Roller

Hello!
Got my power back

What is the difference between people born with the tail and people born with extra fingers? Postanal tail is the result of genome directing growth, right? Is the information for the extra fingers (polydactily) in every human's genome? I would say no. I have a creationist claiming that people born with tails is the same as people born with extra fingers. He's trying to argue against embryonic development as evidence for common ancestry. But all humans have tails during emb. development but none, or almost none, have extra fingers. Is postanal tail a tail or what?

My another question is - what would be the possible scenario for humans and chimps inheriting the ERV's? I know it is through common ancestry, but since ERV's are inserted practically randomly, how did we end up with same ERV's on same loci?

I also said how quadrate and articular bones in reptiles evolved into hammer and anvil in mammals and how that can be seen both in embryonic development and fossil record.
He's response was: "Those bones develop that way, but not because of recapitulating phylogeny." I'll have to ask him to clarify that for me.

What about pharyngeal pouches? They constitute evidence of our aquatic ancestry, right? My creationist is saying that those pouches are just a stage in development of Eustachian tube and the couple of other organs. They really do develop into those organs, but aren't those same pouches developed in gills in fishes?

Thanks!

Coragyps

I don't know the biological details of polydactyl people, but one of the best-studied forms is a Mendelian dominant gene - found independently in some Pennsylvania Amish and African populations, IIRC.
The only reasonable explanation for the shared ERV's is that a specific mama primate had insertions that the babies inherited, and that one of those babies gave rise to chimps, and another to you and me and your creationist.

Oolon Colluphid

Nope. Polydactyly is going to be a mistake in the genetic switching that occurs at the end of the limb bud (I forget the proper name of that). The digits form by apoptosis (programmed cell death) from a single mass, iirc, so they just do it once too often. That’s why one can have an extra finger on just one hand, or webbed toes but not fingers.

The tail thing is a reactivation of normally dormant genes. I gather that we have the same tail-making genes that mice have (I’ve been meaning to ask if anyone’s got more details on that for a while), they just don’t get turned on. Hence we have a coccyx made of small, fused caudal vertebrae, an extensor coccygis muscle that would flex them if only they weren’t fused. I expect that such atavisms are the result of genetic switches being thrown higher up the cascade of control.

In other words, one’s a cock-up, the other’s a coccyx -- that’s grown larger than normal. A larger, longer coccyx has a specific name in biology. It’s called a ‘tail’.
Ask him what a guinea pig’s tail is for.
Then he’s a fool (surprise surprise). Direct him to Scott Gilbert’s Developmental Biology.
Yes. They won’t have extra fingers, because like I say, we start with a nub and kill off the cells in between. Conversely, we all have tails, it’s just that some few people don’t get theirs reduced during development.

Someone else will have to take the ERV bit I’m afraid.
Ask him why they develop that way! (And don’t forget the stapes bone!)
Pretty much. We grow a bunch of pharyngeal arches, forming a structure remarkably like the set-up fish have for their gills, but then they degenerate (apoptosis again, I suspect) to leave our aorta etc. You could also ask him why in birds it’s one (left? right? My books are at home ) aortic arch that’s kept, while in mammals it’s the other. And wy, if that set-up is so great (as it measurably is) for better blood flow / oxygenation at the lungs, only mammals and birds do it, and things like reptiles have the less efficient system.

(I’m working on this one for ‘my’ list, btw, so any and all further info is gratefully received!)

Cheers, Oolon

Roller

Thanks gents!

It seems we're gonna run out of power again. Dang!

Nic Tamzek

Well, I always thought you East-Coasters were in the dark...

RufusAtticus

Actually the human tail develops normally and then another process kicks in and causes it to be reabsorbed. In fact, some researchers found that there are two types of apopotosis at work in human tell development: one for differientation and one for destruction. It seems to me that humans being born with tails is not the result of reactivation of ancient "tail-genes" but the deactivation of the more recent "tailless-genes."

Doctor X

Just for the record . . . we really never develop true gill arches.

I am still angry at The Abyss claiming we breathed water in the womb. . . .

However, what we . . . and other creepie crawlies do . . . is build on what we have.

The problem is your friend just does not want to see the similarities. The basic body structure--location of gut-aorta-notochord-spinal cord--for example is preserved across species--and seen in the embryos.

You probably already know what he is trying to do . . . find a "question" that cannot be answered that will somehow magically stump the scientists and disprove evolution. The fact that developmental genes are conserved across species should indicate should indicate something . . . oh . . . I forgot . . . Big Daddy decided to use the same genes 6000 years ago.

What is interesting is that the development of thine hindquarters--sacral region and sacral nervous system is a separate developmental event from the more "upstream" development--as can be noted in mutations of "caudal agenesis."

--J.D.