In addition to cultural controls acting to maximize fertility, there are important, and often competing, interests of individual families to limit fertility. Unwanted births are dealt with by infanticide in many cultures. Additionally, fertility is regularly controlled by limiting marriage within a culture. Another very important factor in population growth, especially in the tropics, is food availability. Heavy rains in the tropics wash nutrients away, leaving deficient soils. Much of Africa is either too dry or too wet. Africa was, until recently, not densely populated. Since land was available and because more children meant more security and power, a culture evolved that emphasized high fertility, justified by the need for descendants to pacify ancestors. Sub-Saharan (tropical) Africa has the highest birth rates in the world. As an example, Niger, just south of the Sahara desert has a fertility rate of almost eight children per woman while, in the Mediterranean zone, Morocco, just north of the Sahara, but also a Sunni Muslim country, has a rate of only 3.3 children per woman.
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