Posted on 12/21/2004 4:13:57 PM PST by beavus
The human parathyroid gland, which regulates the level of calcium in the blood, probably evolved from the gills of fish, according to researchers from King's College London.
Writing in the latest edition of Proceedings of the National Academy of Sciences, Professor Anthony Graham and Dr Masataka Okabe suggest that the gills of ancestral marine creatures, which were used to regulate calcium levels, were internalised rather than lost when land-living, four-limbed animals – the tetrapods – evolved.
Many physiological processes such as muscle contraction, blood coagulation and signalling by nerve cells, require specific levels of calcium in the body. In humans, calcium levels are regulated by the parathyroid gland, which secretes parathyroid hormone if the calcium concentration in the blood falls too low. This hormone then causes the release of calcium from bone, and increases its reuptake in the kidney, raising the calcium levels back to normal.
Fish don't have parathyroid glands. Instead they increase their internal calcium concentration by using their gills to take up calcium from the surrounding water.
'As the tetrapod parathyroid gland and the gills of fish both contribute to the regulation of extracellular calcium levels, it is reasonable to suggest that the parathyroid gland evolved from a transformation of the gills when animals made the transition from the aquatic to the terrestrial environment,' said Professor Graham.
'This interpretation would also explain why the parathyroid gland is positioned in the neck. If the gland had emerged from scratch when tetrapods evolved it could, as an endocrine organ, have been placed anywhere in the body and still exert its effect.'
The researchers supported their theory by carrying out experiments that show that the parathyroid glands of mice and chickens and the gills of zebrafish and dogfish contain many similarities.
Both gills and parathyroid gland develop from the same type of tissue in the embryo, called the pharyngeal pouch endoderm; both structures express a gene called Gcm-2, and both need this gene to develop correctly.
Furthermore, the researchers found a gene for parathyroid hormone in fish, and they discovered that this gene is expressed in the gills.
'The parathyroid gland and the gills of fish are related structures and likely share a common evolutionary history,' said Professor Graham. 'Our work will have great resonance to all those people who have seen Haeckels' pictures, which show that we all go through a fish stage in our development. This new research suggests that in fact, our gills are still sitting in our throats – disguised as our parathyroid glands.'
Nothing can be proven true, because it's impossible to test an infinite number of possibilities. You can only prove something to be false, which is why scientific study depends on falsifiability. Unfortunately for the graduates of the BTIT and regardless of how much some of the folks on this thread would like to say, falsification of evolutionary theory has not yet happened.
There's nothing wrong with postulating a theory when it's supported by at least SOME kind of hard science. The fact is, there is no hard science to suggest fish crawled out of the muck millions of years ago, grew legs, hair, arms, and hands with opposable thumbs. Evolutionists have yet to show how one genus, family, or species transforms into a different genus, family, family or species. Cross breeding and environmental adaptation cannot explain how man was created by evolutionary processes. Maybe you evolved from apes, but my ancestors are all human.
Be careful quoting Ivy League folks as authorities...
Bill & Hillary went to Yale Law (as did Pat Robertson);
and both
Timothy Leary and Pres. Bush came out of Harvard... ;-)
Those who oppose evolution might benefit by making an effort to understand what they're arguing against.
The Theory of Evolution. (Excellent introductory encyclopedia article.)
It would also be useful to learn what science is: The scientific method.
If you want a hint of the evidence that's been gathered over the generations, check out the links I just posted in another thread: here, post 204.
While in the womb, the child receives all of its oxygen through the placenta. Even if that little snippet of high school biology (which I was told as well, unfortunately) were true, they would be completely non-functional.
Concise & to the point. I wholeheartedly agree.
They evolved together.
Let's say there is a certain species where the offspring are born and left to fend for themselves.
Let's say that one of the mothers in that species has it in her genetic makeup to be a little bit more defensive about her offspring. Those offspring will have a greater chance of survival and then that species will have a greater percentage of individuals with that trait. With each generation, those with even more protective mothers have a higher chance of survival and protectivenes then becomes even more common. After many generations, protectiveness becomes, far and away, the most common trait.
In Nature, there are two main reproductive strategies: Small number of offspring with protective mothers or uncaring mothers that produce large number of offspring to make up for those that die.
I stand corrected. I always thought "reasonable to suggest" meant "reasonable to suggest," and "probably" meant "probably." I guess in scientific circles "probably" means "supported by hard science" and "reasonable to suggest" means "beyond any doubt."
the person evaluating the data can justify his conclusions based on the validity of the assumptions
I can justify many conclusions based on the validity of my assumptions, that doesn't make it hard science. For example, I can conclude that I am a human being, born of two human beings, who were born of two human beings. I can carry this postulate back a thousand generations, and guess what? There isn't a monkey or a fish in my family tree.
Just blowing smoke--since any purported gills are present only at much earlier stages of gestation, maybe they _could_ do the job at supplying O2; please recall many smaller critters (e.g. spiders) don't have lungs in the way "we" think of them...
Cheers!
PS Your initial post could serve as a counter-example to over-reliance on authority, couldn't it? ;-)
And Gilligan evolved from "The Dolby Gills Show".
I'm confident there is a better, albeit more technical, explanation for this condition. That is how she explained it to me. Don't know how common is this condition.
I take the hits. Always.
I've done a little self inspection, and I think the watermelon family is more likely.
Probably? Probably? I don't understand. We KNOW how all this happened. Evolution is a FACT. We've been told this again and again. I am sure any good biology book explains how we went from the primordial slime through each step to what we are now. Why can't they just look it up?
That's called a branchial cyst. It has nothing to do with gills. While we are developing in the womb, for a while we have several sets of structures called pharyngeal arches. Bunches of structures in the neck and face develop from the pharyngeal arches. And it's way more complicated than I could do justice to it to explain (or than you want to hear), but let's just say that if all does not happen as it's supposed to happen, there can wind up being a cyst in the front of the side of the neck. Branchial cysts are pretty harmless, and they're usually only discovered in adulthood, because they can enlarge.
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