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. 

Excrement’s Exciting and Extraordinary Acceptance

In traditional therapies

I think the custom of hiding Easter eggs and letting the children find them is fun for both parents and children. However, how the Easter Bunny became part of it, I do not know, but the Easter egg-laying bunny certainly fooled one of my sons. I had hidden chocolate eggs the night before and to make the whole thing more realistic had scattered near the open window some rabbit dung pellets. When the Easter egg search was over, I asked my son if he’d seen the Easter Bunny’s droppings. He hadn’t and was surprised. But I was most surprised when he explained that he’d eaten them thinking they were nuts!

Actually, rabbits habitually eat their own faeces, because the latter still contain nutrients, being only partially digested and representing fermented products of the rabbit’s hind gut (the cecum). Rabbits are not the only animals that consume their faeces. There are numerous reports that traditionally also some humans in different parts of the world added animal faeces to some of their dishes and even today the world’s most expensive coffee uses beans that have passed through the gut of a Viverra sp., a civet cat, which isn’t really a cat, but despite its omnivorous diet a carnivore that eats and poops out coffee beans.

In my field work as an ethnobiologist I collect information from tribal traditional healers on therapeutic animals and animal products and very often I am told that the faeces, excrement, dung (whatever you wish to call the digestive end product of the food eaten) are an important ingredient in potions and medicines given to the sick. Among  the Tangsa of North-East India, goat droppings are applied to cuts and burns; to treat infections of umbilical cord and naval of a newborn child goat excreta are also used. In Rajasthan, tribal Garasiya apparently use droppings of crows to cure blisters and in parts of East Africa monkey faeces may be used as a remedy for the sleeping sickness. In western medicine sometimes stool (yet another term for ‘faeces’) from a healthy donor is introduced to the gastrointestinal tract of a patient having suffered from severe diarrhoea or colitis (but there are more discreet methods than feeding the material directly to the patient!).  Actually, poop (yet another term) consists mostly of water, but it depends on the species of course. There are likely to be some undigested fibres, fats and proteins as well as blood cell breakdown-products and traces of bile. Therapeutically interesting is the excretal bacterial biomass, which can be very substantial and makeup 25% or more of the dry weight.

Owing to the metabolism of these bacteria excreta can contain a multitude of bioactive compounds, acting as analgesics and antibiotics with anti-inflammatory and anti-pyretic (fever) properties. In Kunming (China), researchers identified useful species of Actinobacteria from the faeces of 31 species of animals and suggested that many of them could be potential new drug sources. Khan and co-workers in Guangzhou showed that Adélie penguin excrements contained compounds that potently inhibited the growth of various pathogenic bacteria. But in many countries (and not just India: former Prime Minister of India, Morarji Desai comes to mind) urine has also widely been used therapeutically and Gahukar, a few years ago, even suggested that cow urine be used as an alternative bio-inspired pesticide.

Looking at my watch ad noticing it’s time for a break, being a bit thirsty (it’s afternoon), I am actually rather happy not  having to choose between civet poo coffee and medicinal teas based on the excreta of a phasmid stick insect and Bombyx mori caterpillars (both used in parts of Asia for asthma, stomach upsets and body pain). I stick to my golden Assam Orange Pekoe tea and certainly don’t want to be reminded of the time when my son not only ate rabbit dung, but as a toddler even chewed on dry dog poo, believing it was dried banana. And if you haven’t had enough of this topic: look up “urumiit”.

© 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. 

biology zoology blog benno meyer rochow sneeze

The Science behind Sneezing

Have your handkerchief handy

Have you noticed that most of the words related to the “nose” start with the letters ‘n’ and ‘sn’? Apart from nose, nares, nostril, and nasal you’d find snot, snort, sniff, snuff, snore, snooze, snub-nosed and, of course, sneeze. The most common reason advanced for why people (and other animals) sneeze is that the act of sneezing removes an irritant or obstruction in the nasal passage. Suffering from hayfever (my children used to have fun chasing me around in the garden with flowers in their hands) I once counted that I was sneezing forty times in a row  – and that was not at all because of an obstruction in my nasal passages (or looking into the sun, which is said to trigger sneezing in some people). So, what goes on?

The allergic reaction to pollen like the one that made me sneeze is probably one of the commonest reasons of sneezing in humans. But it’s complicated, for it involves an oversensitivity reaction in which substance P (cf., my earlier blog) is increased in the nasal epithelium together with other neuropeptides like, for example, calcitonin (cf. also old blog). These and the release of antibodies and histamine by the body’s immune system to the perceived threat posed by the inhaled pollen, lead to the hypersensitivity reactions (e.g. nose and eye itch). All these in conjunction with neurotrophic factors stemming from the allergy, target neuronal fibres like chemo- and pain receptors and those sensing itch, which then send the information to the trigeminal ganglion. The trigeminal nerve that serves also the cheek and orbital region of the face then instructs the sneezing centre in the brain’s medulla to take action.

Action means that effector neurons should become active. Those involved with breathing make sure that deep inspirations occur prior to the sneeze and that the eyes and the glottis close, before through an increase of the pressure in the lungs the glottis suddenly opens and releases in an explosive action air and fluid droplets through mouth and nose. The pressures involved in a sneeze can be 176 mm Hg, which would be one tenth of the pressure of a tyre of a small car or one third of the pressure penguins generate to poop. During a sneeze thousands of tiny droplets of liquid are released up to a metre and sounds accompanying a sneeze can vary from faint to deafening.

People who own a dog or a cat know that their pets may occasionally sneeze spontaneously or when you tickle their nose or when they smell irritating chemicals. The same holds true for humans and I for one avoid the perfume sections of the department store because the odours there could make me sneeze. The sneezing that accompanies a cold is usually related to a mucus build-up in the nasal passages that the sneeze tries to remove. The Galapagos iguana and some marine birds sneeze to remove salt crystals that have accumulated in the nasal passage and need to be flushed out.  All vertebrate animals with lungs and a connection between the nose and the pharynx (that excludes the fish) are said to have ‘choanae’ (= internal nares) and can sneeze. The nose of a fish consists of two nasal openings for the inflow and two for the outflow of the water. Located between in and outflow nares is the olfactory epithelium with its odour sensitive cells. Thus, looking at the head of a fish you will see 4 nasal openings and not just two as in all terrestrial vertebrates. Sneezing in fish is therefore not possible.

Antarctica is a good place for people with pollen allergies. Although you can get cold there, you are not likely to ‘catch a cold’ there, but on one of my trips to the icy continent my friend and colleague Taka Hariyama sneezed (dust does exist in some areas of Antarctica). He sneezed once and seemed happy, exclaiming joyfully “only once!”. I was puzzled why he stressed “only once”, until I learned that ‘sneezing once’ suggests to a Japanese that someone is saying good things about the ‘sneezer’, but that sneezing twice means the opposite. Yet, what it means to sneeze 40 times in a row I don’t want to know.

© 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.