I can't believe it...
excuse the pun... but apparently seeing is believing
of course there are a few problems I find with this...
1- is this meant to all happen in the lifetime of one fish, or is this over a period of time, i.e. across a species...
2- what use does the "eye" in the first few diagrams have, when there are no nerves to connect said "eye" to go to a unit to interpret the signals being received...
without which, there is no use for the eye, and therefore would be making a creature complex in an uneccesary area.
no?
of course there are a few problems I find with this...
1- is this meant to all happen in the lifetime of one fish, or is this over a period of time, i.e. across a species...
2- what use does the "eye" in the first few diagrams have, when there are no nerves to connect said "eye" to go to a unit to interpret the signals being received...
without which, there is no use for the eye, and therefore would be making a creature complex in an uneccesary area.
no?
posted by mrjohnfernandez at 1:31 pm
7 Comments:
1- is this meant to all happen in the lifetime of one fish, or is this over a period of time, i.e. across a species...
The process happens in what might be termed geological time - e.g. over the course of many many millennia. So you'll note that, for example, flatworms are given as an example of a species whose eye is equivalent to the third stage of human eye development.
This slow change is true of many (although by no means all) intricate systems. Gradualism does actually work as a model in a lot of cases, and the eye is one of them.
2- what use does the "eye" in the first few diagrams have, when there are no nerves to connect said "eye" to go to a unit to interpret the signals being received...
The "eye spot" could be more correctly described as a chunk of cerebral cortex. For no apparent good reason, in contrast to every other sense we possess, sight apparently evolved directly from brain matter rather than as a specialised nerve ending. I can't remember off-hand how this conclusion was derived - I can look it up if you'd like.
In "A meaningful world", Witt and Wiker make the point that this process of describing an eye is all very well, but it fails to describe vision. When I look at trees, I don't see a pattern of light and colour - or objects in focus - I see trees. An eye is just one part of a much more complex system that is in fact pretty much inseparable from what it means to be a human being.
An eye is just one part of a much more complex system that is in fact pretty much inseparable from what it means to be a human being.
Of course. However, if one were to say "well, maybe the eye could evolve... but I'm sure this broader system couldn't evolve...", that would be a rather blatant example of goalpost-shifting.
No, it doesn't work like that. What's happening is that a process for the evolution of the eye is being proposed which does nothing except suggest how the physical hardware of the eye might have come about - but the hardware of the eye only has organic significance in conjunction with the simultaneous evolution of changes in the organism as a whole - and most such changes are not only not linked to physical changes in the same area of the organism, they are almost certainly lie in completely different developmental areas.
The goalposts aren't moving. You just gave the implication that they were a lot nearer than they actually were.
What's happening is that a process for the evolution of the eye is being proposed which does nothing except suggest how the physical hardware of the eye might have come about
Right. That's all that it was intended to do. You seem to be saying that it's a poor explanation because it doesn't handle a massive pile of other stuff too - everything up to and including the meaning of life*. That's like saying my car sucks because it doesn't fly.
The only way that it is remotely possible to analyse any system, in terms of evolution or otherwise, is to either create a simplified model of it or break it down into subcomponents. Thus, in principle at least, it's 100% valid for evolutionary biologists to do this when discussing something like the eye. If you could point to any concrete, practical issues, that would of course be a different matter. But saying "well, you may have explained the eye, but you haven't explained the entire context in which the eye operates" is completely unhelpful.
You're not attacking the evolution of the eye here; you're attacking the whole of science. Which I guess is a sensible rhetorical tactic when one's favoured approach doesn't actually put forward any concrete claims of its own, but rather limits itself to undermining the scientific consensus.
* Ref. your comment "An eye is just one part of a much more complex system that is in fact pretty much inseparable from what it means to be a human being."
Yeah. And why doesn't your car fly anyway? ;-)
But there is a serious point here. I am saying that a reductionist explanation is insufficient in such areas. Also, they give the impression that science has achieved more than it has - "Oh", say the audience, "science has explained where the eye came from. If it can do this (which after all was something that troubled Darwin) then it must have done everything." But it can't do this. Firstly because this is a "just-so story" AFAIK - there is no evidence to show that this process has happened through evolutionary history. Secondly, because even if you could trace a succession of organisms in evolutionary history through which this developmental sequence had occurred, you wouldn't really be describing the evolution of vision, only a progressive morphological change. Significant, yes, but such reductionism hasn't really provided an answer.
But there is a serious point here. I am saying that a reductionist explanation is insufficient in such areas.
Undoubtedly there are areas like that. However, just saying "a reductionist explanation is insufficient in this area because this area has a context" is not helpful - every area of science has a context. The question is whether provisionally ignoring the context will still lead to accurate explanations in this area.
Ideally, you'd be telling me precisely what it is about the environment that actively interferes with the accuracy of the model of eye evolution. For example, if it were known (on other grounds) that it was developmentally impossible to shape the skull cavity to support some of the intermediate eyes, that would be a legitimate problem.
Bonus points if you can also propose a less reductionist model. That has the additional advantage that we can then check to see if your criticisms apply to your model. If they don't, there is then no way that you can be accused of merely trying to rhetorically undermine models you don't like the sound of.
Also, they give the impression that science has achieved more than it has - "Oh", say the audience, "science has explained where the eye came from.
If so, that's the fault of the audience not science. What science has done is proposed a hypothetical pathway by which the eye could have emerged, bolstered by concrete examples of each transitional eye occurring in less complex species. That's more than enough to refute the basic claim that the eye couldn't possibly have evolved because it's too cool. Having the concrete examples is also extremely neat.
Of course, whilst a "just-so story" is good enough for refutation, it's not good enough for scientists. I haven't actually checked, but I'm going to predict, based on my knowledge of scientist psychology, that there is at least one group of scientists out there applying modern techniques to the question of how the eye arose. If you doubt me, I'll go see if I can find 'em.
Secondly, because even if you could trace a succession of organisms in evolutionary history through which this developmental sequence had occurred, you wouldn't really be describing the evolution of vision, only a progressive morphological change.
I'm honestly not sure what you're getting at here. What is evolution if not "progressive morphological change"? If you're distinguishing the evolution of vision from the evolution of the eye, I'd note that no-one was actually discussing the former.
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