Coyne vs. Shapiro

Jim Shapiro has been outlining his views on evolution over at the Huffington Post, including a posting entitled, What Is the Key to a Realistic Theory of Evolution?

Not surprisingly, Jerry Coyne does not like it and weighs in with a posting entitled, A colleague wrongfully disses modern evolutionary theory.

Let me focus on a key point of their disagreement.

Shapiro takes issue with the conventional notion that all of evolution has occurred gradually. He notes:

Darwin put it this way in Chapter 6: “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.”

And then cites examples of such cases:

Many genome changes at key stages of evolution have been neither small nor gradual.

[..]

Perhaps the most important evolutionary step of all took place at least one billion years ago, when two or more cells fused to produce the first “eukaryotic” cell having a defined nucleus. This nucleated cell was apparently the progenitor of all “higher” forms of life, including plants and animals. Such cell mergers are known as “symbiogenesis,” long championed as an evolutionary force by the recently deceased biologist, Lynn Margulis .

Coyne responds as follows:

We all know, thanks to Lynn Margulis, that the evolution of the eukaryotic cell involved two rapid evolutionary events: the acquisition of mitochondria via the ingestion of one bacterium by another cell, and, in plants, the origin of chloroplasts via a similar route. Centrioles (a group of microtubules involved in cell division) may have originated via symbiosis. And some species, like lichens, are actually a mixture of two distinct species—in the case of lichens, an alga (or cyanobacterium) and a fungus. That fusion probably happened quickly as well.

Margulis theorized that symbiosis was not only important in evolution, but ubiquitous, involved in nearly all cases of speciation and macroevolution. She was wrong. We know now that the rapid origin of new taxa by symbiosis, while critical for some evolutionary transformations, is rare. It can hardly be used to discount the notion that “Darwinian” evolution is usually gradual.

At this point, it becomes clear Coyne cannot follow the argument. Shapiro was not talking about the origin of mitochondria and chloroplasts. He was talking about the origin of Eukarya, where bacteria and archaea fused to generate the eukaryotic cell plan.

What’s more, Shapiro is not arguing that Margulis was right about symbiosis being behind all speciation. He is arguing that Darwin was wrong in insisting that all biological features were formed by numerous, successive, slight modifications. Coyne’s confusion leads him to think that by noting Margulis was wrong, Darwin was right.

We have an example where the most radical evolutionary transition of all time did not occur through numerous, successive, slight modifications – the eukaryotic cell. And even if Coyne is correct in noting that birds, mammals, whales, etc. arose entirely through numerous, successive, slight modifications, they could only do this because they were built from eukaryotic cells (there are no prokaryotic bird-like or mammal-like organisms). This means that Coyne’s fossil evidence, as evidence of gradualism, is of secondary concern. What is of primary concern is the origin of the cell type that made that evolution possible.

So when we turn to the origin of eukarya, we can ask if there is any evidence that such a transition would (or could) occur without symbiosis? Answer – none. Random mutations and natural selection alone would not have spawned the eukaryotic cell. We are on safe ground in insisting that symbiosis was a necessary step in evolving eukaryotes.

Then we need ask if this necessary step was a fluke, or whether it was something that was bound to happen. The “fluke” hypothesis makes no predictions and thus can always be maintained as someone’s metaphysical preference. The “bound to happen” hypothesis predicts that bacteria and archaea were endowed with preadaptations such that the emergence of euakarya was poised to happen. And there is a growing list of evidence that preadaptation was important in the appearance of the eukaryotic cell plan and its organelles.

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6 responses to “Coyne vs. Shapiro

  1. OK wait. With all due respect the actual endosymbiotic events (including for mitochondria and chloroplasts) may have been quick, however the transformation into the eukaryotic cell plan via accumulations of random mutations, would have been a more gradual process, ie numerous, succesive slight modifications.

    IOW the endosymbiotic events alone were not sufficient, other events had to follow to modify the host and the guests so that they all worked together as one.

  2. Joe,

    I did not say the symbiotic event was sufficient. I proposed it as necessary. Remember that front-loading does not substitute for RM & NS, it channels it.

    As for the adaptive events subsequent to the endosymbiotic unions, the problem there is that ‘gradual’ and ‘slight’ are subjective criteria. Back in the days of the modern synthesis, there was a more objective take on such concepts – the single point mutation. But more than that was likely to be involved. Anyway, I think a good case can be made that the subsequent molding was actually quite rapid. I’ll try to get to that.

  3. Mike,

    Happy Easter. I didn’t say you said the symbiotic event was sufficient. I was just trying to clarify what I was saying. Also it (endosymbiosis) is only necessary in a prokaryote-first world/ euks from proks world.

    But yes, I understand what you are saying with front-loading. It is similar to the way GAs/ GPs go about solving problems.

    And I also agree that with front-loading in a prok to euk world, the transition, after the symbiotic events, would be rapid, meaning there would be some progression with each subsequent generation.

  4. Michael:
    This is slightly off-topic, but I’m curious about your thoughts on this. If the nanotechnologists behind front-loading intended to front-load eukaryotes, why didn’t they just drop eukaryotes onto the early earth in the first place? Now, I myself have an answer to this. The organisms that are capable of surviving the most extreme environments are universally not eukaryotes AFAIK. Thus, it really wouldn’t make sense to place eukaryotes into an early, hostile earth. Still, I’m interested in your thoughts on this (possibly you’ve discussed this elsewhere).

  5. I know, I know- terraforming-> the prokaryotes “paved the way” and as soon as the terra was formed the nudge towards eukaryotes began.

  6. I hope I don’t get blasted for saying what I’m going to say. I think Shapiro is correct that via some symbiotic process two cells merged and voila! A eukaryotic cell. But that two cells could even do that. Come together in a harmonious manner such that the enveloping of one into the other would ‘work’ boggles my mind. For some things I have no problem with saying “add a bunch of time and anything can happen”. But this just leaves me so uneasy.

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