10000-50000 BC is an extremely big time span... a lot of changes took place in human cultures and development during this period. It's impossible to give an answer that will cover all cultures and time periods between 50000 and 10000 BC. I don't think there is any reliable way to estimate how many sex partners anyone had, or how many men reproduced. The only thing you can do as an archaeologist/anthropologist is to look at ethnographic data from more recent cultures and try to hypothesise based on that. But even then you will find that sexual practices and attitudes to sexuality vary tremendously across different geographical areas and time periods.