Sevva Thosham and Science

At home! Had a good day today. Went to the Shiva Temple as it was Pradosha Viradham today. Apparently, it was yesterday in London and today in Sri Lanka. I had no idea why and when people fast for Pradosham. I only had a slightest idea that it is something like Ekadasi. I got a good opportunity to talk to the priest there about religion, which is quite rare and unusual! I always get questions of why, what and how. And it was a time for me to ask some of the Whys I had in my mind though not everything. It is really amazing how science overlaps religion (in general). There is always a strong scientific aspect behind every feature of Hinduism. It was a delight to sit and listen to the priest about the religion and its science.

One of the interesting things I got to know was about the Sevvai Thosham. I did not know much about Sevva Thosham before as there was never a talk about it in my family. As the priest explained, a girl with Sevvai Thosham should marry a man with the same thosham. And that is because of the RH factor in the blood group. RH stands for Rhesus factor.
Everybody is born with a specific blood group with an RH factor being either negative or positive.
Basically, those with RH Negative are said to be Sevva Thosham and they should marry someone who also possesses RH Negative. This is because if the mother is RH negative and the father is RH positive, during pregnancy the mother will be exposed to the child's RH positive. Exposure to the RH positive will cause the mother's body's immune system to make antibodies against it and this may lead to the antibodies destroying the child's red blood cells or may cause severe problems. But if both the mother and the father is RH negative, the offspring will only be RH negative and therefore no harm.
Therefore, those with RH-Negative (Sevva thosham) should marry someone who is also RH-Negative (Sevva Thosham).
Hope this was not confusing :)