What percentage of the Subsaharian African population was slave before the colonization?

i've read a paper that hypothesized that polygamous cultural norms in africa came into existence because of the slave trade. men were in demand far more than women, leading to a gender imbalance, which led to the rise of polygamous marriages for reproductive efficiency. Regardless, it is possible that slavery had wide ranging side effects on populations and social systems

>>17825308
Interesting theory but thats no ask my question

>>17825300 (OP)
About a third or a half

>>17825300 (OP)
>>17826979
Super hard to tell due to lack of comprehensive data (globally, even island palpitation colonies were iffy) and what a "slave" exactly entailed.