wrong
    but he was to proud to back down from what he started
    and the thought of him being second place for all eternity came back in his mind
    so he chose to continue the rebellion
    satan wanted to go after all of Gods creations not just the angels
    but all of the other worlds besides ours that God created
    so much more than just our world was at stake
    satan wanted to break the order of everything God created
    a real physical violent war broke out in heaven
    when God determined to banish them
    satan and his angels faught
    but he wasnt stronger than the lord jesus and his angels
    God had a choice than
    destroy satan and his angels now
    but if God did that
    than everything satan started would have continued on untill everyone would have fallen for the lie
    and God would have to destroy all his creation
    so God said ill allow him to proove to the universe what he is really all about
    when satan saw this opportunity
    he went after us humans
    he said ill know
    if i can get humans to sin
    God will be forced to destroy them
    they will have no hope
    God will be stuck
    and ill make him look like a monster
    satan new Gods law that he can not break his order just like he couldnt break his order to put him as the equal of jesus
    so satan thought we humans would be doomed for eternity
    we would have no escap[e from him
    but he never imagined what God was welling to do
    satan never imagined God was welling to pay the price for our sins
    so the order can continue
    by jesus dying for us
    satan couldnt say God you broke your order you forgave them without the requirments you made
    which is blood for sin and death for sin
    so JESUS WENT TO THE CROSS to destroy all of satans plans
    jesus died so we wouldnt have to pay the price
    so we could have a chance to escape hell
    by jesus dying Gods order would not be broken, so satan couldnt say you broke your order thats what satan was after he wanted to force God to break his order so he can point and say no fair he made an exception for humans but not for us angels,
    jesus also prooved satan a liar
    remember what satan accused God of
    remember when he said you make no sacfices you just make demands
    jesus prooved that their is nothing God asks of us that he isnt welling to do himself
    so the main accusation satan made against God in heaven which practically decieved 1 third of the angels
    was destroyed when jesus gave the sacrficse
    The cross is Gods pure way of prooving his love for you
    than you will still be under the power of satan
    its his pure way of saving you without having to break his order
    and its his perfect way of destroying every accusation satan made against him
    but if you dont give yourself over to the truth that jesus did die for you
    under the sin which satan started in humans
    and in the end you will force God to keep the order
    and he will have to destroy your soiul on judgement day
    he doesnt wanth to do that he doesnt enjoy that
    but he will have to do that to everyone who is nt welling to accept the way hes made for us
    are you really oing to allow satan to conquer you to wave you around like a defeated trophy
    satan already lost when jesus died on the cross he prooved him to be a liar
    but now satan is after collecting tophies
    souls
    herod??? he didnt do much he didnt stop the lord jesus from doing what he came to do, not satan and all of his demons could stop the lord jesus, you should read what i wrote friend youll walk out a diffrent man you will understand why your here?
    dont give him that satisfaction save your soul in JESUS

  4. #4 SqueakyRat
    August 6, 2014

    Geez, RD, you were the fly on the wall, huh?

  5. #5 Richard Dawkins
    August 8, 2014

    Today’s Creation Moment
    The Heavens Declare the Glory of God
    Genesis 1:16
    “And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.” Astronomers who believe in evolution tell us that the stars formed when gas in a nebula began to gather due to gravity. Eventually, that gravity became strong enough to collapse the gas into a star. Astronomers who believe in creation point out that this is unlikely, if not impossible. As we all know, compressed gas wants to expand by moving to areas of lower pressure. A cloud of gas that was large enough to begin compressing under gravity would begin to rotate faster. Magnetic forces would also increase. The increase in pressure, magnetic forces and centrifugal forces would overcome the forces of gravity, preventing the formation of a star. At the same time, blue stars are common in the arms of the galaxies we can see. These stars are considered young because they burn their fuel so fast that they could only last a few million evolutionary years. On the evolutionary scale, they must have formed long after the Big Bang. The number of blue stars would then indicate to an evolutionist that star formation is common. Yet, as we have seen, the forces at work to form a star in this way make these stars either unlikely or younger than millions of years. Perhaps God created the blue stars to serve as a clear indicator to scientists that He created the stars fairly recently.
    Prayer:
    I thank You, Father, for the beauty of the created heavens. The very existence of the stars praises Your Name. Amen.

  6. #6 Davis
    August 9, 2014

    Twenty-five years since Wonderful Life? Yikes. I’m not a biologist, but Gould’s argument makes sense to me. I recently learned that Morris is a believer in Intelligent Design, too.

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