Sentence:  In short, what every student of biology knows – that within nature there is a <WSD>teleology</WSD> having to do with the survival of the species which underpins the distinction between the two sexes and produces between them a natural affinity for one another – no surgeon who knows what is good for him may now say. 
Meaning of the word marked with <WSD> tags:  An instance of such a design or purpose, usually in natural phenomena.