Blog Archives

Dirt is Good, More is Better

Four days after we arrived in India, Maya came down with what seemed like a cold. She had a little fever on the first day, but not after that. Two weeks later, she continues to have a unabated runny nose. During the night, her breathing is a little ragged sometimes, especially if the fan is on, but quite normal at other times. We suspect what she has is more an allergic reaction than a cold, though friends here have colds that seem to last a month. We’ve been careful about boiling filtered water before giving it to her and so far she has not suffered any stomach disorders. One of my fears about bringing her to India was her developing breathing problems or skin conditions as an allergic reaction to the more polluted and dusty air. One of our friends had to hospitalize their child after she developed severe allergic reactions. When I had to cancel a social engagement because she seemed to be bothered more than usual by her cold, they commented that this was common, that their grandchildren all went through some allergic reaction or caught cold when they came to India from the US. One of them was even being treated with Ayurveda as the western counterpart was considered to be non-conducive.

One common folk wisdom is that children growing up in US’s sterile climate are less prepared to deal with the plethora of allergens and microbes that populate India. Shanthala pointed out an article in today’s New York Times titled “Babies Know: A Little Dirt Is Good for You”. The article alludes to what is called the “hygiene hypothesis”, a hypothesis first formulated in 1989 by a British professor of epidemiology, a hypothesis with a comprehensive entry in the Wikipedia. According to this hypothesis, now considered to be well supported by data, a lack of exposure to infectious microbes and symbiotic microorganisms in early childhood leads to a compromised immune system, a system that can’t differentiate between harmless agents such as pollen and harmful ones such as mycobacteria and so reacts to pollen producing an allergic reaction.

People of the new world were wiped out by diseases carried by the old world invaders, diseases to which they had no immunity. White settlers to the US deliberately and systematically sold small pox infected blankets and clothes to the native Americans, thereby wiping out broad swaths without firing a single bullet. Jared Diamond explored and exposited the reasons why Spaniards invaded North and South America and not the other way in his Pulitzer Prize winning book “Guns, Germs and Steel” (Paul Shepard walked similar ground but with a more incisive and unwavering commentary, see his Paul Shepard Reader for example). One of the theories he espoused is that with greater domestication of animals in the old world, people there developed better immunity and to more diseases compared to the new world where domesticable animals were far fewer.

Senses in infants is equal to the adult counterparts between three to six months. As adults, sight is our most advanced and used sense. So why do infants put things in their mouth ? The NYT article also postulates that infants and toddlers explore the world by putting things in their mouth because it provides an evolutionary advantage, by training the immune system. From the article:

“What a child is doing when he puts things in his mouth is allowing his immune response to explore his environment,” Mary Ruebush, a microbiology and immunology instructor, wrote in her new book, “Why Dirt Is Good” (Kaplan). “Not only does this allow for ‘practice’ of immune responses, which will be necessary for protection, but it also plays a critical role in teaching the immature immune response what is best ignored.”

The article quotes another researcher, David Elliot, as saying intestinal worms may be the most significant player in training the immune system. Therapies based on injecting these worms into humans has shown to alleviate the symptoms of patients with autoimmune disorders such as multiple sclerosis. Another researcher, Dr. Joel Weinstock says:

“Children should be allowed to go barefoot in the dirt, play in the dirt, and not have to wash their hands when they come in to eat,” he said. He and Dr. Elliott pointed out that children who grow up on farms and are frequently exposed to worms and other organisms from farm animals are much less likely to develop allergies and autoimmune diseases.

This advice has practical consequences for people such as us, visiting homeland for a few weeks, trying to cram social engagements and valuable time with grandparents, close friends and relatives into a short span. A sick child with a runny nose and a runnier stomach is not likely to permit too much cramming. And I wonder if infrequent exposures help much. There is no dearth of pathogens here. Shanthala was down all of yesterday with a badly upset stomach. Today, she has a sore throat. Sigh. The dilemma of parenthood. Sometimes, I think our parents had it a lot easier.

Parental Control


Since Maya was born, people have been constantly opining which one of us she looks most like. Some see in her the spitting image of my family’s characteristics, some see Shanthala in her, some say that she looks like me but her eyes are unlike either of us, Shanthala herself says that Maya’s chin is unlike either of us. Comments pass from her features to her skin color. She’s much fairer than either of you, some have said while others have said that she has Shanthala’s skin tone. And then they’re amazed at her height (she’s in the 95th percentile for her age and sex) and wonder where that characteristic came from.

Shanthala and I joke (with a hint of seriousness) about the roots of Maya’s seeming impatience or her easy, smiling nature. My parents compare her to my sister in terms of how easy she seems to be to care for. Many say that girls are easier to raise than boys. Maya had a lot of eczema till recently. While she never seemed bothered by it, Shanthala and her parents worried that her skin maybe as sensitive as Shanthala’s was and that she may suffer from skin irritations.

All this is boringly normal, this ongoing back-and-forth between who a child looks more like and which characteristic comes from whom. But it appears that the battle rages inside in very fascinating ways.

It is well understood that a child inherits half the genes from the biological mother and half from the biological father (in a world of donor eggs, donor sperms, surrogate mothers and adopted children, the simple terms mother and father have become too narrow to capture the reality). Typically both copies of the genes are active in the child. But in a less than one percentage of them, one of the copies is turned off. In some cases, it is the mother’s copy that is turned off and in some cases, it is the father’s. Wait, you say, isn’t this what I learned in school about dominant and recessive alleles ? About how blue eyes are a dominant gene over brown eyes and so gets expressed ? Isn’t this what you’re talking about ? Sure, this is true only if both copies differ from each other, not if they’re similar. Also, the discussion revolved around whether a particular gene was dominant over the other.

Here is where a newly discovered technique differs. In some small percentage of cases, the same gene sequence will express a different behavior in the offspring depending on which parent’s copy is turned off. For example, if the copy comes from the mother it produces blue eyes and if it comes from the father, it produces brown eyes (the color of the eyes is used for illustration, it is not a real example of this technique). This seems absurd. The same gene sequence should produce the same behavior, independent of the source of the gene. This mechanism of inheritance where the behavior is determined by which copy of the parent the gene comes from is called gene imprinting (or genomic imprinting) i.e. which parent’s imprint is retained in the offspring’s copy. It is now considered a separate process of inheritance compared to the classical Mendelian genetic inheritance.

But wait, gene imprinting gets even more interesting. In an interview with the magazine Edge, the evolutionary geneticist explains:

This is a complicated process because the imprint can be erased and reset. For example, the maternal genes in my body when I pass them on to my children are going to be paternal genes having paternal behavior. If my daughter passes on paternal genes to her children, even though she got the gene as a paternal gene from me it would be a maternal gene to her own offspring. Molecular biologists are particularly interested in understanding the nature of these imprints, and how it is possible to modify DNA in some way that is heritable but can then be reset.

This would be merely fascinating if it didn’t have startling consequences on the offspring. There are children who always smile and laugh, but sadly also have symptoms that are similar to those with severe autism and they mostly never learn to read or write. Some other children almost not nurse as infants forcing them to be tube fed but in a few years time, they develop an insatiable appetite and develop schizophrenia. The first suffer from a genetic disorder called Angelman syndrome and the latter suffer from a genetic disorder called Prader-Willi Syndrome, the first is caused by mutations to the paternal gene imprinting and the latter is caused by mutations to maternal gene imprinting. Many scientists now speculate gene imprinting to be the cause of many problems that plague us humans from asthma and diabetes to cancer. The reason for this is that one of the copies from the parent is bad, the other copy is present to be used. But in case of gene imprinting, the good copy is turned off and only the bad copy retained, making the offspring more susceptible to disorders.

In 1999, David Haig offered an intriguing hypothesis that suggested that in the battle for imprinting the child, each parental genome approached the union with a view that was beneficial to their side. Evolutionarily, for a mother, it is important to spread her efforts amongst all her children, striking a balance between putting all her eggs into a single child and spreading herself too thin by having too many of them. For a father on the other hand, it was more useful to ensure that his child got the most attention (and resources) from the mother compared to other children (biologically, monogamy is a culturally induced trance, and one that is frequently broken). Thus, mother’s side of the gene pool was growth moderation while the father’s side was growth promotion.

Interestingly, gene imprinting is not known in animals other than mammals. Platypus, for example, the earliest mammals, do not have any genes that are imprinted.

In a recent article in the science magazine, Discover, the excellent science writer, Carl Zimmer, explains all this and takes it one step further. He quotes the work of two evolutionary biologists, Bernard Crespi and Christopher Badcock, who suggest that “our minds too are shaped by this battle between the parental genes”. They hypothesize that autism and schizophrenia are the two faces of this evolutionary conflict between the parental genes expressed in the brain. Carl writes:

One of the most striking contrasts between autism and schizophrenia is how they affect the ability to understand others. Autistic people have a difficult time figuring out what other people are feeling. Schizophrenic people, on the other hand, sometimes do too good a job. They may come to believe that a refrigerator is talking to them, for example, or that people are conspiring against them.

Crespi and Badcock propose that these symptoms result from the genetic conflict. Empathetic children can see how frazzled they’re making their mothers and how much attention their siblings need. Maternal genes should therefore boost our abilities to get inside other people’s heads. Paternal genes, on the other hand, may benefit by reducing these distractions from the business of getting more resources from mothers.

Life is such a wondrous miracle. I’ve often times felt puzzled about how people can accept a simple explanation such as god when there are such fascinating explorations and reasons which can explain how this miracle actually happens. Most of the time, all goes well and we end up with a healthy, normal child. Most of the time. On this Thanksgiving Day, I want to offer thanks and express gratitude for the turns of time that have placed Shanthala and I where we are, with who we are and how we are. And of course for the healthy gift of life that almost didn’t happen, Maya.

References:
- Imprinted And More Equal, American Scientist, 2007
- GeneImprint: The main technical website that discusses everything pertaining to gene imprinting
- Alleles & Inheritance: A webpage discussing the difference between normal and imprinting inheritance