Natural Selection or Luck

[Micaiah]

Today at 06:19 PM chickenman said this in Post #20

survival isn't really the correct definition - you could survive to live 3000 years, if you don't reproduce and pass on your genes, you have a fitness of zero

We've said the population is stable, so does it really matter when the animal reproduces. We simply know that the amount of animals living and dying is in equilibriuum. We can give an average lifespan if you like. How about 15 years?

You should keep in mind that the causes of death are many and varied. The chance of our animal carrying a beneficial mutation dying from any of the causes will be essentially the same as any of the other animals.

 

[chickenman]

you're describing a population that has no basis in reality

in any case, reproduction is still the ultimate decider of fitness, the ones that are able to pass on their genes to the next generation are the most fit - so the creature who is able to survive to reproduce is the most fit

 

[Micaiah]

Can you explain why a stable population cannot occur?

On the law of averages in the population discussed above, the chances of survival are 20%. ie four out of five offspring get killed before they have a chance to reproduce.

Supposing we have 1000 feral horses running around in outback Australia. One mother gives birth to five horses during her life. A fire sweeps through the area trapping and killing one young horse who happens to be in the wrong place at the wrong time. On another occasion, a dingo captures and kills one foal who was a little too far from the parents protection. Another falls in a ditch and breaks its leg. It dies from heat exhaustion. The chance of survival in these cases would be largely unrelated to any small beneficial mutation that may have occured. There would be a number of external factors unrelated to fitness that ones that did or didn't die.

Allow me to repeat my question. Can you quantify the increased likelihood of an animal surviving as a result of a beneficial mutation. How small would that percent increase be before you would conclude it had little impact on survival? Answer the question in the context of the example above if you wish.

 

[chickenman]

the situation is totally artificial, because its never going to occur that 1 in 5 only ever survives

if you want a real example of the increased survival as a result of a beneficial mutation - antiobiotic resistance in bacteria is a perfect example

bacteria that have mutations that render them resistant to antibiotics have a great survival advantage over those that don't in environments that are saturated with antibiotics

thats why hospitals are the breeding ground for Multi-resistant bacteria

 

[lucaspa]

Today at 12:20 AM Micaiah said this in Post #15



Lets consider a stable population of mammals. Assume the parent gives birth to offspring say five times in their lifetime. Since the population is stable, then only one out of the five will survive. The chance of the animal surviving is then 20%, without any reference to a beneficial mutation.

Can you explain why the chance of an animal surviving with a beneficial mutation in this context is greater than 100%.

First, among the five, 2 have to survive to replace the parents.

Second, we are not talking about replacing each individual, just that the total number in the population is stable.  So, for those 5 individuals, none  of them may survive because none of them have a beneficial trait.  Instead, the offspring of another set of parents with a beneficial mutation may survive.  The population stays stable, but the genes of those two parents are eliminated from the pool.  Most examples are not that extreme simply because fitness isn't usually 1.  Also remember, recombination in sexually reproducing organisms.

So, let's try an example where the fitness of A is 0.5 and we have two sets of parents:  Set #1 where the parents are aa and aa while the second set is Aa and aa.  Each has 4 offspring.  Mendelian genetics says Set #1 will have 4 aa offspring.  Set #2 will have two Aa and two aa.  The Aa has a fitness of 0.5 and therefore s = 0.5.  The next generation will have 2Aa and 2aa's in it as opposed to only one Aa in the previous generation. Continue that through the next several generations and you will see that eventually all the individuals will be Aa. 

Third, I said 100% chance of being fixed, not "greater than 100%".  That last is a little tough.

 

[Micaiah]

Why is the situation totally artificial, why can't a population be practically stable.

I've stated that the average number of offspring is five. If you do not like that number for horses, give me another. No one is suggesting this number will be the case in every instant, but it could be sometimes.

We can deal with bacteria another time. I've set the parameters for my questions which you seem to be avoiding. Do you agree that in the cases outlined above the chance of survival had very little to do with a beneficial mutation, and more on other factors which essentially amount to bad luck. Please answer my other questions above.

Can you quantify the increased likelihood of an animal surviving as a result of a beneficial mutation. How small would that percent increase be before you would conclude it had little impact on survival? Answer the question in the context of the example above if you wish.

 

[lucaspa]

Today at 05:36 AM Micaiah said this in Post #21



We've said the population is stable, so does it really matter when the animal reproduces. We simply know that the amount of animals living and dying is in equilibriuum. We can give an average lifespan if you like. How about 15 years?

You should keep in mind that the causes of death are many and varied. The chance of our animal carrying a beneficial mutation dying from any of the causes will be essentially the same as any of the other animals.

You are not stating natural selection.  In wild populations there is always a competition for scarce resources.  It is that competition the determines whether an organism reproduces or not.  Sometimes the competition is simply to survive; other times it is to reproduce.  

The whole idea of a "beneficial mutation" is that it is beneficial in the competition.  You have just changed a "beneficial" mutation to a "neutral" one.

 

[Micaiah]

Second, we are not talking about replacing each individual, just that the total number in the population is stable. So, for those 5 individuals, none of them may survive because none of them have a beneficial trait. Instead, the offspring of another set of parents with a beneficial mutation may survive. The population stays stable, but the genes of those two parents are eliminated from the pool. Most examples are not that extreme simply because fitness isn't usually 1. Also remember, recombination in sexually reproducing organisms.

That may occur but so may my scenario. I am asking you to give an overall estimate of the increased livelihood of survival due to a beneficial mutation. Again I want you to think about the events that lead to the death of the animals in my scenario. They were essentially independent of the beneficail mutation.

 

[Micaiah]

Today at 08:31 PM lucaspa said this in Post #27



You are not stating natural selection.  In wild populations there is always a competition for scarce resources.  It is that competition the determines whether an organism reproduces or not.  Sometimes the competition is simply to survive; other times it is to reproduce.  

The whole idea of a "beneficial mutation" is that it is beneficial in the competition.  You have just changed a "beneficial" mutation to a "neutral" one.

It is wrong to assume that the animals that are the fittest, or that contain the hypothetical beneficial mutation must survive. Who survives is largely a matter of luck in this scenario.

Can you quantify the increased likelihood of an animal surviving as a result of a beneficial mutation. How small would that percent increase be before you would conclude it had little impact on survival? Answer the question in the context of the example above if you wish.

 

[chickenman]

if it has little or no impact on survival then it isn't beneficial, its neutral, or near-neutral, and it will be subject to random genetic drift

 

[Micaiah]

Are you saying it is impossible for point mutations resulting in single nucleotide substitutions to result in evolutionary change.

 

[notto]

Today at 12:37 PM Micaiah said this in Post #28



That may occur but so may my scenario. I am asking you to give an overall estimate of the increased livelihood of survival due to a beneficial mutation. Again I want you to think about the events that lead to the death of the animals in my scenario. They were essentially independent of the beneficail mutation.

That is why no beneficial mutation will help those in your scenario survive. Natural selection can only act if there is a advantage for an organism to live to the age where it can reproduce. A good example in your case would be if all of the sudden the normal food supply for the organism was short. Individuals within the population that had a beneficial mutation that allowed them to consume or retrieve a new food source (think archer fish!) happened, while the rest of the population starved, these new traits would allow those that have it to survive. Eventually, all individuals in the population would have the beneficial mutation.

 

[Micaiah]

As described above by me, an animal carrying the hypothetical beneficial mutation must will still be exposed to the risk of death from a number of other factors, and so its chance of survival will only be affected in a small way by the mutation. It doesn't become magically immune from all the other causes of death as shown above.

 

[notto]

Today at 09:51 PM Micaiah said this in Post #33

As described above by me, an animal carrying the hypothetical beneficial mutation must will still be exposed to the risk of death from a number of other factors, and so its chance of survival will only be affected in a small way by the mutation. It doesn't become magically immune from all the other causes of death as shown above.

That is true, it will not become magically immune from other causes of death, however, the statement that its change of survival will only be affected in a small way is not necessarily correct. It depends on how many of the other threats it is exposed to. The other threats would be considered neutral related to the populations fitness (versus the individual) because the entire population is exposed to them in the same proportion.

Populations evolve, not individuals. The fitness of the population is what affects evolution. If an organism with a beneficial mutation that can be passed on breeds before its death is caused by one of the other factors, then indeed, the mutation was immune to the other causes. It was successfully passed on.

 

[Orihalcon]

it doesn't always have to be exposed to the risk of death. for example, a mutation could occur that make an animal reproduce with double the egg count of normal. it therefore produces more offspring and has increased the chances its genes being passed on without facing death.

in a perfectly stable population mutations either won't happen or all mutations are neutral. if a benefit is introduced that makes an organism rise above the others, within a few generations it could be thrown out of stability. unless the competition somehow manages to increase the kill rate by the same factor as the survival increase given by a beneficial mutation.

 

[Orihalcon]

a mutation doesn't always present itself after the environment. many bacteria could have had a gene for antibiotics resistance before many drugs came out. now that everyone's taking medicine, those bacteria are suddenly surviving better than usual.

 

[Micaiah]

Can you give me an example of such a mutation in the hypothesised recent evolution of the horse. What was the change that occured in one mutation that meant that animal (and we also need to have a mate) was able to survive, where all others died.

 

[chickenman]

here we go micaiah, I found some nice lectures for you

http://www.scar.utoronto.ca/~thompson/course/lecture.html
start reading

 

[notto]

Today at 10:56 PM Micaiah said this in Post #37

Can you give me an example of such a mutation in the hypothesised recent evolution of the horse. What was the change that occured in one mutation that meant that animal (and we also need to have a mate) was able to survive, where all others died.

Here is a brief list that shows the advantages the horse has received that we can see in its history in the fossil record.

http://www.amherst.edu/~pratt/education/horse.html

As far as identifying the actual mutation that caused these changes, I'm not sure what you are looking for.

 

[OldBadfish]

Yesterday at 04:04 AM Micaiah said this in Post #1

I've heard it stated on many occasions that evolution is not random, and things didn't evolve spontaneously by chance. Rather they evolved by a process of natural selection. Is this really the case, or is it essentially luck.

To what extent does natural selection influence the chance of survival of a stable population. Anyone like to try to quantify the improved chances of survival that could result from a beneficial mutation.

Natural Creation?

How many roadblocks will it take to consider spontaneous creation?