Are individual selection events random?

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Severian thinks so!

 

By the way, although a bit off topic, this statement by Dawkins is just wrong. The survival is still random - it is the statistical average which is not random, but the individual survivals are still random. (If I roll a die 10^{8[/sup'] times and average the result I predict (with great accuracy) that I will get 3.5, but each die roll is still random.)}

 

^{If we were to translate his die example into a population, it would be one with 6 members, each having an equally likely chance of death.}

 

^{If this were the case with a population of animals, and the chances of any given member dying were completely random, we would see no trends because there would be no selection. Every single member of the population, regardless of what traits they have, would have an equally likely chance of dying.}

 

^{Severian, this is ridiculous... natural selection cannot be compared to the rolling of a die.}

[Mokele]

Survival (or, more importantly, number of offspring) is alway affected by randomness; the mutant armadillo with a super immune system is just as vulnerable to getting squished by a car.

 

The difference is this: image every individual is one of a set of dice. Most roll normally, but some have an adaptation that makes them weighted so the average is 4.5. If you roll each die, and select only the highest 50%, the duplicate those and repeat, you'll still see the weighted dies becoming more and more common, because they're more likely to roll high (they have a selective advantage). Any given weighted die can still roll a 1, but it's just not as likely.

 

This also leads into another important evolutionary concept: genetic drift, the effect of this sort of randomness in nature.

 

Imagine if you have a mixed bag of red and blue die, all fair, exposed to the same selection regime above. Eventually, you'll wind up with all one color, because random events will influence the ratio one to the other until, by chance, there's only one. If it's an even mix, it's a 50-50 shot who winds up being the last, while that changes if the mix is unbalanced.

 

Now, very imporantly, sample size matters. If you're only rolling 10 dice, a single bad roll for one color will have a much greater effect than if you were rolling 1000 dice. The population will also become uniform sooner. This is why small populations are *bad* (aside from inbreeding); genetic drift is powerful in small populations, and can eliminate alleles, reducing diversity.

 

Also, genetic drift and counteract (or aid, randomly) selection. Go back to the dice example where some are weighted and others aren't. If you have a huge population, you can be reasonably sure that the weighted dice will prevail. But what if you only have 10 dice, one of which is weighted, and that just happens to come up as a 1? Genetic drift, the power of randomness in small sample sizes, has overpowered selection.

 

There are actually equations covering this, predicting population sizes above which selection dominates and below which drift dominates.

 

Mokele

[PhDP]

...a mildly deleterious allele can even drift to fixation if the population is small enough.

 

The statement by Dawkins is just wrong, every undergraduate biology student should know life results from both random and nonrandom survival of more-or-less random varying replicators. It's not surprising however, Dawkins doesn't even seems to acknowledge the importance of drift and mutations.

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It's not surprising however, Dawkins doesn't even seems to acknowledge the importance of drift and mutations.

 

Have you ever read his books? He devoted multiple chapters in The Ancestor's Tale to drift.

[bascule]

The statement by Dawkins is just wrong, every undergraduate biology student should know life results from both random and nonrandom survival of more-or-less random varying replicators.

 

It really sounds to me like you're just arguing semantics here. If life resulted from random survival, then that would imply that every member of the population would have an equal chance at surviving. Non-random doesn't imply that there isn't a random component to it, it implies that there's a discernable pattern. There certainly is.

 

In fact, despite your claim that Dawkins doesn't talk about drift, in The Ancestor's Tale he talked about how, through statistical analysis, we can discern which changes are due to selection and which changes are caused by drift.

 

He talked quite extensively about drift, actually. One other thing he mentioned was that the molecular clock normalizes regardless of reproductive rates. This is because species which reproduce slower have lower populations, and thus a smaller gene pool so genes altered by drift are more readily taken up by the population, however quickly reproducing species have a larger population and thus genes alter by drift get homogenized out.

 

It sounds to me like you're implying Dawkins is clueless and not aware that there are both random and non-random components to genetic evolution. He certianly isn't, in fact he wrote quite passionately about it and what conclusions we can draw from it, as well as what conclusions we can draw from drift (i.e. the molecular clock)

 

The overall tone of his statement in my signature is that selection provides a non-random component to evolution. This is a direct reaction to the creationist strawman of evolution, which claims that evolution is a random process. I'm sure you've all seen this argument: where they talk about the immense improbability that a million monkeys on a million typewriters will happen to type a particular statement. In this strawman, evolution is presented as a completely random process, and selection is entirely ignored.

 

So please, don't strawman Dawkins too, or tell outright lies about him...

[PhDP]

It really sounds to me like you're just arguing semantics here. If life resulted from random survival, then that would imply that every member of the population would have an equal chance at surviving.

 

It's sometime the case. Sometime evolution is purely random, sometime it's partially random and partially nonrandom. Anyway, it's always random at some level...

 

Have you ever read his books? He devoted multiple chapters in The Ancestor's Tale to drift.

 

"Selfish Gene", "Extended Phenotype" and the "Blind Watchmaker". Not the ancestor's tale. I would certainly not being so criticical if I haven't read the "Blind Watchmaker", and, most importantly, if I hadn't encountered so much fans of Dawkins.

 

So please, don't strawman Dawkins too, or tell outright lies about him...

 

He talked quite extensively about drift, actually. One other thing he mentioned was that the molecular clock normalizes regardless of reproductive rates. This is because species which reproduce slower have lower populations, and thus a smaller gene pool so genes altered by drift are more readily taken up by the population, however quickly reproducing species have a larger population and thus genes alter by drift get homogenized out.

 

What lie ? Strawman ? That's quite ironic... I said he did not acknowledge the IMPORTANCE of drift and mutations, he said very often natural selection "solved" the problem of our origins, he said pretty clearly, and quite often, that selection was THE key, the rest was details... Also, he's using strawmans (and sometime just confusing terms and concepts) to discredit neutralism and mutationism.

 

This is a direct reaction to the creationist strawman of evolution, which claims that evolution is a random process.

 

I don't like the idea of replacing a bad argument with another bad argument. However I perfectly understand your motives, and they are indeed noble.

 

It sounds to me like you're implying Dawkins is clueless and not aware that there are both random and non-random components to genetic evolution.

 

Have you read the "Blind Watchmaker" ? The last chapter, "Doomed Rivals", is simply awful. Yes, he IS clueless about a lot of things concerning modern evolutionary biology, and I'm not talking about tiny details...

[FreeThinker]

I think the problem is that Dawkin's statements are often over analysed.

Mutations are random events. Natural selection is very much NON random. However, death can strike the most adapted organism. Saverian attempted to take the meaning of "non randomness" out of context. Sure, a well adapted organism could be killed by lightning , or eaten by a 'lucky' predator. But a organism which is less adapt will have a bigger chance of being eaten. For natural selection to be truly random both , the well adapt and the less adapt, would have to have the same chance of being picked to be eaten. This not the case. The organism with the evolutionary advantage will be in the minority and therefore even chance will be on its side. As it spreads its genes, the populations will slowly start being better equipped at surviving in the particular environment. Eventually a significant portion of the population will be better equipped to survive that the rest. This is where the odd death of the better equipped organisms is even less significant ( as its genes would already be spread through out the population). Natural selection is the random in the same sence as a person choosing a mate. Anyone has a chance of being chosen by a particular member of the opposite sex. However, some individuals have an advantage over others( according to the taste of the selector). Once in a while someone might be tricked into marring someone but usually choosing of a partner is based on preferences and compatibility, not random chance.