Randomness in Evolution: Valid and Invalid Usage

[jimbob]

But that is not what the paper is saying, the authors are saying that this experiment is support for the idea that if one could "rerun the tape of evolution" one would get (significantly) different outcomes. How is this "predictable"?

I explained precisely how, and gave an example of an experiment that verifies that prediction.

Yes but isn't your prediction simply stating that "if an organism's descendants survive until (it is certain that) a trait evolves, then it is certain that the trait will evolve"?

There was the other caveat which you missed out, which was if another incompatible trait hadn't evolved beforehand. For example, a herbivore's descendants might eat the leaves from the top of a tree by becoming smaller, and better able to climb on small twigs, or by becoming larger and reaching these twigs. One reduces the possibility of the other.

I am interested in the discussion that is occurring in evolutionary biology which is between the school of thought that states evolution is broadly repeatable (many paths but few destinations") and the opposing school of thought which states that it is not broadly repeatable, (many paths many destinations).

You are missing out the fact that *eventually* this trait would evolve, if the population hadn't been wiped out in the meantime, or the environment hadn't changed, or if another incompatible trait hadn't evolved first.

I didn't miss that - I already commented on it, in fact.

Fair enough, we were cross-posting.

This is also a very simple ecosystem. With more different types of interactions, and with longer time, there would be more scope for more random events to alter the course of evolution.

So what? Every scientific theory in the history of human thought is subject to exactly the same criticism. They are all simplifications, models for reality that do not take every possible event into account. They tell us what will happen under certain limited and controlled conditions, not simply what will happen.

There are simplifications and simplifications. The experimental setup was designed to minimise the effect of random factors, to investigate whether the same results would occur if you "reran the tape" of evolution. In other words whether evolution is broadly repeatable or not. The authors' conclusion is that it is not even in the simplest of environments.

In any more complex environment, random interactions would be even more important.

But these are nontrivial qualifying statements. Only a tiny minority of any organisms successfully reproduce. Most organisms that have lived have no living descendants. Most species that have existed have no living descendants.

And?

Your prediction doesn't work if the descendants become extinct, which is the usual fate.

As I have said before, if the environment is stable then over short-enough times the randomness is unimportant. Over tens of thousands of generations, random factors significantly alter the course of evolution so that entire ecosystems and their niches work completely differently.

 

[jimbob]

You assertion is only true if the mutation an infinite number of times. If the mutation only occurs a finite number of times, there will still be a non-zero probability that the mutation will go extinct.

Which is exactly what I've been telling you for the last 15 posts. Good to see you've finally caught on.

So you are describing how evolution would work in an impossible situation, not how it does work in reality?

 

[sol invictus]

Yes but isn't your prediction simply stating that "if an organism's descendants survive until (it is certain that) a trait evolves, then it is certain that the trait will evolve"?

No.

Although even that would suffice to demonstrate my point.

There was the other caveat which you missed out, which was if another incompatible trait hadn't evolved beforehand.

I didn't miss that - I mentioned it specifically.

(ETA: actually after glancing through the thread I don't see it. It was in some version of one of my recent posts, but perhaps I edited it out to try to avoid clutter. Anyway I agree that's a caveat.)
.

So you are describing how evolution would work in an impossible situation, not how it does work in reality?

All scientific theories are like that. Deal with it.

 

[mijopaalmc]

Which is exactly what I've been telling you for the last 15 posts. Good to see you've finally caught on.

I acknowledged that way back when you claimed "that eventually, all bacteria in that petri dish - and therefore eventually, in all petri dishes - should have the ability to metabolize citrate":

The crucial thing that you are seemingly ignoring is that it take an infinite amount of time for you to be certain that all the cultures will have evolved the cit+ phenotype. Thus, in any finite universe and for any finite experiment, there is a non-zero probability that you will observe at least one of the cultures will not have evolved the cit+ phenotype. This is, of course, perfectly consistent with evolution being a random (stochastic) process and completely inconsistent with evolution being a non-random (deterministic) process.

You've gone from claiming this is unfalsifiable to claiming that this result falsifies it. You're utterly incoherent.

The claim that phenomenon X will happen given infinite time is unfalsifiable, because an observation that X has not happened by a specific time does not preclude it from happening at any time in the infinite future. Like the apocalyptic visions of the future in liberal Christianity, it can always be claimed that "we haven't waited long enough".

What it is falsifiable is the behavior of populations in finite time and the observation of fixed deleterious mutations contradicts the related (but falsifiable) claim that advantageous mutations always go to fixation. In other words, your claim that advantageous mutations always, eventually go to fixation in infinite is unfalsifiable, but the weaker claim that advantageous mutations always got to fixation in finite time is falsifiable and an has been falsified.

 

[sol invictus]

In other words, your claim that advantageous mutations always, eventually go to fixation in infinite is unfalsifiable, but the weaker claim that advantageous mutations always got to fixation in finite time is falsifiable and an has been falsified.

Incoherent nonsense as usual. The second claim is stronger, not weaker, and I never made it - at least not if you mean some fixed, given finite time.

If you mean any finite time, then the two claims are mathematically and logically identical, in which case you are contradicting yourself.

 

[Wowbagger]

... multicellular life wouldn't evolve on an Earthlike planet within 6-billion years, which is pretty close to the length of time that such a planet is actually habitable.

Well, yes, it would take a long time. But, it would still almost inevitably crop up as a result of the natural progression of symbiotic relationships.

And where do Kimura and Ohta forget to take that into consideration?

I do not know. But, you at least seem to be missing the point. Small selective advantages will magnify over time.

You've made some fine assertions. Now the onus is one you to provide evidence to support them.

It is not a assertion. It is a fundamental fact of biological science, that has been known and well understood by scientists for decades!

One of the best illustrations of this, that I have seen, came from the book The Making of the Fittest by Sean B. Carroll, involving rock pocket mice, which live on both dark lava flows and lighter, sandier rocks. The mice on the darker lava flows have subsequently darker fur.
He worked out, (starting on page 59), two things about them: How long it would take for a black-causing mutation to arise in light-colored mice, and how quickly it would spread.
The details are interesting, and I will see if I can find an Internet link, later. But the bottom line is this:

In a population of 100,000 mice (each with several possible mutation sites that would do it), you would expect the dark gene to occur once every 100 years.
And, even if only one individual gets it, you would expect that gene to spread completely in at most 200 years, assuming it was only a tiny advantage. (This, I remind you, is an evolutionary blink-of-an-eye.)
However: The more of an advantage the dark gene has, the faster it would spread – in as little as 9 years if it was a massive advantage.

 

[Wowbagger]

I would disagree with you on the "general function" argument.

I would say that the evolution of grasses was one of the most significant events of the last 100-million years. There were whole niches that could not exist before then. There could be no niche for "herds of wildebeest" in the Permian Period.

Without Savannah or Tundra, whole ecosystems would be grossly different.

Your example of wildebeest and grasses is too specific. I was talking about general relationship structures. On this planet, we have many examples of one life form being dependent on another – either mutually or parasitically. Chances, are, other planets with life would have lots of them also, even if, for strange some reason, grasses would never be able to grow.

 

[jimbob]

... multicellular life wouldn't evolve on an Earthlike planet within 6-billion years, which is pretty close to the length of time that such a planet is actually habitable.

Well, yes, it would take a long time. But, it would still almost inevitably crop up as a result of the natural progression of symbiotic relationships.

But that isn't inevitable, if multicellular life doesn't evolve before a planet becomes uninhabitable, then multicellular life won't evolve.

Your example of wildebeest and grasses is too specific. I was talking about general relationship structures. On this planet, we have many examples of one life form being dependent on another – either mutually or parasitically. Chances, are, other planets with life would have lots of them also, even if, for strange some reason, grasses would never be able to grow.

I was talking about large herding grazing herbivores, which have appeared in all large areas of grassland.

Of course there would have to be a food chain, and of course there would be primary producers and consumers, etc, but that isn't a very interesting prediction in my opinion. The differences are going to be more important.

Multicellular life or not would make a huge difference to the ecosystem.

 

[jimbob]

.

So you are describing how evolution would work in an impossible situation, not how it does work in reality?

All scientific theories are like that. Deal with it.

I would disagree, the describe how a system works in an idealised manner with some simplifications. They are abstractions. Useful theories help make useful predictions.

What you are saying is "well it might work like that in reality, but it doesn't in theory"

I am stating that theory can account for the case in reality that evolution of traits is not inevitable, but there would be different likelihoods of occurrence for different traits, as the "window" for evolution of any trait is not infinite.

Infinite time, infinite populations or infinite resources are (nearly) worthless simplifications when discussing evolutionary systems.

 

[Wowbagger]

But that isn't inevitable, if multicellular life doesn't evolve before a planet becomes uninhabitable, then multicellular life won't evolve.

Okay, so it is inevitable as long as the planet lasts long enough for it to happen. But, that should go without saying.

I was talking about large herding grazing herbivores, which have appeared in all large areas of grassland.

The predictions, of course, work on a scale: The more general then the more likely; the more specific then the less likely.

Herding, grazing herbivores is kinda mid-range between those two extremes. Perhaps grass won't grow on all planets. But, there is no reason why something like it wouldn't grow on a good number of them. Once you have "grass", I suspect an opportunity for a grazing niche to take off would be nearly automatic.

Of course there would have to be a food chain, and of course there would be primary producers and consumers, etc, but that isn't a very interesting prediction in my opinion. The differences are going to be more important.

Yes, it is true that the differences are going to be important. But, I still think it is interesting to think about the "universals" of life. They also tell us a lot about ourselves, as much as the details do.

 

[jimbob]

Okay, so it is inevitable as long as the planet lasts long enough for it to happen. But, that should go without saying.

But given the observation that it took 3-billion years on this planet, then with the sort of logic used by xenobiologists, a significant proportion of planets where life evolves and where there is the capability of multicellular life evolving would not evolve multicellular life.

It might be better to say that if life evolves on an Earthlike planet, then there is about an 80% chance* of multicellular life evolving. This is far from inevitable.

*I can't be bothered to do the sums, but it is something akin to these odds assuming that life evolved on Earth in the most typical time.


"If I roll a die

and it doesn't fall on a number less than 3,

it is inevitable that it will fall on a number greater than 3"

The qualifying statement is fairly important and arbitrary.

 

[Wowbagger]

It might be better to say that if life evolves on an Earthlike planet, then there is about an 80% chance* of multicellular life evolving. This is far from inevitable.

All right, but it's still pretty darn good, (assuming the number is at least somewhat correct).

Studying what sorts of factors would cause 20% to not evolve multicellular life would be very interesting.

 

[mijopaalmc]

All right, but it's still pretty darn good, (assuming the number is at least somewhat correct).

Studying what sorts of factors would cause 20% to not evolve multicellular life would be very interesting.

Not as interesting as studying the sorts of factors that permitted the evolution of multicellular life.

Why do you assume that there is some phenomenon that must prevent the evolution of multcelluraity?

 

[Wowbagger]

Not as interesting as studying the sorts of factors that permitted the evolution of multicellular life.

Why do you assume that there is some phenomenon that must prevent the evolution of multcelluraity?

BOTH are interesting!

But, it stems from what I understand about evolutionary trends:

1. The opportunity for cells to "experiment" with communal ways is more likely to happen than not, given enough time (even if it is not quite as "inevitable" as I stated earlier).

2. Some of these experiments will yield more efficient resource management for the group.

3. The efficiency will thus turn into a fairly strong selective advantage.

The cells might not be working in a truly "multicellular" way, at this early stage. But, subsequent iterations would improve the relations.

There are several ways "communities" of cells can work together, that form potential precursors to multicelluarism, as we see (for example) in sea sponges and hydras.


If there are any factors that can be identified that would either prevent "experimentation" with communal habits, OR prevent those "experiments" from ever working out to anyone's advantage; I think it would be a fascinating find.

 

[mijopaalmc]

Thought this might be interesting:


The frailty of adaptive hypotheses for the origins of organismal complexity

 

[jimbob]

All right, but it's still pretty darn good, (assuming the number is at least somewhat correct).

Studying what sorts of factors would cause 20% to not evolve multicellular life would be very interesting.

Luck. Brownian motion not moving collections of chemicals into a fortuitous position at an opportune time, for example.



I haven't found much- but this suggests that I was being too optimistic:

http://www.uea.ac.uk/mac/comm/media/press/2008/apr/Is+there+anybody+out+there%3f

I can't find the actual paper, and he is discussing the odds of intelligent life (per solar system I'd imagine) as opposed to multicellular life, but 80% looks too high.

The first difference is that I was working on the assumption that the Earth would be habitable for another 3-billion years (poor google-fu on my part), whilst it looks as if another 1-billion years is a better estimate.

 

[Wowbagger]

Luck. Brownian motion not moving collections of chemicals into a fortuitous position at an opportune time, for example.

"Luck" is a pretty flimsy answer.

The "Brownian motion" argument is better, but even that disappears with the long length of time. Especially in light of networking theories.

I haven't found much- but this suggests that I was being too optimistic:

http://www.uea.ac.uk/mac/comm/media/press/2008/apr/Is+there+anybody+out+there%3f

It looks, to me, like Professor Watson is making the same mistake William Dembski makes.

Recall that (in a nutshell) Dembski argues that evolution of certain things is impossible, because each of the steps would require an astronomically prohibitive probability. For example: He would claim that each of the steps in a protein chain would have the same probability of evolving, as you would have finding a winning lottery ticket on the ground, every single day, for hundreds of years.
Dembski forgets that cumulative probability is important in evolution, not simply "adding up" the probabilities of each of the steps.

Of course, I could be wrong about Professor Watson. But, this paragraph from the article is an example of what leads me to the suspicion:

Prof Watson, from the School of Environmental Sciences, takes this idea further by looking at the probability of each of these critical steps occurring in relation to the life span of Earth, giving an improved mathematical model for the evolution of intelligent life.

It sounds, to me, like he is sidestepping the whole cumulative process of evolutionary systems.

Thought this might be interesting:


The frailty of adaptive hypotheses for the origins of organismal complexity

Yes, but it's old news to me. There is no doubt that genetic drift and other factors make an impact in evolutionary systems. Though, he is using the word "adaptive" very specifically to illustrate that. (And, for good reason.)
If one defines "adaptive" just a little broader, then all that genetic drift could be said to be "adaptive", once it does infer a small benefit to the life form.

From the selfish-gene point of view, any genes: be they useful to the whole life form or not, that manage to replicate themselves successfully - could be said to be "adaptive" at the most basic, fundamental level.

 

[jimbob]

"Luck" is a pretty flimsy answer.

The "Brownian motion" argument is better, but even that disappears with the long length of time. Especially in light of networking theories.

Or asteroid strikes at the wrong time. And anything between these two sizes of effects.


I was saying that when life arose on Earth there was a significant chance that it would never have evolved into multicellular life. If you assume that the most likely length of time is 3-billion years, and there is a window of 5-billion years, then (just because the maths is simple) assume that on 50% of lifebearing planets, it takes less than 3-billion years, and 50% take longer. With an analogous calculation to radioactive half-lives, then by 6-billion years 75% of lifebearing planets would have evolved multicellular life.

In other words, with this simplistic set of assumptions, and a larger window for habitable life, you get a 25% chance that multicellular life wouldn't evolve, because the correct circumstances didn't come around.

It looks, to me, like Professor Watson is making the same mistake William Dembski makes.

Recall that (in a nutshell) Dembski argues that evolution of certain things is impossible, because each of the steps would require an astronomically prohibitive probability. For example: He would claim that each of the steps in a protein chain would have the same probability of evolving, as you would have finding a winning lottery ticket on the ground, every single day, for hundreds of years.
Dembski forgets that cumulative probability is important in evolution, not simply "adding up" the probabilities of each of the steps.

Of course, I could be wrong about Professor Watson. But, this paragraph from the article is an example of what leads me to the suspicion:



It sounds, to me, like he is sidestepping the whole cumulative process of evolutionary systems.

I think not. Dembski is looking at something and saying "what were the odds of that particular mutation occurring", and implicitly assuming that 'On Earth' goes without saying.

He then says that these odds are very small, and doesn't realise that there are multiple other options. The odds of seeing a particular car numberplate on the next car you see might be a million to one against, but if you see a car it will almost certainly have a numberplate.

Professor Watson is saying "what are the odds of intelligent life arising under certain conditions" - I guess "around a G-type star". I read this as arguing that it is unlikely within a certain volume of space.

EDIT: Professor Watson's basis for saying that the odds are highly against intelligent life because we have observed that intelligent life has taken 4-billion years to arise on Earth; i.e, it has taken about 80% of the habitable window to arise on Earth. This must mean it is a low-frequency event, with a low probability within any billion-year period.

I think he is probably being a little too pessimistic, but even if large mammals were the first organisms with the potential of evolving into complex-tool using social animals, then suitable "candidate species" had been around for at least 35-million years without filling that particular niche. This is (optimistically and incorrectly) assuming that there has been a steady progression with increasing complexity with increasing age of the Earth.

 

[jimbob]

Yes, it is true that the differences are going to be important. But, I still think it is interesting to think about the "universals" of life. They also tell us a lot about ourselves, as much as the details do.

I agree with that, but in the current debate within evolutionary biology everyone (AFIK) accepts that there are universals. The discussion is whether the same sets of traits in similar organisms would always evolve with only inconsequential differences or whether the differences would be more fundamental.

In other words, given the KT event, would a hominid-analogue always have evolved within the next 60-million years or so?

 

[Wowbagger]

Or asteroid strikes at the wrong time. And anything between these two sizes of effects.

The opportunity would probably occur more than once. An asteroid would have to strike at "the wrong time", many, many different times. What are the chances of that happening?

In other words, with this simplistic set of assumptions, and a larger window for habitable life, you get a 25% chance that multicellular life wouldn't evolve, because the correct circumstances didn't come around.

For argument sake, if we assume your calculations are correct: That is still some pretty good odds. Yes, that 25% is a significant number. But, that still implies 3/4 of all planets where live arises would obtain multicellular life.

That tells us, at least, that multicellular life is something that replicators will tend to develop towards, and not something that is truly a chance occurrence. Something would have to interrupt the process before it completes - for it not to happen.

By analogy:
Tadpoles will generally develop towards becoming frogs, unless the process is interrupted. You could say the same thing about single cells and multi-cell species: Albeit the time scales are greatly different.

Perhaps, instead of saying certain things are "inevitable", it would be more accurate for me to say that certain things will "tend to happen by default", unless they are interrupted by insurmountable disaster, over and over again, every single time those things try to happen.

Given how many planets there are, success is almost certainly likely on some of them, at least.

Professor Watson's basis for saying that the odds are highly against intelligent life because we have observed that intelligent life has taken 4-billion years to arise on Earth; i.e, it has taken about 80% of the habitable window to arise on Earth. This must mean it is a low-frequency event, with a low probability within any billion-year period.

What this tells me is that it is something that life forms will "develop towards", but it takes a long time to get there. (And, that it could be interrupted before it does, I suppose.)

In other words, given the KT event, would a hominid-analogue always have evolved within the next 60-million years or so?

I don't know if a hominid-analogue would develop, specifically. But, given how many different ways there are for two-leggedness to arise, it seems reasonably probable that circumstances would favor one of them, eventually.

But, I would be in the camp that would say intelligence would have likely evolved on Earth, even if the KT event never took place, though it might not be in the same form. It might not be hominids, nor even mammals for that matter. But, whichever life form manages to acquire it first, would probably dominate the place.