Category Archives: Evolution

Nepal in 1950s

Nepal is a small but ethno-linguistically rich Himalayan country that consists of eight of the world’s tallest mountains. Despite being small, Nepal is home to over one hundred languages. Where did these people originate? What are their histories? Unfortunately, due to scanty archeological and historical data, we do not know much about the Nepali linguistic communities.

Understanding population distribution i.e., where people live may tell us important things about origins and histories of a particular population. Basically, dense localization of a population in a particular area may suggest the population’s historical territory. Similarly, population spread may indicate migratory patterns of certain populations. If multiple populations harbor the same area, it is likely that gene flow between such populations may have occurred in the past.

Thus, to learn about the histories of different Nepali language communities, I looked at the census data from 1952-54, which is the first reliable census of Nepal. I obtained the data, formatted it, and cleaned it up a little bit.For this census, Nepal was divided into 9 census regions and 67 census districts (Fig.1). Although data for district level is available, I will focus on the regional data for this article.


Figure 1: Nine census regions in first Nepali census (1952-54 A.D.)

According to the census data, there were 8,473,478 people native to the 28,770 villages and cities in Nepal. Only five cities had more than 5000 inhabitants: Kathmandu (107K), Lalitpur (42K), Bhaktapur (32K), Nepalganj (11K), and Birganj (10K). Interestingly, Thimi, a town between Lalitpur, Kathmandu, and Bhaktapur also had 8.7K people. Migration rate, defined as people not present in their ancestral homes for six months or more, was negligible: 2.6% for the entire country and between 0.06-4.3% for the nine census regions. This makes sense because Nepal was very remote until recently. The first highway was constructed in 1960s before which traveling was probably very difficult, therefore rare. Closed to the western world until 1950, first available reports have also described Nepal as remote and rural and difficult to travel.

The negligible migration rates indicate that most Nepalis lived in their ancestral villages. Therefore, this census data may be useful in understanding the historical population structures within Nepal. Hence, I first looked at population density in each census region (Fig, 2).


Figure 2: Population density in the nine census regions in 1952-54

In the first glance, most populous region in Nepal was Western Hills and the least populous was Western Inner Terai. However, after accounting for geographical area, Kathmandu valley, which consists of three towns: Kathmandu, Bhaktapur, and Lalitpur, was remarkably the most populous region within Nepal consisting of 5% of the entire population. Around 45% Nepalis lived east of Kathmandu valley, Western Hills comprised of 40% of the population, and 61% of the Nepali populations lived in the Hills (Eastern and Western Hills combined). The least populated region in the country was Far-Western Terai, likely because it was covered with dense malaria infested jungles.



Figure 3: Population size of different ethnolinguistic communities within Nepal in 1950s

From the data, major language groups appear to be Nepali, Maithili, Tamang (Lama), Newari, Tharu, Magar, Rai, and Limbu. Although currently over 100 languages are recognized in Nepal, in the 1950 Census reported around 36 language groups (Fig.3), probably in an effort to not contradict Prithvi Narayan Shah’s Divyopadesh  in which he has proclaimed that Nepal is a common ground of 4 varnas and 36 jaats. Many of the smaller language groups in Terai have been lumped into “Pradesh dialects.” Also, several of the High Himalayan languages recognized today are missing. Because the census was conducted by traditional revenue collectors, known as  jimmewals and patwaris, perhaps the Rana government thought that the burden of visiting the remote High Himalaya was not worth the negligible revenues it would extract from its inhabitants. Therefore, it is reasonable to assume that these populations were not included in the first Nepali census of 1952-54.

My ultimate goal was to find clues about population histories of different ethnolinguistic groups within Nepal. Therefore, I used the “mother tongue” data to first see if I can learn anything about where different language communities lived in 1950s.



Figure 4: Ethnolinguistic diversity within Nepal in 1950

Figure 4 shows what proportion of population in each census region is contributed by which language community. For example, about 55% of population in Kathmandu were Newar, 40% were Nepali speakers, and the remaining 5% were Tamang. Although considered natives of Kathmandy valley, appreciable proportions of Newars were present outside of Kathmandu valley in Central Terai (5%) and Eastern Hills (4%). Newars were absent in all Terai regions.

The census clearly shows that Terai was populated by various non-Nepali speakers. Even in 1950s, it is clear that Nepali speakers were widespread in Nepali Hills and Inner Terai, but were also virtually absent (<5%) from all of the Terai (Fig.4). Given the low migration rates, it is likely that the populations that lived in certain parts of Terai in 1950 were native to that region. For example, the majority of populations in West-Inner Terai (57%) and Far-Western Terai (60%) were Tharu, a tribe that is indigenous to dense, malaria-infested, impenetrable jungles, also known as chaar-kose jaadi that decorated Terai until very recently. Indeed,  Danagaura Tharu (Banke, Bardiya, Dang, Surkhet), Kathariya Tharu (Kailali), and Rana Tharu (Kailali and Kanchanpur) are indigenous to FW Terai. Tharu presence is also strong in  Mid-Western Terai (20%) and Central Inner Terai (12%). Indeed, Chitawania Tharu are known to be indigenous to Chitwan, Bara, Persa in Center Inner Terai. The presence of Tharu is appreciable as well in East Inner Terai (6% of the population in Sindhuli and Udayapur), perhaps due to large populations of Kochila Tharu in this region. They are virtually absent in Kathmandu valley and in the Hills but interestingly, also in the Eastern Terai, which was mostly populated by Maithili speakers, perhaps because this region was once the capital of an ancient Maithili kingdom of Videha.

Tamang and Magar communities were widespread in Eastern as well as Central Nepal. Surprisingly, 33% of Nepalis in Central Inner Terai (Chitawan, Chisapani Garhi, and Nawalpur) were Tamang, although Tamangs were also present in Eastern hills and perhaps even in the high-altitude regions in the East. After Nepali and Tamang speakers, Rai (13%) and Limbu (8%) were the most populous groups in the Eastern Hills whereas  Magar were the third most populous in East-Inner Terai (12%).

Although this data indicates that Eastern Nepal was more diverse than Western Nepal, it is biased against the smaller language communities. For example, almost all of the 14,261 Chepang lived in the Central Inner Terai but they only comprised 6% of the population. Many other language communities have much smaller population sizes (Fig.3). Hence, to know the whereabouts of smaller language communities, I asked what proportions of speakers lived in each census region. In other words, I asked how each language group was distributed across different census regions (Fig.5).


Fig 5: Distribution of language families within Nepal in 1950

This figure clearly shows that many smaller language communities are localized to a particular region, especially in the Hills and Terai of the East. About 60% of Nepali speakers were present in Western Hills, indicating that Nepali speakers were originally residents of Western Hills and later spread rapidly to comprise the majority of populations in many other census regions (Fig 3). Although this is consistent with previous reports of rapid Khas migrations within Nepal, it is important to realize that this migration must have happened steadily over several generations because migration rate throughout the country was very low.

Eastern Hills appear to be very diverse along with Eastern Terai.  Many smaller language communities such as Jirel, Thami, and Sunuwar appear to be residents of Eastern Hills. Although Maithili is the dominant population in Eastern Inner Terai, Jhangar, Dhimal, Bhojpuri, Rajbanshi, and Satar also appear to be restricted to this region. It would be interesting to see when different populations arrived in this region of Nepal and whether any gene flow among these populations have occurred.

Also interesting is the Majwari population, which is present discontinuously in Eastern Terai and  Mid-Western Terai. Who are the Majwari peoples? How and why they moved within Nepal remains to be understood. Similarly, Sherpa seem to have two distinct populations: a strong presence in Eastern Hills and a moderate one in Western Hills. Danuwar also appear to have spread from Eastern to Central Nepal.

This data has shown that smaller language communities in Nepal have historically localized to particular regions whereas larger populations have moved around. However, there are certain populations that present in Eastern and Western Nepal but not in the middle. When did these populations migrate into separate regions? Given migration was negligible in 1950s, did these populations migrated in ancient times? Did they originate from the same ancestral population? How long ago they split? These are some interesting questions that need further work.




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Evolutionary marvels: Biodiversity in animals

Evolutionary marvels: Biodiversity in animals

The Guardian has a dozen #amazing pictures of remarkable animals that inhabit land and the deep seas. “A very worthwhile diversion,” says the New York Times’ Jennifer Kingson.

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09.19. 2013 · 9:45 am

GFP stained Drosophila larva

Please also view Dosophila embryogenesis video

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Bonobo toolmaking hints glimpses of “cutting edge” stone age technology

This is really cool as human ancestors, many millions of years ago, my have started making tools in very similar fashion. Here is the Roffman et al. PNAS paper that describes the findings in detail.

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Genomics for future anthropologists & archeologists

An awesome use of genomics and proteomics in archeology and paleopathogenomics (yes I just invented the word!)

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Origin of species: through gene regulation?

“How does evolution occur?” This has been a central question in biology. Does evolution occur because a new mutation results in a new protein or because the same gene is regulated differently? How do new morphological structures evolve? How does speciation occur? A recent paper in Science ties principles in evolutionary biology, development biology, and molecular biology to answer these exact questions.

Distalless protein (dll), which is highly conserved across many genera, seems to have EVOLVED A NOVEL FUNCTION in a particular species of insect (Rheumatobates rileyi) to generate male specific antennal appendages. Males possessing these appendages have increased chances of reproducing therefore, have higher fitness (see video below). There could be two reasons for the development of these antennal appendages: first, dll in this particular species is shorter than all other species and second, dll is differentially regulated in this species. Although dll in R. rileyi appears to be shortened,  I feel that its differential expression may be more important in creating this morphology. dll is an important protein in development and therefore, it is pleiotrophic (see figure on the right below). Thus, it is likely that any alteration of the original function by the shortened protein would result in death. One scenario could be that a cis-mediated regulatory change in dll expression causes it to be expressed at a novel developmental stage in a novel tissue where some other male-specific proteins are also expressed. Interactions between dll and such male-specific protein(s) results in the formation of antennal appandages.

So, what does this study tell us about how evolution occurs? Well, one way evolution by natural selection occurs is not through new mutations that alters the function of existing proteins but through mutations that result in modifications in regulation of existing proteins to acquire novel function. Existing proteins may acquire novel functions if they are ectopically expressed, i.e, in developmental stages or tissues where they are normally not expressed. Most of the times ectopic expression may either provide no benefit to the individuals or even be detrimental but sometimes, ectopic expression may allow these proteins to interact with other proteins expressed in that tissue at that developmental stage to perform new functions. This new function may confer some reproductive advantage to that individual, therefore enhancing what population geneticists/evolutionary biologists call ‘fitness’. Over time, these individuals will take over in the population. If this population remains isolated from the ancestral population for a long period of time, it may give rise to a novel species (not this study but can be imagined).

This is a cool example of how integrating many areas of biology (evolutionary, developmental, molecular, and entomology) can elucidate novel genetic mechanisms underlying phenotypic diversity.

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Modern human diseases and demographics

Tumultuous effects resulted and continue to result from the massive mixing of the world’s biota when European ships reconnected the American continent to the rest of the world.  Mann traced several of the cascading consequences of “the biggest ecological convulsion since the death of the dinosaurs.”
The first momentous change came from microbial exchange—20 lethal diseases came from Europe to the Americas while only one (syphilis) went the other way.  North America, which had been largely cleared by natives with fire and agriculture, reforested when two-thirds to 95% of the native inhabitants died from European diseases—”the greatest demographic catastrophe in human history.”  That huge reforesting drew down atmospheric carbon dioxide and Europe’s “Little Ice Age” (1550-1800) apparently resulted.
Meanwhile the mountain of silver at Potosí, Bolivia, vastly enriched Europe, which “went shopping” worldwide.  Trading ships coursed the world’s oceans.  One artifact picked up from Peru was the potato—a single variety of the  6,000 available.  When potatoes in Europe turned out to provide four times the amount of food per acre as wheat, the previously routine famines came to an end, population soared, governments became more stable, and they began building global empires.  After 1843 guano shipped by the ton from coastal Peru for fertilizer introduced high-input agriculture.  In Ireland 40% of the exploding population ate only potatoes.  Around 1844 a potato blight arrived from Mexico, and a million Irish died in the Great Famine and a million more emigrated.
In China, which has no large lakes and only two major rivers, agriculture had been limited to two wet regions where rice could be grown.  Two imports from America—maize and sweet potato—could be farmed in dry lands.  As in Europe, population went up.  Vast areas were terraced as Han farmers pushed westward as far as the Mongolian desert.  In heavy rains the terraces melted into the streams, and silt built up in the lowlands, elevating the rivers as much as 40 feet above the surrounding terrain, so when they flooded, millions died.  “A Katrina per month for 100 years,” as one Chinese meteorologist described it.  The constant calamities weakened the government, and China became ripe for foreign colonial takeover.
In America two imported diseases—malaria and yellow fever—were selective in who they killed.  Europeans died in huge numbers, but Africans were one-tenth as susceptible, and so slavery replaced traditional indentured servitude in all the warm regions that favored mosquito-borne diseases.  As one result, four times as many Africans as Europeans crossed the Atlantic and began mixing with the remaining native Americans, giving rise to an endless variety of racial blends and accompanying vitality throughout the Americas.
During the Q & A, Mann described a potential fresh eco-convulsion-in-waiting.  “There is an area in southeast Asia roughly the size of Great Britain that is a single giant rubber plantation.”  Where rubber trees originally came from in the Amazon there is now a rubber tree leaf-blight that is starting to spread in Asia.  “You could lose all the rubber trees in three to six months.  It would be the biggest deforestation in a long time.”  The entire auto industry, he added, depends on just-in-time delivery of rubber.
Stuart Brand’s summary of Charles C. Mann’s talk at The Longnow Foundation in April 2012. I decided to post it because it is one of the most eloquently articulated account of the modern history of Homo sapiens.

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