Evolution: Lamarck + Darwin/Wallace

YoungSpoon

I was reading about Lamarckism, the previous idea to Darwin-Wallace's theory, and it got me thinking if there's any cases where elements of it could be true. In terms of simple adaptions anyways.
For clarification, I'm not claiming D&W's theory is wrong, but wondering if Lamarck may also have been right on some parts.

For example: Giraffes evolved long necks by having to stretch a lot and over time, by elongated muscles and such, then went on to pass the traits to the next gen.

I'm perfectly aware that it happens because of mutation and the breeding of species with favourable traits, but has there ever been an example where this wasn't the case?
Maybe even that this caused the mutations as opposed to them being random?

nozzferrahhtoo

I am aware of none. Nor do I think giraffes had to "stretch". You have the causality slightly backwards.

An animal with a mutated longer neck would have access to food supplies out of reach of the other animals which will confer a retrospective advantage to the animal in question after the mutation. This is however not "why" the animal got a longer neck. The mutation did not "know" to occur because there was food supplies out of reach of the giraffe.

In fact I have heard/read that the long neck of the giraffe had less to do with reaching food and more to do with reaching water on the ground... evolving as it did as a consequence of the longer legs which the giraffe evolved for speed. A little counter intuitive perhaps but much of evolutionary biology is.

Also remember that most mutation and traits are related to the DNA passed on to the off spring. It sounds like what you are proposing is almost like "I stretch and stretch my neck and this action goes into my sperm and edits the DNA for neck length so my child has a longer neck". I am not sure how such a system would even work so I have never really understood lamarckism much myself despite having read much about it.

YoungSpoon

I've never heard about the reaching water one, but it's interesting to hear.

I can't really say that I've got much to back up any of these thoughts. They seem less probable the more I think about them, but it'd be interesting to hear of any proof of non-random mutation.

nozzferrahhtoo

It might be worth reading about something called the "Evolution of Evolvability" which is an interesting subject. I will summarise it here grossly so apologies if the over simplification of it offends anyone who has read about it as much, or more, than I have.

Essentially it is the idea that not only have certain traits evolved over time, but the ability to evolve has also "improved" over time making the DNA more labile and prone to evolve.

So while this subject might not be interesting to your question directly about non random mutation, the fact that the DNA has over time become more labile and prone to evolving in the ways that benefit it is one of the things that might give the illusion of non random mutation and as such it might be of interest for you indirectly.

Capt'n Midnight

The nearest thing to Lamarckism that I know of is that when there is a shortage of food some bacteria's DNA repair mechanisms don't work as well as they would otherwise.

In short mutation rate could increase in times of stress.

But the mutations are still random.




To suggest that a giraffe reaching up will change the DNA in the reproductive organs you would need to propose some mechanism. Unlike insects all of our cells contains one copy of DNA. ( though the mitrocholdrial DNA as a rule comes from our mothers ) Neurons that go from the brain to the bottom of your spine, white blood cells, liver cells, all contain the same DNA and are very different already. Your sexual organs are formed in the womb, so any changes to DNA would have happened before you were born and unlikely to be affected by behaviour after that.


Check out the studies on Dutch grandchildren of those women who were pregnant during the famine in 1945 to see how environment could affect them. The daughters ovaries were forming during the early stages of pregnancy, so it was the grandchildren who were affected. However, IIRC the great grand children were unaffected.

Jimoslimos

nozzferrahhtoo wrote: »

In fact I have heard/read that the long neck of the giraffe had less to do with reaching food and more to do with reaching water on the ground... evolving as it did as a consequence of the longer legs which the giraffe evolved for speed. A little counter intuitive perhaps but much of evolutionary biology is.

I believe the advantage in long necks was to do with fighting/rutting/mating duels (not sure why females would be the same though??). Of course this type of adaptation comes with its disadvantages so a point of equilibrium is reached, where the neck length is sufficient to win mating bouts but not so long it causes health problems.

nozzferrahhtoo

To be honest I reckon it has a lot to do with all three of the suggestions, and more that have not been suggested. Whether it be better access to food sources, easier access to water, or as male bouting.

Within evolution it is very common for a mutation to confer more than one advantage to the host. It is human error more than anything else that tries to look for, and latch on to, a single reason for it.

The one error to avoid of course is to suggest that the mutation was "to do" with ANY of these things per se however. The DNA did not say "I better make a longer neck so my progeny will be better at mating duels. The mutation just happened. It continued because it just happened to confer some number of advantages.

Certainly the water comment is interesting however. The evolution of long legs gave them a speed advantage given they can reach speeds of up to 60kph. Massively long legs however clearly makes water holing massively difficult and a mutation for a longer neck would certainly counter balance that disadvantage. And there is nothing to worry about there as to why the sexes both have it.

All interesting stuff however but on the topic of the actual thread it is sufficient to point out that mutation happened, it conferred an advantage, and so it was propogated. There was nothing about a giraffe stretching up a lot that suddenly edited the DNA in it's sex cells to say "Ooops, better make the next generation a bit longer necked to cope with this".

Capt'n Midnight

nozzferrahhtoo wrote: »

Within evolution it is very common for a mutation to confer more than one advantage to the host. It is human error more than anything else that tries to look for, and latch on to, a single reason for it.

Because of redundancy in the genetic code there is a good chance that a change in DNA might not have any effect. It takes three bases to code one amino acid. In about half the cases a change in the third base may not change the amino acid being selected and even if it did the substituted amino acid would likely be similar so not having a huge change in the protein produced.

But when the proteins are changed in critical areas or when DNA transcription regulation mechanisms are changed the effects of a mutation are usually bad for the organism.

Forget this hero living in a post-apoclyptic wasteland scenario common to scifi , after a real nuclear war almost all the survivors would suffer from the radiation. This is not about mutations, just to show that massive changes might appear beneficial to some, but are disasterous to most.

It might be better to say a mutation can confer more than one change to the host.

YoungSpoon

Thanks for clearing that one up for me. It wouldn't be very plausable for the mutations to be non-random, but many theories can be incomplete so it's always good to look at other possibilities.

lockman

Have been following this thread with interest.

I am currently reading a book entiteld "Evolution in Four Dimensions" (by Eva Jablonka and Mario J. Lamb; published by MIT Press), subtitled "Genetic, Epigenetic, Behavioural, and Symbolic Variation in the History of Life" (published in 2006) which deals with the modern view(s) on evolution from many different perspectives.

It is a fantastic discourse on some modern views of evolution. For instance, chapter 3 deals with mutations and is entitled "Genetic variation: blind, directed, interpretive?" and argues that certain mutations are more than just random events (in reference to some of the earlier posts) and in certain cases are directed or semi-directed (not directed per se by creators or designers, more that evolution by natural selection has resulted in mechanisms that alter DNA in response to signals cells receive from other cells or the environment). She cites some evidence of such mechanisms (see Cairns, 1988*; McClintock, 1984** - note this line of thinking (non-random nature of mutations) has been around for some time.

* Carins, J., J. Overbaugh, and S. Miller. 1988. The origins of mutants. Nature 335: 142-145.

** McClintock, B. The significance of responses of the genome to challenge. Science 226: 792-801.

Am only about 1/3 of the way through this book, but it is thought-provoking to say the least. It certainly has challenged my own views on what i interpreted evolution to be, how it works and so on. Would encourage anyone with an intereste to read.

Amazon link:
http://www.amazon.co.uk/Evolution-Four-Dimensions-Epigenetic-Philosophical/dp/0262600692/ref=sr_1_1?ie=UTF8&qid=1333215110&sr=8-1

IrishKnight

Well, one would claim that DNA Methylation is a form of Lamarckism (sorta)

For those that don't know, sitting on top of the genome is the epigenome. Sorta like the software to the genomes hardware. Each cell type would have it's own epigenome which tells a liver cell to be a liver cell etc. Thing is, the epigenome can change with time.

So if you take two twins when they are born they will have the same epigenome, but over time, due to their experiences, it will change. Thing is, some of these can be inherited. See, http://www.news.leiden.edu/news/dutch-hunger-winter.html

Some people are calling it lamarckism but I think that is more tough in cheek than anything else