Evolutionary Theory Evolves? - Survival Of The Fittest Is Likely False Study shows

GetHyped
reply to post by FriedBabelBroccoli

 

How would Astyanax's definition be in any way relevant? He's not the author of the paper.

By the way, "survival of the fittest"? Haven't heard that one in about 150 years and it wasn't a valid description even back then so I don't see why you're getting so hung up on this simplistic and inaccurate definition of evolution.

I am not defending "survival of the fittest" . . . have you even read the thread?

It would be members Boncho and Asyntax who are complaining about not having the "inaccurate definition of evolution" . . . . .

-FBB

reply to post by FriedBabelBroccoli


So what is your definition of evolution and do you subscribe to it?

GetHyped
reply to post by FriedBabelBroccoli

 

So what is your definition of evolution and do you subscribe to it?

Oh, just looking for something to argue with FBB about eh?

Get your stars?

I was just presenting the study for others to be aware of it, do have any questions regarding the study?

-FBB

reply to post by FriedBabelBroccoli

The title of your thread is "Survival Of The Fittest Is Likely False Study shows". You're not prepared to discuss the very topic upon which this thread is based?

Evolution is not "survival of the fittest" so it is perfectly on topic to ask you what is your definition of evolution and whether you subscribe to it. Otherwise people might think you're attempting ignorant swipes at a topic you don't understand simply because you have a hidden agenda.

zilebeliveunknown
Theory of evolution had worked to the point where humans became self aware. From that moment the theory of evolution isn't applicable any more to our species. Our society isn't based on the premise of 'survival of the fittest' even though there are groups who behave like this. Societal norms are different than in animal societies. I cannot simply eliminate someone else in order to gain their teritory and food resources.

You can't just go out and shoot some guy and move into his house, true. But that doesn't mean evolution doesn't affect us still. You still compete with other people, right? For example, you can get a promotion someone else did not get. This gives you access to more resources.

But there are big differences compared to how animals and plants evolve, ill give you that.

OK sorry for this large amount of text. But trust me, this is a good explanation of fitness in the study, and how natural selection actually plays a role in the simulation. If anyone has any questions please ask me. And so you don't think I'm talking out of my a$$, I have a Masters in biology with a focus in genetics and cell biology.

***

here is what is happening in the simulation:

Phenotype = a specific RNA shape which can be predicted based on the genotype using a computer program.

Fitness is 1+S1 for phenotype 1 (grey in Fig 3A) and 1+S2 for phenotype 2 (red in Fig 3A). Phenotype Q (blue in Fig 3A) has a fitness equal to 1.

The authors have set S2>S1, therefore in terms of fitness P2>P1>Q

What does fitness mean? Read the quote below:

At each generation
T, N parents are drawn with replacement with probability
proportional to their fitness 1+s with the constraint that the
population size (or carrying capacity) N is fixed. Each parent gives
rise to one offspring, and the offspring make up the population for
the next generation.

So the chance that an individual will reproduce and give rise to offspring in the following generation depends on their fitness. So the predicted shape of the RNA (the phenotype) determines how likely it is they will get the chance to reproduce. But there is also the chance for mutation:

During reproduction, each base in the
genotype of length L mutates to a random alternative base with
probability m.

Initially, the entire population will be phenotype Q (blue), however due to mutations between generations there is a chance that some individuals with phenotype 1 (grey) and phenotype 2 (red) will appear in later generations. The chance of a mutation causing 1 (grey) is much higher than for a mutation causing phenotype 2 (red). This is because there are more genotypes that can create the shape for phenotype 1 (grey) than for phenotype 2 (red). There are two possibly outcomes:

1) likely: an individual (or individuals) with phenotype 1 (grey) appear due to mutation. They have a better chance of reproducing than individuals with phenotype Q and eventually 1 will replace Q as the dominant phenotype and become fixed (all individuals will have P1 except few mutants).

2) unlikely: an individual (or individuals) with phenotype 2 (red) appear due to mutation. They have a better chance of reproducing than individuals with phenotype Q and phenotype 1, and eventually Phenotype 2 will replace Q (and Phenotype 1 if it exists in the population) as the dominant phenotype and become fixed (all individuals will have phenotype 2 except few mutants).

So we can say that fitness is this study is determined by the predicted secondary structure of the RNA sequence (genotype) which determines the odds of reproducing.

Clearly fitness is directly tied to reproductive success, which is what Darwin was discussing with his theory of natural selection. Darwin said that certain traits (phenotypes) might increase the chance of reproduction. Darwin wasn't aware of genes (Mendel's pea plant study was not widely known until after the time of Darwin), but he knew that offspring tended to look similar to their parents, and he proposed that if a trait increased the chance of reproduction, then individuals with that trait would have more offspring, and therefore the next generation would have more individuals with that trait. When most modern biologists say fitness in relation to genetics and evolution this is what they mean: those that are more fit have a better chance of passing their genes onto the next generation. If you can find a biology dictionary in the library look up fitness and you will see that what I am saying is correct. Here's an example from an online biology dictionary:

In biology, Darwinian fitness or simply fitness of a biological trait describes how successful an organism has been at passing on its genes. The more likely that an individual is able to survive and live longer to reproduce, the higher is the fitness of that individual.

www.biology-online.org...

Clearly, the researchers that performed this study built an algorithm for natural selection into their simulation. One based on phenotype determining reproductive success i.e. fitness.

Hope that made sense. It's 6 am where I live, but if there are any questions (or you think I made a mistake) please ask.

reply to post by Malthus

So we can say that fitness is this study is determined by the predicted secondary structure of the RNA sequence (genotype) which determines the odds of reproducing.

Thank you, Malthus.

This is correct, of course. I fail to see how it eliminates the tautology, though.

If the probability that a certain phenotype will appear in a population is lower than the probability that it will outbreed other members of the population, how high can the latter probability — which one might ordinarily use, might one not, as an indicator of selective fitness? — actually be? Shouldn't the first set of odds be factored into the second set? And wouldn't that reduce the second set, thereby in turn affecting the first yet again? I suspect the answer, if there is a good one, will be too mathematical for me. But try me.

Fitness is 1+S1 for phenotype 1 (grey in Fig 3A) and 1+S2 for phenotype 2 (red in Fig 3A). Phenotype Q (blue in Fig 3A) has a fitness equal to 1.

The authors have set S2>S1, therefore in terms of fitness P2>P1>Q

Earlier, I posted this:

Astyanax
it seems to me that 'fitness' in the model being studied is nothing but a mathematical term, one that is used as a weighting factor in the equations and is not related to any actual, physical determinants of biological fitness.

Your explanation above seems to bear this out, unless they built a whole mathematical environment, tested various toy phenotypes against them, and based their assignment of fitness values S1, S2 on how the phenotypes actually fared.

Is this what they did?

*

reply to post by FriedBabelBroccoli

Sooooooooo basically you agree with exactly what their models show,

I neither agree or disagree with what their model shows. I can't do either until I understand better how they have applied the concept of fitness. That is why I asked for their definition of it.

but you think the "most fit" is whatever is most prevalent at any given point in time . . . . . ?

I don't think the definition of 'the fittest' is simply 'the commonest'. My earlier comment was with respect to the experimental model, not to real organisms in the real world. Anyway, my definition of fitness, as GetHyped pointed out, is irrelevant to our discussion of the paper. It might affect my opinion of the conclusions of the paper, but I don't have any yet.

reply to post by FriedBabelBroccoli

Bringing forth more viable offspring does not equate to being a better survivor . . . the difference may seem like semantics or extremely subtle but it is a serious issue.

Unless you want to change the definition of fitness to the actual ability to reproduce this is a fundamentally different mechanism driving the phenomena. Currently fitness is tied to the ability to actually survive which increases the chances of being able to reproduce at some point. The study is demonstrating the strongest link is actually the reproduction process itself.

These are very different things.

Yes and no.

It is an interesting nuance to the natural selection process, but there is no fundamental change to the understanding of the process. 'Fittest' means the one most able to spread through a population, which usually means to reproduce most successfully. This is what it has always been; there is no need to 'change' the definition.

1) a mutated individual must itself to be able to survive to reproduce.
2) many different individuals with different mutations may be able to survive the changed environment (or take greater advantage of the existing environment)
3) some mutated individuals and their offspring may be better at reproducing in that changed environment than other mutated individuals
4) the individuals that reproduce better will pass on their gene more successfully than others - that is the bottom line.
5) differently mutated individuals may mate and their mutations be 'blended' (if you will)
6) the POPULATION will gradually become dominated by the genes from the most successful reproducers
7) It is the POPULATION that evolves, not the individual
8) it is the POPULATION that survives, not the individual
9) It is the POPULATION that survives in the environment that is the 'fittest'.

As 'boncho' said it is mostly a semantic argument, because the POPULATION can only 'take advantage of' mutations that exist in its gene pool at the time a response is required to some environmental change. There may be many different possible 'solutions' to the requirement, but only those that are available when required are in any way relevant.

'Survival of the available' is a non-sense description for two reasons: 1) clearly, if a mutation does not appear in the population gene pool at an appropriate time, it cannot contribute to the survivability of the population and 2) not all available mutations survive.

What this study is apparently saying is that sometimes there might be two mutations in a gene pool, both of which successfully respond to the environmental change, one of which is in many more individuals than the other. The low frequency mutation may be judged to be 'more fit' than the high frequency mutation by us outside observers. However in real life the high frequency mutation, which is 'good enough but not the best' by our judgment, may win because it can establish itself throughout the population quicker than the low frequency mutation.

'Survival of the frequent' is a useful description of the process, but it is still 'survival of the fittest'. The key here is that it is an outside observer that is making a judgment call on which mutation is more fit; nature may produce a different result.

Like I said at the top, It is an interesting nuance to the understanding the natural selection process, but it does not represent a fundamental change to that understanding.

Edit: I think Malthus said pretty much the same thing I did.

reply to post by FriedBabelBroccoli

Gee I wonder why? This was the reason I asked you for the definition you were using as I suspected it would be something ridiculous like this.

HIS 'personal' definition is irrelevant to the definition as encoded in the model. He wants to know what definition the AUTHORS ENCODED IN THEIR MODEL. Did they use an example they actually found in nature or did they use an artificial construct.

If they use an actual example, they may be supplying an answer to an actual occurrence that hadn't been explained previously.
If they use an artificial construct, they may only be raising an hypotheses that can then be looked for in nature.

Why is that so hard to understand? It isn't rocket surgery.

reply to post by Astyanax

Your explanation above seems to bear this out, unless they built a whole mathematical environment, tested various toy phenotypes against them, and based their assignment of fitness values S1, S2 on how the phenotypes actually fared.

Is this what they did?

They just set one phenotype as having higher fitness than the other. They didn't build a mathematical environment to test the phenotypes against.

If the probability that a certain phenotype will appear in a population is lower than the probability that it will outbreed other members of the population, how high can the latter probability — which one might ordinarily use, might one not, as an indicator of selective fitness? — actually be? Shouldn't the first set of odds be factored into the second set? And wouldn't that reduce the second set, thereby in turn affecting the first yet again? I suspect the answer, if there is a good one, will be too mathematical for me. But try me.

The probability of the phenotype appearing and the any measure of selective fitness are both independent variables. They don't influence each other. However, they both contribute to the probability of any phenotype outbreeding the others in a population (dependent variable). The equation is something like:

probability of appearance * measure of selective fitness = probability of phenotype outbreeding others

Edit: I think Malthus said pretty much the same thing I did.

thanks for the acknowledgement. yes you said pretty much the same thing the math in the study is pretty complex, but what is describes really it's pretty simple and nothing revolutionary. this study is interesting in because it demonstrates just how strong an effect "arrival of the fittest" can have on evolution.

reply to post by Malthus

it demonstrates just how strong an effect "arrival of the fittest" can have on evolution.

Maybe. In any event, the important question has yet to be answered: How, exactly, do the fittest "arrive"?

reply to post by Malthus

1) likely: an individual (or individuals) with phenotype 1 (grey) appear due to mutation. They have a better chance of reproducing than individuals with phenotype Q and eventually 1 will replace Q as the dominant phenotype and become fixed (all individuals will have P1 except few mutants).

2) unlikely: an individual (or individuals) with phenotype 2 (red) appear due to mutation. They have a better chance of reproducing than individuals with phenotype Q and phenotype 1, and eventually Phenotype 2 will replace Q (and Phenotype 1 if it exists in the population) as the dominant phenotype and become fixed (all individuals will have phenotype 2 except few mutants).

So we can say that fitness is this study is determined by the predicted secondary structure of the RNA sequence (genotype) which determines the odds of reproducing.

If phenotype 2 is fitter than Q, it is still survival of the fittest. (However people want to describe the term.)

If phenotype 1 is fitter than 2, they say less prevalent, one could also say less likely, that does not seem to play into their definition of fitness.

In biology, Darwinian fitness or simply fitness of a biological trait describes how successful an organism has been at passing on its genes. The more likely that an individual is able to survive and live longer to reproduce, the higher is the fitness of that individual.

Follow my train of thought here. You say:

So we can say that fitness is this study is determined by the predicted secondary structure of the RNA sequence (genotype) which determines the odds of reproducing.

Passing on genes is more complicated than simply reproducing. As the study points out. In it they determine fitness without accounting for the rarer mutation. In other words, if the more common mutation is more likely to pass on (because its more likely to happen), that shouldn't play into the fitness rating? The study explains in detail what happens leading up to genetic variation and dominance, which is great, but to say it completely changes the landscape or some other nonsense, I just don't see it.

In any case, you and rnaa cleared up a few things and a great addition to the thread. I am not fond of biology, (and never have been.)

The little I do know though, still leads me to believe this as semantics, making a statement like "survival of the most prevalent." is just like saying we found a "second earth" a few light years away, oh but gravity is x times stronger, it never gets over -50 and it has about a million other things that might kill us there. (Not to say it wouldn't be valuable or interesting.)

The expressions are great at popularizing something but are not entirely accurate.

The opposite of natural selection and survival of the fittest would be a population full of genetic mutation with no similar phenotypes. That simply isn't the case. Or, say we were created by a god, with only one phenotype. No variation at all. Again, this kind of thing would suggest that natural selection, or survival of the fittest would not apply in the least. Or maybe we're clones…

Survival of the prevalent, would suggest that phenotype q remained fixed even after the environmental change, because 1 and 2 never had enough numbers to make an impact. In other words, "survival of the available" would suggest that environment and fitness have little importance.

Long live the mutants.

How about a thought experiment; lets consider a population of humans living in equatorial Africa. Malaria carrying mosquitos are rife in Equatorial Africa.

In this experiment I am pulling numbers out of thin air. I do not pretend that they represent actual survival rates in any populatin study ever recorded. It is just to illustrate the "survival of the frequent" idea.

Suppose one year a generation of 210 children is born within this population.

• 100 of these kids are just kids, like kids anywhere: if they catch malaria, and are untreated, 80% of them will die. Call these kids the "A group". (about 47%)
  
• 100 of these kids are born with a mutated gene that provides an increased chance of survival: if they catch malaria and are untreated, only 20% will die. Call these kids the "B group". (about 47%)
  
• 5 of these kids are born with a mutated gene that provides a much better chance of survival: if they catch malaria and are untreated, only 10% will die. Call these kids the "C group". (about 5%)
  

So there is a Malaria Epidemic and every kid gets malaria.

80% of the A group dies leaving 20 survivors. (18%)
20% of the B group dies leaving 80 survivors. (73%)
10% of the C group dies leaving 4 survivors. (8%)

The survivors all grow up and have kids of their own. Lets say they all have one child born each year (all with A group mates - the reason this is critical is explained below). When the oldest is 3 years old there is another epidemic.

80% of the A Group 2nd generation dies( 60 individuals ). 12 survivors. (5.6%)
20% of the B Group 2nd generation dies( 240 individuals ). 192 survivors. (89.7%)
10% of the C Group 2nd generation dies( 12 individuals ). 10 survivors. (4.6%)

Three years later it happens again.

80% of the A Group 3rd generation dies( 36 individuals ). 8 survivors. (1.6%)
20% of the B Group 3rd generation dies( 576 individuals ). 461 survivors. (93%)
10% of the C Group 3rd generation dies( 30 individuals ). 27 survivors. (5.4%)

So in 3 generations the 'less fittest' has beaten out the 'greatest fittest' because of shear numbers of availability.

Notice that I set the 1st gen C group to 5 just to keep it in the picture all the way through. Clearly, if there was only 1 individual in that group it may or may not have survived that 1st round. Model assumptions are all important.

By the way, the 'B group' gene mutation DOES exist in nature (but I don't have any idea what the actual mortality rate is - the point is that it is not 100% successful). If ONE parent passes the gene to its child, the child has an increased chance of survival if it contracts malaria. Unfortunately, if BOTH parents pass the gene to the child, the child is likely to have 'Sickle Cell Anemia', and if left untreated has a much reduced chance of surviving childhood.

I'm not aware of a 'C group' gene mutation. The point here was to show the possibility of a higher fitness being beaten out by a lesser fitness.