Re: There's something fishy about human brain evolution

r norman wrote:
There is one species of frog, Rana cancrivora, that can tolerate
seawater. It uses urea as part of the mechanism to maintain
osmoregulation is such circumstances even though its skin is
permeable. That is the trick used by sharks, and the coelocanth, but
nowhere else among tetrapods as far as I know.

Iodine is widely found in soil and is available in plants grown on
such soils. Iodide ions in seawater (and soil) gets oxidized to
iodine which is volatile and is found in air (about 0.7 micrograms per
cubic meter). It then rains down to be absorbed by soil. There are
areas where the soil is deficient in iodine/iodide and in those
regions, animals can suffer from thyroxine deficiency. Severe
maternal iodide deficiency does cause poor fetal growth and brain
development.

I didn't know of the marine frog. Would you elaborate a bit on the
function of urea in it?
Reason for request: IMO rather than primarily "waste products, heat
regulators, or friction enhancers" as I've seen written, I think the
primary function at least "originally" of eccrene sweat (slightly
saline water), sebum (acidic oil), and urea (slightly alkaline?) was as
anti-pathogenic skin covering, especially in the presence of sunlight
(UV/IR), thus protecting against a diverse array of microbes, some of
which were tolerant of acid but intolerant of salt (fungal), others
tolerant of salt but intolerant of acid (algae), etc. No doubt this is
known, but I haven't seen anything written that includes the
combination of these protectants working together with sunlight to
shield the human body, largely effective in seaside and freshwater
environments, unless skin is penetrated or wounded, or the pathogen
enters via an alternate route (orifices).
This shield of overlaying grids on human skin includes:
1.dead proteinacious squamae (continuously shed skin flakes physically
removes pathogen)
2.acidic sebaceous oils
3.saline eccrene sweat
4.alkaline urea?
5.sunlight
6. possible ochre/fat (iron:anti-pathogen?) inland
7.clothing (terrestrial thorns & grasses blades) not needed on tropical
beach?

But why would frog need urea on skin? Dave Deden

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