अमेरिकेचे हॉर्वर्ड विद्यापीठ आणि हैदराबादेतील सेंटर फॉर सेल्यूलर अँड मॉलेक्यूलर बायलॉजी यांनी एका संयुक्त प्रकल्पाद्वारे भारतातील ७३ जाती समूहांचा वांशिक अभ्यास केला. या अभ्यासाचे निष्कर्ष ‘अमेरिकन जर्नल ऑफ ह्युमन जेनेटिक्स' या नियतकालिकाच्या ८ ऑगस्ट २०१३ च्या अंकात प्रसिद्ध झाले आहेत. हे निष्कर्ष भारतातील जातीव्यवस्था आणि वर्णसंस्था यांविषयीच्या परंपरागत धारणांना धक्क देणारे आहेत.
या अभ्यासाचा थोडक्यात गोषवारा असा :
१. चार हजार वर्षांपूर्वीच्या आधी पर्यंत भारतात दोन स्वतंत्र वांशिक समूह अस्तित्वात होते.
- उत्तर भारतात राहणा-या लोकांचा समूह.
- दक्षिण भारतात राहणाया लोकांचा समूह.
३. आजपासून सुमारे १९०० वर्षांपूर्वी पर्यंत हे लोकसमूह तयार होण्याची प्रक्रिया सुरू होती. म्हणजेच या लोकसमूहात परस्पर बेटी व्यवहार होता.
४. १९०० वर्षांपूर्वी म्हणजेच साधारणत: इसवी सनाच्या पहिल्या शतकात या लोकसमूहांनी आपल्या समूहाबाहेर विवाह करण्याचे बंद केले. आज जे लोकसमूह अथवा जातीसमूह भारतात दिसतात, ते लोकसमूह २ हजार वर्षांपूर्वी बंदिस्त झालेल्या समूहांचे वंशज आहेत.
हा अभ्यास तंतोतंत खरा मानला तर आजची भारतीय जाती संस्था सुमारे १९०० वर्षांपूर्वी अस्तित्वात आली, असे म्हणता येते.
या अभ्यासावर आधारित एक बातमी टाईम्स इंडियाने दिली आहे. या बातमीचा तपशील असा :
genetic study finds : Caste bar on marriages became entrenched 2000 years ago
Courtesy : Times of India
NEW DELHI: In a fascinating study of how different types of populations mixed in India, scientists have found that there were three stages of intermixing.
In ancient times, over 4000 years ago, there were two separate populations based in north and south India with no mixing. Then, in the second stage between 4000 years ago and 1900 years ago, comes a phase of widespread intermingling of populations, which penetrated to even the most isolated groups. Finally, from around 1900 years onwards, several subgroups of the already mixed population stopped marrying outside their group, and thus became frozen.
Scientists from Harvard Medical School, US, and the Centre for Cellular and Molecular Biology in Hyderabad provide evidence for this sequence of development through analysis of genetic material from 73 Indian population groups. The findings were published on August 8 in the American Journal of Human Genetics.
"Only a few thousand years ago, the Indian population structure was vastly different from today," said co-senior author David Reich, professor of genetics at Harvard Medical School (HMS) in a statement issued by the HMS. "The caste system has been around for a long time, but not forever."
Prohibition to marrying outside a defined community is called endogamy. It is one of the cornerstones of India's caste system. The decline of intermarriage between different communities as found by these scientists is due to the spread of the caste. This transformed India from a country where mixture between different populations was rampant to one where endogamy became the norm.
Earlier, in 2009, Reich and colleagues had analyzed 25 different Indian population groups and found that all populations in India show evidence of a genetic mixture of two ancestral groups: Ancestral North Indians (ANI), who are related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI), who are primarily from the subcontinent. However, this analysis could not clearly define the timeline. So, the researchers analysed genetic material from almost triple the number and came up with a much clearer idea of the changes in India.
How do genetic scientists get to know so much about the past of different populations? The genomes - strands of DNA - of Indian people are a mixture of segments of ANI and ASI descent. Originally when the ANI and ASI populations mixed, these segments would have been extremely long. However, after mixture these segments would have got broken up and reshuffled as genetic material from the father and mother combined.
By measuring the lengths of the segments of ANI and ASI ancestry in Indian genomes, the scientists are able to obtain precise estimates of the age of population mixture. They found that mixing and shuffling of genetic strands continued between 4200 years to about 1900, depending on the population group analyzed.
"The fact that every population in India evolved from randomly mixed populations suggests that social classifications like the caste system are not likely to have existed in the same way before the mixture," co-senior author Lalji Singh, currently of Banaras Hindu University, and formerly of the Centre for Cellular and Molecular Biology said in the HMS statement. "Thus, the present-day structure of the caste system came into being only relatively recently in Indian history."
But once established, the caste system became genetically effective, the researchers observed. Mixture across groups became very rare. This has led to another consequence - the preservation of certain types of diseases within endogamous groups.
"An important consequence of these results is that the high incidence of genetic and population-specific diseases that is characteristic of present-day India is likely to have increased only in the last few thousand years when groups in India started following strict endogamous marriage," said co-first author Kumarasamy Thangaraj, of the Centre for Cellular and Molecular Biology in the HMS statement.
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