A while back, in an essay entitled “The Fossils Are in Your Head”, I explored our distant fish ancestor’s emergence from the water 365-million years ago. I described how gills became the things of the throat; adenoids, pharynx, larynx (causing the looping of the Recurrent Laryngeal Vagus Nerve from the brain, under the heart aorta in the chest, and back up to the throat), and also the transition of swim bladders into terrestrial lungs.
Along a similar track:
This evening, listening to Doctor Karl’s Podcast, at 29minutes 22 seconds, a caller to the show posed a question, the answer to which I thought was quite intriguing – so I thought to share it.
The question involved ocean fish – why every other creature needs to drink fresh water, but ocean fish don’t.
The answer was quite intriguing:
Ocean fish have kidneys that work overtime – filtering out all the salt, sustaining the fish with water. Makes sense.
Meanwhile – all land dwellers are “fish gone wrong” – because, as the Doc puts it, you will be pleased to hear: “God made a mistake”.
He went on to explain how human kidneys will filter in a day about 200 to 250kg’s of blood – that’s a ¼ of a ton of blood – and will extract from it around 1,5kg’s of salt – which is a vast amount – the equivalent amount “as if we were still in the ocean(!!)” – and then, because we are no longer in the ocean, it puts it back, save for 80-thousanths of 1 gram which goes out in the urine.
The whole process is a huge metabolic cost; but we do it because that is the way the kidneys set up originally and there has been no evolutionary pressure to change it.
His parting words resonate: “Evolution doesn’t have to be perfect, it just has to be good enough”.
Oh… and the next caller’s dog had just come back from being de-sexed at the vet, but turned out to be a hermaphrodite – or, more correctly, ‘intersex – and he goes on to talk about Joan of Ark actually being a man who was intersex.
You gotta listen to Doc Karl (and The Naked Scientists) – brilliant stuff.
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