Academic journal article Science and Children

In Early Migrations, Humans Accumulated Harmful Mutations

Academic journal article Science and Children

In Early Migrations, Humans Accumulated Harmful Mutations

Article excerpt

Modern humans (Homo sapiens) are thought to have first emerged in Africa about 150,000 years ago. One-hundred-thousand years later, a few of them left their homeland, travelling first to Asia and then to the Americas.

Researchers recently developed theoretical models predicting that if modern humans migrated as small bands, then the populations that broke off from their original African family should progressively accumulate slightly harmful mutations. Moreover, this "mutational load" of a population should then represent a way of measuring the distance it has covered since it left Africa. Simply put, an individual from Mexico should be carrying more harmful genetic variants than an individual from Africa.

The main reason for a higher load of harmful mutations in populations farther away from Africa? Natural selection is not as powerful in small populations. Harmful mutations were purged less efficiently in small pioneer tribes than in larger populations. In addition, selection had less time to act in populations that had broken away from their African homeland and thus settled far later. …

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