liquid

Hello Bloggins.

I have a (very!) passing knowledge of embryology. There are several factors that 'tell' an embryo how to grow, and most of these are not actually down to the DNA alone.

It's all a matter of triggering the correct protein construction from all the coding hidden in the DNA. We don't know everything about it by a long stretch, but we do know that one of the most important factors are gradients.

It is these gradients that exist naturally in the womb that provide both orientation and triggering for all the different cells. It's a very subtle process.

When I say gradients, I am talking about gravity, pH gradients, chemical gradients, temperature gradients and so on.

These create what are referred to as growth fields in the embryo, areas where certain types of growth is promoted and other inhibited.

For instance, the <a href="http://www.mun.ca/biology/scarr/Hampe_experiment.htm" target="_blank">Hampe Experiment</a> is a fascinating case that provides both evidence of common descent and how growth fields affect embryo development.

Another example of the 'wrong' sort of growth being triggered by being in the wrong environment is the
<a href="http://www.devbio.com/chap06/link0601.shtml" target="_blank">Kollar and Fisher Experiment</a>, which incidentally shows the existence of genetic code for avian teeth!

It is from experiments like this that we know that conditions during embryo growth are as important as DNA itself in determining the phenotype of an organism. In humans, we see problems like thalidomide disabilities, and I would not be too surprised if some instances of tail growth were due to an aberrant promotor field or the lack of an inhibitor.

scigirl

Very clever.

Not true! I just did a search for information on the Egyptian Pyramids and the first two sites I got were fundie sites. (Fundies can't even believe in the pyramids anyway, cuz aren't they older than 6000 years? )

Anyway....

<a href="http://www.ucalgary.ca/UofC/eduweb/virtualembryo/db_tutorial.html" target="_blank">The Virtual Embryo </a> has a bunch of stuff.

I personally like the Xenopus sites (being very partial to frogs and all).

Scigirl

BLoggins02

I'd like to thank everyone for their contributions. I can certainly understand the role of gradients now in embryonic development. One look at tronvillain's link convinced me of that. And the Hampe experiment, WOW! Someone should show that to creationists some time, of course they would probably fail to understand the significance.

Morpho wrote:
Yeah, sorry about that, it was late last night and I was tired from last week. It just upset me that I was getting non-answers to my questions. My bad

On a related note, where ARE all the Trolls? Without them, we have to resort to having educational and informative discourses such as this one. Educational and informative? Yes; but not anywhere NEAR as much fun

liquid

Yes I have actually brought up the Hampe and Kollar&Fisher experiments several times when talking to creationists, but only in speculative 'fishing' manner.

All three times it has just lain untouched until it sank off the board. They just don't want to know. <img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" />

The problem is that although these are pretty interesting experiments (and there are others like them), creationists tend not to debate the issue of common descent in itself. They simply don't accept that one animal being like another animal is evidence for descent - after all we already share much of our DNA with even wildly different organisms - this is just a practical demostration of that.

Oolon Colluphid

I've used the Hampe and Kollar and Fisher experiments several times. I've yet to hear an even half-decent reply from a creationist about them (in fact the only reply I've ever had was from Douglas, who muttered something about never having said birds never had teeth... <img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" /> ). These things are great because it's usually the creationists who've got the one-liners.

Back to the topic... the best book on the whole matter is apparently Gilbert's <a href="http://www.amazon.co.uk/exec/obidos/ASIN/0878932437/qid=1011469481/sr=1-1/ref=sr_sp_re/026-1218815-8527636" target="_blank">Developmental Biology</a> (UK link cos for some reason this £36 book is $95! ) . I expect seccond hand copies of the previous edition shouldn't be too hard to come by. The supporting website is very useful too: <a href="http://www.devbio.com/" target="_blank">http://www.devbio.com/</a>

For me, this is is one of the most fascinating evolution-related areas of all science. The evolution connection is clear: evolution works by modifying pre-existing embryological processes. And -- creationists please note -- its evolutionary connection is one of the hottest areas of research, with so-called evo-devo going way beyond mere Hampe-type experiments. One day not too distant, according to a New Scientist article last year, we should be able to infer an Archaeopteryx's genetic code, and grow one...

Cheers, Oolon

[ January 19, 2002: Message edited by: Oolon Colluphid ]</p>

BLoggins02

I liked the Devbio website. I wonder if I can find The Art of Genes at my local Barnes and Noble, I don't think Amazon has an excerpt.

Edited to Say: Nevermind, the do have an excerpt. I must have been expressing my "blind" gene at that moment

[ January 19, 2002: Message edited by: BLoggins02 ]</p>

Oolon Colluphid

It's always worth having a look at <a href="http://www.abebooks.com" target="_blank">www.abebooks.com</a> -- it's great because it lets you search by country.

Cheers, Oolon