Putting aside minor schools of thought, and creationism-evolution hybrids, how many major differences are there between current evolutionary theories (or whatever a part of a theory would be called)?
For instance, I was reading some of Gould’s, R.I.P., old essays in the * NY Review of Books *. In one he mentions debates about the level at which adaptation occurs. For instance, Darwin thought it was strictly at the level of organism. A minor group now, largely non-biologists, think it happens at the level genes.
And to address the OP, I don’t think you’d call any of the differences ‘major’. All the current theories rely on the same mechanisms and predict essentially the same things. The differences more are akin to the differences between Republicans and Democrats than they are to the differences between Fascism and Amish Socialism.
There are various modification to the general theory which invoke various Lamarkian style mechanisms or that hypothesise greater or lesser amounts of gene interaction within an organism or even a population. But these all seem to just focus on the degree of importance of various factors, rather than totally rejecting that these factors play some sort of role.
I don’t fully understand the comment in the OP about adaptation occurring in organisms as opposed to genes, but it seems to be an example of this focus on levels of importance. If adaptation means an organism being physically altered from the previous generation, that’s occurring at the organism level. If you define it as a change in the structure of the genes that produce the phenotypic changes then it’s occurring at the level of the gene. I doubt you’d find any scientist that would dispute that organisms/populations adapt and that that adaptation is caused largely by genetic changes.
Gould proposed that there were various loci for selection, not adaptation. Selection can occur at the gene level, the individual level, or the population/species level. Darwin championed the individual level, and others, such as Dawkins, appear to champion the gene level as the primary locus of selection.
Adaptation, however, occurs at the population level. An individual may (or may not) be adapted to an environment, but only populations can actively adapt.
Just commenting that you would not be likely to find a scientist alive today who would not concede that all three have a role to play. This is the type of thing i was saying above: the differences seem to be about the degree of importance of the various loci, not that any of the mechanisms doesn’t play any role at all in selection.
Mostly. There are mechanisms by which stress on individuals causes heritable changes in genotype of that individual.
Before The Origin of Species was published, Dawin was well aware of some problems with his theory. Amoung these problems was a 19th century misunderstanding of how genetics worked. As an aside, I have always wondered about Dawin’s reluctance to publish, if he had had the insight/courage to propose that the then current understanding of genetics must be wrong then his monumental acheivment would have been crowned with something that could easily be tested. But I digress.
I highly reccomend that you read The Selfish Gene by Dawkins. The theories popularised by Dawkins are generally refered to as Neo-Dawinism i.e. Dawinism taking into account the known laws of genetics. Neo-Dawinism assumes that selection takes place on the level of the genes and I think that it is fair to say that most scientists accept that this is where most selection takes place.
However, it does seem clear that at least some selection takes place at other levels too. When the environment changes and for example, effects a food source or brings to preiously separate populations into contact then an entire population with one attribute may survive where a population of the same species but with a different attribute does not. Just how important are these other levels of selection is a moot point. Not very IMHO.
There is more to evolution than genes. There is culture. Any creature that can imitate behaviour that it witnesses can have a culture and this is the basis of the theory of memes (which Dawkins also discusses at the end of The Selfish Gene). For example, populations of Orca that eat fish or sea lions have quite different cultures - even though there genes may be identical - and selection pressure can favour one culture over another. There is a lot more to memes than this, you may care to read The Meme Machine although I am not at all sure that this is the last word on the subject.
And then there are examples of limited Lamarkism. The only example I know of is the imune system of mammals - a mother can pass on imune system information to her young through her milk.
Well, it seems that there’s already some disagreement here. According to the Gould article, Dawkins latter gave up on being so focused on genes. (If you subscribe to the on-line version of the NY Review of Books, you can read Gould’s past articles on this topic. These, and articles by Searle are well worth the price of admission.)
Maybe somebody can clarify for me the difference between selection and adaptation. I think, in part, the Gould article I read might have been saying that selection at the gene level can’t happen often since organism have so many emergent properties that genes are just recordkeepers of what works. Or something like that…help? And I have no idea what Lamarkism is. Help on that, too?
Gould did champion alternative evolutionary mechanisms although not to the exclusion of Darwinian/Neo-Darwinian theories.
I don’t know about Dawkins giving up being focused on genes, though it could be so. It is true that his later and more ‘popular’ books did not focus on the genes so very much, I just assumed that this was because he wanted get more general points across to a more general audience.
Jean-Baptiste Lamarck proposed a mechanism for evolution that relied on an organism being able modify its body by behaviour (e.g. a proto-giraffe reaches up to eat leaves high on a tree which causes it to stretch its neck). And then by some unknown mechanism (Lamarckian inheritance) the change is passed on to its decedents (so giraffe necks get longer each generation).
This idea was popular before Darwin and even he accepted that it could play a role in evolution. The reality of evolution was widely accepted among Dawin’s piers - Darwin provided Natural Selection as a credible mechanism.
Of course, we now know how inheritance works and Lamarckian inheritance is impossible. But there are a couple of loopholes: acquired characteristics can be passed on via the immune system and by culture.
A heritable change in genotype, regardless of the mechanism, is not adaptation. Adaptation is the process whereby the phenotype of a population changes to “fit” the environment.
I would disagree with both the statement and the assessment. Natural selection primarily acts on phenotypes, not genes. It is not possible for a gene to be selected for unless the entire organism passes the selection filter; that is, the individual must not be selected against, which means the entire genome goes along with it, not individual genes. Many scientists, including the late Gould and the not-so-late Ernst Mayr reject the so-called reductionism of applying selection primarily to genes.
Of course, this is not to say that selection doesn’t occur at other levels; as noted previously, it does. But the key point is that the individual is the most statistically significant level. Selection itself is a statistical phenomenon, rather than a law or guarantee of survival / reproduction.
See here, particularly the last paragraph, for a summary of Lamarck’s theory.