A Miracle: Mule Mare Gives Birth

With all sick people having sex with the animals, we won't be surprised to find a human-chimp hybrid one day. But this won't be a threat for the human species, as normally, hybrids between two different species, even if offering beneficial traits, are sterile. And in many cases, hybrids are not viable at all and this is explained by a theory stating that hybrid incompatibilities (such as death or sterility) are caused by genes that have evolved from a common ancestor but diverged in each of the species.

In the common ancestor, these genes may have worked perfectly well together. But, as each gene evolved in its own species, it began to code for proteins that no longer work in other species.

If we refer to a mule, the result of a cross between a horse mare and a donkey stallion, this is valid: mules are known to be sterile. Just for the beginning, you should know that donkeys have 62 chromosomes, whereas horses have 64. The mule has 63 chromosomes which cannot evenly divide in the sperm or eggs.

Still, miracles can happen: on the Mesa, in the Grand Valley town of Collbran (Colorado), Kate, the mule mare has given birth to a mule foal at the ranch of Larry and Laura Amos. This is an extremely rare occurrence, every once in a million years.
The foal was born in late April, shocking the Amos. Mule fertility is such a rare event that the Romans said "Cum mula peperit" ("when a mule foals," or, if you like, "when hell freezes over.")

The foal cannot be technically a mule (50 % horse and 50 % donkey), as it must have been fathered by a horse or donkey stallion and would have to be either 30 % horse and 70 % donkey, or 70 % horse and 30 % donkey.