Is Evolution Gradual or Punctuated?

[John_Harshman]

@gbrooks9

Perfect DNA replication can be the mortal problem for any life, when looked at from the perspective of a whole population, rather than the perspective of a single individual.

It’s also physically impossible. But yes, there are theories that the rate of mutation in a species is under some form of selection, whether at the individual or the population level. Your statement may perhaps also explain why there is sex and why purely clonal animal species are rare and possibly short-lived. Though even there exceptions exist, as bdelloid rotifers.

[gbrooks9 (GeorgeB)]

@Ashwin_s

No, but I will read through it if you can share the details.

I think you will realize you’ve seen this video before…

The Evolution of Bacteria on a “Mega-Plate” Petri Dish (Kishony Lab)

Best arguments against Design (refreshed)

@anon46279830, You are using a script intended to refute an Atheistic view of Evolution. Here, the view is that God guides the evolution of humanity, as well as all the other creatures. It appears random from one view, but it is intentionally guided from a divine perspective. You use a very odd sentence: “When a change arrives, the environment is altered to suit it and encourage more change along that line so long as the environmental modifications are not unlike something they could encounter in nature.” In other words, if I understand you correctly, you propose changing the environment of, say, a test population of fruit flies, every time there is a mutation. If the population is big enough, there is a mutation (somewhere in the population) most every generation. And while we now have the technology to determine that there has been a genetic change in some sub-groups, but not others, we are certainly not in a position to know what the ultimate affect of a mutation might be.…

[T_aquaticus]

@Ashwin_s

At any point of time doesn’t the no: useful variations in the total no: of available mutations have to be random?

Selection will increase the frequency of beneficial mutations.

@Ashwin_s

Are you assuming that a fixed percentage of mutations will provide useful variations according to whatever environmental change is going on? (If the ratio of useful variations to total no: of mutations is random, then rate of change should be random).

The rate of morphological change is determined by selection, not mutation rate.

@Ashwin_s

I don’t see how anyone can predict this… or how this can be anything other than a random value.

That’s a failure on your part. Biologists can see how selection can influence the rate of morphological change.

[John_Harshman]

@Ashwin_s

Except that there is no guarantee any of this variation is useful.

Of course there’s no guarantee. But if variation is random, and there’s enough of it, some is likely to be in a useful direction. Random variation still has a distribution.

@Ashwin_s

Are you assuming that a fixed percentage of mutations will provide useful variations according to whatever environmental change is going on?

No. I’m assuming that variation will have a distribution, and that some portion of that distribution will be useful. And I see no reason why that distribution should change. Random does not mean unpredictable; single events are unpredictable but the distribution is not.

Here’s what I’m talking about:

The Evolution of Bacteria on a “Mega-Plate” Petri Dish (Kishony Lab)

[Ashwin_s]

@T_aquaticus

Selection will increase the frequency of beneficial mutations.

Provided they turn up. There is no guarantee that they do. In fact, if the percentage of animals that go extinct is anything to go by, the mutation that ensure survival in case of big changes rarely turns up.

@T_aquaticus

The rate of morphological change is determined by selection, not mutation rate.

Again, you are assuming that there is a variation readily available to be selected for. And that too again and again.

@T_aquaticus

That’s a failure on your part. Biologists can see how selection can influence the rate of morphological change.

Except when the species goes extinct…
It seems as if you are looking at a tiny part of the picture. I.e a small lineage of organisms that has successfully survived.

[T_aquaticus]

@Ashwin_s

Provided they turn up. There is no guarantee that they do. In fact, if the percentage of animals that go extinct is anything to go by, the mutation that ensure survival in case of big changes rarely turns up.

They only need to appear at a rate sufficient for some lineages to survive.

@Ashwin_s

Again, you are assuming that there is a variation readily available to be selected for.

The continuation of life on the planet Earth demonstrates that they are available.

[Ashwin_s]

@John_Harshman

Of course there’s no guarantee. But if variation is random, and there’s enough of it, some is likely to be in a useful direction. Random variation still has a distribution.

So it’s a statistical thing… the reason I ask is because there are two variables here-

1. One that the mutation actually causes some change in phenotype.
2. This change helps in surviving in the current environment.

Is there some kind of generic pattern to this? (like a binomial curve or something?).

Or does the distribution change in every scenario?

In which case an overall prediction should be very hard to pull off.
Though I can see how predictions or measurements could be made with specific scenarios like antibiotic resistance in bacteria.
Cool video there…
Thanks to @gbrooks9 also for sharing it.

[Timothy_Horton]

@Ashwin_s

Provided they turn up. There is no guarantee that they do. In fact, if the percentage of animals that go extinct is anything to go by, the mutation that ensure survival in case of big changes rarely turns up

You ignore the fact the average time for a species to remain in existence is over a million years, with some species lasting up to ten million years. Even with that in many cases the lineages didn’t go extinct. One species evolved enough morphological change over time to be considered by science to be a different species

[John_Harshman]

@Ashwin_s

Is there some kind of generic pattern to this? (like a binomial curve or something?).

I don’t think we know, nor do we know how the distribution changes. What we commonly observe in the present, though, is that there is phenotypic variation in all directions around the population mean, and it can often be represented by a gaussian distribution. For additive genetic variance, which is also common, that would reflect an underlying binomial distribution.

[T_aquaticus]

@Ashwin_s

Is there some kind of generic pattern to this? (like a binomial curve or something?).

There is a generic pattern for substitution mutations where some mutations are more common than others. In general, transitions are more common than transversions and CpG mutations occur at the highest rate. You can read more here:

Mutations Are Consistent With Biochemistry

In a previous thread I discussed what science meant by random mutations and how this term is defined by experimental results and statistics. A lot of this work was done in the 1940’s and 50’s, and since then many new facts have been discovered in the field of genetics, such as the discovery of DNA. This gave rise to the field of molecular biology and allowed us to understand biology at the molecular scale. So what exactly causes mutations? We once again have to reiterate the the limited scope of science. What science can do is put forward hypotheses and see if the evidence is consistent with that hypothesis. What science can not do is make ontological statements about absolute truth. With that in mind, the next few posts will discuss the evidence that links mutagenesis (the production of mutations) with the biochemistry of the cell and why scientists aren’t simply assuming that mutations are caused by biochemistry.

[Ashwin_s]

@John_Harshman

I don’t think we know, nor do we know how the distribution changes. What we commonly observe in the present, though, is that there is phenotypic variation in all directions around the population mean, and it can often be represented by a gaussian distribution. For additive genetic variance, which is also common, that would reflect an underlying binomial distribution.

Thanks for the info.
Since we don’t know how the distribution changes, how does anyone connect the rate of change of environment to rate of phenotypic change?

Since evolution is a complex process with many different subprocesses at play, I would guess that there should be no set trend for phenotypic change Vis a Vis rate of environmental change.

@T_aquaticus

There is a generic pattern for substitution mutations where some mutations are more common than others. In general, transitions are more common than transversions and CpG mutations occur at the highest rate. You can read more here:

I was asking something else. @John_Harshman answered my question.

@Timothy_Horton

You ignore the fact the average time for a species to remain in existence is over a million years, with some species lasting up to ten million years. Even with that in many cases the lineages didn’t go extinct. One species evolved enough morphological change over time to be considered by science to be a different species

I am not sure the last lines are true. Entire species don’t evolve morphological changes, populations do.

Morphological change is not a reason for a species to disappear from the planet. Extinction is.
Edit: are you suggesting that the vast majority of the extinction events are not dead ends?

[John_Harshman]

@Ashwin_s

Since we don’t know how the distribution changes, how does anyone connect the rate of change of environment to rate of phenotypic change?

Such evidence as we have suggests that the rate of phenotypic change is not generally limited by available variation but by the pace at which fixation can proceed, at least over the short term. It’s interesting that long-term rates of phenotypic change (over millions of years) are considerably smaller than short-term rates of change (over a few generations), which suggests that either environmental change is usually episodic rather than continuous.

@Ashwin_s

Morphological change is not a reason for a species to disappear from the planet. Extinction is.
Edit: are you suggesting that the vast majority of the extinction events are not dead ends?

There’s a thing that paleontologists call pseudoextinction, which means that a population changes enough that paleontologists (who have only morphology to work with) classify it as a different species, while the morphology no longer exists, so that “species” is extinct. There are many problems with this, the greatest of which is equating species in the biological sense — reproductively isolated populations — with this morphological notion of species. Best not to go there.

[Ashwin_s]

@John_Harshman

It’s interesting that long-term rates of phenotypic change (over millions of years) are considerably smaller than short-term rates of change (over a few generations), which suggests that either environmental change is usually episodic rather than continuous.

Or it could be that you are assuming a connection with environmental change is a main feature.

[John_Harshman]

@Ashwin_s

Or it could be that you are assuming a connection with environmental change

There has to be some connection if you think a) there’s adaptation and b) adaptation eventually reaches an equilibrium in a stable environment. Now the second isn’t strictly true, but it certainly gets to a low level of change after a while.

[Ashwin_s]

@John_Harshman

There has to be some connection if you think a) there’s adaptation and b) adaptation eventually reaches an equilibrium in a stable environment. Now the second isn’t strictly true, but it certainly gets to a low level of change after a while.

The implicit assumption being that adaptation is more effective when involving a change in environment.
It need not be so. An adaptation could just make an organism more effective in an existing environment.

The idea of stabilization seems to be connected to reaching an optimal form.

[John_Harshman]

@Ashwin_s

The implicit assumption being that adaptation is more effective when involving a change in environment.
It need not be so. An adaptation could just make an organism more effective in an existing environment.

Yes, and we do see adaptations of that sort. However, it’s also observed that adaptation eventually slows down in an unchanging environment, though it never quite stops. That’s a lesson of the Lenski experiment. So the way to keep the ball rolling at speed is to keep the environment ahead of it.

[Ashwin_s]

@John_Harshman

Yes, and we do see adaptations of that sort. However, it’s also observed that adaptation eventually slows down in an unchanging environment, though it never quite stops. That’s a lesson of the Lenski experiment. So the way to keep the ball rolling at speed is to keep the environment ahead of it.

This need not happen in nature. The environment could cause the ball to roll back…
Environmental change will be tuned to encourage specific adaptations only in the case of designed experiments. Otherwise, it could be changes such as from a low light environment to one with more light and vice versa… from high temperature to low temperature and vice versa… predators migrating into the environment and vice versa…
Environmental change could lead to loss of adaptations as much as gain.

It looks totally random imo.

Edit: and a lot of environmental change might be totally neutral in terms of the change in phenotypes.

[John_Harshman]

@Ashwin_s

Environmental change could lead to loss of adaptations as much as gain.

I think you’re confused as to what “adaptation” means. Environmental changes promote increased adaptation to that environment, which may result in loss of adaptation to another environment. Sure, if environments shift back and forth randomly without ever getting anywhere, nothing’s going to happen. But long-term trends do happen.

[Ashwin_s]

@John_Harshman

I think you’re confused as to what “adaptation” means. Environmental changes promote increased adaptation to that environment, which may result in loss of adaptation to another environment. Sure, if environments shift back and forth randomly without ever getting anywhere, nothing’s going to happen. But long-term trends do happen.

Or they are thought to have happened.
Bottomline being that environmental change need not cause adaptations to emerge or even stack up in all cases.

[gbrooks9 (GeorgeB)]

@Ashwin_s

Environmental change could lead to loss of adaptations as much as gain.

@Ashwin_s,

Don’t forget that “environmental change” could include changes in food supply or changes in predators.

You didn’t see my “Behe’s Adam” creation? It’s a conceptualization of Adam … without having an important adaptation degraded by specializing to a land-based life-style!:

As you can see… Adam no longer suffers from having over-specialized… and when the Great Flood comes, his descendants will be ready!

Or, @Ashwin_s,

a person could understand that if a species doesn’t degrade some of its prior adaptations to other situations… they will not be able to specialize very well to their new environment. God has designed quite a system with the elements of Natural Selection!

In any case, it looks like you have gone back to arguing against Godless Evolution… BioLogos is probably where you want to argue that lame duck.