New Model of Evolution Reveals How Cooperation Evolves
technologyreview.com
technologyreview.com
For example: say you had a savannah with grass and tall trees populated by 4-legged horse-like animals that survive by grazing on the grass. We can look at such a scenario and say that it would be advantageous for some sub-population of those horse-like animals to grow longer and longer necks until they were capable of also grazing on the trees (doubling their available food supply, relative to their neighbors), but it will never happen! In each generation there will be a distribution of neck lengths, and as there is no advantage to those with slightly longer (but not long enough to reach the trees) necks, the distribution will remain unchanged. This is the basic Hardy-Weinberg principle.
The only way you get giraffes is if the trees start out much shorter, so that the horse-like animals are capable of grazing on them. Then the trees that are slightly taller will have an advantage, and the distribution of tree heights in the population will shift. This will give an advantage to the horse-like animals with longer necks, causing their distribution to shift, and on, and on. This is the basic Red Queen hypothesis.
So saying that an organism that has an inherent capacity for adaptation, or one that knows to cooperate with neighbors, would be better able to survive than the alternatives doesn't mean crap. If you cannot provide a mechanism (backed by a mathematical model) of how such traits arise, then evolution doesn't care.
That is what makes this work so particularly interesting. The authors are providing a model to explain how a mechanism for the selection of cooperation could occur.
This idea is easily discredited, even "disadvantageous-but-viable" mutations are prized possessions among my offspring. Environments change, and whether or not my lineage goes unbroken is a result of its ability to survive those changes.
Those environmental changes are unpredictable. phenotypes that benefit me now do not necessarily benefit me in the future. If it is my goal to extend my lineage as long as possible, then my optimal strategy must give extra value to diversity.
Since every organism possesses a lineage that goes back to the origin of life, it's fair to say that cooperation for the goal of increasing diversity is a pretty heavily selected for trait.
First, to clarify the last sentence above, selection does not happen at the level of an individual. Selection is a statistical process that requires a population of individuals.
For evolution by selection to occur, there has to be 1) variation in traits (i.e. "Phenotypes"), 2) the variation in these traits has to be in part heritible (i.e. Have a genetic basis), and 3) there have to be average differences in success of leaving offspring that themseves go on to reproduce, etc, etc, based on the trait differences amongst individuas.
In other words, without a constant source of selection, there is no way for a trait to become fixed in a population.
It seems like you're making the mistake of thinking that traits we see were necessarily being actively selected for. It's like saying that because we see an increase in complexity in organisms over time, that evolution is selecting for complexity (its not).
It's true that more diverse populations can withstand changes to the environment better. But to then say that the trait of diversity is selected for is a huge stretch. If diversity has no current value then it won't be selected for, and will be selected against in competitive environments. Evolution doesn't have a way to see into the future in that way. Diversity might be selected for in cooperative populations, but only when diverse behavior provides an immediate benefit to the population.
Model A: Let's say there is an environmental change every 100 years, and if a population is not diverse enough, then it dies. After 1000 years, we would expect the only populations to be around would be those that are diverse.
Yes, it is true that if there there is a short-term advantage to nondiversity in a population, then it will evolve to be nondiverse, and it will die - in this sense you're right that evolution does not see into the future. However, given the existence of diverse populations assuming the Model A, we can conclude that these populations have found a local minimum of fitness in which diversity is advantageous. Further, there might be "genetic guards" to nondiversity, such that fixation of a gene promoting nondiversity is rare (because this would resilt in extinction!), either through social sexual selection or by such a mutation being a rare event.
But any mechanism in which "diversity" is advantageous will be advantageous for more specific reasons. Diversity is just too unspecific. Perhaps you're speaking in terms of group selection, so in a sense evolution evolves diversity in populations. But I don't think this works either. Aside from group selection itself being highly questionable, every environmental event in your Model A would reduce the diversity of the remaining populations. Remaining populations were more diverse in the past (owing to their ability to survive abrupt environmental shifts), so any trend in diversity is in fact downward on large timescales. On short timescales, diversity only grows when there are no selective pressures at work on a given gene. There just is no pro-diversity selection going on.
The only organisms which can be said to have been successful are the ones who are either alive today, or were the n-grandparents of the organisms alive today. Zero organisms alive today have n-grandparents whose reproductive strategy did not encourage diverse offspring. Not all diversity is adaptive, but exactly no anti-diversity is adaptive. Therefore diversity is selected for.
An obvious counter example seems to be species that reproduce through cloning.
>Therefore diversity is selected for.
"Selected for" has a precise meaning. You guys are using it way too loosely. Selected for simply means the differential survival of one trait over another. There is no time where "diversity" (that isn't really a more specific adaptation) is selected for.
(For example, I could easily say that versatility is selected for rather than diversity. But who cares? We're not saying anything scientific if it doesn't have a formal definition.
I just don't see this as being meaningful. There is no heritable "diversity" trait. You can apply these concepts at the population level, but only very loosely.
The other problem I have is that any metric of diversity decreases over time for a population. Normally when we say evolution selects for trait X, your metric for X increases over time. Instead of diversity being selected for, its more like the gas that drives the engine of evolution. Without diversity in a population, natural selection can't happen. But the diversity comes first.
That seems like too big a statement to be true. You're saying there is no structure which controls the variability of any phenotype? No gene that decides how much butterfly wing splotches vary? No gene that decides the difference between the shortest and longest legs in a family of mountain goats? No heritable diversity traits across the entirety of life?
Putting aside how unlikely that seems to me, if it was true... How could you possibly know such a thing? You can't prove a negative.
I think you're reading diversity to mean something different than the previous responses intended. Surely there are genes to control a phenotype. The issue under discussion is whether evolution selects specifically for genetic variation within a population (diversity of a population), without a more basic selection going on. My argument is that selection happens at the level of an individual and so it makes no sense to say that evolution selects for population diversity; there is no organism level selection mechanism that is the proxy for diversity at the population level, as there is in other purported population/species level selection events.
I disagree with that, it happens at every level, from the continental down to the molecular.
Here's a question: are humans individuals, or are we colonies? What about an ant? Is it an organism, or is it an organ? I am not aware of a clear answer to these questions, so I would be excited to hear from you if you know of one.
The problem is that evidence for this has been extremely hard to come by.
> I am not aware of a clear answer to these questions, so I would be excited to hear from you if you know of one.
Richard Dawkins' The Selfish Gene very elegantly explains the evolution of cooperative/altruistic behavior through analyzing the dynamics of gene selection. It's a great read for anyone interested in the finer details of evolution. The main takeaway is that cooperative behavior in organisms can be understood as genes encouraging their own proliferation by increasing the fitness of its copies in other organisms; a gene to help my brother is really a gene helping itself.
You also never responded to the fact that humans are colonies, not single organisms, and yet I assume you believe humans are subject to selective pressure?
You misunderstand. My point about organisms was that selection happens at the level of organism, which was an imprecise way of saying organisms are what either procreates or dies, and so this is the level at which selection events occur. So any purported selection at a different level must have some organism-level proxy.
The statistics of what survives and what doesn't can still show effects happening at different levels. So when I speak of gene selection, I'm speaking from a statistical perspective. When I said that diversity isn't itself selected for, I meant that there is no strictly "diversity" selection happening at the level of organism.
>You also never responded to the fact that humans are colonies
Yes, humans are "colonies", meaning that we show cooperative behavior. But I don't see how that's relevant, at least in light of ways to understand the evolution of cooperative behavior at the gene level.
Try to find a reputable scientist who will tell you there is an unambiguous distinction between an organism and an ecology. You won't find one, because there is no line. Nature doesn't care if you're a hive or a molecule.
How about viruses? Those aren't organisms, they can't reproduce at all. Just like an organ, or a gene, they need a host to replicate them.
Is it your opinion that viruses aren't subject to selective pressure?
You seem to have trouble comprehending what's being said in context. Try to stop taking things out of context and then nitpicking them. If you came away from anything I've said thinking that I don't think viruses are subject to selective pressures, then you just didn't understand any of it.
What about mutation and recombination?
Recombination is a trait that increases diversity of a population, but its also a trait that increases the fitness of the individual organism's lineage as it allows greater diversity of genetic material and interactions between genes in its offspring. So there is an organism level effect that promotes the selection of recombination.
I originally granted that there are traits that can be seen to promote population diversity, but that they would be selected for by the increased fitness at the organism level, not because populations with more diversity better survive random black swan events.
The article doesn't address this second-order effect of innovation. Instead it seems to take a basic result of evolutionary game theory and cast it in a model from physics.
Having a slow metabolism is usually bad, but if there's food shortage it becomes an advantageous trait. Dwarfism is similar.
That's why larger/stronger/faster cats like the saber-toothed cats died and now we have smaller cats, for instance.
To me it seems like the paper isn't really offering a fundamentally new explanation of how these traits arise, it's just providing a sophisticated analysis of the dynamics.
MIT Tech Review has often news about fascinating research, but one has to adjust for some amount of unnecessary hype.
In other words, the field of evolutionary biology today has its Newton's laws and Maxwell equations, but we're missing anything like the Standard Model. The authors of this work have been at this for a number of years. A sophisticated analysis of the dynamics is a key and very important step in beginning to develop a "grand unified theory" of evolution.
either you're a team player or else. Collective punishment comes to mind too as a very effective way to induce cooperation/alignment inside the collective which is going to be or threatened to be punished.
Game theory is enormously insightful, but It leaves out a great many factors that are very important in the real world, such as communication between the parties,uncertain rules, and reputation.