body language - nature or nurture?

Body language is part of human evolution, but as with many other aspects of human behaviour, the precise mixture of genetic (inherited) and environmental (learned or conditioned) influences is not known, and opinions vary.
Julius Fast noted this, especially regarding facial expressions. To emphasise the shifting debate he cited for example:
Darwin's belief that human facial expressions were similar among humans of all cultures, due to evolutionary theory.
Bruner and Taguiri's opposing views - in the early 1950s, after thirty years of research, they largely rejected the notion that facial expressions were inborn.
Ekman, Friesan and Sorensen's findings - in 1969, having discovered consistent emotional-facial recognition across widely diverse cultural groups, which supported Darwin's evolutionary-centred ideas.>The discussion has continued in a similar vein to the modern day - studies 'proving' genetic or environmental cause - 'nature' or 'nurture' - for one aspect of body language or another.
The situation is made more complex when one considers the genetic (inherited) capability or inclination to learn body language.
Is this nature or nurture?
It's both.
Body language is partly genetic (inborn - 'nature') - hugely so in certain aspects of body language - and partly environmental (conditioned/learned - 'nurture').
Some body language is certainly genetically inherited and consistent among all humans. Other body language is certainly not.
The use and recognition of certain fundamental facial expressions are now generally accepted to be consistent and genetically determined among all humans regardless of culture.
However the use and recognition of less fundamental physical gestures (hand movements for example, or the winking of an eye), and aspects of personal space distances, are now generally accepted to be environmentally determined (learned, rather than inherited), which is significantly dependent on local society groups and cultures.
Certain vocal intonation speech variations (if body language is extended to cover everything but the spoken words) also fall within this environmentally determined category.
In summary, we can be certain that body language (namely the conscious and unconscious sending and receiving of non-verbal signals) is partly inborn, and partly learned or conditioned.
Body language is part 'nature' and part 'nurture'.