Should have read, when it first came out, Dr Mark Singleton's
Yoga Body: The Origins of Modern Posture Practice (Oxford University Press, USA, 2010).
Turns out that yoga has been shaped as much by India as by Western and Christian influences!
I suspected a bit of this, but not the huge role of the Young Men's Christian Association (YMCA), with the Indian branch of which I was associated in the 1970s, without realising any of it!
In my family there was a long-standing interest in everything to do with traditional things, including massage, ayurveda, homeopathy, aromapathy....
Well, if you are interested in Indian spirituality or even just in yoga, Singleton is a "must read", full of interesting, shocking and amusing information. The book is simply and clearly written, but has the full academic panoply of notes and references to document Singleton's findings.