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Horses and donkeys are different species but they can reproduce and have children (mules)... but these cannot reproduce further.
Humans actually also had various species (Denisovan, Neanderthal) which most likely coexisted at the same time and there's evidence they could have sex (well, that you can always have...) and children. Right now there's just homo sapiens left.
A fascinating book on this subject - Harari "Sapiens" (2014)
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