I am reading Matt Ridley's latest book "The Rational Optimist: How Prosperity Evolves." Ridley argues that humans developed a capacity for trade long before the advent of agriculture. It is in our nature. There is no tribe on earth that doesn't engage in trade and commerce. He says that it is incredibly patronizing to suggest that westerners have markets and commerce and that other people's just give each other gives to lubricate social cohesion. After almost a million years of gene culture co-evolution, humans can hardly survive without trading things and ideas. A great example of this was the Tasmanians. After 1000s of years of isolation they lost all of their technology till they had no better tools than Neanderthals. Ridley points out that the capacity for advanced technology lies in the collective brain, not in individuals. Without the ability to trade with their neighbors, Tasmanians could not tap this collective brain. As a result, their technology withered and dwindled.
I am only about a 4th of the way through so more to come. Cool stuff!
Monday, May 24, 2010
Sunday, May 16, 2010
What is the best evolutionary explanation for the existence of 2 sexes?
In hindsight, it isn’t that hard to see the benefit of 2 sexes. Even bacteria have an archaic way to recombine genes. Genetic recombination is necessary to weed out bad mutations and makes it possible for beneficial mutations arising in different individuals to end up in the same individual. However, it is not obvious how such a system can arise through the process of natural selection. Natural selection cannot plan ahead, only what is immediately beneficial can be selected for. An organism that can reproduce asexually will be able to pass on more of its genes than one that only passes on half, therefore we should expect that species should tend to lose the capacity for sexual reproduction as its benefits are long term and natural selection cannot plan ahead.
Another problem is that if we are to have genetic recombination, then why are there only 2 sexes? If a mutation arose that allowed an individual to mate with either male or female, wouldn’t such a trait be favored by natural selection since such an individual would have access to twice the mates? Overtime, this third sex would dominate; it is interesting that such a system is not widespread.
I was fascinated by Nick Lane ideas on these issues in his book Power, Sex and Suicide. Mitochondria have their own genomes and are passed on only through the maternal line. Over time, genes from the mitochondrial genome have migrated to the nucleus but no eukaryote has lost all of them. There are a core set that are always retained in the mitochondria. Lane explains that this is because local regulation of energy production on the mitochondria is very important. The micromanagement of the production of energy in each mitochondrion from the nucleus would be an extremely complex mechanism that perhaps could not evolve step by step by natural selection and that is why we don’t see it. So, like it or not, we are stuck with a separate mitochondrial genome. As such, we need a mechanism to pass on the mitochondria. That is where the 2 sexes come in. We need to have a specialized sex that is in charge of passing on the mitochondria. There are elaborate mechanisms in place in many different species to make sure that male mitochondria do not make it into the offspring. This implies that there are good reasons why the mitochondria from both parents can’t mix. Some diseases can be traced to events where these mechanisms fail and an individual has a mix from both parents. Lane believes that the mitochondrial genome has to match up with the genes that are in the nucleus. It is easier for these to match up if all of the mitochondria are the same. Regardless of the reasons, mitochondria coming from 1 parent seems to be very important. According to Lane, regardless of any benefits we may see in hindsight, without the need for a specialized sex for passing on the mitochondria, there would be no mechanism for maintaining the 2 sex paradigm we see with only rare exceptions across all eukaryotes.
Another problem is that if we are to have genetic recombination, then why are there only 2 sexes? If a mutation arose that allowed an individual to mate with either male or female, wouldn’t such a trait be favored by natural selection since such an individual would have access to twice the mates? Overtime, this third sex would dominate; it is interesting that such a system is not widespread.
I was fascinated by Nick Lane ideas on these issues in his book Power, Sex and Suicide. Mitochondria have their own genomes and are passed on only through the maternal line. Over time, genes from the mitochondrial genome have migrated to the nucleus but no eukaryote has lost all of them. There are a core set that are always retained in the mitochondria. Lane explains that this is because local regulation of energy production on the mitochondria is very important. The micromanagement of the production of energy in each mitochondrion from the nucleus would be an extremely complex mechanism that perhaps could not evolve step by step by natural selection and that is why we don’t see it. So, like it or not, we are stuck with a separate mitochondrial genome. As such, we need a mechanism to pass on the mitochondria. That is where the 2 sexes come in. We need to have a specialized sex that is in charge of passing on the mitochondria. There are elaborate mechanisms in place in many different species to make sure that male mitochondria do not make it into the offspring. This implies that there are good reasons why the mitochondria from both parents can’t mix. Some diseases can be traced to events where these mechanisms fail and an individual has a mix from both parents. Lane believes that the mitochondrial genome has to match up with the genes that are in the nucleus. It is easier for these to match up if all of the mitochondria are the same. Regardless of the reasons, mitochondria coming from 1 parent seems to be very important. According to Lane, regardless of any benefits we may see in hindsight, without the need for a specialized sex for passing on the mitochondria, there would be no mechanism for maintaining the 2 sex paradigm we see with only rare exceptions across all eukaryotes.
Sunday, May 9, 2010
Critique of evolutionary theory
for my Evolution capstone course, we are each supposed to bring in an argument against evolution which according to the professor will fall into 1 of 3 categories. I know I've heard this before but I don't remember what they were. Anyway, I'm sure most of the examples that students will bring in will be from intelligent design advocates associated with the religious right. However, according to Kenneth Miller, in his book Only a theory, many of the creationist arguments that come from the religious right were actually borrowed from the extreme academic left. Case in point, a recent book that Nature called a "misguided attack on evolution", What Darwin Got Wrong by philosopher Jerry Fodor is a great example. His central argument is that natural selection cannot tell the difference between adaptive traits and freeloader traits. I have addressed this topic at length in previous posts and I believe it is a pretty inane claim coming from such a supposedly sophisticated philosopher. I don't believe that there is a meaningful distinction between a selfish freeloading trait and a truly adaptive trait (see my last few posts on this topic.)
Another claim he makes is that evolution is a historical process and as such isn't truly testable. I like the way that Nick Lane addresses this claim in his book Life Ascending in his chapter on the evolution of the vertebrate eye. He points out that when investigating the evolution of a particular phenotype, we actually can make specific predictions. It doesn't matter that the process actually occurred long ago. The fact is, we can make predictions about how some structure evolved and we can confirm or falsify these claims as the data comes in from genome sequences and other sources. For example, we can make the claim that the vertebrate eye evolved by the process of natural selection. The common ancestor of invertebrate chordates and vertebrates did have a retina. In fact, the sea squirt today has a retina but no lens. So, to confirm this claim we would need to show that the specialized lens proteins that exist in the vertebrate eye were already present in this common ancestor. What is important to note here is that these kinds of claims are definitely falsifiable. If these apparently specialized proteins just appeared out of thin air, that would be a huge blow to natural selection. Potentially, if such a pattern emerged, then evolution by natural selection could be falsified. But, according to Lane, this is not what was found. He explains that vertebrate eye crystallin proteins were sequenced in the 80s and all of the proteins used to construct the vertebrate eye can be found in other parts of the body fulfilling other completely unrelated tasks. In fact, in the sea squirt which does not have a lens over its retina, some of these crystallin proteins are performing other functions nearby in the brain. This example is not isolated of course and there are many different ways that predictions can be made about the path that natural selection has taken which can then be tested as data becomes available. Fodor's criticism is indeed misguided.
Another claim he makes is that evolution is a historical process and as such isn't truly testable. I like the way that Nick Lane addresses this claim in his book Life Ascending in his chapter on the evolution of the vertebrate eye. He points out that when investigating the evolution of a particular phenotype, we actually can make specific predictions. It doesn't matter that the process actually occurred long ago. The fact is, we can make predictions about how some structure evolved and we can confirm or falsify these claims as the data comes in from genome sequences and other sources. For example, we can make the claim that the vertebrate eye evolved by the process of natural selection. The common ancestor of invertebrate chordates and vertebrates did have a retina. In fact, the sea squirt today has a retina but no lens. So, to confirm this claim we would need to show that the specialized lens proteins that exist in the vertebrate eye were already present in this common ancestor. What is important to note here is that these kinds of claims are definitely falsifiable. If these apparently specialized proteins just appeared out of thin air, that would be a huge blow to natural selection. Potentially, if such a pattern emerged, then evolution by natural selection could be falsified. But, according to Lane, this is not what was found. He explains that vertebrate eye crystallin proteins were sequenced in the 80s and all of the proteins used to construct the vertebrate eye can be found in other parts of the body fulfilling other completely unrelated tasks. In fact, in the sea squirt which does not have a lens over its retina, some of these crystallin proteins are performing other functions nearby in the brain. This example is not isolated of course and there are many different ways that predictions can be made about the path that natural selection has taken which can then be tested as data becomes available. Fodor's criticism is indeed misguided.
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