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

[Patashu]

Ok so you are saying mutation is only semi-random?
Like if something survives, suddenly mutation becomes less random...

Mutation is completely random. Natural selection is random but acts apon mutations in a statistically significant manner. Members of a population with a detrimental mutation will be less likely to survive than those without the mutation and thus over time less and less members of the population will retain the detrimental mutation. (Hence differential reproductive success; the more reproductive success a mutation grants, the faster it will become prominent over time on average. Vice versa for detrimental traits.)

 

[BVZ]

Ok... but theoretically, mutations will still play a role. So if tall and short mutated, why will they not simply mutate again (resulting in a population of tall, medium & short when only medium is optimum) OR mutate to tall or short anyway, against the environment OR mutate away from being giraffes completely because randomness simply is random?

They will.

Mutations are random.

Any mutation can have any of the following effects:
1) The giraffe can be too tall.
2) The giraffe can be the perfect hight.
3) The giraffe can be too short.
4) The giraffe can be dead.

Since mutations are random, it can be any one of the 4.

Now, lets look at each one in turn.

1) The giraffe can be too tall.

When this happens, the giraffe will (statistically) have less offspring, and so, the following generation of giraffes will have less of this mutation. (One for each child.) The generation after that will have less yet, until the mutation dies out.

End result: Mutations that cause the giraffe to be too tall will die out, leaving giraffes that are better adapted.

2) The giraffe can be the perfect hight.

When this happens, the giraffe (statistically) will have more offspring than those that are any other hight. This means that the next generation of giraffes will contain more of this specific mutation than any competing mutations.

End result: Mutations that cause the giraffe to be the perfect hight will slowly spread, since they out compete other mutations.

3) The giraffe can bee too short.

When this happens, the giraffe (statistically) will have less offspring than those that are the perfect hight. This means that the next generation of giraffes will contain less of this specific mutation.

End result: Mutations that cause the giraffe to be too short will die out, for exactly the same reason as mutations that cause the giraffe to be too tall dies out.

4) The giraffe will be dead.

Certain mutations are lethal, and the fetus is aborted, or the fertilized egg doesn't get very far. Even giraffes born with lethal mutations might not reach reproductive age.

End result: These mutations are never propagated, and results in a dead end.

Now that we have examined all the possibilities, it should be clear that no matter what happens, in each and every possible case, the mutations that cause the giraffe to be the perfect length will cause the carrier of that mutation to have more offspring.

This means that there will be more genomes containing this mutation. The same thing will happen the next generation. Those with the beneficial mutation will have more offspring. Depending on total population size, a point will be reached where any giraffe looking for a mate will have a hard time selecting a mate that does NOT have this mutation. Once this point is reached, the mutation becomes fixed, and all giraffes in that particular population will have the mutation. The mutation is no longer the exception, but rather the rule.

Does this answer your question?

 

[BrainHertz]

Ok so you are saying mutation is only semi-random?
Like if something survives, suddenly mutation becomes less random...

Mutation is random.

Mutation + selection is statistical across a population, and the result is pretty predictable.

You have a range of some parameter (let's say height) in a particular population. The actual height of any particular specimen of that species is random within the distribution determined by the population genetics.

Selection pressure from the environment results in the statistics of the initial population's descendents being modified (but likely not by very much) such that over time the environment causes the selected for parameter to drift in a direction such that it is a better fit for the environment.


I think this will be my last post on this thread... I've been as polite as possible in my responses to you and it would be nice if you could actually return the favor.

 

[Naraoia]

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.

Let's say I tried to interpret what you meant. That doesn't mean I understood what you meant. Did I get it right, though?

Oh... so not only is life evolving a random event. Life surviving once it has evolved is another random event...

No, no, no. Let's go back to the dice.

If I throw my die a few times, what number it ends up showing is random. Therefore, if I get a winning number it is purely by accident.

However, once I've thrown the die and it gave me a number, it is the rules that decide if I win. If "survival" was also random that would be equivalent to throwing a die and then flipping a coin to decide if it was a winning throw, but that's not what happens in die games, is it?

Similarly, survival given a mutation is not random - it is, to a greater or lesser extent, determined by the interaction of the mutation with the local environment.

and every time a subsequent descendent mutates that is another random possibility. Have you ever thought about how these odds stack up, realistically?

No, because that's not how it works.

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?

It is not, although I'm not sure what you mean by learning. I assume you mean a mutation. If you are a sexually reproducing creature mutations only get passed on if they occur in sex cells, because normally that's your only part that contributes to your offspring. Actually, the mutations that get passed on don't affect the organism in which they originally occurred (i.e. the parent who produced the mutant sex cell). They only appear in the offspring, who gets all its cells from the single mutated parent cell.

BTW, you don't "learn" how to use your DNA. It's pretty much automated. Chemistry usually works fine all by itself

Besides which "multiply and multiply" means "mutate and mutate" to you (so there is no guarantee of anything being passed on)...

"Multiply and multiply" means "reproduce". Which almost inevitably comes with germ line mutations, but that's another story.

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

No, not indefinitely. Producing more sperm (and maintaining the bigger balls necessary) is also more costly than producing less of it. You only have a finite amount of energy and nutrients to spend on your various functions - if you want to give more to the balls, you have to take away from somewhere else. If the costs of increased sperm production outweigh the benefits, the organism must find other ways to increase its fitness.

 

[Naraoia]

But wait a minute, how does a harmful change get

• recognised
• discarded
• protected against

It all happens randomly?

The answer is it doesn't get "recognised". It just fails to work. That leads to automatic discarding. If something in your computer goes wrong it doesn't need you to check and find the problem before it crashes.

Protecting against (any mutation, not just harmful ones) happens by various DNA repair mechanisms. Without them, our mutation rate would be orders of magnitudes higher than it is now - in fact, a working genome the size of ours would be impossible. However, repair isn't perfect either, thus we occasionally do get mutations and evolution is possible. (Actually, a perfect repair mechanism would be very bad: it wouldn't leave room for adaptive change, so your perfect organism would be extinct the moment its environment changed)

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

What with what?

 

[Naraoia]

Read the quote a few centimeters above what I wrote.

I read it, that's why I'm confused. *shrug*

You are acting bemused but your reply isn't relevant. The poster suggested that equilibrium is maintained by things cancelling each other out, but neglected to think that maybe if things always cancelled each other out, they might never be in the first place.

And what if they didn't always cancel out?

Why should mutations be additive simply because creatures reproduce?

Umm, huh?

Simple thought for you: will the nylon-eating and ordinary bacteria cease to be nylon-eating and ordinary? The answer is no.

Completely and utterly irrelevant. Your question was, IIRC, something like, why doesn't random mutation lead to random elimination. I gave you a random mutation (the one that enables the nylon bugs to live on nylon), organisms with and without it, and asked you if you think they would be eliminated randomly in an environment where there's only nylon to eat. I said nothing about further mutations. Answer my question please. Or at least think about it.

Ok, you sound very smug at this point (I don't mind but) it does not follow that because something randomly mutates it automatically has the will to survive. By my account, that requires at least one extra and non-coincidental mutation (of which many are required when all factors leading to life as we know it are considered).

No, it does not follow. That's why you have suicidal people. But in the long run, suicidal mutations simply won't survive. Since the suicidal ones die out pretty quickly, you only see creatures that are either non-suicidal, or acquired the suicidal trait de novo.* Why would any of that require anything "extra and non-coincidental"?

Why don't all forms of life always have the will to live?

BECAUSE. MUTATIONS. ARE. RANDOM.

There's no guiding hand that carefully removes any new suicidal mutation before it could affect an organism - therefore these traits will pop into existence now and then, even though they pop out again very quickly.

*It should be noted that I don't think suicide in humans is quite as simple as this; nor do I think it's strongly heritable (and therefore it's quite a bad example when you want to discuss evolution). However, in general, any organism that lacks the "will to survive" - which could include not wanting to eat, not liking sex, or any number of other behavioural traits - is automatically out of the "struggle for existence".

 

[Naraoia]

If by tightly trapping them you mean crushing them to death, then yes, I agree with you - Grasshoppers always die when you "trap" them.