The Parsis and gene-culture coevolution

Parsi population in India (Chaubey et al. 2019, Fig. 1)

Increased longevity is associated with 217 of the 420 genetic variants that are specific to the Parsi mitochondrial genome. Others are associated with reduced sperm motility, Parkinson's, Alzheimer's, and cognitive ability. Did Parsi culture select for a slower life history?

Human evolution did not end in the Pleistocene. It continued and even accelerated as hunting and gathering gave way to farming, starting some 10,000 years ago. At that time the rate of change to our genome increased more than a hundredfold. Humans had by then spread over most of the Earth’s surface, from the Tropics to the Arctic. They were adapting not to new natural environments but to an ever-widening range of new cultural environments (Cochran and Harpending, 2009; Hawks et al., 2007; Rinaldi, 2017). Recent human evolution has thus followed an exponential curve, with more genetic changes taking place over the last 10,000 years than over the previous 100,000. Because those changes have primarily been adaptations to culture, they tend to affect mind and behavior.

Trade is one aspect of culture. It requires the ability to perform various cognitive tasks, like bargaining, calculating, writing, budgeting, planning, and so on. The more a community specializes in trade, the more natural selection will favor those who are better at such tasks.

I have previously discussed this evolutionary trajectory with respect to the Igbo of Nigeria. I will now discuss it with respect to the Parsis of India.

History

The Parsis’ ancestors left Persia for western India when Muslim armies invaded their homeland in the seventh century. After settling in India, they had no further contact with other Persians for centuries. There was initially some intermarriage between Parsi men and local Gujarati women, but with time the community became endogamous (Chaubey et al., 2017; Qamar et al., 2002; Quintana-Murci et al., 2004).

In 1638, the traveler John Albert de Mandelslo described them as engaging in “all trades”:

Their habitations are for the most part along the Sea-coast, and they live peaceably, sustaining themselves by the advantage they make out of the Tobacco they plant, and the Terry they get out of the Palms of those parts, and whereof they make Arak, in regard they are permitted to drink Wine. They intermeddle also with Merchandise, and the exchange of Money, and keep Shop, and are of all Trades […]

They have a very great respect for their Doctors and Teachers, and allow them a very plentiful subsistence, with their Wives and Children, though some among them intermeddle also with Merchandise, which they are permitted to do according to their Law, but these are not so highly esteemed, as those others who spend all their time in teaching Children to read and write, and explicating their Law to the people. […]

They are the most self-ended and covetous sort of people in the World, using all possible industry to over-reach and circumvent those they trade withal, though otherwise they have an aversion for theft. They are of a better Nature than the Mahometans, at least if it may be said there is any good Nature consistent with a self-seeking mind, when it is once possessed with the basest and most infamous of all Vices, Avarice. (Olearius, 1642. pp. 59-61)

Meanwhile, the Parsis were coming to the notice of English merchants in Bombay. The latter viewed them more favorably, seeing them as kindred spirits: "Active, robust, prudent, and persevering, they now form a very valuable part of the company's subjects on the western shores of Hindostan where they are not only protected, but highly esteemed and encouraged. They never interfere with the government or police of any country where they settle, but gradually and silently acquire money […]” (Forbes 1813, p. 411). They thus grew in number around the Bombay headquarters of the British East India Company. While in 1700, "fewer than a handful of individuals appear as merchants in any records; by mid-century, Parsis engaged in commerce constituted one of the important commercial groups in Bombay" (White, 1991, p. 312).

By the nineteenth century, the Parsis had become “the foremost people in India in matters educational, industrial, and social. They came in the vanguard of progress, amassed vast fortunes, and munificently gave away large sums in charity” (Dhalla, 1938, p. 442). Today, they are leaders not only in business but also in science, academia, and entertainment (Wikipedia, 2022).

Gene-culture coevolution?

Greg Cochran and Henry Harpending were the first to suggest that the Parsis’ specialization in trade favored some individuals over others within their community. Successful Parsis had an affinity for certain cognitive tasks, even if that affinity increased their risk of getting certain diseases, particularly neurological ones:

[…] the Parsi are an endogamous group with high levels of economic achievement, a history of long-distance trading, business and management, and who suffer high prevalences of Parkinson disease, breast cancer and tremor disorders, diseases not present in their neighbours. (Cochran et al., 2006)

Indeed, the Parsis are much more at risk of Parkinson’s disease than are other Indians or even people in developed countries. Strokes are at least twice as common among them, and essential tremors are exceptionally frequent (Gourie-Devi, 2014). That disease profile has a genetic basis. According to a study of autosomal, Y chromosome, and mitochondrial DNA, the Parsi genome has variants associated with neurological disorders, such as early epilepsy (Lopez et al., 2017). A complete survey of the Parsi mitochondrial genome has found variants associated with reduced sperm motility, Parkinson's disease, Alzheimer's disease, breast cancer, and cognitive ability. Interestingly, increased longevity is associated with 217 of the 420 variants that are specific to the Parsi community (Morawala-Patell, 2021).

The Parsi way of life seems to have selected for a slower life history. In other words, they space out their births, invest more in each child, and raise their children over a longer period. As for the variants linked to Parkinson’s and Alzheimer’s, they may be due to rapid selection for cognitive ability in a small population. Natural selection has to make do with the genetic variants available, which are fewer in a small population than in a large one. Therefore, the best variant will less likely be one that increases cognitive ability without causing adverse side-effects. Eventually, as new variants appear through mutation, the “make-do” variant will be replaced with a better one.

Rapid cognitive evolution has produced similar outcomes in other trading peoples. Ashkenazi Jews have higher incidences of nine neurological disorders of genetic origin: Tay-Sachs (two unrelated alleles), Gaucher's (five unrelated alleles), Niemann-Pick, and Mucolipidosis Type IV. Those disorders increase the capacity of neural tissue to store sphingolipids, which help neurons grow. In short, nine mutations in the same metabolic pathway have independently become much more prevalent within the same small population and the same narrow time frame (Cochran et al., 2006; Diamond, 1994).

That isn't chance. That is strong natural selection, most likely through heterozygote advantage. In other words, there are adverse effects only if the same allele is inherited from both parents. If only one parent has it, as more often happens, the child will be not only healthy but also better at processing information in the brain.

Conclusion

The Parsi lifestyle seems to have favored those individuals who had a slower life history, higher cognitive ability, greater foresight, and a longer learning period. Over generations of selection, such qualities would have become more and more prevalent among the Parsis, eventually defining them as a community.

Those qualities ensured the community’s survival through thick and thin.  Today, however, the Parsis are faced with a demographic crisis that seems to defy solution. From 114,000 in 1941, they have fallen to less than half that number. More than 30% of them do not marry, and an equal proportion are over 60 years old. The average Parsi woman gives birth to less than one child during her lifetime (Dore, 2017; Patel, 2011; Singh and Deb, 2020).

In a post-religious world, that fate seems to befall any community that likes to plan for the future. Such people understand the long-term costs of marriage and children, so they wait until they are financially ready. In time, that life choice becomes permanent. If the same life choice is made by enough people, it will become the new normal, and the pressure of conformity will deter even more people from getting married and having children.

Religion used to prevent that sort of dysfunctional conformity. Today, we’re largely free of religion, and yet we don’t have more freedom. There is simply a new normal that we follow just as unthinkingly. The key difference is that the new normal, unlike the old one, hasn’t been tried and tested over generations. It’s “experimental,” though not in a scientific sense. Few scientists would bother with an experiment whose outcome is so obvious.

That outcome, and its apparent inevitability, has led to a dark mood within the Parsi community, as described by a novel set in present-day Bombay:

“Demographics show we’ll be extinct in fifty years. Maybe it’s the best thing. What’s the use of having spineless weaklings walking around, Parsi in name only.”

[…] “Extinct, like dinosaurs. They’ll have to study our bones, that’s all.”

[..] “If, if, if,” said Dr. Fitter. “If we are meant to die out, nothing will save us.” “Yes,” said Inspector Masalavala. “But it will be a loss to the whole world. When a culture vanishes, humanity is the loser.” (Mistry, 2002, pp. 46, 385, 388)

References

Chaubey, G., Q. Ayub, N. Rai, S. Prakash, V. Mushrif-Tripathy, M. Mezzavilla, A.K. Pathak, R. Tamang, S. Firasat, M. Reidla, et al. (2017). “Like sugar in milk”: reconstructing the genetic history of the Parsi population. Genome Biology 18: 110. https://doi.org/10.1186/s13059-017-1244-9

Cochran, G., J. Hardy, and H. Harpending. (2006). Natural history of Ashkenazi intelligence. Journal of Biosocial Science 38: 659-693. https://pdfs.semanticscholar.org/4440/4954e85b0134c24163ae445e7c591097a2c9.pdf   

Cochran, G. and H. Harpending. (2009). The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books: New York.

Dhalla, M.N. (1938). History of Zoroastrianism. New York: Oxford University Press (electronic edition 2003). http://www.avesta.org/dhalla/dhalla_history.pdf

Diamond, J.M. (1994). Jewish Lysosomes. Nature 368: 291-292. https://www.nature.com/articles/368291a0   

Dore, B. (2017). Glimmer of hope at last for India's vanishing Parsis. BBC News. https://www.bbc.com/news/world-asia-india-40628310#:~:text=More%20than%2030%25%20of%20Parsis,which%20a%20population%20remains%20steady  

Forbes, J. (1813). Oriental Memoirs Selected and Abridged from a Series of Familiar Letters Written During Seventeen Years Residence in India, Including Observations on Parts of Africa and South America, and a Narrative of Occurrences in Four India Voyages, Volume III, London: White, Cochrane, and Co.

Gourie-Devi M. (2014). Epidemiology of neurological disorders in India: review of background, prevalence and incidence of epilepsy, stroke, Parkinson's disease and tremors. Neurology India 62(6): 588-598. https://doi.org/10.4103/0028-3886.149365    

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) 104: 20753-20758. https://doi.org/10.1073/pnas.0707650104   

López, S., M.G. Thomas, L. van Dorp, N. Ansari-Pour, S. Stewart, A.L. Jones, E. Jelinek, L. Chikhi, T. Parfitt, N. Bradman, M.E. Weale, and G. Hellenthal. (2017). The genetic legacy of Zoroastrianism in Iran and India: insights into population structure, gene flow, and selection. American Journal of Human Genetics 101(3): 353-368. https://doi.org/10.1016/j.ajhg.2017.07.013   

Mistry, R. (2002). Family Matters. Toronto: McClelland & Stewart.

Morawala-Patell, V., Pasha, N., Krishnasamy, K., Mittal, B., Gopalakrishnan, C., Mugasimangalam, R., Sharma, N., Khanna-Gupta, A., Bhote-Patell, P., Rao, S., Jain, R., and The Avestagenome Project. (2021). The first complete Zoroastrian-Parsi mitochondrial reference genome and genetic signatures of an endogamous non-smoking population. Meta Gene 28. https://doi.org/10.1016/j.mgene.2021.100882  

Olearius, A. (1642). The Voyages & Travells of the Ambassadors Sent by Frederick, Duke of Holstein, to the Great Duke of Muscovy and the King of Persia: Begun in the Year M.DC.XXXIII. and Finish'd in M.DC.XXXIX. Containing a Compleat History of Muscovy, Tartary, Persia, and Other Adjacent Countries. With Several Publick Transactions Reaching Near the Present Times; in VII. Books. Whereto are Added the Travels of John Albert de Mandelslo (a Gentleman Belonging to the Embassy) from Persia Into the East-Indies. London: Dring and Starkey.

Patel, D. (2011). Understanding Parsi population decline in India: A historical perspective. Jawaharlal Nehru Centre, Mumbai. http://zoroastriansnet.files.wordpress.com/2011/05/2011-05-understanding-parsi-population-decline-in-india-nehru-centre.pdf  

Qamar, R., Q. Ayub, A. Mohyuddin, A. Helgason, K. Mazhar, A. Mansoor, T. Zerjal, C. Tyler-Smith, and S. Qasim-Mehdi. (2002). Y-chromosomal DNA variation in Pakistan. American Journal of Human Genetics 70: 1107–1124. https://doi.org/10.1086/339929    

Quintana-Murci, L., R. Chaix, R. Wells, B. Spencer, M. Doron, H. Sayar, R. Scozzari, C. Rengo, N. Al-Zahery, et al. (2004). Where West Meets East: The Complex mtDNA Landscape of the Southwest and Central Asian Corridor. American Journal of Human Genetics 74: 827–845. https://doi.org/10.1086/383236  

Rinaldi, A. (2017). We're on a road to nowhere. Culture and adaptation to the environment are driving human evolution, but the destination of this journey is unpredictable. EMBO reports 18: 2094-2100. https://doi.org/10.15252/embr.201745399   

Singh, S., and R. Deb. (2020). Socio-demographic changes among the Parsis in Delhi, India. International Journal of Social Sciences 9(4): 253-262. https://doi.org/10.30954/2249-6637.04.2020.7  

White, D. (1991). From Crisis to Community Definition: The Dynamics of Eighteenth-Century Parsi Philanthropy. Modern Asian Studies 25: 303–320. https://doi.org/10.1017/S0026749X00010696

Wikipedia. (2022). List of Parsis. https://en.wikipedia.org/wiki/List_of_Parsis