Saturday, April 19, 2008
Friday, April 18, 2008
There has been limited support for this hypothesis, and most of the others, because so many hypotheses make the same predictions that one can rarely conclude that a particular factor is at play unless one ignores all the other possibilities (which seems to be the standard practice.)
This paper from Proc.Roy.Soc.B. takes an interesting new tack, looking not at whether males that are shorter lived than their mates are taking more risks, but rather at whether their short-livedness can be explained by increased mortality during the season of risk taking.
Here is the abstract:
Male excess mortality is widespread among mammals and frequently interpreted as a cost of sexually selected traits that enhance male reproductive success. Sex differences in the propensity to engage in risky behaviours are often invoked to explain the sex gap in survival. Here, we aim to isolate and quantify the survival consequences of two potentially risky male behavioural strategies in a small sexually monomorphic primate, the grey mouse lemur Microcebus murinus: (i) most females hibernate during a large part of the austral winter, whereas most males remain active and (ii) during the brief annual mating season males roam widely in search of receptive females. Using a 10-year capture–mark–recapture dataset from a population of M. murinus in Kirindy Forest, western Madagascar, we statistically modelled sex-specific seasonal survival probabilities. Surprisingly, we did not find any evidence for direct survival benefits of hibernation—winter survival did not differ between males and females. By contrast, during the breeding season males survived less well than females (sex gap: 16%). Consistent with the ‘risky male behaviour’ hypothesis, the period for lowered male survival was restricted to the short mating season. Thus, sex differences in survival in a promiscuous mammal can be substantial even in the absence of sexual dimorphism.
Wednesday, April 16, 2008
The first story was about an extremely bright 15 year old who sat down to read the science on global warming, decided she didn't believe humans were causing the change, and then set up a hugely popular website 'debunking' the climate change 'hysteria' and attacking the scientists who support it. She objects not only to their conclusions, but to their dismissal of those who make the arguments she makes.
The second was about the Pope, and his visit to the US. One of the main goals of this tour, and this pope, is the War on Relativism. The pope argues that in this modern era, people believe that there is no objective truth, that every viewpoint is equally valid, and therefore anyone can believe anything they want. He argues that if there is no objective truth, we are all lost in a swamp of uncertainty, and life is not only meaningless but unpleasant.
So the 15 year old thinks that anyone who looks at the evidence and makes up her mind should be taken seriously, and the Pope thinks we need to have one objective truth arbitrated by the Church. To my way of thinking, they are both wrong.
Science (as a process and a culture) is neither a free for all where every view is equally valid, nor a dictatorship where those in high status can pontificate and the 15 year olds have to listen. Science is, in the words of Ernst Mayr, "one long argument," but it is a highly organized argument. There are only certain ways one is permitted to advance one's viewpoint. One can present data, but one cannot engage in personal attacks (although Mayr himself was well known for questioning the intelligence of those who disagreed with him). One can criticize, or tear to shreds, the logic used by other scientists, but one cannot simply refuse to listen. One can question the motives of others, but then still has to look at their arguments. If evidence is legitimate, one has the responsibility to be open to being won over. Personal attacks like 'quack', 'pseudo-scientist', 'corporate whore' and so on are to be reserved for those who grossly violate these rules. The only way this argument ever reaches an endpoint is if everyone on one side is either won over or dies of old age. Even then, if someone thinks they have found new evidence that the world is in fact flat, they can reopen the argument. Science does not deliver absolute, unquestionable truths.
But while you can argue anything you want, if your argument does not meet certain standards, it, and you, will be dismissed out of hand. Your statements must be logical, consistent with and based on data and must demonstrate knowledge of and meaningful response to what has been said and written before. If you want to argue that the world is flat, you'd better have a good explanation for all those data that seem to suggest a spherical Earth. And how a flat Earth came into being, and tides, and cosmology, and so on and so forth. There is a strong scientific consensus on the basic shape of the Earth (although there are bulges and deviations from sphericallity that still need to be better understood), because there is overwhelming evidence from a wide range of disciplines. The same can be said for the reality of evolution, the Holocaust, global warming, and a variety of other topics where the argument continues despite being settled in the minds of almost all scholars.
Those who oppose the consensus view on these issues generally point out that science is not "majority rule." As an example, the great majority of geologists long thought that plate tectonics was a ridiculous idea, and if the majority had ruled, we would have rejected what is now a foundational (possibly even bed-rock?) concept of geology, geography and evolution. It is therefore important to address this objection, because while true, it is a straw man. No reasonable scientist believes that truth can be arrived at through a popular vote of experts. That is not how the long argument works.
The relevant fact is not that the vast majority of informed scientists now accept plate-tectonics, but rather that we had that argument, and the plate-tectonics skeptics were unable to explain the data. Skeptics were converted, or gradually modified their views, or retired, and the number of supporters increased. The heroes in this story, from my perspective, are not those who believe because their teachers told them so, but those who were open minded enough to carefully change their minds.
We now accept plate-tectonics because the skeptics, being good scientists, had no choice but to look at the evidence presented, and there was eventually no logical way to cling to the view that continents are too big to move. "Eventually" being several decades.
So maybe several decades from now, we will have rejected evolutionary theory, decided that the Holocaust was just a historical ploy by the Jews for sympathy in their bid for an Israeli state, and realized that the global climate is just naturally cycling? Possible, but not likely, for several reasons.
First, plate-tectonics was a new idea that opposed everything humans had always assumed about our world. It was a hard idea to wrap a mind around. Creationism is not a new, radical and difficult to comprehend idea (my niece is dating a creationist who says he believes it because it is easier to understand than evolution, and his family believes it). Nor is a naturally controlled climate, or anti-Semitism. The idea of plate-tectonics overcame a distinct disadvantage these other ideas don't have.
Second, plate-tectonics took so long to gain acceptance partially because it took that long for technology to improve enough to produce convincing data. But during those decades, data gradually accrued. These other ideas have been around for decades, or millennia, and during that time the evidence has increasingly pointed against them.
Third, there was no lobby or faith pushing plate tectonics. No one stood to get rich or win political points by arguing that the crust of the earth moves and changes. Quite the opposite. The same cannot be said for Ahmadinejad, Bush and Exxon-Mobil.
Finally, and most importantly, there never was a body of data showing that the continents had always been in their current locations. That was the null hypothesis. We have enormous bodies of data supporting the reality of evolution, the Holocaust and anthropogenic climate change. Those who argued for plate-tectonics did not have to ignore or misinterpret a similar body of data presented by the other side. Scientific creationists (pseudo-scientists), scholarly anti-Semites (quacks) and professional global warming deniers (corporate whores) have to do exactly that. The only way to advance their views within the rules of the scientific process is to take all that data, and show us why it is fake or misunderstood. It is because they can't do this that they are disrespected. (Let me here be entirely clear that these insults are not intended to include either the pope or the teenager, both of who are honest non-scientists.)
The argument cannot be won, so there will always be Flat-Earthers, Static-Plate-ers, Creationists, and deniers of the Holocaust and Global Warming. And those people have the right to their points of view. And we have the responsibility to look at any new evidence they produce, if it really is new and it really is relevant evidence. We don't have to pay attention to people who, for the 5 millionth time, argue that the human eye is irreducibly complex and therefore there is a God. They violate the rules of the argument both by ignoring what has already been said, and by foregoing logic, and thereby forfeit their right to be taken seriously.
So, all of that said, how would I reply to the young woman who doesn't believe in human caused climate change, and to the Pope? To her I would say, "It is great that you are getting into science, and you absolutely have the right to come to your own conclusions. Based on your statements, I believe you have misunderstood much of what you read, and been mislead by those with a financial interest in misleading the public. I encourage you to learn more about the conceptual fields on which the science rests." To the Pope I would say, "The days when the Catholic Church was the unquestionable arbiter of truth for western civilization are long gone. At no point in the foreseeable future will the Church, or any other entity, resume that role. I respectfully suggest you accept this and guide the church into a new and more constructive role."
Tuesday, April 08, 2008
Mutation, and the ability to repair it, are incredibly important drivers of evolution on just about every level.
Last month's PNAS has two cool articles on bdelloid (pronounced DELL-oyd) rotifers and their ability to repair mutations, which demonstrate this extremely well. Bdelloids are the group of rotifers that reproduce only asexually, unlike the Monogonont rotifers I study, which alternate between sex and asex. Asex doesn't allow natural selection to remove deleterious mutations nearly as effectively as does sex (i.e. Muller's ratchet), so most species that go asexual quickly build up an enormous mutational load and die out after some hundreds or thousands of generations. But bdelloids have apparently been happily asexual for billions of generations. So how have they avoided Muller's ratchet? By not allowing it to turn in the first place, apparently. One doesn't need natural selection to remove mutations if one can repair them one's self.
Bdelloids apparently are degenerate tetraploids, meaning instead of two copies of each chromosome, at some point in their evolutionary past they had four, but those four then diverged somewhat into two pairs. Still, this means they have four copies, on separate chromosomes, of most of their genes. And it appears they can use these four copies as templates to repair each other. If one copy might have a mutation, check it against the other three, find the differences and correct them.
The utility of of this system in the short term (on the time scale that natural selection functions) is demonstrated by two other super-powers of bdelloids. First, they can dry out completely, at any life stage, and when rehydrated will repair all the damage to their chromosomes and resume life where they left it. Second, they can continue reproducing at radiation levels five times higher than what most anything else can stand, because every time the radiation damages their DNA, they just fix it. Bdelloids don't need to worry about cancer, apparently.
So with all these advantages, why haven't bdelloids taken over the world? Why doesn't everything do the bdelloid? Presumably because there are disadvantages in other contexts. Bdelloidism removes mutations so effectively, it seems unlikely very much macro-evolution could take place. After all, the repair mechanisms remove pretty much all mutations, and have no way of knowing if that particular mutation would have been advantageous. Once a bdelloid, always a bdelloid. Bdelloids might also be slow on the micro-evolution side of things. If selective pressures shift, having genetic variation is essential to any sort of adaptive response. Mutations are the ultimate source of genetic variation, so if they are all repaired out of existence, it may be hard to adapt. Finally, I would guess (not knowing the details of the repair mechanism) it is physiologically expensive to do all that checking and repairing all the time.
Now I find myself wondering about the demography of bdelloids. Hmmmm.
Wednesday, April 02, 2008
This afternoon, I was considering the question of why we evolved to have our anus placed such that feces, after leaving the rectum, have ample opportunity to contact the surrounding skin, which then need to be cleaned. And then I began trying to imagine other places a human's digestive tract couple potentially end, and what the advantages and disadvantages would be. What would it be like, for instance if our genitals were behind, rather than in front of, our anuses. And, taking a comparative approach, I thought about what I know about the anal anatomy of other species, and how they clean themselves, or avoid the need to do so. And all in a purely intellectual context, without the slightest feelings of revulsion, shame or titillation. Yet somehow, I knew that one is expected to keep that sort of speculation to one self. Unless one is a biologist. And even so, I probably won't bring it up to my neighbor on the train tomorrow.