Evolution thoughts: directed evolution

[Stephanie]

Evolution thoughts for today: directed evolution

1. We are fixated on germ cells. Somatic cells can evolve as well. A beneficial mutation in a somatic cell can be passed to its offspring. Adapted offspring can outcompete others. Cancer is one example, but is it possible to evolve a better stomach lining, not just stomach cancer? Who decides? However, somatic evolution dies with you, right?

2. Haploid germ cells are produced from somatic cells. Can evolved somatic cells, inexact copies of the DNA of the original zygote, produce germ cells?

3. No one has found any mechanism for "directed evolution," the idea that the environment pressures a germ cell change in the adaptive direction. The idea is Lamarckian, to be sure. However, the speed and detail of evolutionary change test even Dawkins blind watchmaker explanations and leave one wanting for some direction.

4. Look at 3 in light of 1 and 2.

 

[BillHoyt]

Evolution thoughts for today: directed evolution

1. We are fixated on germ cells. Somatic cells can evolve as well. A beneficial mutation in a somatic cell can be passed to its offspring. Adapted offspring can outcompete others. Cancer is one example, but is it possible to evolve a better stomach lining, not just stomach cancer? Who decides? However, somatic evolution dies with you, right?

2. Haploid germ cells are produced from somatic cells. Can evolved somatic cells, inexact copies of the DNA of the original zygote, produce germ cells?

3. No one has found any mechanism for "directed evolution," the idea that the environment pressures a germ cell change in the adaptive direction. The idea is Lamarckian, to be sure. However, the speed and detail of evolutionary change test even Dawkins blind watchmaker explanations and leave one wanting for some direction.

4. Look at 3 in light of 1 and 2.

Stephanie,

First, welcome to the JREF board!

Second, there are very few scientists who would agree with what you've written, I'm afraid. Ted Steele, IIRC, in Australia, is one of the few "neo-Lamarckians" out there. His recent book on the subject, whose name I can't recall, offers some interesting evidence and many (frankly) lame arguments.

If you look at what happens in a diploid organism, though, I think you'll start to see the problem. Let us say that something the organsim has encountered causes a change in a soma cell. This would normally, of course, have to be a mutation of the DNA. How is this transmitted to the sperm or ova? How does it get there? How many of them flow to the sperm or ova?

If this thing did happen, then why has experiment after experiment trying to show such a mechanism failed? From cutting mouse tails onto changing plants via somatic changes, they have almost all failed.

Now, to muddy the waters a bit, there are some interesting intergenerational things that happen that seem to stave off the effects of mutations or to alter the translation of DNA in the progeny. These are mostly short-lived changes, lasting into the next generation and then going away, and they are almost all connected with proteins whose purpose seems to be to ensure survival under conditions of extreme heat or extreme cold.

Cheers,

 

[arcticpenguin]

However, the speed and detail of evolutionary change test even Dawkins blind watchmaker explanations and leave one wanting for some direction.

I do not agree. Life has apparently been around for billions of years. Can you imagine that span of time?

A bacterium, under ideal conditions, can reproduce itself in 15 minutes or less. Do the math, and tell me how many generations could occur in a one billion year span

 

[hgc]

Re: Re: Evolution thoughts: directed evolution

I do not agree. Life has apparently been around for billions of years. Can you imagine that span of time?

A bacterium, under ideal conditions, can reproduce itself in 15 minutes or less. Do the math, and tell me how many generations could occur in a one billion year span

I did the math. It's 35,040,000,000,000 generations (that's 35 trillion), based on a 365 day year. So it's actually more. Actually, my calculator did it, but I pressed the buttons.

Stephanie:

... Cancer is one example, but is it possible to evolve a better stomach lining, not just stomach cancer? Who decides? However, somatic evolution dies with you, right?
...

Who decides? Ever heard of natural selection? Am I missing something here?

 

[hgc]

Actually, I was being dense about the Lamarckian topic of the original post. I'll slink away now.

 

[Dancing David]

Hi Stephanie,

I am dense but how can a somatic change be passed on to offspring?

Is this reference to baceria.

Welcome to this wacky island, the natives are friendly but beware the trolls!

 

[NWilner]

Stephanie is on to a deeper subject than it seems at first blush.

The idea of a single organism evolving a stomach somatically during life is -- quite a concept. There isn't a real reason why individual somatic cell lines could not evolve, is there. When she says "who decides?" she alludes to one of the central questions in all biology: how does the organism "get" its cells to behave for the benefit of the entire organism, not just their local benefit? Who decides if a stomach evolves in an organism? Does the organism have a "say" or do the individual cells decide? I use "decide" in the evolutionary sense.

The issue of control of cells versus cancer, i.e. how do you get differentiation of cells, how do you control them, is maybe the most incredible biological issue I can think of.

Arcticpenguin correctly counts bacteria generations, but these aren't elephant generations. Yes, we all (I think) believe that natural selection works. Stephanie says maybe it works on the individual cells as well as on the organism level. THe only trouble is: how to get that evolved cell to be a father of a germ cell. No way I know, but hey, I don't know it all. And it's not impossible, i.e. a violation of the laws of physics or something.

I would like to hear some more serious biologists weigh in here. But I think this is more than meets the eye.

 

[BillHoyt]

The idea of a single organism evolving a stomach somatically during life is -- quite a concept.

Let's pose a question for Stephanie and you to reflect on: define evolution. Do it two ways, please. The first is at the level of the organism. The second is at the level of the genes. What is the basic definition of evolution at those two levels?

Cheers,

 

[Paul C. Anagnostopoulos]

Stephanie asked:

2. Haploid germ cells are produced from somatic cells. Can evolved somatic cells, inexact copies of the DNA of the original zygote, produce germ cells?

Not in human females, where all eggs exist at birth. Not in human males, where germ stem cells in the testes divide to produce sperm cells. Those germ stem cells can certainly contain mutations, but I don't think there is the equivalent of selection occuring among those cells, so they are not "evolving."

~~ Paul

 

[Morwen]

Here's an interesting thing: although in animals the somatic and germinal lines are well defined and separated, and they do not mix, this is not the case in plants. At some point during plant development, some somatic cells are "directed" towards a germinal pathway and turn into gametes. How this happens I'm not sure about, I'd have to look it up if you want details. But the fact is that, in plants, the germinal cell lineage is not isolated from the somatic lineage, which raises lots and lots of interesting questions, many of which still have no answer. Plants manage remarkably well to keep their genome free from deletereous mutations and they do not seem to have unexpected evolutive effects from this trait of their physiology. There's evidently more here than meets the eye, although nothing that suggests Lamarckism in any form: no hint of any inheritance of acquired characters at all.

Funny world. We know so little yet... That's why it's so much fun! There are questions to answer!

 

[BillHoyt]

Here's an interesting thing: although in animals the somatic and germinal lines are well defined and separated, and they do not mix, this is not the case in plants. At some point during plant development, some somatic cells are "directed" towards a germinal pathway and turn into gametes. How this happens I'm not sure about, I'd have to look it up if you want details.

What you describe here is pretty much the same for animals, Morwen. Perhaps you're trying to describe the Weismann barrier that seems to be present in animals, but is not as clear-cut in plants. This "barrier" was conceptual and attempted to explain why Lamarckianism did not work. In plants, the "breakdown" has been shown on three fronts that I can recall:

o CSPs (cold shock proteins), which show changes in the progeny that are due to parental activation of these proteins under extreme cold conditions,
o HSPs (heat shock proteins) - see above, except under extreme heat conditions,
o suggestions in the literature of next-generation, non-mutational responses to chemicals taken up by the parents

But the fact is that, in plants, the germinal cell lineage is not isolated from the somatic lineage, which raises lots and lots of interesting questions, many of which still have no answer. Plants manage remarkably well to keep their genome free from deletereous mutations and they do not seem to have unexpected evolutive effects from this trait of their physiology. There's evidently more here than meets the eye, although nothing that suggests Lamarckism in any form: no hint of any inheritance of acquired characters at all.

Funny world. We know so little yet... That's why it's so much fun! There are questions to answer!

Yes, there are many questions to answer. That is the delight of science. But your plants that "keep their genome free from deleterious mutations" is certainly a mystery to this strip-club bouncer. Where do you get this from?

Cheers,

 

[NWilner]

Personally in my heart of materialist hearts, I would not be surprised if somehow someway there is discovered a mechanism for directed evolution. I say this with full acceptance of the natural selection mechanism and the teriffic work by Dawkins to describe "Mt. Improbable."

"Directed" is not meant to describe a conscious direction. Direction in this sense means, maybe, like work hypertrophy of muscle in response to load. Muscle gets stronger when worked. It doesn't mutate randomly and then get selected. It has a direction.

Can organisms respond to the environment like muscle to work?

 

[Morwen]

What you describe here is pretty much the same for animals, Morwen. Perhaps you're trying to describe the Weismann barrier that seems to be present in animals, but is not as clear-cut in plants. This "barrier" was conceptual and attempted to explain why Lamarckianism did not work.

I confess I had never heard of the Weismann Barrier until now. I did a little digging via Google and found some info; it's an interesting concept.

What I was -badly- trying to point out is that, taking the developmental pathway of an animal embryo (say a fly embryo) and a plant embryo (say an A. thaliana seed), the stage at wich, in the animal, the germ line is segregated from the somatic line happens far, far sooner than in the plant. I choose the two models for plant and animal development because there is a lot of info on each of them.

In Drosophila, after the germ band elongation stage, the germline cells have already been differentiated from the somatic line, and are tucked away from then onwards, completely apart from the rest of the organism and rather below the outer cell layers. This happens at stage 9, less than 4 hours after fertilization. Events that might affect the germ line here are of the kind that you point down below, triggering HSP or CSP, but apart from that, the germ line is quite safe from environmental factors. Or, rather, safer than the somatic line.

Not so with plants. Gamete formation starts when flowers develop, which happens roughly 25 days after sowing, at stage 5 or 5.10. During these 25 days, the cells that will eventually be fated as the plant's germ line have been exposed to the same kind of stress than the rest of the plant, from chemical stress to high salinity, drought, sun damage, or mechanical attacks. And, of course, everything that might trigger the HSP or the CSP. After the plant has its set of gametes, it's possible to talk about the Wiseman barrier, but since before that no discrete set of cells has been fated to be germline cells, there's no point.

So, apart from the events that might cross the Weismann barrier, one has to take into account the fact that plant germline has been in a "higher risk" environment than the animal germline, so to speak.

In plants, the "breakdown" has been shown on three fronts that I can recall:

o CSPs (cold shock proteins), which show changes in the progeny that are due to parental activation of these proteins under extreme cold conditions,
o HSPs (heat shock proteins) - see above, except under extreme heat conditions,
o suggestions in the literature of next-generation, non-mutational responses to chemicals taken up by the parents

Of that I know very little. There were some HSP studies in the lab I worked in, but they were more related to the behaviour of transposons, I'm afraid.

Yes, there are many questions to answer. That is the delight of science. But your plants that "keep their genome free from deleterious mutations" is certainly a mystery to this strip-club bouncer. Where do you get this from?

Cheers,

I expressed myself badly. My apologies. Certainly plants do have deleterious mutations. What I find surprising is that, given that their gametes were originally somatic cells, which tend to be more vulnerable to DNA damage, all experiments show that the rate of mutation in plants is not significantly higher than in animals, who keep our cell line segregated and more protected (relatively speaking) during the greater part of our development. There are many hypotheses to explain this fact, but so far none of them has been proven to the satisfaction of all.

 

[athon]

This idea isn't quite Lamarckian, I'm afraid. Neo-Lamarckians explore the concept of increased complexity in direct response to an environmental stress, which does happen in a few bacteria such as E-coli. It is a new twist on an old theory.

Again, I'd like to say 'welcome', Stephanie, and I hope you get something out of associating with this little motley crew of strugglers.

The idea of somatic evolution has been touted before, but unfortunately seems to be one of those 'has merit in theory, but no evidence' kind of things. Somatic mutation can be passed on through only one of two ways:

from germ cells - in other words, only if the mutation occurs in a diploid, 'pre-gamete' cell.

passed through translocation: uncommon, to say the very least.

For an organism of any complexity to have a series of cells mutate beneficially is probably rare, but could happen. Developing a stomach might be a little much, but to have a cell mutate during development to provide the body with a slight biochemical advantage is not impossible in the scheme of things. The problem occurs when you consider that evolution tends to work best with successive mutations, which cannot happen with a limited cell line, i.e., a single organism.

Good thought, though.

Athon

 

[Dymanic]

About the closest thing to a mechanism for directed evolution is the Baldwin effect. This applies to organisms in which learned behavior is a significant factor. It basically says that in such organisms, some aspects of behavior are determined at run-time, rather than at design-time (sometimes called 'phenotypic plasticity').

So if there is some really cool behavioral adaptive peak nearby in design space, any lucky individuals who start out with factory settings that happen to be closer to the combination that produces that adaptive behavioral trick will be more likely to stumble on it within their lifetimes, at which point (though not before) it becomes visible to selection. Subsequent generations will then start out with even fewer connections that require setting, and so will have an even better chance of hitting the right combination sooner, etc.

By partially side-stepping the combinatorial explosions that tend to occur around the number of connections involved in complex behaviors, even a slight amount of help from this effect could streamline the process considerably (but probably doesn't go far enough to qualify as 'directed' -- a concept which cannot possibly be meaningful beyond the scope of local optima anyway).

 

[BillHoyt]

However, the speed and detail of evolutionary change test even Dawkins blind watchmaker explanations and leave one wanting for some direction.

Here is a recent article demonstrating a remarkably fast rise of cadmium resistance in a worm, followed by a remarkably fast fall of this resistance (after humans managed to lower the levels of environmental cadmium.)

The worm turned (twice)

Cheers,

 

[Dancing David]

I am very willing to consider that an organism could have a propensity for somatic adaptation, and that could be passed down through the generations, This would also likely select for increaded chance of a somatic change, but maybe not.

 

[BillHoyt]

I am very willing to consider that an organism could have a propensity for somatic adaptation, and that could be passed down through the generations, This would also likely select for increaded chance of a somatic change, but maybe not.

What you describe here has already been shown for the immune system. There are genetic code regions that appear to become hyper-mutation regions when an organism is subjected to foreign invasions. Antibody variation after antibody variation are tossed out in an attempt to quell the invader. When one of these variations is successful, a monoclonal antibodies modelled on that are created and dispatched until the invaders are gone. The immune system retains a memory of the successful antibody design and produces copies of this same design whenever the invader reappears. This is a kind of evolution and is the basis of vaccination. The information, however, is not directly passed onto the next generation.

Cheers,

 

[c0rbin]

Welcome to the board, Stephanie.

I am not a professional scientist, so anything I spout is informed opinon at best. You will find many professionals here, though, who can help you out, as you have probably already scene.


NWilner Said

how does the organism "get" its cells to behave for the benefit of the entire organism, not just their local benefit? Who decides if a stomach evolves in an organism? Does the organism have a "say" or do the individual cells decide? I use "decide" in the evolutionary sense.

I think that by using words like "decide" one muddies the water in regards to evolution. If anything "decides" what genes get passed to the next generation, it is the environment.

In our case, sometimes violent Eugenics are employed. But for the organism in the long, long run, from the bacteria to the elephant, the environment pulls the strings.

 

[NWilner]

The immune system example is interesting. Now figger a way to pass that to the next gen!

"Who decides" is an anthropomorphic figure of speech. I thought that was clear from the context.

The biq question is how the organism gets certain cells to do things that are not in the immediate interest of those cells. Cancer, methinks, is when this doesn't happen as planned, i.e. the cells no longer have the greater interest of the organism "at heart."

Similar question: how do you tell a bone cell to be a bone cell, how do you tell it when to divide and when not to. Who controls the division so that your arms are the same length?