Was just having a quiet listen to a program on BBC Sounds.
CrowdScience
Were humans ever semi-aquatic?
What evidence is there for a semi-aquatic period in human evolutionary history? That’s the question that’s been bothering listener Dave in Thailand. He thinks our lack of hair and love of water might indicate that, at some point, we were more water-based than we are now. But what does science have to say on the matter? The theory that our ape ancestors returned to the water for a phase in our evolutionary history is a controversial idea that most scientists disagree with. Anand Jagatia chats to Dr Melissa Ilardo, assistant professor at the University of Utah, about our dive reflex - a physiological response we display when submerged underwater, which helps direct oxygen towards vital organs. But this is not a response that is unique to humans - it is found in all mammals. Experts say it developed long before all apes split off in the evolutionary tree. To find out more about the theory itself Anand hears from John Langdon, emeritus professor at the University of Indianapolis. He explains why the aquatic ape theory is not generally accepted by anthropologists, what the fossil record can tell us about our evolutionary path and why evolution is much more complex than the aquatic ape hypothesis suggests. While there may be little evidence of a semi-aquatic period in our evolutionary past, there are some communities around the world that have adapted to utilising their watery environments in more recent evolutionary history. Anand speaks to Dr Nicole Smith-Guzman at the Smithsonian Tropical Research Institute who has found evidence that ancient populations in Panama were habitually diving in the sea for shells and seafood. She explains how she can piece together evidence from different sources to detect the activity of ancient populations. And Dr Melissa Ilardo explains how evolutionary pressure can cause physical changes in isolated communities, as our bodies ultimately adapt to help us thrive in more watery environments.
We were able to show that a gene called PDE10A seems to be influencing this large spleen phenotype. And what we think is happening is that the gene modulates thyroid hormone levels and then the thyroid hormones in turn increase red blood cell count (potentially) which increases spleen size.
(My transcription and surely errors are likely! Also, the context is important. Don’t just read this and take it at face value.)
Just goes to show....T3 is one of the most important hormones involved in the functions the body.
I once asked the geneticist (who did some non-thyroid related investigations for me) about possible genetic issues relating to a particular thyroid disease.
His responsive, " We just do not know right now, but who knows what variants may be revealed in the future".
Back to the subject above...
Semi aquatic?
I hate being in water, other than in my bath tub!
Text from the programme...
a physiological response we display when submerged underwater, which helps direct oxygen towards vital organs.
We know that one role of thyroid hormones is to promote oxygen delivery to tissues. So, if thyroid hormone cellular levels are low, oxygen levels are also likely to be low.....not condusive to an aquatic life!
Having had thyroid related problems, possibly all of my life, might we conclude that's why I prefer to venture no further into water than a relaxing warm bath!!
J9’s daughter here. I do find it extremely unlikely that we were ever as a species more inclined towards a semi aquatic lifestyle, as animals which evolve for that generally evolve to become quadrupedal and we have actively evolved to become bipedal and to walk great distances across grasslands as we moved out of woodland areas. The fact alone that a bipedal stance is relatively uncommon suggests that we went through an evolutionary bottleneck and became extremely well suited for our particular niche of being high stamina walkers and fast on foot. Why would we, after specialising seemingly so perfectly, randomly become semi aquatic? Of course I do not doubt for a moment that there would have been some instances of people perhaps diving to kill fish and other marine organisms with spears, however I do not think this could be classified as is becoming semi aquatic and is simply a display of our opportunistic nature. In regard to the near complete loss of our hair, my personal favourite theory is that we lost hair on our faces predominantly to aid with non verbal communication, and whilst I do not personally have a theory on hair loss on the rest of the body it could easily be that we had a sparser covering simply because when we evolved we lived in a warmer climate. I am by no means a paleoanthropologist, but this is my opinion on the matter.
Considering we spend the first 9 months of our lives in an aquatic environment I guess we could be classed as semi-aquatic… or is that too simple a thought?
True - up to a point! But had I just said "mammals", I would have been conscious of the egg-laying monotremes Duck-billed Platypus and Echidnas.
Obviously, I could have got round that in other ways but I also thought to keep it simple. And avoid the question as to exactly how aquatic dolphins, whales, etc,, actually are! Clearly they are more aquatic than humans but where do they lie between semi- and fully-?
This is becoming quite the rabbit hole… I think dolphins and whales are more aquatic than most mammals, but they still have to surface to breathe air, otherwise they’d drown like the rest of us. I’d say they’re somewhat more aquatic than humans and other land bound mammals, but not entirely the way fish are… 🥴
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Carbs and thyroid
Epstein Barr Virus at the root of hypothyroidism and much else. Any thoughts? 
The thyroid doesn't secrete 20% T3 and 80% T4, (according to the individual data from Pilo's 1990 study) - this was an AVERAGE.
