Tomatos, color blindness, autism, Down syndrome & evolution

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eikonabridge
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11 Feb 2017, 9:21 pm

Tomatos, color blindness, autism, Down syndrome, and evolution

"A Genetic Fix to Put the Taste Back in Tomatoes"
https://www.nytimes.com/2017/01/27/science/better-tasting-tomatoes-genes.html

In their haste to develop tomatos that are disease-resistant, damage-resistant, and have more appealing look, scientists have forgotten one important thing: taste. Only after I read the title in the news did I all of a sudden realize, yeah, it's so true. Today's tomatos don't taste as good as they used to. That goes to show that genetic engineering is a tricky business. It's easy to lose sight of the big picture, when you focus only on some narrow aspects.

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https://en.wikipedia.org/wiki/Color_blindness#Epidemiology
Color blindness, in its deuteranomaly form, happens at about 5.0% for the male population, and 0.35% for the female population. Or roughly 1 out of 20 people. We often look at color-blindness as a defect, as an anomaly.

But Mother Nature does not make mistakes at that level. Color blindness is heraditary, meaning that it has survived the test of evolution. In other words, color blindness is there for a reason.

The gender imbalance of color-blind people actually is already providing us an important clue. Having a fraction of color-blind male population helps to the survival of a clan. This is still pretty much true today. It only takes a few minutes of googling and you can find out why. As it turns out, color-blind people are much better at discerning through camouflage. They are excellent spotter and snipers, and ever since World War II, all the major militaries in the world have come to rely more heavily on color-blind people for spotting and sniper jobs. Contrary to intuition, color-blind people actually see better in battle field.

If we take the recently published prevalence rate of 1 out of 68 children for autism, that's 1.5% of the population. Again, at this rate, autism is something intended by the Mother Nature. And again, the male dominance of autism points to the military advantage of having a fraction of population being autistic. Where do you think all the military technology comes from?

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This brings to the question: at what rate should we consider something as being intended by Mother Nature, and what what rate should we consider something as being anomaly?

One common mistake in analyzing effects of evolution is to look at it as the individual level. Ever since our ancestors started to live collectively, evolution was no longer about the survival of an individual, but about the survival of a clan. Different clans do compete for resources, and warfare was a way of life ever since our ancestors learned to throw stones. So the unit of competition is not an individual, but a clan.

So, when we talk about normalcy of some genetic conditions, we must specify the size of the clan we are looking at.

But what defines a clan? Since clans compete militarily, clans are separated by their highest military sovereignty structure. The population controlled by a sovereign, independent military structure, is a clan. In modern days, clans are more-or-less equivalent to countries. If there are iron-clad military alliances, clans can cross national borders. (Whether NATO countries form a clan or not, it's highly questionable. Case in example: war in Cyprus between Greece and Turkey, being both NATO members.)

There is something in statistics called the "square root law." Case in example: the birthday problem. This famous problem asks for the size of a classroom necessary for two people to have the same birthday, with probability greater than 50%. We know there are 365 days, so many people would guess it's about half of that, or around 180 students. But the correct answer is actually 23 students, which is closer to 19.1, the square root of 365. The square root law is also observed in "Brownian motion" or "Random Walk". The same law is seen in Poisson distribution, where the mean is equal to the variance (square of standard deviation). The square root law tells us that something is an outlier in a population of size N, if its incidence rate is below 1/Sqrt(N).

Applying that to color blindness, it means that for a clan of size 400, we can no longer view color blindness as an anomaly. I believe large settlements in upper paleolithic era (50,000 years ago) could already achieve that size.

As for autism, that's 68*68 = 4,624 people, or 5,000 people, roughly speaking. Human clans reached that size when we had agriculture. That is, autism became something intended by Mother Nature probably in the neolithic era, somewhere around 10,000 years ago. The appearance of autistic traits in human must have predated that a lot more. (I tend to link it to the Behavioral Modernity, or 50,000 years ago. At that moment, autism was not common to all clans, as the clans were much smaller in size.) Autism is not a mistake. It's in the plans of Mother Nature.

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As for Down syndrome, its incidence rate is about 1.7 per mille (0.17%) in the USA, or 1 out of 600 live births. That means that for a clan of size 600*600=360,000, or one third of a million, Down Syndrome cannot be viewed as anomaly, or mistake. The USA has a population of 330 million people, that's one thousand times larger.

But what could be the evolutionary intent of Down syndrome? That seems like a puzzle. What advantages do Down syndrome people contribute to the survival of a clan?

Notice that unlike the genetics of tomatos, color blindness and autism that we have discussed so far, Down syndrome people don't reproduce. At least they don't reproduce with ease, and trisomy at any rate disappears in the gametes due to meiosis. This leads to many people to consider Down Syndrome as a true anomaly: an unintended defect that just cannot be eliminated through the evolution process. See for instance https://www.quora.com/Why-is-it-that-conditions-like-Down-Syndrome-are-still-prominent-today.

But I beg to differ. Down Syndrome would be impossible to eliminate through evolution, if humans live and compete individually. However, as I have pointed out, humans live collectively, and the unit of competition is not an individual, but a clan. If Down Syndrome is truly just a burden to a clan, this clan would not be able to compete with another clan that does not produce Down Syndrom people. Yet Down Syndrome has survived evolution, until today, though countless battles between clans in our past history. That means it is intended by Mother Nature, that it serves a purpose...however modest that purpose may be.

Ever after human societies reached over 1/3 of a million size, Down Syndrome should not be viewed as an anomaly. In China's Qin dynasty, there were estimate of 20 million people (from Wikipedia), which originally came from 7 warring states. So, it's fair to say that in bronze age, humans already reached clans of 1/3 of a million people. Since 2,000~3,000 years ago, Down Syndrome was no longer an aberration of nature. All on the contrary, we should take it as something intended.

So what purpose does Down Syndrome serve? How can it possibly make a society stronger and more resilient in battles between clans?

Well, one simple answer is labor subsitution. But I think it goes beyond that. The effect of labor substitution is so miniscule (0.17%) that I don't think that can translate into military advantage. What I think is going on is that there was correlation between a compassionate society and its organizational efficiency. If whatever organization/institution (e.g.: religious clergy, philosophers in the past, and governments in the present) was compassionate enough and at the same time had influence over policy makers, that can explain why taking care of people with Down Syndrome becomes correlated with a stronger clan. I compare this to social welfare programs and affirmative actions in countries like the U.S.A. A compassionate society is one that is strong enough to afford these activities. Compassion needs planning and organization. And planning and organizational skills are what make a clan survive in battles.

I wear eye glasses. A lot of geeks wear eye glasses. It's not that wearing eye glasses is a big advantage to evolution. It's the other way around. Having near-sighted people is a sign of an evolved society.

So, at very least, Down Syndrome is there to help us remember that, we are humans. At very least it has that purpose. No different than why people follow religious rituals or routines. Or why people celebrate a day like Thanksgiving.

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It's tempting to think about eliminating Down Syndrome people altogether. Matter of fact, in some countries, it has been observed that the Down Syndrome prevalence rate has been dramatically reduced due to prenatal genetic screening.

But as in the case of tomatos, if we narrowly focus on some partial aspects, after a while, we may wake up to realize that, somehow, our tomatos just don't taste as good as they used to.

What I mean is, genetic engineering is a tricky business. It's very easy to make mistakes, and you will only realize about your mistakes years later. As the the movie "Jurassic Park" puts it best: "Life...finds a way." You may think you are clever, but Mother Nature has a way of gettting back at you.


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18 Feb 2017, 9:46 am

There are obviously some numerical errors in my previous message, but the ball-park numbers are still correct and the general timelines remain unchanged. I'll make those corrections elsewhere.

After I finished writing my previous message. I checked into the case of schizophrenia as well. The interesting thing was that the general framework carried through smoothly.

Worldwide, schizophrenia is diagnosed for about 1% of the population. Again, Mother Nature does not make mistakes at that level. So naturally many researchers have looked into the genetic advantage of having a sub-population with schizophrenic manifestations. Even Wikipedia has a page for it. Also, Joseph Polmeni and Jeffrey Rice has an excellent summary paper.

https://en.wikipedia.org/wiki/Evolution_of_schizophrenia
http://journals.sagepub.com/doi/pdf/10.1177/070674370304800107

To me, a satisfactory explanation must address the following characteristics of schizophrenia:

(*) Age: contrary to autism, the onset of schizophrenia happens only in adulthood, typically after a person has become able to have children. For men, the onset is typically around 18 years old. For women, it's typically around 25 years old.
(*) Gender: no significant prevalence rate difference across genders, certainly not at the level of color-blindness or autism. Some studies have found negligible gender difference, some other studies have found the male-to-female rate below 2. Typically a gender ratio is 1.4:1 is quoted nowadays.
(*) Square root law: at 1% prevalence level, it means schizophrenia became accepted by Mother Nature when human clans reached the size of 10,000 people. That is, urban life style (in the form of villages or even cities) was already in place, supported by agriculture.
(*) Stability: prevalence of schizophrenia is fairly uniform across cultural/ethnic groups.
(*) Delusion: schizophrenic people hearing voices and have delusion

I find the "group-splitting" explanation put forth by Stevens and Price (in their book "Evoluationary Psychology") to be the closest to an ideal answer. To make a long story short, they presume that tribal communities must eventually split to maintain optimum number. What Stevens and Price did not know was the square root law, so they placed schizophrenia much further back into the hunter-gatherer era.

Instead of reproducing here their explanation, let me merge everything I know or have found together here for a concise version.

When human clans settled into sedentary life style, where agriculture guaranteed stable supply of food, it was very easy for a clan to become complacent. In their neglect for defense, outsider "barbarians" may easily snatch away their lands and infrastructure. But, once these "barbarians" settled down became complacent themselves, some newer "barbarians" would in turn eliminate the previous "barbarians." Now, human evolution is all about the survival of a clan and its genetic pool. The endless cycle of newcomers to agricultural villages/cities would introduce all too much genetic variation and instability.

This is where schizophrenia came in to rescue. The schizophrenia people often heard voices. People around them tended to take that as a sign of the ability of the schizophrenic people to communicate with a different world. Furthermore, schizophrenia, through evolution, tended to happen after adulthood, when the carriers of the trait have already assumed authority and/or have become an authoritative figure. The gender-balance of schizophrenia further indicates that it is unrelated to battle field advantages: unlike color-blindness or autism, schizophrenic people were not responsible for fighting or helping to fight. Now, when it came to conflicts, humans had two choices: fight, or flight. If schizophrenic people were not on the side of fight, then they were probably on the side of flight. So, in all likeliness, what happened was that schizophrenic people tended to hear voice telling them to move away from their existing clan, to go to some sort of a "promised land." This type of phenomenon happens all the time. I have seen and met with people that have followed cult leaders to move their entire families to places far away on the planet. Even in the bible, Moses with his Exodus is a perfect example. I cannot claim ownership on this idea, as Christian Bale, who played Moses in the movie "Exodus: Gods and Kings” (2014) has made this observation (that Moses might be schizophrenic) and stirred quite a controversy.

(As is well-known, the history of the Exodus is in itself questionable https://en.wikipedia.org/wiki/The_Exodus#Historicity)

With the "exoduses" from schizophrenic, shaman-like leaders throughout human history, human clans have avoided complete and utter destruction from competing clans. To live another day, so to speak. With that, the genetic traits of human clans have become stabilized. That is, schizophrenia, through its exoduses, is a stabilizing factor in human's genetic pool. This helps to explain why the prevalence rate of schizophrenia is so stable across ethnic/cultural boundaries.

So I believe Stevens and Price got the ball-park idea right. Schizophrenia does have an important evolution role to play.

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I just find it amazing that we are starting to understand Mother Nature's messages to us. If we are patient enough, and if we keep our heads cool and our minds open, we can learn a lot from her.

As for autism: have you guys been patient enough to listen to Mother Nature's message?

I see so many autistic children grown up to be comatose adults, simply because their parents want their children to be "normal." They emphasize on verbal and social development, and at the end of the day achieve neither. Then these autistic adults have serious problems at getting jobs out there, because their parents never wanted to develop these children's technical skills. These parents never drew pictures for their children. They didn't see the point.

All these autistic children have their wet spots on their dew leaves. Yet parents keep pounding on the dry spots. The parents manage neither to grow alfalfa grass nor giant sequoia trees, inside the brains of their children.

It's a parent's choice. You make your choices, your children pay the price. As simple as that. No need to cry. No need to run around asking for help when your children cannot find jobs, or hold on their jobs. It's all your choice. Mother Nature has delivered to you the brightest minds in the human race. As they say say, you break it, you own it.


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09 Mar 2017, 12:11 am

Here I have talked about 4 most common atypical genetic conditions (AGCs), with their prevalence rates:

(a) Color blindness (gene carrier): one in 12.5
(b) Autism: one in 68
(c) Schizophrenia: one in 100
(d) Down syndrome: one in 600

which translate to threshold clan sizes of

(a) Color blindness: 156
(b) Autism: 4,624
(c) Schizophrenia: 10,000
(d) Down syndrome: 360,000

These are the 4 most common AGCs. There are some others, like sickle-cell disease (SCD). But in the case of sickle-cell disease, it's geographically correlated to presence of malaria (thus higher in black population). So that case is well-understood and should be treated separately.

Now, there are generally speaking 4 archeological eras. They are also known as the 3 archaeological ages or the Three-Age System. In the 4 eras, we have simply further split the stone age into its paleolithic and neolithic eras.

(a) Paleolithic era: stone tools
(b) Neolithic era: pottery, agriculture
(c) Bronze age: kingdoms
(d) Iron age: empires

The clan sizes of these 4 archeological eras roughly match up with the threshold clan sizes of the 4 most common atypical human genetic conditions. There is a one-to-one correspondence between the technological innovations and the atypical genetic conditions:

stone tools <---> color blindness
pottery <---> autism
bronze <---> schizophrenia
iron <---> Down syndrome

Is this purely a coincidence? Perhaps not. Along the human history timeline, each technological innnovation brought about a higher level of organization of society. With that increase in clan size, new atypical genetic conditions (ACGs) became incorporated as standard stocks in the human genetic pool.

So I searched a bit regarding the earliest case of Down syndrome. There were a few false claims. But nowadays, the accepted earliest case of Down syndrome is dated at 1,500 years ago in Medieval France.

http://www.livescience.com/46721-earliest-down-syndrome-skeleton-discovered.html

Furthermore, it was clear from the burial setting of the skeleton that this 6 year-old child was not stigmatized. In other words, there was compassion in place. The timing and the compassion aspect very much match with what I have described as the evolutionary role of Down syndrome. In short, I don't believe it will be easy to find Down syndrome skulls/skeletons older than, say, 4,000 years. (Iron Age started in Europe about 3,000 years ago.) As for autism, I hope one day we will find positive DNA proof that it existed already 10,000 years ago.

I've looked for other common atypical human genetic conditions. From what I have been able to find, the four conditions that I have described here, are also the top 4 conditions in terms of prevalence. And their prevalence rates (or threshold clan sizes) more or less line up linearly on a logarithmic scale.

Image

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There is a wide gap between the threshold clan sizes of color blindness (156) and autism (4,624). I have claimed before that autism is responsible for Behavioral Modernity, which happened about 50,000 years ago in the Upper Paleolithic era. I guess I have to revise it a bit, now. Standard autism is tied to the emergence of agriculture, not to Behavioral Modernity. Autism in all likeliness was responsible for the emergence of written language, and is what gave us written history, after all. But Behavioral Modernity must come from something slightly different. A better candidate is the Broad Autism Phenotype (BAP), or the engineering mind. BAP's prevalence, if we take the percentage of people working in science/engineering fields as a proxy, it's closer to 5%, or 1 in 20. That translates to a threshold clan size of 400, and sits between the cases of color blindness (156) and autism (4,624). BAP is precursor to standard autism, and BAP is a better candidate as an explanation for Behavioral Modernity.

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A scientist friend asked me: if these conditions such as color-blindness or autism are beneficial to the clan, how come we don't see their prevalence rate increase?

First of all, there is a confusion here that needs to be clarified. The unit of competition for purpose of evolution, is not an individual. It's not like colorblind people or autistic people are competing against neurotypical people and killing each other for the dominance of their respective gene pool. They all belong to the same clan. The unit of competition is a clan. In other words, my friend has fallen into the classical trap in the analysis of evolution: thinking in terms of individuals instead of clans. Within the same clan, the relationship between the various subgroups is actually closer to collaboration, than to competition.

Secondly, it's about the genetic composition of the whole clan, not about propagation of individual genetic traits. For instance, Down syndrome people don't really procreate, at least not easily. It makes no sense to talk about Down syndrome people eventually dominating over the typical group. It's instead about the probability, or relative prevalence, of genetic traits of subgroups within a clan. Similarly, aside from color blindness (which is almost strictly hereditary), conditions such as autism, schizophrenia and Down syndrome are not strictly hereditary. That means that these subgroups also contain children from neurotypical parents, due to natural mutations. The converse is also true: the offspring of these three groups can be neurotypical.

Because the nature between the subgroups is that of collaboration, the prevalence rate is much more stable than the case of competition. Here I have assumed stable prevalence rates of these genetic conditions after crossing over the threshold clan sizes, which should be a good first approximation. That does not mean that the prevalence rates will never change. They can, just not as dramatically. The observed prevalence rates reflect roughly the optimum mixture as dictated by evolution.


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15 Mar 2017, 10:47 pm

The "exodus" interpretation of schizophrenia is really no joke. The median prevalence rate of the migrant group is 1.84 times higher than the native-born group (it climbs up to 4.69 if mean is used instead of median). See this study (its Table 10 contains the numbers):

A Systematic Review of the Prevalence of Schizophrenia
Sukanta Saha, David Chant, Joy Welham, and John McGrath
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1140952/#!po=45.6938

Migrant Status and the Prevalence of Schizophrenia
As predicted, prevalence estimates for migrant groups tend to be higher than estimates for native-born populations. This finding is consistent with past systematic reviews of the incidence of schizophrenia [1,33]...
[1] McGrath J, Saha S, Welham J, El Saadi O, MacCauley C, et al. A systematic review of the incidence of schizophrenia: The distribution of rates and the influence of sex, urbanicity, migrant status and methodology. BMC Med. 2004;2:13.
[33] Cantor-Graae E, Selten JP. Schizophrenia and migration: A meta-analysis and review. Am J Psychiatry. 2005;162:12–24.


So, it's not just one study. There have been many studies on migrant status and higher prevalence of schizophrenia. You can simply google for "migration and schizophrenia" and you will find plenty of sources confirming this observation. In short, I am not hallucinating, nor are Stevens and Price. These guys nailed it.


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18 Mar 2017, 10:13 am

I read a bit more into schizophrenia and color blindness. All the information is readily available via googling.

In the paper

"Schizophrenia and Migration: A Meta-Analysis and Review", Elizabeth Cantor-Graae and Jean-Paul Selten, Am J Psychiatry 2005; 162:12–24

they analyzed and summarized the results of 50 studies throughout the world. The average risk of schizophrenia in the migrant group is 2.9 times higher than the non-migrant group. One study might be wrong. But 50 studies? That qualifies as "irrefutable evidence."

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As for color blindness, I found out that originally all mammals were tetrachromats:

https://en.wikipedia.org/wiki/Tetrachromacy

so, in a sense, compared to our ancestors, we are all color-blind, because we've already lost one type of cone. The majority of mammals actually evolved into dichromats, retaining only two types of cones. So, in a sense, human dichromats are more advanced in evolution, than the "normal-vision" trichromat people. It's also interesting to find out that many women retain a minute degree of tetrachromacy, that's why women can tell color better than men, it's really not a myth. Of course, men are the ones shouldering the responsibility of protection and defense (at least in the past), so it's no wonder they have to resort to lesser color vision (so they can detect camouflage and see better in the battlefield.) (My wife immediately took offense, she said I was implying women are more primitive than men, ha ha.)

It goes to show that we are often misled by our own prejudice. Dichromat color-blind people are in a sense more advanced in evolution, than the rest of the "normal" people. Nowadays only some birds, fish, amphibians, reptiles, insects and mammals retain tetrachromacy. But then, none of us really want to be a fish or a bird, right?


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