Embryos Can Smell Too

Comparing the embryonic development of various animals, Ernst Haeckel's Art Forms in Nature                   

Among the myriad ways olfaction is set apart from all other senses, this is perhaps the most important – Smell is the first sense to develop in ontogeny (the ‘lifetime’ of an organism), and begins in the womb.

We know babies can hear in the womb, but it isn’t often considered that they can smell too. Smell is a form of chemosensation. And if we think of an embryo as floating in a chemical soup, it makes sense that such an organism would be able to sense its surroundings. Possibly more surprising than this, it should be noted that adult humans have olfactory receptors in other parts of their bodes besides the nose. Certain organs are populated by the same nerve cells that relay the presence of aromatic molecules to our thinking brains via olfactory perception.

Here we must distinguish between sensation and perception. It is a misnomer to say that an embryo, or any such simple organism, can smell. Can you see with your eyes closed? Well, yes, but it depends on what you mean. The photoreceptors in your eyes still work whether your eyes are open or closed. In fact, they never stop working. The “seeing” part of you may stop, but the receptors are on all that time, ready to be stimulated by the most gentle of photon showers. (And when there is none – they make things up!) Babies in utero too can sense light levels in this way – but is that “seeing”? Not so much. And is it the same with smelling? Sort of. Perception requires a brain, but to sense does not. Plants can smell. Not really though; they can only sense chemicals.

Back through the mirror again, what does it mean for adult humans to smell, to perceive chemical signals? It is not a cognitive sense, or should we say a ‘cortical sense’. Smell is different in the way it uses a cortex, the perceptual-processor that creates an experience in our minds. For smell, the ‘processor’ is the limbic system itself, a beta-brain that runs inside, underneath, or within our more advanced human brains. This limbic system-chemical signal interaction is much more akin to the way a plant “sees” a sunset than a human. And so, to say that an embryo can smell, is less of a stretch than to say that it can see.

It makes matters more complex, however, when the chemical environment of the organism in utero actually affects its adult behavior. But because smell is a learned perception – an emergence of episodic memory – the osmic sensorium that we experience today and ultimately the way we respond to it, is predicated upon the very primitive origins of our ontological journey.

Post-Script

Study shows embryos can learn

phys.org, Dec 2014

Pond snails are able to sense chemicals released by their predators whilst they are still embryos in the egg and alter their behaviour accordingly, according to new research at Aberystwyth University and the University of Exeter and Plymouth University

When snails are exposed to predator smell during this very early developmental stage, they are better able to avoid predatory fish once they hatch...

The ability to respond to potential predators while still in the egg may be extremely important in allowing young vulnerable snails to survive.