The Sound of Noise & Silence

Among many things we will remember after the coronavirus pandemic, the world was quieter than normal. When I compared a busy avenue-street intersection in Manhattan before and during the lockdown, I found a 6 decibel (dB) difference, four-fold in amplitude. (The vast range of sound detected by the human ear needs the logarithmic scale.) A lower density of traffic on the ground, underground and overhead was mostly responsible, with contributions from building work, human voices, and so on. In suburbia, it is weed whackers, chainsaws, and trucks that make most of the racket, and sometimes neighbors too! You can check out a noise map for your region and community here.

Human ear and listeningI can’t think of any virtues for noise, though we don’t agree on the main offenders. Objections are sometimes muted by vested interests. Noise is in the ear of the beholder. Sounds that some heads perceive as musical turn others in disdain or even pain. I remember marveling at the virtuosity of nightingales singing through the night in Languedoc. The volume can reach 95 dB, above the threshold of harm for human hearing.

… That thou, light-winged Dryad of the trees

In some melodious plot

Of beechen green, and shadows numberless,

Singest of summer in full-throated ease …

John Keats: Ode to a Nightingale

Music is mostly regarded as the antithesis of noise, but commonly causes hearing loss. Rock music at concerts and through headphones, for instance, but players of classical music are also at risk, especially French horn players, and when did you see them wearing ear protection? A trombone and trumpet can even register around 110 dB.

The world gets ever noisier, affecting mental well-being and wildlife. The background soundscape can swamp bird song and amphibian calls needed for wooing mates and defending territories, and sound from shipping and industry is conducted faster and farther through water, harming marine life. Even national parks can be noisy. I registered 65 dB at a car park in Yellowstone and had to hike far from human activity to find a nadir of 30 dB, equivalent to a soft whisper from signing leaves and boughs in still air.

We may seek quiet places for peace, but, please, not too quiet. Plunging below 30 dB is strange and uncomfortable, though few people experience it. When I sat in an anechoic chamber in a lab the ringing in my ears was unpleasant, like so much static (tinnitus). Exploring a labyrinthine cave was probably as silent as outer space, but I never noticed discomfort one day deep underground because I was lost and focused on finding a way out! Just as our brains can blot out noise, they can filter out silence too.

While noise irritates, silence is fascinating, even when it makes us feel uncomfortable. When John Cage’s enigmatic 4’33” composition was performed in 1952, the audience heard the soloist close the piano keyboard for the 3 movements. That’s all, except it wasn’t strict silence—someone coughed and there was a ripple as another suppressed a giggle. Some people interviewed afterwards said they felt insulted or cheated, whereas others said it made them watch and listen more intently than usual. I never heard this composition live, although I often listen in solitude or helped by watching dogs teach alertness to everything around, even when they seem to be dozing. May a quieter planet continue to reign after the pandemic.

 

About Giant Eggs & Double Yolks

This week’s gift from a neighbor’s chicken coop included one extra-large egg. After hard-boiling and cracking open we found a double yolk, which some say is a good omen on our wedding anniversary. The following conversation over a meal would be unlikely in most homes, but perfectly natural in ours.

“Have you ever seen a giant human egg?” I asked my wife, Lucinda Veeck. I have only had a few hundred eggs under my microscope, but Lucinda has examined tens of thousands over a long career in her IVF lab.

Chicken egg with double yolkShe said it happened once. It was obviously immature because there were two nuclei in a cell enclosed by a membranous ‘box’ (the ‘zona pellucida’). A normal egg contains one nucleus and it vanishes shortly before ripening at ovulation by ejecting a surplus set of chromosomes in a cytoplasmic bleb. This elimination is so a fertilizing sperm can add a matched set to restore the pair.

Now here’s the thing. Her giant egg was not a microscopic version of the cooked egg. If a hen bird ovulates two yolky eggs simultaneously, which happens occasionally, they are quickly bathed in albumen, then enclosed in a common membrane and a shell during their journey down the oviduct, a process that takes about 24 hours to laying. As the nuclei are in separate yolks, the outcome is a normal genetic makeup with two chicks hatching from the same egg, although the cramped space affects their viability . The closest parallel is when non-identical human twins are conceived after a double ovulation.

But the nuclei in Lucinda’s giant shared the same cell, so their DNA would be inherited together. Had it been mature for fertilization the embryo would likely have three sets of chromosomes (two female and one male), called digynic triploidy, and fail to develop.

We explored explanations for its origin. If you have seen densely packed eggs in biopsies of young human ovaries you might wonder how they manage to grow independently instead of being swayed by neighbors, like people jostled in a football crowd. Sometimes they lose autonomy. I have seen two or more eggs combined inside follicles of every species examined, up to 14 in dog ovaries, although some looked unhealthy from the competition.

When boxed inside their own membrane eggs can’t fuse to make giant eggs. They have unique genetic makeups, just like eggs from separate follicles that go forward to make non-identical twins. But what happens when they coexist in a ‘box’ and don’t fuse to form a single cell?

Lucinda saw an example five days after an IVF procedure. It was a double embryo at the blastocyst stage with about 64 cells each. If separated for implanting in the womb, it seemed likely they could make non-identical twins, but if they had originated from a fertilized egg that had split instead of from two separate eggs they would make identical twins. It’s possible that they could unite (or reunite) to make a singleton pregnancy, and, if originating from two fertilized eggs, the baby would inherit mixed genetic lineages, a known condition called chimerism.

In the interests of being (somewhat) intelligible, I avoided more abstruse explanations and outcomes. With so many ways that development can go awry, it is a marvel that we turn out well, or mostly, and I am thankful for my genesis otherwise you wouldn’t be reading this post. I usually avoid writing technical stuff, but correspondence is welcome from readers who like to crack eggs.

Next Post: The Sound of Noise & Silence

Graying, Viruses and Broken Hearts

A long time ago I made a discreet survey of male manes. Perhaps it was an idle way to cure boredom on journeys, but the more I looked the more convinced I became that men who turn gray when young have vigorous crops when they are old. A premature gray head of hair is a lesser stigma than a bald one, but I wonder if it is worn at a price.

I admit there is nothing simple about this (or any) biology, and we are fools to draw a hasty conclusion from extrapolation. Hair can change color and density for many reasons, not least from diet, disease, and aging. Stress can be a factor too. After my mother narrowly survived pneumonia around the time she delivered my youngest brother her hair suddenly turned to silver from dark brown. Surely it was more than a coincidence.

We crudely judge age from hair, although it’s a dishonest guide even for those who wear it au naturel. But sometimes when I see a heavy crop of gray I wonder if it is standing up like a warning flag. I generally ignore anecdotes in medicine but sometimes they get you thinking. I have a friend about the same age with a full head of white hair I envy, but I would rather have a bald pate than his heart attack that came out of the blue (pardon the pun). We thought he had healthy decades ahead of him as someone who lived carefully.

The doctor shrugged when my friend asked, ‘Why me?’  No one had an answer, except to say, ‘It’s in his genes.’ The word genetics covers a multitude of ignorance, although there’s bound to be truth in it that science will uncover one day. Cardiovascular disease cuts a broad swath with its scythe as the biggest killer in developed countries, men ahead of women, but it sometimes runs deep in families predisposed to it at youngish ages. The character of our manes is also inherited, and so I muse whether heart and hair are linked. The oracle was in his hair.

Perhaps is the cautious answer scientists give to the curious public who want a clear-cut answer, preferably not about mice! But mice are in the vanguard of biomedicine. In a paper published this month from the University of Alabama a link was found between the innate immune response and melanocytes in mice. I must backtrack to fill a gap.

Courtesy Open Clipart

Hair follicles contain melanocyte stem cells that produce melanin pigment granules to give color to growing hair. Those cells are lost with age, which makes hair progressively grayer until it eventually turns ‘white.’ [Strictly speaking not white but semi-transparent to reflect light.]

Are melanocytes connected with heart disease? It’s not a question you often hear. There is no direct physical connectivity, of course, but a link exists with the immune system. Melanocytes do not originate in the conventional immune system but they work in many ways like immune cells defending the body against external danger. That makes sense for cells stationed at the surface of the body where they are guardians against infection as well as providing melanin to protect the more vulnerable parts of the body from solar radiation. Melanocytes deserve a lot of credit.

The researchers studied a transcription factor called MITF we can call a ‘gene switch.’ It operates in both melanocytes and immune cells. When they switched MITF off in mice the immune system was activated as if it was responding to an infection. At the same time melanocytes were depleted and the fur turned gray. But if graying is a sign of galvanized immunity how does this link with broken hearts?

Heart disease is regarded as an inflammatory response that can be caused by ‘alien invasion.’ There is firm evidence that common bacterial and viral infections can promote plaque formation in arteries by inflammation, and when plaque peels off it can block blood passing through the vessel to cause a heart attack.

What might this mean for health and disease, for hair and baldness, and for my friend? Would he have been healthier had he turned bald instead of gray? Of course, he would not have avoided his fate by dyeing or shaving his head.

If he had a viral load years ago, especially if it was chronic although not necessarily obvious, the MITF switch would be turned off in his immune cells so they could respond to the challenge. Plaque formation would be the trade-off of inflammation. At the same time the same switch would trigger graying.

This speculation doesn’t explain why men who turn gray prematurely tend not to go bald. And it leaves unanswered the bigger questions why some men turn gray early and any definite connection with heart health. My friend’s attack might have been caused by lifestyle or an infection, and aggravated by the very thing he could never avoid. His genes. We will understand some day if the MITF switch has differential effects in men with early graying from the writing in their DNA code, but for the present we have to turn to mice for provisional evidence. It’s intriguing that when the researchers examined a strain genetically prone to graying they found that when the immune system was stimulated the animals went gray at younger ages.

My theory of hair and heart won’t help my friend. But perhaps at the first signs of graying if men in their early 30s and 40s test blood markers of inflammation they might dodge the bullet by reducing other risk factors in their lives to normalize their fate. Forewarned is forearmed, as they say.