[Certhas]

I don't think the person being replied to necessarily meant that, but cultural is often used in this context as a racist term, as in: "Africans will always have many kids, it's their culture", where before the more overtly racist "nature" might have been used.

The implication being that the cultures of (some) people are unchanging and fixed. I think you'd agree with a statement like: Cultures and family values do change all the time, due to a variety of factors like better medical care, and economic empowerment, in reasonably predictable ways.

So it's not unchanging cultural differences between Africa and Europe that drive the different fertility rates, but rather different socio-economic factors that drive a different family culture. Changing the socio-economic factors will change the culture surrounding families, just as much in Africa as it did in Europe, the Middle East, Asia, etc... at various times in the last century and a half.