Saturday, October 22, 2016
Note: This program first aired on October 22, 2016.
Earlier this fall, a listener contacted me suggesting a topic for the show. He had just replaced his glass hummingbird feeder with a polycarbonate plastic one, in a successful attempt to thwart the yellow jackets that were frequenting the feeder. He wondered though, about the possible contaminants, especially BPA, that the birds might be exposed to. Anticipating the arrival of the ruby throated humming birds in the spring and watching them feed in our yards all summer long rank high among summer pleasures for many Mainers. But with growing awareness that problematic plastic additives show up anywhere, and everywhere, it has been only a matter of time until some one put two and two together and asked this question.
Plastics are polymers, chains of individual units (monomers) strung together chemically. Most plastics are a mix of different kinds of hydrocarbons, with various additives to give them specific physical attributes. These additives have various levels of fidelity to the plastic they are part of, and some readily leach out of the plastic into the environment. Awareness has grown in the past 10 years of this potential problem with the consumer goods and food packaging we contact on a daily basis.
Some chemical additives may be inert, other are quite biologically active and that is the crux of the problem. Bisphenol A, or BPA, the additive my listener asked about, is used in polycarbonate plastic, the kind that lexan water bottles, protective eye wear and DVDs are made of. It has proven itself to be, as many plastic additives are, a potent estrogen mimic, meaning, it binds to the same receptive sites in cells that naturally occurring endogenous estrogen does.
Estrogen is the female sex hormone in all vertebrates, from fish to mammals. It plays the same role throughout the vertebrate group, in carefully timed pulses it guides the development of the reproductive system. The biological or anatomical sex of an individual is the result of the relative balance of estrogen and male sex hormones like testosterone, and the timing of the exposure of cells to these hormones. Through the study of developmental biology, we’ve learned that the critical period for this exposure is very early in embryonic development.
Having an environmental estrogen out there can mess up this system, throwing off the balance of hormones, and the timing of exposure. And that is where most of the permanent impact of chemicals like BPA lies, by mimicking estrogen and flooding estrogen receptors in the cells of vertebrate embryos BPA can interfere with the normal development of the reproductive system of exposed organisms, be they fat head minnows, Japanese quail, or human beings.
Most of the research on the impacts BPA on wildlife has been on freshwater aquatic vertebrates, as it is easy for BPA to get into surface water through municipal water treatment facilities and industrial run off. The research on birds is much more limited, but that which is out there points to embryonic exposure leading to persistent malformations of oviducts and the shell gland (leading to thin and weak shells) in female birds, and changes to brain development in male birds leading to reduced copulatory behavior. These are problems, that, while initiated when the birds were embryos, don’t show up until they reach sexual maturity.
All of this bird research has been on model organisms like Japanese quail or domestic chickens, using exposure vectors like injecting BPA directly into eggs, or dipping eggs in an aqueous solution containing BPA. No one has looked at BPA’s effect on wild birds like humming birds, exposed through the parent’s ingestion of BPA laden sugar water from your new plastic hummingbird feeder. All we can say is that there is a demonstrated estrogenic effect in some birds in experimental conditions, but that the impacts on wild populations with more natural exposure are unknown. If there were negative effects to hummingbirds, I would expect them to be reproductive.
And before you all start writing me telling me that you can get BPA free polycarbonate and other plastics, yes, you can. It turns out that many of the chemicals used to replace BPA are simply other bisphenol chemicals, or are less well studied, and when they are investigated, turn out to have similar biological actions. So just because it says BPA free, doesn’t mean it is necessarily great.
If you are worried about the reproductive health of the hummingbirds who visit your yard, you may want to continue your search for the perfect glass feeder, or better yet, cultivate the original hummingbird feeder, a yard full of flowers.
Excellent review article in Dose Response, focusing on aquatic vertebrates https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4674185/
Full text of a Swedish PHd dissertation from the University of Uppsala on environmental endocrine disruption in birds: https://uu.diva-portal.org/smash/get/diva2:165990/FULLTEXT01.pdf
Environmental Defense Fund on BPA free: https://www.edf.org/health/three-reasons-bpa-free-wont-protect-you?utm_source=ggad&utm_medium=cpc&utm_campaign=gr-bpafree&gclid=COXaxd316c8CFQkkhgodBkkBtg
Other sources on BPA alternatives: http://www.the-scientist.com/?articles.view/articleNo/45789/title/Effects-of-BPA-Substitutes/
And from UCLA http://newsroom.ucla.edu/releases/chemical-used-to-replace-bpa-in-plastic-accelerates-embryonic-development-disrupts-reproductive-system
Saturday, October 1, 2016
Note: This program first aired on October 1, 2106.
I was asked by a listener recently about the place of mosquitos in the world. The combination of news stories about the Zika virus and developing a vaccine on the one hand, and rampant species extinction on the other got him wondering—why don’t we solve the Zika problem by trying to extinct the mosquito? At least that would be an extinction that solves a human problem. If things are going extinct anyway, why not try to get some benefit from that? The real question here is: are mosquitos good for anything?
And the answer is of course, it depends on who you ask. The typical answer to this oft asked question (why can’t we just kill all the mosquitos) is that they provide critical ecosystem services, in the form of being food for other animals in various ecosystems. Scientists are not unified on the impact of eliminating mosquitos (of which there are over 3500 known species, only a couple of hundred of which bite humans). Many say that the positive public health benefits far out weigh any temporary ecological disruption, and that any unoccupied former mosquito niche would be filled immediately by another organism. There are varying opinions and findings about the true role of adult or larval mosquitos in various food webs; they have been on the scene for over 100 million years, allowing plenty of time for elaborate co-evolution with predators, yet food web studies often demonstrate that mosquitos do not make up a large percentage of the food items in the stomachs of insectivorous predators. Male mosquitos do not bite, and feed on the nectar of flowers, and thus serve a pollination role, though none of the plants typically serviced by them are of any economic importance to humans. So the summary on this commonly held wisdom is maybe, perhaps there would be some impact to various ecosystems, and some specialized predators would go extinct, but nothing that we know as of now that would negatively impact humans.
On the other side of this question asks why would we kill all the mosquitos, if we could? Mosquitos are flies, in the order Diptera, a group of insects with mouthparts specialized for piercing and sucking. Their life history requires a blood meal for development of the eggs, hence only the females bite. It is this biting habit that makes them an annoyance, a public health problem and an excellent means of transportation, again, depending on who you ask. Many of the diseases that affect millions of people throughout the world, particularly the economically developing, tropical and sub tropical world, are spread by mosquitos. Malaria, dengue fever, west nile virus, triple E, chikungunya virus, yellow fever, a host of encephalitises, zika, all these are spread either from human to human, or from zoonotic (or animal) host to human, through mosquito bites.
The problem is that mosquitos exploit an ecological niche that includes us warm blooded nutritious humans, and are at the same time exploited by pathogens that use mosquitos to transport them around. Mosquitos are really just a proxy species for the pathogens we would like to rid the world of. A patsy. Purposeful extinction of mosquitos would be an attempt to extinct the pathogens that we would like to avoid. It is these pathogens that kill hundreds of thousands of people, mostly children a year, and sicken millions more. To return to that original question, are mosquitos good for anything—if you were to ask a malaria plasmodium, or a west nile viron, the answer would be a resounding yes.
It was John Muir who once said “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” * And Aldo Leopold said “To keep every cog and wheel is the first precaution of intelligent tinkering.” ** This classical American environmental thinking argues strongly against taking out an entire family of organisms, it's flipside is the same logic that hunted large predators to near extinction throughout North America. But I doubt the Muir and Leopold were thinking about malaria, and deep human suffering.
I think what my listener wanted to know is if we did succeed in taking out all mosquitos, would it initiate some kind of ecological collapse? Are mosquitos a keystone species? The answer is potentially no, especially when colored with the anticipated reduction in human suffering. With that card on the table it may be difficult to get a truly unbiased assessment. Which is doesn’t even take into account if purposeful extinction would be possible, though people are working hard on this front all the time.
I’d like to see us use our ingenuity to find a way to prevent contact between the disease spreading mosquitos and humans, rather than pursue what are likely to be toxic extermination methods. I think we can go a lot further to reduce human suffering and eliminate, what one scientist called, collateral damage. These are difficult philosophical questions—I appreciate you asking them. Keep them coming.
I include this for the table of mosquito borne diseases part what down the page: https://en.wikipedia.org/wiki/Mosquito-borne_disease
The journal Nature has addressed this very same question: http://www.nature.com/news/2010/100721/full/466432a.html
*From My First Summer in the Sierra
**From Round River: From the Journals of Aldo Leopold
Saturday, September 17, 2016
Note: This program first aired September 17, 2016.
Our bodies are over 60% percent water. We can only live a matter of days without water. Water covers 71% of the surface of this planet.
It should be no surprise that people attempting to live according to traditional, earth centered, non western value systems hold water to be sacred. Call them Indians, native peoples, first nation, aboriginal, tribal, many of these communities still hold to ideals that see water as the sacred blood of the earth, as the first medicine. And so it should be—all life depends on access to clean water.
Water is a polar molecule, making it a wonderful solvent, readily dissolving any substance that has an atomic electrical charge. Liquid water is fluid, and can easily transport any other fluid substance in it, even if that substance is non polar, having no electrical charge, and can’t dissolve in the water. Even if that substance is crude oil.
Crude oil is made up of a mixture of many different fractions of hydrocarbons, ranging from the heavy end with things like asphalt and paraffin, to the light end with things like the methane and propane, some of the constituents of natural gas. Crude oil contains other substances, related to the hydrocarbons we burn in our cars and furnaces, things you might have experimented with in organic chemistry class, like the aromatics benzene, toluene, and xylene. And even though the aromatics come from crude oil, something we typically think of as insoluble in water, these light fractions are soluble in water. They also have a low atomic weight, so they evaporate into the air quite readily as well. And worst of all, they are carcinogenic.
This is the kind of thing you think about when you learn that an oil transporting pipeline is about to be built through a river that is your source of drinking water. You think about the pipeline leaking, and the heavy fraction of the crude oil, being denser than freshwater, sinking to the bottom of the river, virtually impossible to clean up, and the lighter more soluble fractions traveling with the water to be taken up by municipal water systems down stream. You think about how common it is for pipelines to break, and in isolated rural areas how long it takes for people to notice.
These are the things I was thinking about as I stood in the rain attending a solidarity event for the Standing Rock Sioux tribe in North Dakota. The Standing Rock tribe has been protesting the fast track approval of the Dakota Access pipeline, its permitted path through off reservation sacred sites, and its crossing of the Missouri River, the drinking water source for the tribe and rural farmers and ranchers downstream. Native tribes from all over north America have been converging on the protest encampment at the Sioux reservation in a show of solidarity, and events like the one I attended, organized by Wabenaki leaders here in Maine, are popping up nationwide. You don’t have to be Native American to understand that water is sacred, though watching the Wabenaki prayer ceremonies made me realize that I lost the language of sacred connection many generations ago. Nor do you have to be a scientist to understand the linkage of water pollution and illness, and unfortunately I speak that language all too fluently.
Water is not unique in the universe, in fact the only reason we have it hear on Earth is that it came here the same way all the other matter on Earth did, as an aggregation of space dust and rocks. But water is what makes this planet unique, and what makes life possible on this third rock from the sun. The Standing Rock Sioux know it, and so do you.
Yep, pipelines do leak into rivers: https://usresponserestoration.wordpress.com/2014/06/20/as-oil-sands-production-rises-what-should-we-expect-at-diluted-bitumen-dilbit-spills/
People say these pipelines don’t leak. Really? http://www.npr.org/sections/thetwo-way/2016/07/25/487357502/canadian-oil-spill-threatens-drinking-water
Another one: http://news.nationalgeographic.com/news/energy/2015/01/150120-oil-spills-into-yellowstone-river/
A map of the pipelines: https://www.propublica.org/article/pipelines-explained-how-safe-are-americas-2.5-million-miles-of-pipelines
Saturday, September 3, 2016
Note: This program first aired on September 3, 2016.
Last week we talked about fungus, and they ways it makes a living in this world. The mushrooms we see in the forest are just the tip of the fungal iceberg, the vast majority of fungal biomass in the forest is subterranean. These are the bundles of fungal fiber called mycelium, and if the mushroom’s job is reproduction of the fungus, the mycelium’s job is to nourish it.
There are three ways that fungi can get food from the environment; they can parasitize another fungus*, they can decay organic matter, or it can form a relationship with a plant in an “I’ll scratch your back if you scratch mine” symbiosis called mutalism. We covered parasitism and saprotrophism earlier, leaving mutalism for today.
It turns out that many of those mushrooms you see erupting from the forest floor are from fungal biomass that is in direct relationship with the trees that make up that forest. The individual hyphal filaments that make up the mycelium, or all that fungal biomass beneath the surface of the soil, get up close and personal with the tiny root hairs, or rootlets from the tree and form what is called a mycorrhizal relationship, “myco” referring to fungus, and “rrhizal” referring to roots. Trees and their fungus typically form what is called an ectomycorrhizal relationship—meaning the fungus only just barely infiltrates the upper layers of the rootlet tissue, squeezing in between the cells of the root outer cortex, forming a sheath. The conjoining of the tree roots with the fungal mycelium effectively expands the tree’s root system by orders of magnitude, and even directly connects it to other trees of its species if the mycelium forms an ectomycorrhizal relationship with more than one individual.
Typically a fungal species has only one suitable tree species it can pair with, though often trees can have many different fungal partners. Many of the trees I see daily are obligated to form relationships with fungal partners; they cannot grow without the assistance of the fungus. Those groups include pines, oak, beech and spruce. Other tree species are facultative, and can grow without a fungal partner but grow better with one. Examples include maples, juniper, willows and elms.
I said this is an I’ll scratch your back if you scratch mine kind of situation, both partners benefit from this trans species contact. As I noted, the tree gets a major extension of its root system, gaining what one source called “hundreds of thousands of kilometers’ of individual hyphae, collecting water and inorganic nutrients from the soil. Essential nutrients like phosphorous and nitrogen are limited in the terrestrial environment, and the fungus is able to aggregate these and make them more available to the tree than they would be otherwise. The fungus also is able to collect water from the soil, though there can also be instances when the plant gives moisture to the fungus as well. And in some cases the fungus produces plant growth hormones, stimulating tree root growth. What we know for sure the fungus gets out of the relationship is carbon, in the form of sugar. 10 to 15 % of the carbon fixed by the tree gets channeled to the mycorrhizal partner. Both players are able to trade something they are good at getting from the environment for something they need, to the benefit of everyone.
This kind of relationship isn’t limited to trees and mushrooms. Many herbaceous plants and agricultural crops form mycorrhizal relationships as well, relationships characterized by even deeper infiltration of the fungus into the plant tissue. And in a totally different part of the world, coral reefs, we see the mutualistic symbiosis of coral polyps and photosynthetic plankton, swapping carbon in the form of sugar in return for inorganic nutrients. In a great example of convergent evolution, many realms of life species have evolved to swap resources in order to increase their competitive fitness. That is the cool thing about evolution, when something works, it keeps popping up independently on the tree of life.
So many of those mushrooms you see in the woods this fall, are part of a legacy of remarkable biological cooperation.
* or plants or even animals!
Saturday, August 27, 2016
Note: This program first aired on August 27, 2016.
Last week we looked at mushrooms, and talked about how they are the reproductive structures of certain kinds of fungus. Mushrooms are simply the above ground spore making structures of an otherwise underground organism, one made of miles of bundles of filaments called mycelium. If the mushroom’s job is to make spores, then what is the job of the mycelium, all the fungal biomass we don’t see? Just like in other realms of life, different life stages have different jobs for the organism, and the mycelial job is feeding. Fungus are heterotrophs like you and I, they rely on food sources outside of their bodies (unlike plants—which create their own carbohydrates). As heterotrophs we eat food, ingesting the complex material which is then broken down into smaller more accessible biological molecules and absorbed directly into our bodies in our guts. Fungus don’t have mouths or guts, but they still digest food using the same process. They excrete the digestive enzymes onto the material they are eating, and once that material is broken down into smaller molecules, it can be absorbed by the fungal filament. For example neither humans nor fungus can absorb cellulose, one of the primary molecules of wood, and much plant material. When humans eat cellulose, we call it insoluble fiber, and though it has health benefits, we don’t digest it and don’t get any nutrition from it. When the mycelium of certain fungi encounter cellulose, they are able to produce enzymes that break the cellulose down into the individual molecules of glucose it is made from. Fungi can then absorb the glucose, gaining nutrition from the cellulose. The ability to digest cellulose and lignin, the other primary constituent of wood, is one of fungi’s super powers.
There are lots of fungi out there, but we’ve been trying to limit our discussion to mushrooms—so do all mushrooms eat wood? No, in fact there are three different modes of nutrition for the mushrooms that we see out in the woods. The first, and least common, so we’ll get it out of the way, is parasitism. There are fungi that parasitize other fungi! Parasitism is a symbiosis that is typically thought to benefit one partner and have a negative impact on the other. The parasitic fungus benefits by stealing nutrition from the parasitized fungus. In our region the most common parasitic fungus you will see is lobster mushroom, which is a fungus that doesn’t make its own mushroom, but hijacks the mushroom of other species. I’ve talked about Lobster mushroom before on the show.
The second mode of nutrition for mushrooms is to be a decomposer or saprotroph. This is the default or ancestral mode of fungal nutrition, the ability to excrete digestive enzymes into the environment and break down complex organic molecules into simple (and thus absorbable) organic molecules is the hall mark of this kingdom of life. If it weren’t for fungi (and many bacteria as well), we would be overwhelmed with dead organic matter, and in fact life would stop because it would run out of raw materials. Fungi are the recyclers of the biological world, they process millions of tons of organic waste a year, turning dead material back into building blocks like carbon dioxide and individual mineral nutrients that can be used again by plants to make more food. The balance between the carbon taken out of the atmosphere by plants and the carbon put back into the atmosphere by animals, bacteria and fungi is what keeps climate relatively stable*, at least until plate tectonics changes atmospheric circulation** and weather patterns change, and throw that balance out of whack, driving extinction and more importantly evolution. Heady stuff for those little mushrooms along the trail.
I said there are three modes of nutrition for fungi, but we are out of time for today, so we will look at the third, and if you are a plant, most interesting mode, next week.
*Before the geologists get mad at me--Yes, the rock cycle plays a really important part in this as well--carbon going into and coming out of geological sinks like limestone...
**And influences the rock cycle by exposing or burying carboniferous rocks...
All the same ones as last week plus:
About external digestion: http://bugs.bio.usyd.edu.au/learning/resources/Mycology/Feeding/extracellDigestion.shtml
Still one of my favorite theories out there, even if it is now being challenged: www.scientificamerican.com/article/mushroom-evolution-breaks-down-lignin-slows-coal-formation/
Saturday, August 20, 2016
Note: This program first aired on August 20, 2016.
There’s fungus among us. Though it has been a dry summer, in the past few weeks, right after each heavy rain, on the trails I run I see mushrooms pushing their way up out of the forest floor. Russulas and Lactariuses, coral fungus and boletes, an occasional amanita and delicious chanterelles. And those are just the groups I can identify with relative ease.
Mushrooms are the reproductive structures of certain kinds of fungus, ascomycetes and basidiomycetes. There are many other kinds of fungus out there as well, but they don’t make mushrooms (think mold and yeast and a bunch of stuff that is essentially invisible to human eyes). As the reproductive structures of ascomyctes and basidiomycetes, they emerge when environmental conditions favor fungal growth. The timing of these appearances gives a clue as to what those favorable conditions are. It has been a dry summer, dry enough that all of the organic matter that makes up the upper layers of the forest floor is dry, and we’ve experienced a few small forest fires. Scary stuff in our dense, low fire frequency eastern forest. The mushrooms we see emerge after damp weather are the result of the action of billions of fungal filaments below ground in the soil. These filaments, called mycelium make up the bulk of fungal biomass, at least in terms of the mushrooms we see in the forest. The mushrooms are truly only the tip of the ice berg.
Mycelium are made up of even smaller individual filaments called hyphae, and grow through the soil in the forest feeding on organic matter. Like the fine hair like roots of plants, these microscopic fillaments don’t do well when the soil is very dry, their movement and metabolism are aided by the water that makes the soil damp. Hence, a nice flush of rain that wets the forest soil results in a boom of mycelial activity, and it is when compatible mycelium meet up underground that a mushroom results. Rapid increases in mycelium increases the chance of these meetings, hence mushrooms appearing overnight after wet weather. The mushroom’s only job is to create spores, which can result from sexual reproduction between those two compatible mycelia, and are a dispersal mechanism for fungus. Tiny and airborn, spores can travel great distances on air currents, and if they land in the right spot, can germinate and form a new hyphal strand. If that strand of hyphae finds what it needs it continues to grow and becomes multistranded mycelium. If it runs into another mycelium from the same species, and they are compatible mating types, they will merge and share their genetic information, and build a mushroom from this conjoined mycelium. In special cells in the mushroom (typically on the gills underneath the cap) meiosis will occur and the spores that are formed will contain a mix of genetic information unique from either parent.
If that is the job of the mushroom, what is the job of all that mycelium in the forest soil? We’ll answer that question next week.
Mostly books this time around:
David Arora, Mushrooms Demystified
George Barron, Mushrooms of Northeast North America
Lawrence Millman, Fascinating Fungi of New England
Elizabeth Noore-Landecker, Fundamentals of the Fungi, 4th ed.
James, Timothy (2007). "Analysis of mating type locus organization and synteny in mushroom fungi: Beyond model species". In J. Heitman; J. W. Kronstad; J. W. Taylor; L. A. Casselton. Sex in Fungi: Molecular Determination and Evolutionary Implications. Washington DC: ASM Press. pp. 317–331.
Saturday, July 30, 2016
Note: This program first aired on July 30, 2016.
This week’s show originated as a question from my nephew. He was wondering why hair turns gray. I have thought of that myself, as I sport a head full of white hairs, which started losing color far ahead of the curve early in my 20s. And the answer to the question is of course, complicated and partially unknown.
To start we have to look at where hair, and fur color comes from. Hair is made of several layers of a structural protein called keratin (the same thing your finger nails are made of). It grows from collection of cells, which some sources refer to as a mini-organ, called a follicle. The skin of most mammals is studded with hair follicles, it is a defining characteristic of the group. The color of hair is controlled by cells around the follicle called melanocytes, who’s job unsurprisingly is to generate a pigment called melanin. Melanin gives hair its color, by being injected into the filamentous protein we call hair, as it grows. The variety of hair colors we see in mammalian animals is determined by the mix and balance of different types of melanins, broadly speaking, eumelanins are black and brown, and phaeomelanins are lighter, reds and yellows.
Human hair has three develpmental stages: anagen or growth phase, which lasts for years, catagen or transitional phase, as the hair transitions from active growth to being shed, and telogen, a quiescent phase that ends with the hair fiber being shed. While we look mainly at what is going on with the hair itself, these phases represent dramatic differences in the functioning of the hair follicle. As the hair is growing in anagen, the melanocytes are pumping melanin into the hair fiber. When the follicle enters catagen, the first thing that happens is the melanocytes stop melanin production and undergo apoptosis, which is programmed cell death. Individual melanocytes then only get to produce melanin for a single strand of hair. Hair pigmentation shuts off in the transitional phase of hair growth, and if it doesn’t turn back on when the cycle starts over, the resulting hair that grows will be colorless, or white.
Now I said that not only does the melanocyte stop producing pigment, it actually dies, and in order for the next hair that grows to have pigment a new melanocyte has to form. And that is where the root of all this going gray as a normal part of aging happens. The new melanocytes arise from stem cells, melanocyte stem cells, which can mature into a pigment producing cell when needed. These stem cells continually divide and create more stem cells, so there is always a supply on hand when the hair follicle returns to the anagen active growth phase. The current thinking is that mammals go gray as they age because stem cells start to lose their integrity the older they are. The older you are the more damaged the cells in the melanocyte stem cell reservoir are, so the chances of a functional stem cell being able to mature into a pigment producing cell go down. The more times cells divide, the more chances there are for errors in transcription, the copying of genetic information. That is why age impacts cellular health, in general, the older a cell is, the more times it has divided. Cells only have so many times they can divide, before the telomere mechanisms inhibit further cell division and the cell effectively is put out to pasture. When we get very old, we don’t have any melanocyte stem cells left. Normal aging (which really means the changing of our cellular DNA, or shortening of our telomeres, that occurs during cell division) results in this decrease in stem cells, but cellular stress in the form of mutagens that damage DNA can as well, things like Xrays and UV light.
Many questions remain about this going gray business. The diversity of pattens of human graying is thought to be genetic but we don’t know why, and are there implications for other stem cells in the body, do all your stem cells function the same way? Why do dogs go gray around their muzzles but not other parts of their bodies? Why do some mammals not go gray at all? Many questions, fewer answers, but that is actually a good thing. If we had all the answers there would be nothing left to do. So please, keep your questions coming.
More than you ever wanted to know about hair: https://repositorium.sdum.uminho.pt/bitstream/1822/15299/1/2010%20Biology%20of%20Human%20Hair%20Know%20Your%20Hair.pdf