They did control for obvious appearance differences (e.g. color & type of clothing, hair length) and morphology (e.g. height/body size), even people's approach. But not more subtle traits such as gait, waist-hip ratio, odor...

One hypothesis suggested that in early history, women may have more commonly caught smaller prey (birds) than men did, and this fear could be evolutionarily ingrained.

To be fair, I don't think most birds have a good sense of smell (as dogs, cats, deer etc have) so that would discount odour. I suspect if there is a factor here it may be something that is obvious to the birds.

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