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How does migration affect human population growth compared with fertility and mortality?

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Common wildebeest — population ecology A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

In population ecology, human population growth is determined by the combined effects of fertility, mortality, and migration. While migration—defined as a permanent change of residence—can augment or deplete a population, its impact on overall growth rates is generally far smaller than the influence of changes in fertility and mortality.123

A high rate of natural increase (the difference between fertility and mortality) can be offset by significant net out-migration, just as a low rate of natural increase can be countered by high levels of net in-migration. However, fertility remains the primary driver of global population trends; for instance, the recent decline in the world's population growth rate is attributed primarily to lower fertility rather than migration patterns.12

It is important to acknowledge that throughout history, migration has frequently been associated with profound human suffering, including violence, bondage, and mass mortality, rather than being solely a demographic variable. Ethical principles demand that we recognize the immense human cost often embedded within these population movements.3