biology zoology blog benno meyer rochow eyebrow

Eyebrows and Eyelashes

Do they have any uses at all?

When I was a child, I often heard some adults remark what beautiful eyelashes that boy has. But as I grew older and taller the eyelashes became shorter and shorter. But what is it with eyelashes that so many people love about them? Certainly not all love them, because when my daughter Yamuna was two or three years old, she kept pulling out their exceedingly long eyelashes, because she must have felt that they were obstructing her visual field and sometimes were getting into her eyes. Trobriand Islanders, as Malinowski in his famous 1929 book The Sexual Life of Savages described (and I can support on the basis of my own observations during four stays on the Trobriand Islands), are proud not to have eyelashes as it indicates to a young girl that she’s had many lovers and therefore must be an attractive girl. Eyelashes are bitten off and eyebrows, too, are kept very short. In fact, all facial and bodily hair is considered ugly.

Some birds and many species of mammals (especially those feeding on grass and sedges or leaves of shrubs and trees) also have eyelashes and some even have noteworthy brows (although the latter are often not recognizable, because of the surrounding fur). The fact that more species which seek their nourishment in trees, bushes, grasses, etc. possess eyelashes than carnivores could suggest that one function of eyelashes is that of a warning device: if something unexpected touches the eyelashes, a nerve impulse from a pressure or stretch receptor at the base of an eyelash is sent to an appropriate eyelid muscle to close the eye to prevent damage. There is no need or time wasted to think of closing your eye: a reflex arc takes care of that. Eyelashes of camels and other mammals living in sandy surroundings serve to protect their eyes against windblown dust particles and give their eyes as well as those of ostriches, giraffes, horses and cows, etc. expressions that resemble those seen in humans. Animals like mice and kin seem not to have long eyelashes as their long whiskers alert them of danger.

Eyelashes and those of eyebrows are structurally and embryologically identical to those of the rest of the body and grow for a while, then fall out, and re-grow. There are, however, some difficulties to explain differences: while eyelashes become shorter as a person ages and the amount of hair on the scalp gets less with age (or may even disappear altogether), eyebrows tend to become fuller and bushier. Although some of the eyebrow’s hairs may function as touch receptors (similar to eyelashes) and can be quite long as in seals (where they may convey information to the seal about currents and swim speed), their main function in terrestrial animals and humans is a different one. It is actually very easy to find out how useful eyebrows are, when you go for a run in a warm, tropical country and the sweat begins to run off your forehead into your face. Getting the slightly salty sweat into your eyes irritates the eyes, but well-developed eyebrows ‘channel’ the sweat to the sides and keep your eyes functioning. A very similar observation you can make when it rains and you have no umbrella to protect yourself against the rain.

Prominent eyebrow ridges further enhance the protective function, shade the eye and reduce injury and radiation effects. A few isolated and long, bristly hairs are often found above the eyes of rodents.

Yet, eyebrows, can also express feelings, moods and intentions and that may be important for animals like apes, monkeys and humans, in which the colour of the eyebrows may be different from that of the surrounding skin and the hair on the scalp. Perhaps that is the reason why women often darken their eyebrows and, removing excess hairs, turn them into thin lines to show without words what they feel. (Besides, it may reduce the chance of Demodex mites colonizing the eyebrows and eyelashes).

© Dr V.B. Meyer-Rochow and, 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 with appropriate and specific direction to the original content. 


Hated by many but liked by some

Finding a cockroach in an unopened bottle of Cola isn’t exactly “cool”. Seeing them scuttling along the kitchen floor at a top speed of 2 metres per second in the large Periplaneta americana and leaving their distinctive odour on some plates they might have run across at night isn’t very pleasant either and yet, there is some information about them which is not entirely negative.

First of all, despite their less than positive reputation, they are not know to carry or transmit diseases; they neither sting nor bite and amongst several cultures in various countries cockroaches and their egg cases are a part of the traditional armamentarium to combat certain diseases and dysfunctions. In the year 2000 E.M. Costa-Neto and M.V.M. Oliveira published an article in the journal Human Ecology Review, titled “Cockroach is good for asthma: zootherapeutic practices in NE-Brazil”; the world’s largest cockroach farm is breeding 6 billion cockroaches a year, using artificial intelligence to manage a colony larger than the world’s human population – all for medicinal uses or a source of protein for livestock feeds. There are many such cockroach breeding facilities in China, but no other matches the productivity of that in Xichang (S.W. Sichuan province). If after all this, I now report that some people enjoy eating cockroaches, fried in oil and seasoned with spices, I suppose nobody will be surprised any more.

I loved to use cockroaches in my comparative physiology course “Animal Senses and Behaviour”, because it was easy to demonstrate electrophysiological recordings with them and the fact that they “hear” with the two horn-like projections (known as “anal cerci”) at their rear end. To prepare them for the recordings is easy, as their ladder-like ventral nerve cord is accessible from the dorsal side of the animal after most of the inner organs have been removed. With two fine silver hook electrodes pushed under the connectives between two nerve ganglia, I could then carefully lift the nerve cord ever so slightly above the cockroach’s body liquid and record its nervous activity to be displayed on an oscilloscope. I then got my trombone and played short bursts of low or high frequency tones. The lowest frequencies picked up by the anal cerci elicited a train of responses in the nerve cord and showed the students that the information from the anal cerci was passing on the way to the brain of the cockroach through the ganglia responsible for leg movements. The same preparation was also useful to demonstrate the response to shadows when I passed my hand or my fingers across the insect’s eyes.  I need to add that cockroaches (and some mutations like white-eyed individuals) have been used in research on vision and visual information processing in a variety of scientific laboratories. Most roaches, are easy to breed, are undemanding, live for 6 months and some, like the Hissing Roach, even make pets.

That one can even have fun with cockroaches I learnt when I was a sailor, because ships almost always have cockroach stowaways, especially the small German species Blatta germanica. A bit of ground coffee put in a glass with butter or some other fat smeared on the upper rim of the glass’ inside would trap some of the nocturnal creatures and, competing with each other, we could find who had caught the most roaches the next morning. We also organized cockroach races to see who had the fastest insect.  Cockroach species occur in a variety of habitats (and not just in human dwellings). That there are even aquatic species that dive into a stream or pond, I only learnt recently in Northeast India, but that some species give birth to live young and feed their offspring with a kind of “milk” or that some can reproduce without males, I knew before. Having been around for about 300 million years, the cockroach “tribe” will almost certainly still be there when humans have become extinct. So: hats off and some respect to these little unwanted and unloved champion survivors. There is even a song dedicated to them: the Spanish folk song “La cucaracha” and when a cockroach would fly into our house in Jamaica (they DO fly when the temperature is well above 30⁰C), I did not kill it, but picked it up and returned it to the garden. Sounds crazy to many, I guess, but will be understandable to some (I hope).

© Dr V.B. Meyer-Rochow and, 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 with appropriate and specific direction to the original content. 

Is the y-chromosome in humans destined to disappear?

I think there are probably few matters that men tend to worry more about than their masculinity. When years ago I saw the announcement of a public talk on “The Disappearance of the y-Chromosome”, I simply needed to hear what that was all about. Since I listened to that talk at that time, a great deal more research data are available on that topic. Fact is that all “maleness” is conferred by the y-chromosome and “femaleness” by the X-chromosome, both being termed “sex chromosomes”. But while women have two X-chromosomes (= XX), men only possess one X and a much smaller y-chromosome about one fourth the size of the X (=yX). Chromosomes (of which all humans have 46  -not counting chromosome number anomalies) occur in identical pairs and that holds true also for the two X-chromosomes in a woman. However, a man’s single y-chromosome’s partner is an X and because of their much different sizes the two chromosomes cannot recombine and repair each other if some bad mutation has occurred on one of them. Think of heaemophilia, which is due to a bad gene on the X-chromosome, but doesn’t make a female ill if she has another “healthy” X. Men do not have that luxury and develop the sickness.

Now assume a bad mutation occurs on the y-chromosome and there is no chance to repair or compensate for it? The only way to weed out the bad gene is to lose it, to delete it and by having to do this repeatedly over millions of years, the y-chromosome is bound to get smaller and smaller. It now contains no more than perhaps 50 genes, while the X-chromosome contains about 20 times that many. According to some researchers, like world famous Australian geneticist Dr Jennifer Ann Graves, about 300 million years ago sex-chromosomes were not yet terribly different from the other chromosomes known as autosomes, but with one of them (the one carrying the gene for maleness) beginning to lose genes, the fateful decline in genes took its course and from about 200 million years ago saw the development of differently sized X and y-chromosomes plus a loss of about 10 genes every one million years. With only 45-50 genes left on present day human y-chromosomes, one can expect the y-chromosome to have disappeared in 4-5 million years. Not so, according to Dr Jenn Hughes, who argues that gene loss affecting the y-chromosome in humans is not constant as only one gene disappeared in the last 25 million years.

However, even she has to admit that ultimately there is the possibility that in many, many millions of years to come, human males (if humans are still around) could be without their little “y”, but not necessarily without the organ many men are usually so worried about. There are, after all, already a few species of mammals, for instance the famed but endangered spiny rats of Amami and Oshima islands in Japan, in which males have no y-chromosome at all. Since the offspring of these rats is not hermaphroditic, but differentiates into male and female individuals (in which the brain of male rats expresses genes to produce hormones that are involved in seminal vesicle protein 5 [Svs5] and cytochrome P450 1B1 [Cyp1b19] syntheses, but the brain of female rats upregulates serine or cysteine peptidase inhibitor and other molecules typical for females), some chromosome other than the “y” must have taken over its function. Yet, what, when, and how exactly that happened is still uncertain.

Virtually all of the few genes still present on the y-chromosome are “maleness”-genes and the SRY-gene is the most important one, as it causes the development of external and internal male genitals. Other genes are involved in regulating sperm and seminal fluid production. How important the y-chromosome is, one can see in cases of people with a multiple X and one single y-chromosome: even XXXy individuals have male genitalia! And one more important aspect of the y-chromosome: because of mutations on it, it allowed researchers to track people’s migration routes out of Africa from 100,000 years ago to now.

© Dr V.B. Meyer-Rochow and, 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 with appropriate and specific direction to the original content.