This is the most misinterpreted and a classic example of following a tradition blindly without knowing anything about it. Sadly (believe it or not but) it is still being carried out in some areas in India. Sati is the act of a woman Immolating herself on the pyre of her dead husband. Here, there is no scientific reason for this. Remember the three wives of dasharatha and Kunthi devi from Mahabratha. They were all widows through out the Epic right!
It is said to have started earlier way before 7th or 8th century during the invasions of muslim rulers from outside India, wherein the noble women preferred burning on the pyre along with their husbands rather than undergo humiliation, torture and disrespect at the hands of the invaders should their husbands die at the war. But slowly this turned into a custom of forcefully burning a women on the pyre of her husband.