Unexpected Symbionts: What if Your Health could Benefit from Creatures you Normally Despise?

 

"Lice Capades" (2007). An absolutely wonderful episode of the "South Park" series. The world as seen from the viewpoint of lice. Fantastic. 

In Italy, there is a legend that says you may be cured of hepatitis b (jaundice) by eating lice. It is not just a vague legend, I personally know people who swear they were cured of jaundice by doing exactly that. Apparently, in the 1960s, there were still people who sold live lice packed in a small wafer (where they got the little beasties is anybody's guess). No trace of this story can be found on the Web nowadays, I can only relate it from what relatives and acquaintances tell me. But I have no reason to doubt that it was a common belief some 50 years ago, although it may have been limited to Tuscany, or perhaps only Florence. There are reports of people eating lice in other cultures and, of course, monkeys, apes, and other furry animals do that all the time. 

About this story, let me say that I am a big fan of evidence-based medicine and I am the first to doubt this story (and, also, I never had lice in my life). But, once you acquire the concept of "holobiont," you start reasoning that lice must have accompanied the human organism for millions of years. And, if they did, there has to have been some reciprocal adaptation and -- why not? -- mutual benefit. Of course, as a human being, you won't even remotely imagine that lice may be good for your health. But are you sure? 

At this point, you start searching the web and, surprise! (or maybe not), you immediately find an article titled "Unexpected Benefits from Lice" Look, this is serious stuff, evidence-based, not old folks' tales. And they say: 

Parasites such as lice have a role in the conditioning of a 'natural' immune system and reducing the likelihood of immune dysfunctions,

Of course, that's true for mice, but there is no reason to believe that it wouldn't work for human organisms, as well. Some people have said exactly that, "lice can be good for you." Maybe that's a bit optimistic but, surely, there is no reason to fall into hysterical reactions when dealing with lice in children. In some cases, lice may be bad for your health, but the little critters are not a major threat.

So, may lice be a symbiont rather than a parasite? As usual, the boundary between the two categories is fuzzy. Likely, no creature living inside the human holobiont is 100% parasitic. Most of those that lived with us for millions of years surely have at least some beneficial effects. And let me tell you just one thing: my mother-in-law holobiont had flatworms for most of her life. She turned 100 two months ago and she is in reasonably good health for her age. Would there be a correlation? At least, you can't rule that out!

You see how ideas interlock with each other and branch out generating new ones? Once you have the concept of holobiont, you have access to a whole new host of concepts. It is the beauty of the world we live in: truly Gaia takes many forms!

Forests and Climate Regulation: a Talk by Anastassia Makarieva

 

The Evolution of Human Empathy: From bronze age warriors to us, and beyond

 The human mind is the most complex entity we know in the whole universe. One of the fascinating things about it is how it has been evolving over time. What could have been the thoughts of a bronze age warrior? What thoughts did an ancient hunter-gatherer think? Why do we think the way we do, nowadays? As Sir Thomas Browne said, these are puzzling questions, but, like the song the Sirens sang, not beyond all conjecture. And here I am presenting a sweeping review in this area that starts with the work by Julian Jaynes on the mind of our remote ancestors, connects it with the most recent result of genetic studies, and even tries to peer into the future: how will the human mind evolve? Another question not beyond all conjecture. We may be moving toward much more complex and intricate forms of empathy than those we know nowadays.

 

The Mind

The mind is a tool, this much is clear. Of course, it is a special tool, able to do many things in many fields. But it is a tool and it has evolved to perform the tasks it performs. Do you remember Darwin's finches? They are birds with beaks of different shapes that were the source of inspiration for Darwin's idea of evolution: the beaks adapted to the different kind of food eaten. The human mind does the same. If it is like it is, nowadays, it is because it is functional to what it does. 

That applies also to the entity we call consciousness. We can define it as the capability of "modeling oneself" just like we can model other people's behavior in order to predict it. You probably heard the story of the "mirror neurons," brain structures specialized in understanding the behavior of other people. In a way, it means reading other people's mind. Your dog can do the same: dogs have mirror neurons, too. You can use the term "mirroring" or also "modeling." It doesn't matter the term. if you can model other people's behavior, you have a certain degree of empathy. And, very likely, high empathy and self-consciousness go together. They are two axons of the same neuron. 

Empathy is surely useful for us in many circumstances (also for dogs). You need to know if the person you have in front is there to help you or he wants to use his battle-axe on you. But that doesn't require much effort in terms of sophisticated mind-reading. Where modeling truly shines as an evolutionary tool is in the mating game. At least in our modern world, the competition for mates is fierce and ruthless and it involves many factors. Surely money and status count, but empathy does a lot as the capability of mirroring your perspective mate means behaving in a way that you know that he/she will appreciate. Ask any pick-up artist about that and he'll confirm that it is the tactic they use. Also, if you ever chatted with a professional sex worker, you may have noted how they have an uncanny ability of reading your mind and say exactly what they know will please you. The whole game is played by modeling another person's mind inside one's own.

So, it is no surprise that most of the modern literature and fiction deals with what we call "romance," men and women getting together. We seem to be deeply interested in the courtship rituals and about everything involved with it. It is one of the top skills of our mental arsenal. But have we always been like this?

 

The Evolution of the Mind

At which point in their evolutionary history did humans develop this exquisite ability of reading each other's minds -- including their own -- that we have today and we also call empathy? There are cartoons that describe cavemen using their stone axe to stun a woman before pulling her by the hair all the way into their cave. But that's of course a little unlikely to have ever been our ancestors' behavior, to say the least! But how did cavemen woo their women? Of course, the entity we call the "mind" leaves no fossil record, so what do we know about the empathy capabilities of our remote ancestors?

The first to pose this question was Julian Jaynes with his "The Origin of Consciousness and the breakdown of the bicameral mind" of 1976. It was a milestone in the field: Jaynes analyzed ancient written records and he concluded that the people living during the bronze age were not really "conscious" in the modern sense of the term. They had what Jaynes called a "bicameral mind." They would "hear voices" in their minds and act accordingly, but we have no evidence that they had the kind of self-recognition that we normally have today.  

The idea of the "bicameral mind" as described by Jaynes has been often criticized and, indeed, there is no proof that the inner mechanisms of ancient minds worked the way he proposed. But it doesn't really matter whether the "voices" are the result of the interaction of the two halves of the brain or they originate in some other sections of the brain. The point is that the behavior of the people described in such documents as the "Iliad" or some books of the Bible is completely different from that of modern people. The ancient just seem to lack empathy, they act like automata, without evident feelings of love, compassion, or concern for other people. In modern terms, we would define bronze age people as "autistic." Maybe it is a literary style, but Jaynes' idea that people truly behaved in this way makes a lot of sense. 

Just as an example: think of the Iliad. The story start with Paris, a Trojan prince, stealing Helen from her husband, Menelaus, king of Sparta. Then Paris is killed, and Helen marries another Trojan, Deiphobus. Finally, Menelaus kills Deiphobus and takes Helen back. Does the Iliad report of anyone caring about what Helen feels during these events? Was she unhappy, concerned, sorry, or what? No -- nobody gives a war cry about that. Another example: consider the case of  Tamar and Judah, as reported in the Genesis. In the story, the only problem for Tamar is how to give children to Judah's clan despite the death of her first and second husband, both sons of Judah. And nobody cares about what Tamar feels. Nor, there is any feeling or care for what Tamar's husbands feel, or pity for their fate.

Now, let expand the discussion a little. Jaynes had only written data, so his analysis couldn't go further back than the 3rd millennium AD, more or less. Before that age, there are no written records, at most pieces of statuary that might be interpreted in various ways, but that don't tell much to us about how people thought or behaved at that time. 

But we now have genetic data that, amazingly, give us a chance to go well  beyond the "literacy limit." I refer to the recent discovery of the "Y-chromosome bottleneck" in humans (Karmin et al., 2015). I described these findings in some detail in a previous article on "The Proud Holobionts." Here, let me summarize these results.

 

The figure above, (Karmin et al., 2015) reports the degree of diversification of the human Y-chromosome and of the mitochondrial DNA (mtDNA) over time. Both are elements of the genome that are passed only from male to male (Y-chromosome) and female to female (mtDNA). So, the curves are roughly proportional to the active male/female reproducing population. 

For most of the record available, some 50 thousand years, the population of reproducing males is smaller than that of the females, roughly a factor of three. It doesn't mean that there were less males than females in these populations. Then as now, the male/female ratio for the people alive at any given moment was approximately equal to one. But not every human being manages to leave descendants: many disappear from the genetic history of the species. For some reason that would be long to discuss, females are normally more successful than males at that and that's what we see in the curves of the study. 

But the study shows an impressive and unexpected feature. A "bottleneck" in male diversification that takes place between 7,000 to 5,000 years ago. In this period, there was only about one reproducing male out of 20 reproducing females. 

If we now compare with Jaynes' data, we see that he placed the bicameral mind as existing approximately during the 3rd-2nd millennium BCE, while the breakdown took place during the late 2nd millennium, roughly with the end of the bronze age. So, Jaynes' time window overlapped in part with the bottleneck. What he was seeing was the climbing side of it. He saw modern consciousness appearing (re-appearing?) with the male reproductive effectiveness gradually regaining the normal value of 1:3 with respect to the female effectiveness after a period of eclipse. But what does that mean?

 

Interpreting the data

We said that the conscious part of the human mind is mainly a tool used to find sexual partners. So, the mind must have adapted to the social and economic structures of society as they changed and evolved. Then, let's start from the beginning, the left side of the curve reported by Karmin et al. from ca 50.000 to 10.000 years ago. We see that during that period the average the reproductive success of human males was about the same as it is today, that is one male reproduced for about three females .

We know in those remote times, humankind was mainly practicing a hunting and gathering lifestyle. What were people's minds like at that time? Of course, we have no written records from those times. But we still have hunter gatherers around in our world, so that we can have some idea of how they think. Helga Ingeborg Vierich has lived with hunter-gatherers and she reports that they are kind and considerate, and rarely polygamous. In their societies, males have about the same chance as females to marry outside the group. Women have positive roles in society, separate but not inferior to the roles of males. On this point, I can also report my personal experience with the Roma (the Gypsies) who are perhaps the closest approximation to a hunter-gatherer society existing in Europe nowadays. In terms of empathy, I can tell you that their skills in reading the mind of a gajo (a non-Rom) are nothing less than exquisite. They need these skills in order to survive in a world where the gaji are a large majority. If empathy is a useful skill in a monogamous, relatively egalitarian society, then our hunter-gathering ancestors clearly had it, just like our modern hunter-gatherers do (and the Roma, too).

Then, there came the "bottleneck" that corresponds approximately to the end of the Neolithic and the start of metalworking, first copper then bronze. As it normally happens, technology changes society, sometimes very deeply. The bronze age saw people moving away from the traditional hunting-gathering lifestyle to that of farmers and pastoralists. It is normal (but with plenty of exceptions) that pastoralists tend to live in patrilinear "demes" (you can call them "clans"), a term used in biology to indicate groups in which individuals tend to mate mainly with other members of the deme. 

In human patrilinear demes, males tend to remain within the deme, while females are more mobile and move from a deme to another (it is called exogamy). In this kind of society, women marry a clan, not a person, just like Tamar did in the Biblical story. Even in the case of Helen of Troy, the story of her abduction may refer to a form of exogamy.

In this kind of patrilinear societies, we can imagine that there is little need for either males or females to develop the kind of empathy that we moderns need. Neither Paris nor Helen are reported in the Iliad to have been "in love" with each other in the modern sense of the term. There is nothing romantic in their relation. In general, if a woman marries a clan, then she doesn't care whether the male they mate with is nice, considerate, and gentle. What counts is how many sheep the clan has. Maybe this is a little schematic (a lot), but it seems to fit with what we know of the age described by Jaynes. 

These genetic data are in line with the interpretation that the age of the bottleneck corresponded to an increasing population of pastoralists living in patrilinear demes. This is explicitly discussed a 2018 paper by Zeng et al. They explain the bottleneck as due to evolutionary competition between demes, rather than individuals. A deme can "die" either because it is outcompeted by the others for scarce resources or because its members are killed in battle. Since the males in a deme are closely related to each other, there is a good chance that, when the deme dies, their Y-chromosome disappears from the human genetic history. Females, instead, owing to their exogamic habits are more likely to have their genetic signature survive, being spread over several memes. 

Can these social changes affect the genetic build-up of the human mind? We cannot say for sure, but don't forget how powerful evolution is in shaping the functioning of living creatures. The whole "bottleneck" episode lasted a few millennia and Cochrane and Harpending suggest in their "The 10,000 year explosion," that the human genome could change significantly in such a short time. For instance, they note that bronze age people had a significant brow ridge that was later mostly lost. Human females of the late bronze age didn't seem to like this feature very much in their males, just like modern human females don't. But no amount of cultural change can make you gain or lose a prominent brow ridge. It can only be genetic.

But it is not really fundamental to decide whether the big changes we see across the bottleneck are genetic or cultural: let's just say that they occurred, quite possible because of a mix of the two factors. Then, everything clicks together, more or less. The bottleneck was caused by the rise of a patrilinear society organized in small demes, then it disappeared when the demes were superseded by new social organizations: cities, states, and empires. Kings and emperors didn't want their subjects to fight tribal battles against each other. So, they broke the deme structure in various ways -- they never were able to eliminate them completely, but their importance was enormously reduced. With this, the old bronze age "bicameral" mind became obsolete. And evolution did its job: what is not needed or is harmful, disappears.

The rise of monogamy

Over the past 2-3 thousand years, we see a gradual tendency for rigid clans to disappear and a certain degree of egalitarian society developing. Monogamy becomes more and more common, at least for the average people (kings and emperors are not bound to their own laws). Monogamy was not only a social custom, but often enforced by laws and by religious commandments. The main reason for this development is that monogamy is a useful feature for a military empire (and all empires are). Armies need soldiers and cannot tolerate that soldiers fight with each other for females. Instead, if every male has one female, at least on the average, there is no need for internecine fighting among males to hoard as many women as they can. And so all the men of the empire could be turned into fighters to use against external enemies. Then, if the state takes care of enforcing monogamy, soldiers can embark in a long campaign in remote lands knowing that, at least theoretically, their wives will be waiting for them. The Romans, the paradigmatic military society in history, were strictly monogamous, at least with respect to the marriage of free Roman citizens. That was typical for most empires in history.

Monogamy may be one of the main reasons for the development of the emphatic mind we all have. If you live in a relatively egalitarian society, you have a large number of potential partners: choosing the best one becomes a difficult game that requires sophisticated empathic capabilities in order to convince a perspective mate that one is the right partner for him/her. It is a game where you have to deploy all sorts of strategic skills to optimize your chances. And it is a risky game: you may not be able to find the right partner or you may need to settle for a less-than-perfect partner. You may know the story of the man who had decided he would never marry until he could find the perfect woman. And after much searching, he found her. The problem was that she was looking for the perfect man! 

So, you see how difficult the game is, and you probably experienced that yourself. For sure, bronze age people wouldn't do too well at it. Imagine a bronze age warrior walking into a modern ballroom. He would stand in front of a girl and state, flatly, "I have plenty of sheep and you are to be my woman." Not exactly the best strategy to win the hearth of the prom queen.   

Then, of course, monogamy was never perfect and it was always accompanied by the activities that we call "philandering" for males. For females, we use terms such as strumpet, harlot, trollop, slut, or whatever. It doesn't matter, it is still the same game and it requires empathy. Married men are easily convinced by women who woo them, while married women have sophisticated ways to let men understand that they are happy to be wooed. But no modern woman would be interested in an affair with a bronze age man, no matter how many sheep he has. And no bronze age woman would be interested in an affair with a man who doesn't have any sheep. Empathy rules the game, that much is certain.

So, we can explain why the Western civilization has developed so many examples of what we call today "romantic fiction," from the saga of King Arthur, to modern telenovelas. It is probably a form of training for young minds that emphasizes such feelings as romantic love and typically involves a couple of lovers who face all kinds of obstacles but who, eventually, are reunited all thanks to being faithful lovers. This kind of fiction would be most likely totally incomprehensible by our ancestors. Imagine asking Tamar (the one of the Genesis) "but do you love your husband?" I can see her face looking like if you had asked her, "do you like French cuisine?" Some people have tried to cast Tamar in the role of a modern character with results, well, lets say not completely satisfactory (more details at this link).

 

The Final Question: How about the future of the mind?

After a few thousand years of prevalence, monogamy is clearly in decline. It never was perfect but, once, it was enforced by law and customs and, in some countries, you can still be stoned for being an adulteress. Even divorce used to be illegal in many Catholic countries up to recent times. Today, these rules have mostly disappeared, although 19 US states still define adultery as a crime and there exist two countries in the world where divorce remains illegal, the Philippines and the Vatican. 

This relaxation of the monogamy rule can be explained as the result of the decline of the role of males as fighters. Up to a certain time, not many decades ago, wars were won by the state that could line up the largest number of poor clods in uniform and have them march forward while being shelled by the enemy artillery. That's not so important anymore and the development of drones and war-robots has made the very concept of "soldier" obsolete.

The current situation is basically unheard of in the history of humankind. There has never been an age in which males had become useless as military machines. This point may not have been understood by the leaders, yet, but it seems clear that, if there is little or no need males as soldiers, there is little or no reason to enforce rigid codes and laws on sexual behavior for them and their wives. 

That's rapidly modifying the standard way of thinking about sexual codes of conduct, especially in the West, even though we can probably rule out that it is modifying the human genetic code (yet). In any case, the current way of thinking of Westerners is as far away as that of bronze age warriors as it could be. The focus on mind-reading is being turned to one's own mind and modern Westerners can be defined as extreme cases of narcissists, interested only in their own well being. It is what we call the "me-generation."

The problem with the me-generation is that it is generating a class of people who think they can do everything that pleases them. And the only thing that's worse than a narcissist is a rich narcissist. One of the things human males like to do is to hoard women in personal harems, as it was the use in some societies in the past. So, if a male is both a narcissist and he has enough power in the form of money, what can stop him from having multiple female partners in the form of occasional or stable concubines, or even in the form of a traditional harem? 

The current laws and customs prevent the men in the most visible positions from explicitly expressing their sexual habits, but if you look at the recent sex-scandal involving Jeffrey Epstein, you can notice that there are things going on with our leaders that don't appear in the media. Even without concubines or harems, already now, we might say that in the West the elites enjoy "time-dependent polygamy," in the sense that they periodically switch from an older wife to a younger one. That, of course, deprives young and poor males of suitable female partners, but it is the law of money. In time, we might see the development of a rigidly stratified society where the elites accumulate women just like they accumulate money. 

Then, if women are seen as accumulated capital, there follows that methods are needed to make sure that they are not stolen or lost. Eunuchs are a traditional way to keep women in their place -- and they also help solving the problem of excess males. But there are even more invasive methods to control women. Several societies in our time practice "female genital mutilation." The idea is that if a woman feels pain during sex, she will be less interested in cheating her husband (or harem master). In its extreme form, infibulation, the woman is treated like a coffer that can be locked and unlocked at will. Female genital mutilation is not so popular nowadays in the West but, who knows? Fashions change so rapidly!

Chances are that someone who owns a harem of infibulated women doesn't think of them in terms of romantic love, not any more than one of our billionaires have romantic feelings for their stock portfolio. Indeed, it is often reported that the rich are nasty, unfeeling, and uncaring for others. That's what you would expect. Why would the rich need to care for others? They don't need empathy-based skills. Then, the women in a harem would hardly be thinking of their master as someone to love in romantic terms. To say nothing about the eunuchs. 

So, if these habits were to become the rule in the future, then the human mind could change, culturally and perhaps even genetically. Evolution, cultural and genetic, does it work of eliminating those features that are not needed, think of the wings of the dodo bird. So, the sophisticated empathy capabilities that we had developed over the past 2-3 thousand years could disappear in a few centuries. Then, future scientists may discover a second bottleneck in the human Y-Chromosome diversity and wonder what caused it.

But there are other possibilities and it is not farfetched to think that the next step for society will be to discover that the modern obnoxious alpha-males and their manic sex-habits are not only useless, but expensive and dangerous. So why don't we just get rid of most of the males, leaving around just the tiny number needed for reproduction? After all, it is a choice that ants and bees made millions of years ago. Their social organization is called "eusociality" and human society already has some of its characteristics, so that it can be defined as "ultrasocial".

Is it possible to transform human society in such a radical way? Why not? We evolved, and we keep evolving. Already, the features of our society would be completely unrecognizable to someone living just a few centuries ago. And if ants and bees (and also the naked mole rat) evolved toward eusociality, there is no reason to think that we can't follow the same steps. Nate Hagens has been discussing how our society is already moving toward what he calls the "superorganism" -- a term used also for anthills and beehives.

Our society is already much more complex than the patrilinear demes of the Bronze Age and a future eusocial version would be even more complex. In the network of complex subsystems we live in, and in those in which we may live in the future, empathy deals with many more things than just finding a sex-mate. As Chuck Pezeshki notes, empathy is not a rigid concept, it is a process that evolves toward more complex and sophisticated forms (this figure is from Pezeshki's blog).

So, humans might be moving toward a version of empathy that will be highly sophisticated and structured as it can be in a universe that we are perceiving as more and more complex, a hierarchy of systems that we call "holobionts" and that culminates on this planet with the highest level holobiont of all, the entity we call sometimes "Gaia." Developing this kind of empathy could place humans truly in harmony with nature and with their own species. It would be a form of empathy that we can imagine as connected to what we call today the "religious experience." And maybe they'll perceive things that current humans cannot even imagine. It would be the "revelation through evolution," a concept that Michael Dowd has perceived. The Goddess Gaia revealing herself in her full glory,

And onward we go, evolving all the time. 

___________________________________________________________

h/t Michael Dowd, Chuck Pezeshki, Nate Hagens, Maria Mercedes Sanchez, and Helga Ingeborg Vierich,

What makes us holobionts: Touching each other as a gift of love.

Image from Nella Turkki's dance project, "I, Holobiont"

 

Touching each other is part of what makes us fellow holobionts, part of the greater holobiont that we call the Ecosphere or, sometimes "Gaia." In his book, "Thank God for Evolution," Michael Dowd doesn't mention the term "holobiont," but he gives us a poignant description of what it means touching each other, starting at page 231

The Furry Li'l Mammal in each of us craves touch and tenderness. Without touch, a baby dies, the human heart aches, the soul withers. Touch is not only a biological need; it is a profoundly elegant and essential form of communication. . . . For millions of years our mammalian ancestors were reassured by parents or comrades not through words but through touch. For 99.9 percent of our mammalian journey, there were no words. The need for touch begins for mammals at birth and continues until we die. . . . There is healing in touch, too. Because tender touch communicates love and care, it triggers metabolic and chemical changes in the body that assist healing. Touching also stimulates the production of endorphines -- natural body hormones that control pain and embrace our sense of well-being.

And, let me add, touching each other means exchanging our skin microbiota: it means exchanging the skills that the small creatures that populate our skin use to protect us from harmful creatures and chemicals. Touching each other is a reciprocal gift, it is a gift of love.

Onward, fellow holobionts!  

_______________________

Below, you see the front cover of Michael Dowd's beautiful book "Thank God for evolution" (2008). But if you want to know why exactly ancient Christians used a fish as a symbol of their faith, you have to read the book by myself and Ilaria Perissi "The Empty Sea" (in Italian), or wait for the English version to be published by Springer (should be soon)

 

Cancer and holobionts: is there a link?

 

Image from Vyshenska et al, 2017

I have been studying the work on cancer of the Italian researcher Stefano Fais. You can find a recent review of his work at this link. Basically, Fais sees tumor cells as the result of an unbalanced metabolism that leads these cells to develop on their own, even using anoxic processes to grow. He maintains that it is possible to slow down the development of these cells by making their metabolic growth processes more difficult, in particular using proton pumps to make their local environment more basic. 

I am not expert enough to be able to give an informed judgement on these ideas. But, as you may imagine, it led me to consider if there were a link between cancer and the concept of holobionts and, yes, there is a line of research in this area. Several researchers seem to be exploring the idea that cancer is the result of a "dysbiosis," that is an unbalance of the host's microbiota. For instance, in a 2014 work by Apidianakis, we can read:

".... the host genetic background and that of the microbiome, define the intestinal hologenome, which is influenced by age and the environment toward homeostasis or disease. Thus, the intestinal disease may ensue when the intestinal hologenome is imbalanced, that is, when a genetically predisposed or old host interacts with its dysbiotic microbiota in an inadequate or harmful dietary or lifestyle-shaped environment."

The problem, here, is that there is no link whatsoever with Fais's idea that tumors are related to acidity. Maybe there is a link, somewhere, but the story is horribly complicated and I leave it here. It is just a note that you may find interesting and perhaps worth studying in depth.

Genes, Demes, and Holobionts: What genetic studies tell us of the behavior of our ancestors

 

 Once you discover the concept of "holobiont," its ramifications keep surprising you. Here is a brief discussion of how the competition among the human meta-holobionts called demes affected and was affected by the human sexual behavior. 

How could it be that for a few thousand years only one human male out of about 20 females left descendants? What had happened that had removed so many males from the human gene pool? This is a story that would require an entire book to explain, but it is so fascinating that I thought I could write a quick survey, here. 

So, take a look at the image above. It is taken from a 2015 article by Karmin et al.  There is a lot of information in that figure, but let's concentrate on the left graph. It shows the degree of diversification of the human Y-chromosome over time. You know that the Y-chromosome is something that only males have in humans, so the curve is roughly proportional to the active male reproducing population. The more diversified it is, the more males there are around, reproducing. Be careful: this is not the total male population. It is the population of those males who reproduce. Males who never mate with a fertile female don't appear in the graph. Note also that females are tracked using their mitochondrial DNA that they inherit from their mothers.

As you can see, the population of reproducing males is always smaller than that of the females (right graph). That doesn't mean that the total number of males (reproducing + non-reproducing) is smaller than that of the females -- for all we know, these numbers have remained comparable over human history. It seems that human males always have more competition and more troubles to reproduce than females (if you are male, you understand what I mean). So a sizable number of males always disappear from the genetic history of the species, even though they did exist and maybe they were also sexually active. It is just that they left no descendants.

But the impressive feature of the male curve above is the dip that takes place between 7,000 to 5,000 years ago. Hard times for males: only about one reproducing males out of 20 reproducing females. Ouch! (or maybe not so much of an ouch for those who did reproduce, who had 20 females each). That's weird: how can that be?

As always, we should take into account that all scientific results are affected by uncertainty. But this work seems to be solid and so far it has not been challenged. So, the question is, what happened that made our female ancestors so selective in choosing just one male in 20 as the father of their children? 

You bet that a lot of hypothesis have been proposed to explain this catastrophe that hit human males in their reproductive success (but, again, it doesn't mean they didn't have female partners, just that they didn't mate with them when they were fertile). But what happened? An epidemics? The wrath of God? The spread of the fashion of monastic life? 

It is a long, long story and we are far from having understood this pattern. But I think that a 2018 paper by Zeng et al. gave the correct interpretation. It all has to do with demes.

One more paragraph, one more thing to learn: what the chuck is a "deme"? Well, it is a known concept in biology, although not so common for most of us. Basically, a deme is a relatively stable group of individuals who often mate within the group and rarely outside. In human terms, you may think of a deme as the equivalent of a "tribe" or a "clan." 

A characteristic of human demes is that they are often patrilinear: that is, they are dominated by a male hierarchy: there is a patriarch on top, his son, grandsons, and maybe great-grandsons. The females are more mobile. They practice exogamy, that is they tend to marry outside the deme (clan). The exchange of females among tribal groups is well known in anthropology. 

Now, you see here the holobiont emerging: a deme is a kind of a holobiont, we might call it a "meta-holobiont" in comparison to the normal human holobiont. But a holobiont is a holobiont is a holobiont. It is a group of organisms that collaborate in a symbiotic structure. Not just that, but demes practice "holobiont sex" by exchanging genetic material in the form of female organisms. See how many patterns tend to repeat? Wonderful!

Here goes the explanation by Zeng et al., that I think makes a lot of sense. As all holobionts, demes have a finite lifetime. They can die because of various natural reasons, starvation, disease, etc. Or they may be killed by aggressive neighborhood demes. And here is the trick. In a deme, there is very little differentiation in the Y-Chromosomes. The males are all related to each other and you know that brothers all have the same Y-Chromosome. So, the deme dies, the Y-chromosome dies. How sad! Those males who were part of that deme don't pass their Y-Chromosome to their descendants, so they disappear from the human genetic history. But so is the way things are. The great holobiont called Gaia loves life, but She knows that there cannot be life without death.

But the death of a deme doesn't mean the disappearance of the female genetic imprint. Not at all. Since females practice exogamy, likely, the females of a dead deme had sisters in other demes that survived. Besides, killing a deme in war doesn't mean that the winners exterminate all the females, not at all and for good reasons! Males consider the females as a war prize. Nowadays we tend to think that killing males and raping their females is not a very nice behavior, but it was very common in history (and still is). 

And here goes the final trick that explains the whole story. The drop in the reproducing male number takes place in a period of great expansion of the human population. It means that the demes were closer to each other and fighting for increasing scarce resources. It meant holobiont-style selection. Those demes that were less efficient in exploiting the available resources, and also less effective in war, disappeared, and with them a lot of Y-chromosome lineage. And that's what you see in the curve. Amazing!

But then, what happened that restored the chance of reproducing for human males? Well, there came the age of kingdoms, and then the age of empires, and kings and emperors don't like clans to fight against each other. They want all the males to fight for them, and that changed everything. Another long story that I'll tell in another post. But all these stories that deal with holobionts are fascinating! 

And here is how Conan the Barbarian interprets deme competition

 

Longevity secrets of a 100-year old holobiont

 

These four holobionts are related by vertical gene transmission through their female organisms. Among other things, their mitochondria have all the same DNA. The oldest of the three, Liliana, is 100 year old. There follow Grazia (68), Donata (31) and Aurora (1). Photo taken in July 2020

When my mother-in-law, Liliana, turned 100 last month, several people asked me what is the secret of her longevity. Not only it is not usual to reach that age, but to reach it in relatively good conditions. Liliana surely has problems: she walks very slowly and she tends to forget things. But her mind still works and, the day of her birthday, she categorically refused to be carried to the garden where we were having the celebration. She insisted to walk there by her own, even climbing the steps of the stairs leading there. It took her a lot of time, but she made it.

As you know, there is an entire field of research that studies centenarians. In particular, the gut microbiota of centenarians seem to age together with the main organism, but we don't know exactly how longevity is related to these modifications. So, here I'll just tell you something about Liliana and you may make your own deductions on what may be the ways to reach a very old age, still healthy.

First of all, Liliana was born in 1920 and she was young in a world that was very different from ours. The kind of diet, the way of living, the ways of seeing the world -- she might as well have been born on another planet. Imagine a world where there is no central heating, no TV, no telephone, where women still washed clothes by hand and hung them to dry out of the windows. A world without showers, only bathtubs where the water had to be heated by a wood fire. In the morning, there were standalone washbasins in the bedrooms where you could wash your face when you woke up. In winter, it was not uncommon to find that the water had frozen solid in the basin. 

It was a world where cars were rare and reserved for the rich: life was mainly within the area that could be reached on foot. And when a boy wanted to woo a girl, he would normally use a method already described by Boccaccio in his "Decameron" (14th century), that is making "passes" on foot under the windows of his beloved. Liliana confirmed to me that this was the way her future husband courted her, in the late 1930s. 

Coming of age in Italy during the 1930s meant a very different kind of life for women. Liliana never learned to drive a car and she can't even ride a bicycle. She completed he middle school curriculum ("scuola media" in Italian), but even for a middle-class girl, as she was, it would have been considered a little weird to continue her studies. She was supposed to become a housewife, and she did: she never had a salaried job during all of her life, although she worked occasionally as a seamstress. But her life was far from being easy. She went through the ordeal of WW2 when she survived the bombings and the shelling of Florence. Her boyfriend was drafted in the Italian army and he barely survived the war in North Africa, then he was wounded in the Italian civil war in 1944. The war may have been a watershed for many people alive today: those who survived it were especially resilient people. 

So, Liliana had an eventful life. One reason was her decision to marry a Sicilian man, something that was considered a scandal in his family. In the 1940s it was like, say, if today a middle-class American girl were to decide to marry a poor boy from Afghanistan. For Liliana, that implied several adventures but she was stubborn. She wanted that boy and she had it. Eventually she settled with her husband in the house that her grandfather had bought for the whole family in Florence and where she is still living today. She had three children, all born at home. Right now, she has four grand-children and two great-grand children.

As you can imagine from what I just told you, Liliana could be, and still is, a rather stubborn character. But I can also say that she is not very aggressive, she has always been flexible and friendly to everybody. A positive character in many ways, I have never seen her truly angry or mad at someone. Maybe this easygoing character was a help for her in getting old so gracefully. 

How about Liliana's diet? I can tell you that if you want to have some idea of what Liliana eats today, you can find it in books such as  "A Room with a View" (1908) by E.M. Forster and "Etruscan Places" (1932) by D.H. Lawrence. Incredible as it may sound, there was a time when the British would complain about Italian cuisine: the tasteless soups, the hard-to-chew boiled meat, the uninspiring kind of cheese made from sheep milk, and the mysterious castagnaccio that, according to Forster, tasted "partly of the paper in which it was wrapped, partly of hair oil, partly of the great unknown." And I have a feeling that Forster really wanted to write "the great unwashed." 

Today, Liliana still eats those thin soups that Lawrence hated and that nobody would want anymore in Florence. She eats cheese, eggs, and a little meat, not much but she is not vegetarian. She likes cooked vegetables, she seems to be a little wary of raw greens and she never cultivated anything edible in her garden -- she was a housewife, not a peasant. She is not fond of pizza, but occasionally she eats it. She never went to a Chinese restaurant in her life, she knows what a "hamburger" is (she can make them at home) but she has no idea of what a McDonald's restaurant might look like. She doesn't drink wine and she has never tasted beer in all her life. One characteristic that may be relevant to her longevity is how she tends to eat slowly. And she never-ever was overweight.

Then, how about Liliana's microbiota? We have no analysis of it, but I can tell you that she had flatworms in her gut for a long time. Some people say that flatworms are part of our biome and that they are good for health. On this point, I can't say much, but surely flatworms didn't harm Liliana. Then, I can also tell you that she never took a shower in her life and she never washed her hair with soap. On this, she seems to have been extremely modern, following the advice we are receiving today from James Hamblin in his recent book "Clean." Hamblin has not been taking showers for 5 years, not much in comparison to Liliana who has been shower-less for much longer. In both cases, anyway, the effect on preserving one's skin's microbiota seems to have been good. At 100, Liliana still has thick, white hair. 

What else? Liliana told me that once she took a bath in the sea. She didn't like it and she never wanted to repeat the experience. She hated the sunshine and she would never dream of sunbathing. She never took an airplane flight, her longest trip ever was from Florence to Sicily, for her honeymoon. It was just after the war and the trip took two days by an old, chugging steam train.

Among other things, Liliana always maintained a deep distrust in medical doctors and in medicines. For most of her life she succeeded in not seeing doctors and avoiding pills of any kind. Now, of course, she needs various pills everyday, but not so many. Ah... and of course she never smoke cigarettes nor indulged in any kind of what we call today "recreational drugs." She did like coffee, though, although she can't drink it anymore.

So, where is Liliana's secret of longevity? Hard to say. Maybe we could conclude that it consists in not taking too many showers, eating a little of everything, and slowly. Maybe eating thin soups helps, just as having survived a major world war. And a little coffee won't harm you. But maybe the main point is to stand by one's ideas but also take life as it comes. We are all holobionts, just passengers of the ecosystem of this planet that's engaged in an immense journey that has been ongoing for billions of years. And onward we go, fellow holobionts!