Genetics as the myth buster: Indian edition

Whenever Zack Ajmal posts a new update to the Harappa Ancestry Project he appends some data to his ethnic database. This sends me to Wikipedia, because how many people are supposed to know what a "Muslim Rawther" means? Well, if you are a Muslim Rawther, and perhaps from Southern India, you would. But South Asian ethno-linguistic categories and hierarchies are notoriously Byzantine, and I have difficulty making sense of them. This isn't too surprising in my case, as my family's background is relatively mixed in the very recent past (e.g., Hindus and Muslims, and people of various caste backgrounds), so we're not the sort who can go at length about our pure ancestry and all that stuff. Unfortunately, Wikipedia isn't always useful, because the people editing the entries on particular South Asian ethnic groups are often people from those ethnic groups, so you get a lot of extraneous information, and a particular slant on how awesome and high achieving the group (also, sometimes there's funny stuff about how notoriously good looking that particular caste!). On occasion there are other sources which are informative. For example, Zack has several individuals from the Tamil Nadar caste. I know a little about this group because 1) I have a friend whose family is Nadar (he's American, so saying he's an American Nadar is pretty worthless), 2) The New York Times profiled the group last fall. When Zack noted that a group termed Tamil Vishwakarma had submitted entries, I went to Wikipedia. That was the first time I'd heard of the group. This is what I found: