Some thing about random changes.
Consider a polyfatous [ very faaat] boy, he wants to drink some drink. so he goes in kitchen and takes the ingredients of that drink, and then mixes them. Mixing is a change here. He only mixed those ingredients which were required, so his mixing [= change ] was not random, it occured in some definite direction. If this change had to be non-random he would have mixed every available ingredient. Same is the case with
Lamarkism , in it, changes in DNA occur in definite direction, and in the mutatiions there is no any definite direction of changes,
Thus, probably , DNA chnges due to lamark effect cannot give rise to entirely new thing.
Thus, ex-lamark effects [ eg. mutation] are also required to explain evolution.
The idea of inheriting parents traits is foolish. The animals do not desire to have longer neck. Especialy lower animals dont desire anything and plants cannot have so diffrent way of evolving since thay have the same genetical structure. The elongation of giraffs neck is product of natural selection. The animals with longer neck had a better chance of survival and they left more offspring that had longer necks too.
How can any biologist today that knows basics of genetics even consider this idea? If parents can pass on their acquired traits than that would mean that new genetic material can be integradted in the dna. But not in the dna of somatic cells, eg. muscle in the body of a spotsman, but in the gamets wich have no relations with lifting weights. New dna can be inserted trough virus infection but you can hardly say that it was deliberatly done by the parent. The only other way in wich parents can stir the development of the offspring is by the citoplasmatic induction. The unevenly distribution of citoplasmatic componetnts in the ovum may determine the way of embryonal development. But again it is not the delibarete stiring.
In regard of the elevating number of persons with glasses that can be explained by the higer control of eye sight in the 20th century than in the 18th. It is posibly though that since we have a organised society for a few thousends of years that selectiv pressure on poor sighted individuals has loosen up and that those poor sighted individuals are not excluded from the reproductive genetic pool of human populations so their number trough time could increased.
There is one more problem with using the words like "desire" and "wanting" in the biology. These words automaticly implicate religion and/or some kind of higher, havenly premade plans for all beings. This can make conflict somewhere there isn`t one so it is best not to use them.
That said, I do believe that some acquired non-hereditary traits can be passed between generations. As an example let us examine the giant sloth. If it is in fact advantageous to be larger, this may eventually lead to the selection of sloths whose genetics code for a larger sloth. Over thousands of generations natural selection would favor these slarger sloths, and voila!...giant sloths. But one nice thing about growing giant is that it is controlled by hormones. Envoronmental factors can easily alter the production of growth hormones. Ergo, a regular sized proto-sloth (with regular sized sloth hereditary genes) can grow larger due to envoronmental factors. When our large proto-sloth is pregnant, it's environmentally induced levels of growth hormone can act on the fetus, resulting in...another large sloth that still does not contain large-sloth genes.
That was obviously a hypothetical example. How about a scientifically documented, practically common knowledge example. The immune system.
mithrilhack wrote: Plus I'm not sure if the mom's growth hormones will affect the baby for the rest of its life.
I agree with this. Maybe if the enviromental factors remain the same (favorable for giant growth) troughout the offspring life but in the moment the factors change even slightly everything would go back to normal beacause it`s not genaticaly determined.
What did you mean by immune system? That the babies after birth have temporary imunnity gained from their mothers?
Back to sloth. Maybe the effect of the growth hormones won't be so dramatic as to produce a giant adult, but what they will do is produce a larger than normal baby. If the environment of this offspring is not the same as the one it's mother was exposed to, and there is no environmental influence on hormones, there is no reason this sloth would end up much larger than any normal sloth. And most importantly, all things being equal, the size found in it's mother will not be passed in any way to the subsequent generation.
This is in essence why nobody in their right mind should be arguing for Lamarckism. I only wanted to point out that by complete fluke Lamarck was partly right; that some traits can be passed without involving hereditary DNA. But the traits that may be passed through one generation do not enter into the hereditary blueprint of that generation. This is the key to true evolution. Learning to play piano and having the genetic coding for cystic fibrosis are two entirely seperate things.