It's not though. Literally at all. "Experimenters' (possessive) sex" : so, their biological sex is the only thing they can posses in this sentence. They can't

It's not though. Literally at all. "Experimenters' (possessive) sex" : so, their biological sex is the only thing they can posses in this sentence. They can't "possess" sexual reproduction in this context, that would not make any sense. This is just simple grammar. Gender would also make zero sense because this is not an article about gender. I can understand the confusion if English isn't your first language but outside of that it's very clear.