Query: what is the evolutionism for scale? Why are animals different sizes?

[TeddyKGB]

Ok and you are saying that

• it stays that way by chance
• it doesn't mutate out of control
• none of the animals choose to breed against it

is there an evolutionism for why these three are also the case?

Jebus, no. You are doing an almost indescribably bad job of interpreting and paraphrasing BrainHertz in this thread.

Try avoiding the rewrites and instead ask questions based on what is already written.

 

[Gottservant]

None of the following reply constitutes a complete answer.

Mutations are random, yes, but if they are all either neutral or detrimental

How did you come to the conclusion that all mutations are either neutral or random?

(because the species has already reached the top of a fitness 'mountain' and can't improve unless the environment changes or a slightly higher area can be found) then the species will remain more or less the same. It's kind of like a chemical system in equilibrium; even while you have tons of molecules reacting in both ways, the net effect cancels out so there is lots of movement and yet no movement.

How does something that cancels itself out ever become more than something which is cancelled out?

Asking whether mutations are stronger then selective pressures or not is meaningless. Selective pressures act[/i] on mutations. It's like asking whether x is stronger or weaker than f(x).

It is not irrelevant. Why is it that random mutation does not lead to random elimination?

As for the grasshopper, detrimental traits can be kept in the genome if they are detrimental but not quite detrimental enough to be weeded out. An example would be cancer in humans; it's the biggest killer today, but only because so many humans grow to old age when it becomes prominent. In the past this would rarely have been a problem. In addition, most cancer will occur well after the human in question has reproduced, if he plans to, thus not effecting reproductive success. You could also consider a trait that is detrimental but can't be removed by mutation without upsetting some other benefitial trait (for example, the way the optic nerve is arranged in the human eye creates a blind spot, but to fix it and move it the right way around is impossible; you'd have to travel through intermediate stages where the eyes do not work for millions of years, a clear disadvantage)

Ok. But you are not focussed on why I raised this detrimental trait. How is it that even though something negative about an organism might make it want to die that the creature necessarily tries to survive? How does survival become a concern of a creature by chance?

 

[Blayz]

Anyone worked out what an "evolutionism" is yet?

 

[anonymous1515]

Anyone worked out what an "evolutionism" is yet?

Hah. Still thinking that one through......

 

[anonymous1515]

How did you come to the conclusion that all mutations are either neutral or random?

Mutations are always random. However, from the perspective of the phenotype of the organism (i.e. its outward appearance, behaviour, etc) they can be one of three things: beneficial, neutral, or deleterious.

What patashu was saying is that if an organism reaches the upper boundaries of a certain trait (i.e. it can't get any larger because of various constraints), then selection will act to stabilize the trait.

For example, take a population of giraffes. Within the population, there will be individuals with shorter necks, medium necks, and longer necks. Now, these giraffes live in an area full of very tall trees, so selection is favouring longer necks. However, at some point the giraffe's neck may become so long that it can't support it's neck any more. At that point, selection would favour a medium-large neck length. Giraffes with necks that were too long would not be able to lift their heads, and would be at a fitness disadvantage. Giraffes with long-medium necks would be tall enough to reach the leaves, and would still be able to lift their heads. As such, selection would maintain the neck size at a medium-long neck size.

There are also constraints that may keep organisms from getting bigger or smaller. For example, a single cell can only become so large before it can no longer effectively manage it's nutrient uptake and waste export.

In trees, gravity is a major constraining force on tree height. It is just TOO hard for trees to transport water and nutrients up to very very high leaves, so there is an upper boundary on tree height imposed by gravity. That is why you don't see any 500 foot trees around.

It is not irrelevant. Why is it that random mutation does not lead to random elimination?

Natural selection. Hence the selection.

 

[Dal M.]

Did you know that the grasshopper, if trapped, automatically dies?

I'm surprised no one's called him on this bit of folksy-sounding nonsense yet.

 

[Hnefi]

I'm surprised no one's called him on this bit of folksy-sounding nonsense yet.

Yeah, I've caught plenty of grasshoppers in my childhood days, and they never died. They tended to leap away very quickly once I opened my hands or whatever container I caught them in.

 

[CACTUSJACKmankin]

Ok. But you are not focussed on why I raised this detrimental trait. How is it that even though something negative about an organism might make it want to die that the creature necessarily tries to survive? How does survival become a concern of a creature by chance?

Survival is not a concern by chance. Natural Selection will generally select for genes of self preservation. Actually personal survival is not the top priority, it's reproductive success. There are a number of animals that die not long after giving birth or use flashy colors and loud sounds (dinnerbells for predators) to attract a mate. Just because it has a fatal trait doesnt mean it will not keep trying to stay alive long enough to reproduce.

 

[Naraoia]

Are you saying mutations are regulated now? My understanding was that mutations were perpetually random. If it is true that mutations are perpetually random, there can be no stand still. Either mutations are weaker than selection pressures or they are stronger, are they not?

I smell a huge bunch of misunderstandings here... Anyway, let me cook up an analogy and try to explain how "regulation" comes into the picture of random mutations.

I'm sure you have heard of games of dice.

Let a die throw represent a mutation. Die throws are random (random enough for our purposes, anyway), just as mutations are.

However, what a certain throw gains you is regulated by the rules of the game. For mutations, the "rules" are set up by your environment. Two sixes may be the best throw in one game but a devastating loss in another. Similarly, being a bit larger than the rest is good for a stag, but very, very bad for an elephant on a small island where food is very limited.

How can there be standstills? I don't think there ever truly are, but, in theory, if an environment stayed stable long enough, the organism living in it could reach the best (physically/chemically/whatever) possible fitness. Then any change from that would be harmful and get discarded, and the population as a whole would stay the same.

Mutations would still appear, and still appear randomly, but now all of them would be harmful - which means basically all of them would disappear (this is not strictly true: especially in small populations, even slightly bad mutations can spread due to pure chance.)

But honestly I don't think there's such a thing as an evolutionary standstill.

First, organisms never quite live in a constant environment. If nothing else, a yearly variation in the amount of rain can kick off selection.

Second, organisms interact with other organisms, which means that a subtle change in one population can act as a selective pressure on a population of another species. The only way, say, a predator-prey arms race could ever stop is the extinction of one or both parties.

If mutations are weaker than selection pressures, how do they ever work? If they are stronger how do they ever stop?

This question makes no sense to me. Saying mutations are weaker than selection pressures is like saying dice are weaker than rules. What does that even mean?

Let me describe a particular creature in a particular situation as an example: the grasshopper. Did you know that the grasshopper, if trapped, automatically dies?

Where did you get this? I mean no offence, but it sounds like pure baloney... I've caught plenty of grasshoppers, and they all seemed quite alive when I let them go...

If a grasshopper dies, it does not pass on its genes, naturally; so this is a situation in which survival is not enough. People suicide as well. One must ask "how is it that survival ceases to be enough for the grasshopper, if it is evolved to survive" don't you think? After all, it may be trapped merely temporarily!

Setting your doubtful claim about grasshoppers aside, this is what natural selection is all about. Variation. Individuals aren't the same. Some people turn suicidal - big deal, they are less fit than the ones who happily go on living and reproducing. And the reason most of us don't commit suicide is because suicide is, well, quite detrimental to fitness. It will never spread in the population. In that sense, we have evolved to survive. However, there is nothing to say detrimental traits cannot appear in an individual. Ever heard of genetic diseases?

"If we are evolved to survive why do some of us commit suicide" is like asking "If cheetahs evolved to run fast why are some cheetahs slower than others?". In other words, one bloody stupid question.

I realise at this point that the issue of how a mutation becomes a controlling factor has split into two issues: how does it lead to the right responses to the environment and how are those responses recognised as right. As you can see I am able to learn from this.

(1) A mutation itself doesn't respond to anything. When it leads to the right response, it's purely by accident.

(2) Right responses are recognised by a very simple principle. If you get it wrong enough, you won't leave descendants. If you get it right, on the other hand, you will multiply and multiply.

There is no conscious "recognition" here. Very simple example, and quite directly tied to reproduction: sperm count. If you produce no sperm because of a mutation, that mutation obviously won't make it into the next generation, because you'll have no descendants at all. On the other hand, if you produce more sperm than your rivals, and several of you happen to befriend the same females (female chimps, for example, are rather promiscuous) - guess who's gonna be the father of most kids, simply by sheer numbers?

 

[Naraoia]

How did you come to the conclusion that all mutations are either neutral or random?

How did you come to the conclusion that he was saying this???

How does something that cancels itself out ever become more than something which is cancelled out?

Huh?

It is not irrelevant. Why is it that random mutation does not lead to random elimination?

Simple thought experiment for you:

If you drop 50 nylon-eating and 50 ordinary bacteria in a Petri dish containing only nylon as food and check back a week later, do you think you will still find equal numbers of nylon bugs and ordinary bacteria? Why or why not?

Ok. But you are not focussed on why I raised this detrimental trait. How is it that even though something negative about an organism might make it want to die that the creature necessarily tries to survive? How does survival become a concern of a creature by chance?

It becomes a concern of a creature because those that weren't concerned with it are - gasp! - dead, or quickly will be. And it so happens that such concerns can be inherited - so if your ancestors were concerned with survival, chances are that you will be as well (unless you have some mutation(s) that makes you unconcerned - then you will join the ranks of the unconcerned dead.)

 

[BrainHertz]

Ok and you are saying that

• it stays that way by chance
• it doesn't mutate out of control
• none of the animals choose to breed against it

is there an evolutionism for why these three are also the case?

What do you mean by "out of control"?

If the ecological niche changes, the species will drift towards a new equilibrium. Is that what you meant?

 

[Belk]

I'm smarter than to start by venturing my own thoughts here, but I am grateful that there are many who believe in their status as experts enough to help me out.

Again, don't try to put prejudice on me, I haven't stated an opinion at all.

Oh Goody! A Gottservant thread! <Grabs popcorn and pulls up the Barcalounger>

 

[BVZ]

And somehow that happens by chance?

(don't worry I read everything else you wrote)

Like... you accidentally get giraffes of the right size over time and then all of a sudden they are always the right size.

Not quote... but you are sort of going in the right direction.

Lets say you have a population of giraffes. Lets say there are a thousand of them.

If you measure them all, you will find that they will not all be the same hight.

In any environment there will be a perfect hight for a giraffe to be. If they are too tall, they will have a harder time supporting their heads. They will burn more energy pumping blood that high. They will use more energy maintaining the extra muscles.

But if they are too short, they will have a harder time feeding themselves.

So, there will be a balancing point or a sweet spot.

(Keep in mind that this perfect hight depends on the environment. If the trees are not that high, then the perfect hight will be lower, because giraffes that spend less energy growing that tall will be more successful, since they are more efficient.)

Anyway, back to the thousand giraffes.

You will have a bunch of giraffes that are not tall enough.
You will have a bunch of giraffes that are the perfect hight.
You will have a bunch of giraffes that are too tall.

Statistically speaking, the guys in the middle will have more offspring.

This implies that the next generation (again, statistically speaking), will have more members that fall into the sweet spot, since offspring get their genes from their parents.

This will continue generation after generation.

Now, chance DOES play a role.

Mutations are random.

Each generation, brand new mutations will be introduced. Since we are only looking at hight in this example, there are three possibilities.

1) A mutation can increase the hight of a giraffe.
2) A mutation can have no effect on the hight of a giraffe.
3) A mutation can decrease the hight of a giraffe.

This is random, in other words, how a mutation changes the hight of the giraffe born with that mutation is random.

Now, the perfect hight for a giraffe to be depends on the environment the giraffes are in.

You can have environment A, where a mutation is beneficial, and then you can have environment B, where the EXACT SAME mutation is deleterious.

Now, lets assume that the environment remains relatively static.

What will happen is that over generations, the giraffes will become increasingly adapted, until pretty much the entire population is the perfect hight for a giraffe to be.

Since they are all INSIDE the perfect region, any movement will move them OUT OF that region. Imagine that the perfect hight for a giraffe is 8m. Lets say that you have a giraffe that is exactly 8m high.

Now, it should be obvious that you cannot change the height of the giraffe, without moving it AWAY from 8m. In other words, any change in hight will make the giraffe LESS FIT.

So, once a population is very well adapted, all mutations will either have no effect, or they will be deleterious.

Now, imagine that the environment changes suddenly. This can happen for a variety of reasons. Lets say, climate change causes trees to be much lower.

Suddenly, all the giraffes that used to be perfect are not perfect anymore. Suddenly, mutations have the possibility of being beneficial again. Since it is possible again, and since they are random, beneficial mutations moving the giraffe population towards the new perfect hight can happen again.

Giraffes will adapt to the new environment. (Or they will go extinct.)

Now, imagine a population of giraffes. The one group stays where they are (group A), but a portion of them wander off into a different environment (group B).

What will happen is that the first group will evolve towards whatever is good in their environment, while the second group that migrated will evolve into whatever is good in their new environment.

Also, mutations keep happening, so any mutation in group A will be exclusive to group A, while any mutation in group B will be exclusive to group B. The result of this is that mutations will move the two groups AWAY FROM EACH OTHER.

If the groups remain apart long enough, their genes will no longer be compatible, and once this happen, they will continue moving away from each other.

Interestingly enough, both groups will still be giraffes. All ancestors of a population of giraffes will always be giraffes.

Another interesting thing about this process is that you won't see sudden changes. All changes are gradual. Each child will look pretty much the same as it's parent.

Does this answer your question?

 

[RecentConvert]

This thread is ridiculous...

Gottservant, you know that selection and random mutation can cause a difference in the size of a population. You've seen it happen, yourself. There are all manner of dogs, some very big and other very small. How did they get that way? Because of the natural variance in size and selective breeding. The variance is due to random mutation (among other factors) and happens in every population, everywhere. The selection that happens in the wild is called natural selection and works exactly the same way as breeding...

That's where different sizes come from...

 

[Gottservant]

Anyone worked out what an "evolutionism" is yet?

Evolutionism: an explanation designed to fit a theory in which any explanation is "ok" as long as it points to something perpetual (and not something final).

 

[Gottservant]

In trees, gravity is a major constraining force on tree height. It is just TOO hard for trees to transport water and nutrients up to very very high leaves, so there is an upper boundary on tree height imposed by gravity. That is why you don't see any 500 foot trees around.

Yes but where are all the trees that repeatedly try to be taller than 500 ft?

Mutation doesn't stop just because selection has taken place.

 

[Gottservant]

Yeah, I've caught plenty of grasshoppers in my childhood days, and they never died. They tended to leap away very quickly once I opened my hands or whatever container I caught them in.

You probably didn't trap them tightly enough.

What did you assume that everything automatically wanted to survive? I thought an evolutionist would say there was no "telos" to justify that...

 

[Gottservant]

Natural Selection will generally select for genes of self preservation.

Self-preservation is a gene?

So you think a grasshopper's genes for survival compete with its genes to die when it is trapped?

Not so... all grasshoppers die when trapped.

 

[Gottservant]

Two sixes may be the best throw in one game but a devastating loss in another.
[...]
This question [whether mutations are stronger or weaker] makes no sense to me. Saying mutations are weaker than selection pressures is like saying dice are weaker than rules. What does that even mean?

Have a look, you state earlier in the same post that you understand what I mean. Sometimes mutations are not enough to beat the rules, sometimes they are.

(1) A mutation itself doesn't respond to anything. When it leads to the right response, it's purely by accident.

Oh... so not only is life evolving a random event. Life surviving once it has evolved is another random event... and every time a subsequent descendent mutates that is another random possibility. Have you ever thought about how these odds stack up, realistically?

(2) Right responses are recognised by a very simple principle. If you get it wrong enough, you won't leave descendants. If you get it right, on the other hand, you will multiply and multiply.

That doesn't follow. Morever, how is the learned experience of how to use your DNA communicated in your DNA for future generations (after you have learned it) by accident? Besides which "multiply and multiply" means "mutate and mutate" to you (so there is no guarantee of anything being passed on)...

If you produce no sperm because of a mutation, that mutation obviously won't make it into the next generation, because you'll have no descendants at all. On the other hand, if you produce more sperm than your rivals, and several of you happen to befriend the same females (female chimps, for example, are rather promiscuous) - guess who's gonna be the father of most kids, simply by sheer numbers?

So perforce selection, everyone's sperm count perpetually increases. Not to offend, but to me that sounds ridiculous.

 

[Gottservant]

How can there be standstills? I don't think there ever truly are, but, in theory, if an environment stayed stable long enough, the organism living in it could reach the best (physically/chemically/whatever) possible fitness. Then any change from that would be harmful and get discarded, and the population as a whole would stay the same.

But wait a minute, how does a harmful change get

• recognised
• discarded
• protected against

It all happens randomly?

I think you are confusing what you grow with what you learn (they are not the same thing).