Aquatic Ancestors and Breathing through the Ears: Nonsense or not?
Provocative statements, based upon good arguments, can inspire researchers to take a fresh look at old questions. As Prof. Popper once stated: “If a hypothesis, which most people think is probably true does turn out to be true … little progress has been made. If a hypothesis, which most people think is improbable turns out to be true, then a scientific revolution occurs and progress is dramatic.” However, one needs to be critical (and knowledgeable) and when I came across a statement that morning sickness in humans occurred only in meat-eating societies and that it was linked to reducing the risk of animal-borne diseases affecting the foetus, I dismissed that idea, for the originators of that claim had completely ignored the largest group of vegetarians on Earth, the Hindus (and they know “morning sickness” very well!).
I must admit though that it rattled me quite a bit when years ago I heard of the theory that held that our human ancestors, after having abandoned the life of fruit collectors and leaf-munching apes on trees, had evolved into aquatic apes, wading into the water of shallow tropical bays in search of shellfish and other seafood. That theory claimed to explain why only humans but not apes possessed extensive subcutaneous fat deposits and minute hairs on the back that grew in patterns advantageous only for aquatic animals. Other features, seemingly typical of humans like the dexterity and sensitivity of our hands, the presence of plentiful hair on our heads but nowhere else on our bodies in comparative density, and even our weekly rhythmicity, could be neatly accommodated in this theory. But why the coastal existence was abandoned in favour of hunting and gathering food in the savannah remains to be explained. Moreover, a total lack of fossil evidence of the supposed aquatic ape stage casts a big shadow on this idea.
Another provocative idea that caught my attention goes back even further in our evolution and suggests that 360 million years ago the earliest terrestrial vertebrates used their ears to breathe. This idea was not inspired by the huge, flap-like ears of elephants, but by the undisputed fact that the same three little bones present in the middle ear of birds and mammals are part of the jaw apparatus in fishes. One of these three ear bones, known as the stapes, is the hyomandibular of the fishes and that same little bone with the long name is involved in producing ventilator movements of a fish’s gills. The gills, however, are the fish’s equivalent of a terrestrial animal’s lungs.
When some 360 million year old fossils of the terrestrial Acanthostega gunnari (a kind of walking fish considered the earliest semi-terrestrial 4-legged animal) were discovered and an examination revealed no clear evidence of a tympanic membrane, but an ear-hole in the skull and nearby a short and strong stapes instead, incapable of transmitting sound waves, it seemed logical to assume that the ear-hole was actually letting in air and involved in breathing. There is, apparently, still one species of fish, called Polypterus, existing today, which has lungs and no trachea, using instead a spiracle (that is the name for the hole under debate, whose origin lies with the gills) through which air, as well as water, can flow. Interesting that our earliest terrestrial ancestors were supposed to have been breathing through their ears? Well, whether correct or not, I think so.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2019.
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