What is the etymology of タマ in タマを取る?


It seems that when spoken by/in regards to Yakuza, the phrase タマを取る means to
`take someone's life`. However, I've seen [some explanations](http://zokugo-
dict.com/16ta/tama.htm) saying タマ comes from 頭{あたま} and
[others](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1324025188)
say that it comes from 魂{たましい}. Where does it actually come from?




I think it is from 頭 because タマをとる mostly means "take a boss's life of
Yakuza". Bosses are sometimes called 頭.

