Thank you for your comment and for your interest in our work.

I fully agree with your comment on cause/consequence. However, we were very cautious as to not assume cause consequence and we never did. Females could be copulating more with males to get meat and males could be giving meat to females to increase their copulation frequency. However, we never suggest one possibility or the other and in fact its not necessary for one behaviour to precede the other. We simply say that there's a correlation between these two variables and that this indicates that by exchanging meat for sex, males increase their mating success and females increase their caloric intake. We never state in the paper that chimps are 'paying for sex'.
In an exchange, it doesn't necessarily matter who gives what first and there's not necessarily such an order of events.

Although its possible that chimps who failed to get regular sex learned to be selfish about their food and this possibility was never excluded in our paper, a mechanism of rewarding successful hunters is a completely different issue. Why would a female take it upon herself to reward a successful hunter by copulating with him, unless she is getting a direct benefit? This doesn't really make evolutionary sense unless its accompanied by other controls. Or else, how would such a mechanism evolve?

I hope I have addressed your concern and I'd be happy to hear your thoughts on this matter.