Oolon Colluphid

Hi folks

Okay, hands up, who here is a developmental biologist? Peez? Pz?

As anyone sad enough to follow my posts will know, I’ve been thinking about fused bones, eg the coccyx, tarsometatarsus (or some such ), and so on. The idea being to add it to ‘my’ list, as in, if a single bone is required, why don’t these things form as a single bone. Pointless bit of design.

Then it occurred to me that the reverse seems to be true too. In the foetus, our distal limbs -- forearms and legs -- start as a single bone, then there’s apoptosis (‘programmed’ cell death), whereby the cells in the middle die off, forming two bones, the radius and ulna, and tibia and fibula.

So the opposite of the above: if two bones are needed, why start with a single one? And forming cells, only to have them die off in order to make the end result, seems weird too (in the manner of the foetal baleen whale teeth). So, pointless bits of design.

Now, my question. Is this actually right, or at least, to what extent? Arm and leg bones seem fair enough, since presumably femurs and pelvises, scapulas and humeruses form separately (or do they?).

But once one gets into ankles and wrists, fingers and toes, it may actually be simplest to make a lump and then divide it up, for subtle joints and digits.

If I’m accusing the designer of doing things in a convoluted manner, I’d better not use an example of it where it’s actually the most sensible way!

Can anyone say whether apoptosis as a whole is a round-about way of doing it -- could most things sensibly form separately if they were from-scratch designed -- or whether more restricted examples (eg tibia-fibula) only are safe... or am I barking up the wrong tree entirely?

Cheers, Oolon

Non-praying Mantis

Oolon,

I wouldn't necessarily say that apoptosis is bad design. I suppose that you could equate apoptosis to a sculptor carving away pieces of marble to make a statue.

Not that this leads any creedance to ID "theories" at all.

Anyway, that's my 1/50 of a dollar...

NPM

RufusAtticus

Well one of the hallmarks of human development is out fetal tail. This tail is lost in most instances by the time we are born due to apoptosis. The odd thing about it is that there are two different processes of apoptosis that occur in out tail, one minor one and one major one. I suspect that the minor one is not unique to great apes, and represents the evolutionary remnants of proper tail formation. The major one on the other hand is the unique feature that causes the regression and absorbtion of the tail. So here is a situation that involves not only the wasteful distruction of an entire appendage, but the is an extra, unneccessary process at work.

Oolon Colluphid

True, one could. But then, the sculptor hasn’t himself deliberately added the marble he’s subsequently carving away! A sculptor is removing what he has to start with; a developing foetus is growing. In these cases, growing something that’s not ultimately needed, only to dispose of it before the product is finalised. IOW, nice try, but still looks like an unnecessarily complicated, wasteful piece of design.

That, I suppose, is at the heart of my question: do the cells programmed to die form some sort of essential, unavoidable scaffolding, without which it is impossible (impossible, that is, to design it any other way) for the two bones to form, or for carples to separately form, or whatever...? Fine, throw away the scaffolding. But if you can manage without the scaffolding in the first place, don’t erect it!

Yeah, I know that the various elements interact, as with Hampé’s chick leg experiment, where one part of the leg tells another what to do. But we’re talking about, does it have to be that way? Not what is, but whether it’s possible to do it less wastefully.

It’s anyone’s guess how one would construct the genetic control of these things, but it seems to me that a highly intelligent designer ought to be able to find a way to activate the genes for ‘lay down calcium, form bone here’ anywhere he bloomin’ wanted to, and so wouldn’t need to make cells whose purpose is to die in order to make the required result. It’s not like having a single forearm bone is useful for part of the life-cycle..

Note once again, too, that this poor design is one that the creator used repeatedly in a vast range of different ‘kinds’: humans, dogs, apes, bats, cats, birds, whales, turtles, even skinks (hell, I’m guessing on those last two, but rather than check, I’ll make an evolutionary prediction out of it!).

Cheers, Oolon

BioBeing

Apoptosis is used for more than just developing fetuses. The process is going on all the time in our bodies to kill off unwanted cells - those with too much UV damage for example. Although if it was truly efficient, we wouldn't ever get skin cancer...

As to apoptosis in embryos - the skin between the embryos fingers was always my favourite. Why do we start out with webbed hands, and then loose those webs? Were we once aquatic, or is this "good" design? Of course an intelligent designer could do it differently, but wouldn't that then be like the babel fish

pz

I'm not sure what you're getting at here. What is "poor design"? Apoptosis in development seems like an inefficient mechanism, since you're generating new cells and then wastefully killing them, but on the other hand, if your goal is to generate an autonomous developmental process that uses a minimum amount of hardcoded specification, it may be a clever way to achieve your goal.

Non-praying Mantis

Actually, we don't start off with a webbing of skin between our fingers, we start off with a "solid" hand bud, and then the actual fingers are formed by killing the intervening cells between them.

NPM

ps418

Well, I'd say that development is full of all sorts of curiosities that make sense only in light of historical constraints. But I wouldn't go so far as to bash apoptosis itself.

For example, cell apoptosis can often be induced by genetic damage, which reduces the probability that a cell will start dividing inappropriately. In fact, I've learned that one of the nasty things that nicotine does is inhibit apoptosis of airway epithelial cells. Normally, many airway cells would die due to exposure to mutagens in tobacco smoke, but the nicotine inhibits that response, thus increasing the probability that the right set of oncogene mutations will occur in some airway cells.

Patrick

Oolon Colluphid

Hmmm. Thanks for the input folks. It seems to me that I’m still on safe ground bashing the apoptosis for forming tib-and-fibs, radius-ulna, as there seems no reason why these bones could not form separately.

So, apoptosis as a general mechanism may be fine: it may well have a role to play in a genuinely intelligent designer’s means-to-an-end. But the actual (proposed) designer used it in places where a simpler method was available, and doing so is pointless and wasteful: making cells that are due to die in order to make two bones, instead of just making two bones.

I take it that the apoptotic (?) cells between tib and fib are not some unavoidable scaffolding then? Can’t see how they can be, even after a good ol’ browse in Gilbert’s Developmental Biology, but still...?

Cheers, Oolon

Kosmo

This is an interesting question. Considering the universality of the apoptotic processes involved in formation of the individual bones it WOULD seem unavoidable.
Whether or not the cells destined for apoptosis serve the purpose of providing a scaffolding per se is perhaps irrelevant with respect to some other function necessary for proper development.
For example, development of the central nervous system (CNS)involves the release of trophic substances that induce sprouting of axons from neural stem cells toward the source of the substance. Other stem cells not specific for that trophic factor (but in the same vicinity) die out. Release of different trophic factors is subject to various environmental stimuli and as such provides a certain plasticity in the CNS development of an individual. So while some of the stem cells ultimately die off due to lack of trophic inducement, I don't think it's proper to view this process as a 'wasting' of cells. The potential provided by these cells is advantageous for the individual.

Of course, I don't mean to suggest that the apoptosis involved in shaping of the primordial bones is mechanistically or (please forgive me) teleologically similar to that in the CNS. Rather I merely suggest that 'scaffolding' should be considered in a broader metaphorical sense that doesn't preclude the idea that developing this way is better than developing individual bones from the get go.