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This meant the vast majority of the increase in twinning rates was due to high numbers of dizygotic or non-identical twins - twins born from separate eggs.

"The twinning rate in Africa is so high because of the high number of dizygotic twins - twins born from two separate eggs - born there," he said.

Non-identical, or dizygotic, twins occur when two separate eggs are fertilised, each by a different sperm, and develop in the womb at the same time.

However, monozygotic and dizygotic adult twins have equally similar microbiota, suggesting environment rather than genetics may drive familial similarities.

“Monozygotic is what people mean,” Boklage continued, insisting on the terms “monozygotic” and “dizygotic” when referring to twins.