Shared Evolutionary Origins
Horses and donkeys belong to the same genus, Equus, and diverged from a common ancestor relatively recently in evolutionary terms. This close relationship means their chromosomes are similar enough to pair during reproduction, allowing them to produce offspring.
Compatible Reproductive Systems
Both species have comparable gestation periods, reproductive anatomy, and hormonal cycles. A male donkey (jack) can successfully mate with a female horse (mare), and a male horse (stallion) can mate with a female donkey (jenny), resulting in live young.
Mules, Hinnies, and Fertility
The offspring of a horse and donkey are usually mules (jack father, mare mother) or hinnies (stallion father, jenny mother). Most mules and hinnies are sterile because the mixed chromosome set from each parent prevents normal gamete formation.
For more details on equine hybrids and chromosome differences, see Mule – Britannica.
