Yawning? 

I Hope It’s Never Happened Reading “Bioforthebiobuff”

At high school we had a history teacher by the name of Dr. L., who had spent 11 years in a Soviet prisoner-of-war camp before being released in 1955. He used to put the history book on the classroom’s desk, positioned himself comfortably on a chair near the side of the classroom and asked some of the best readers in class to take turns to read from the book. That’s how his lesson went. Although he can perhaps be forgiven for killing our interest in history by this behavior of his, his antics were also a cause of hilarity, especially when we noticed the regularity of his yawns and could predict when another big yawn of his would appear (silently counting: 14, 15, 16, 17, “yawn”!). But what made him yawn so much? Boredom, lack of sleep, or something else? And why is it so ‘contagious’? Mirror neurons perhaps?

The common view has always been that yawning was related to a lack of oxygen, a build-up of carbon dioxide and a room that was too warm and stuffy. Consequently, a call to open the window and let in ‘fresh air’, could often be heard in situations where people were seen to yawn frequently and appear sleepy. Yet, numerous studies have shown that lack of oxygen and carbon dioxide increases are by themselves not a cause of yawns. The situation is complex and although the amount of yawning appears to be correlated with boredom and sleepiness, it must leave us puzzled to notice that even after a good night’s sleep we wake up and then more often than not yawn upon awakening. Why yawn at that time? And cooling the brain in the morning or at other times by gaping wide: does it make sense? The idea that yawning is a component of thermoregulation has not yet achieved the acceptance it hoped to get.

If we examine objectively what happens during a yawn, we notice that it involves a wide open mouth and a long and deep inspiration of several seconds, sometimes accompanied by some soft vocalization during expiration. It is an involuntary behaviour that can be triggered by thinking and reading about yawning and/or seeing someone yawn. Yawning is communicative and is generally coupled with inactivity, lethargy and sluggishness (sometimes worry as well). To suppress the yawns can be difficult, especially when hindered to move as in boring meetings, lectures, and waiting rooms. And this actually gives us a clue: our bodies need us to stretch occasionally, to shake our arms and legs, to release tension.

The realization that yawning is a stretch response has been gaining attention ever since it was observed that when hemiplegic individuals that not normally can move their arms do move them when they pandiculate with an associated yawn. Yawning when pandiculating, i.e. stretching and thereby contracting and relaxing muscles, reduces muscular tension, is resetting and restoring the control over muscles, something that is critical for posture and movement and something that yoga instructors constantly emphasize. Obviously, the fact that the slow expiration following a yawn is associated with a sympathetic activation marked by an increase in blood pressure, suggests that at the start of the yawn it is associated with a sympathetic suppression that favours a parasympathetic dominance. This might also explain the observation of a paraplegic’s involuntary movement of its toes during a yawn.

Yawning must have ancient roots in the animal kingdom, for it can be observed in almost any animal group and is not even restricted to vertebrates alone as this delightful recording of a yawning leech shows here . Lizards, frogs, toads and even fish can be seen to yawn and all of them are ectothermic (often referred to as ‘cold-blooded’). As such, they would not be expected to use the yawning response to cool their brains as has been suggested for mammals, but could find yawning useful in connection with stretching and therefore the restoration of muscle control. Yawning:  a kind of physical exercise without having to get up? I think that that is a distinct possibility.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

Less Attractive

But More Successful in Attracting High Quality Males

Sexual dimorphism in which males and females differ from each other morphologically is widespread among animals and occurs in many groups, e.g., to name but a few: insects, spiders, fishes, birds and even mammals. It puzzled already Charles Darwin why, for instance, some male moths and male beetles frequently had much larger and seemingly better developed antennae (which during Darwin’s time had not been identified as the sensors for odours, but were seen merely as touch receptors).  He and many other researchers felt that the larger development of certain structures in male animals served as ‘advertisements of prowess and vitality’ and indicated to a female the presence of a superior sex partner. That enlargements and greater conspicuousness of structures increased the chances of being recognized (and preyed upon) could, of course, have been a handicap, which is why Zahavi suggested females chose males because they had survived and reached sexual maturity despite being more vulnerable and in greater danger of being attacked than cryptic ones.

What, according to Australian researchers Mark Elgar et al. had not fully been considered till 2018 in the discussion of sexual dimorphisms and attractiveness (at least with regard to insects in which female individuals release some odoriferous chemicals known as pheromones) was the role sensors play. Large and often plumose antennae in insects contain receptors that detect the presence of molecules in the air, i.e. chemicals released by plants, possible food items and, of course, females in case of moths and many beetles. Some of these sensors or so incredibly sensitive that only a few key molecules need to be present for the males to respond to. In case of some moths, a male can smell a female 10 km away. To maintain the sensitivity of sense organs, whether they be mechano-, photo- or chemoreceptors and to process the information received by them is energetically expensive as my former colleague Dr Simon Laughlin at Cambridge University has shown. Consequently, as has been argued, those males with the most highly sensitive sensors are more ‘valuable’ than males, whose sensors only respond to the most obvious and strongest stimulation. But how to eliminate the latter and favour the former?

Maybe some female moths and beetles that attract their males with pheromones have found a way. If a female sends out a strong pheromone signal, the latter will disperse widely and reach a huge number of possible male partners, including those that have rather insensitive “noses”, in other words do not exactly possess a highly developed sensory system. But they are not the males the females want to have as “fathers for their babies”; the females want those males that are alert to the slightest of stimulation and what better way to get their attention than to emit only a fraction of the pheromone that is so successful in reaching all kinds of males near and far? This is apparently a strategy that works, because young females which because of their age can afford to be choosy, use it, while older females that have not obtained a partner increase the amount of pheromone they emit.

Whether this idea of “less being more” can be applied to vertebrates as well has not been tested (yet). However, if we take an unbiased, objective look at our own species, aren’t we observing that it is those who are beautiful and attractive as young individuals that need less make-up, lipstick, and other beauty-enhancing stuff than physically less fortunate females, who want to become more noticeable to men through exaggerations? And isn’t the use of perfume, wrinkle-hiding cream, eye-catching jewellery increasing among older females? Perhaps there is indeed a parallel to female moths and beetles. But what about the males that the females attract? There, too, could be a parallel: the less sharply observant and somewhat superficial males do not see beyond the make-up on the skin, the red colour of the lips and the artificially enhanced signals of the female. It takes “sensitivity” and “smartness” (as in case of the male moths and beetles), for males to identify a quality female. And yet, it seems enhanced female signalling is there to stay  –  in moths, beetles and humans as well.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

Some Animals Can Do It

Wouldn’t it be nice if we could do it too and close our ears

The daughter of one of my friend’s has recently learned to swim  –  and she loves it. But what she does not love, is having to shake out the water in her ear after a swim. So, she asked me why we can’t close our ears. Nice question, and I answered I don’t think dogs and cats can close their ears either when they swim and whales and harbour seals (so-called phocids) don’t have any ears at all  -well, at least those parts of the ear that you can see, i.e. the outer part, the so-called “pinna”. But it made me think, because in Antarctica I was surrounded by fur seals (so-called otariid seals) and they all had small, but very prominent ears. Besides, even though whales and phocids lack the pinna, they can certainly hear quite well under water and possess all the inner ear structures (like ear canal, middle ear and cochlea ) that are similar to even our own ears.

All diving animals, whether they be whales, phocids and even walruses (none of which possessing external ears) or whether they be those with ears such as otariid fur seals and sea lions or otters and hippopotamuses or the aquatic insectivores known as desmans or egg-laying platypuses: they all can hear under as well as above water. However those with visible ears have means to prevent water from entering their ears and hippopotamuses, for example, angulate their small ears backward and close the ear canal by contraction when they dive; desmans achieve the same result by glandular swellings to seal up their ears temporarily and eared seals like fur seals are capable of controlling the state of their ear canals by muscles when diving or when in air. Rising pressure expels the air that happens to be trapped in the outer ear when the fur seal dives and improves underwater hearing. 

In the aquatic mammals that lack an outer and visible ear like whales, harbour or hooded seals and walruses, adaptations to hearing under water are a little different. There is no need to close the outer ear, because there isn’t one. However, hollow structures like ear canals and the air-filled middle ear (connected via the Eustachian tube to the respiratory tract) need to be protected against a collapse during a dive owing to the increasing pressure.  During dives the tissues around the external ear canal and the middle ear fill with blood to occupy any air spaces and as the air spaces get smaller and smaller with depth, hearing under water improves. In phocid seals the middle ear bones are less separated from the skull than those of the fur seals, and that enhances sound amplification, but fur seals are better in determining the direction of a sound under water. The underwater sounds of the latter range from about 1000 to 4000 Hz, but those of whales and phocids cover ranges from 40 to 8 kHz and 100 to 15 kHz, respectively. Some species of dolphins (with very long ear canals) can even hear frequencies across the enormous range of about 100 to 150 kHz.

Other adaptations include copious amounts of earwax (especially in the ears of walruses) and elastic fibres in the walls of the Eustachian tube. An interesting adaptation to strengthen the ear canal lateral to the eardrum (the well known tympanic membrane that causes the problem in our ears when it’s blocked and we are in an aeroplane or are diving) are the so-called exostoses and the latter are thought to facilitate deep dives into very cold water. Exostoses do sometimes also occur in humans, where they are often referred to as “surfer’s ear” and involve benign, non-tumorous, firm and sessile, often bilaterally symmetric, nodular bony growths within the ear canal. Their occurrence seems to be closely connected with the amount of time a person spends surfing or diving in cold seawater. Can this similarity to phocid seals and other diving animals be used by people who champion the idea that during the evolution of humans there was an aquatic period? It’s a long shot and I doubt it very much. But what this blog has shown once again is that responding to a child’s question is something not to dodge, because it makes you think. And that can only be something positive.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2022. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.