Fertility Rates Vary Dramatically Within India By Region

UPDATE June 19, 2017 in response to the comments:

Razib Khan notes the huge range of lifetime fertility rates for women in different parts of India at the Brown Pundits blog. The high fertility areas, for example, in the Himalayan foothills, have fertility rates comparable to Nigeria (at the peak in the 5.0 to 6.0 range). The low fertility areas, mostly in Southern Indian, have fertility rates four times as low, comparable to Italy or Japan (as low as 1.2). He states before providing a table with the state by state figures:

The map above shows the most recent district level fertility rates in India. It is immediately clear why comparing India to Pakistan and Bangladesh (let alone Nepal, Sri Lanka, or Bhutan) is a major error. 

In some of the northern regions of the Hindi-speaking “cow belt” as well as the lightly populated Northeast the total fertility rate is similar to what you find in Nigeria, between 5 and 6 children per woman. For comparison the TFR for Saudi Arabia is 2.75. For Bangladesh it is 2.20 and for Pakistan it is 3.6. In contrast, much of the South, Punjab, and West Bengal have below replacement fertility.

In the comments, he notes that data is not available from the gray area (basically Kashmir) due to political turmoil there.

The cause isn't obvious, leaving us to speculate based upon correlations rather than causation. Generally speaking linguistically Indo-Aryan, Munda and Tiberto-Burmese regions seem to have higher fertility than linguistically Dravidian regions. Alternatively, fertility is lower in places where crops with Sahel African crops thrive and is higher in places where Fertile Crescent Neolithic crops and rice farming are employed.

This is contrary to the historical stereotype of Northern India as more urban and developed and Southern India as a more rural and less developed. On the other hand, megacities in Southern India may be larger than those in Northern India, and the size of the largest cities is usually a good proxy for economic development.

It is also seemingly contrary to the usual rule of thumb that unpredictable risks of death are disproportionately and non-linearly associated with higher fertility levels (i.e. people overcompensate for the marginal risk of losing a child by having more children). Deaths from natural disasters are clearly more common in low fertility areas of India than they are in high fertility areas. And, the infectious and parasitic disease load is likewise probably higher in low fertility areas of India than they are in high fertility areas.

Of course, Razib's core point that South Asia is not demographically homogeneous is all well demonstrated by this data point.