Evolution of the cichlid mandible

Posted 15 November 2005 by PZ Myers

When we look at the face of another person, we can recognize specific features that have familial resemblances. In my family, for instance, I can recognize a "Myers nose" that my grandmother and my father and some of my siblings and kids have, and it's different than my wife's or my mother's nose. These are subtle differences in shape—a bit of a curve, a knob, a seam—and their inheritance suggests that these differences are specified somehow in the DNA. If you think about it, though…how can whether the profile of a nose is straight or curved be encoded in a linear stretch of nucleotides? The complicated answer is that it isn't—morphology is a consequence of epigenetic interactions during development—but we know that the alleles present in the genome do contribute in some significant way to three-dimensional form. How?

We don't know all the details. This is one of those huge research problems that has gaping holes, full of promise and interest, where we don't understand exactly how all the pieces fit together. However, here's an important point that is relevant to other, larger issues in evolution: even where we lack full information about mechanisms, we can roughly perceive the shape of the answer, and that helps us rule out many alternative explanations and guides us in the general direction of a more complete understanding.

People's noses are a difficult subject for research; we don't get to define human crosses, people tend to be a little snippy about telling them who to breed with and taking their genes apart, and humans are awfully slow to breed. Fish are better experimental animals, much more pliable and faster and more prolific in their breeding. Some fish, such as the African cichlids, also have highly diverse populations and species with easily recognized and often quite dramatic morphological differences—and we can explore how those differences are generated by genetic and molecular differences in development. In particular, we can start to figure out how fish jaws are shaped by developmental processes.

Continue reading "Evolution of the cichlid mandible" (on Pharyngula)

7 Comments

Sir_Toejam · 15 November 2005

cool stuff.

i was a grad student at berkely in the same lab as Axel Meyer when he was there, and i remember George Barlow talking about some of this work even back then.

have you ever checked out his work:

http://www.evolutionsbiologie.uni-konstanz.de/index.php?section=10

cheers

PaulC · 15 November 2005

If you think about it, though...how can whether the profile of a nose is straight or curved be encoded in a linear stretch of nucleotides? The complicated answer is that it isn't---morphology is a consequence of epigenetic interactions during development---but we know that the alleles present in the genome do contribute in some significant way to three-dimensional form. How?

Obviously, there is some kind of tiny 3D model of a nose somewhere in the embryonic cell, for it strains my credulity to imagine otherwise. Our nose eventually takes its form through a process of... of... intelligent nose shaping.

We don't know all the details. This is one of those huge research problems that has gaping holes,

Well, that settles it then. You admit that you cannot rule out the possibility of an intelligent nose shaper and yet you present your just so story about "epigenetic interactions" and "alleles" as if it were a fact! ...OK, back to earth. Remind me again how it happens that the IDers have rejected vitalism? If they really believed that a scientific theory cannot have any gaps, then they should be just as incredulous about the naturalistic basis of development as they are about evolution.

Russell · 16 November 2005

This is all very well and good, but fish don't have noses.

I have inherited a rather unfortunate family nose, which I believe resulted from some kind of lateral gene transfer from a parrot. I was hoping that gene therapy might offer some hope, but probably not in my lifetime.

Norman Doering · 16 November 2005

PaulC wrote: "Obviously, there is some kind of tiny 3D model of a nose somewhere in the embryonic cell..."

Well, maybe if you use this new microscope you can find that tiny 3D model of your nose:

http://www.newscientist.com/channel/mech-tech/dn8319.html
Ultra-sensitive microscope reveals DNA processes

harold · 16 November 2005

Russel -

"This is all very well and good, but fish don't have noses.

I have inherited a rather unfortunate family nose, which I believe resulted from some kind of lateral gene transfer from a parrot"

You know, I'm no ornithologist, but I'm pretty sure parrots don't have "noses" either, although they do seem to have nostrils.

Granted, genetic material transferred from a parrot to a human could still hypothetically impact on nose morphology. (Technically, it's not impossible that a viral vector could carry some parrot genome material to a human genome.)

More likely, your nose is the result of sexual selection - your ancestors found mates who prefered that particular nose morphology.

Alan Fox · 17 November 2005

Isn't there some linkage between the genetic dispositon for a large nose and the size of another vital organ?

Alan Fox · 17 November 2005

Is there a possibility that non-coding DNA could carry information connected with embryological development?