COLLBRAN — When it reportedly happened in Morocco five years ago, locals feared it signaled the end of the world. In Albania in 1994, it was thought to have unleashed the spawn of the devil on a small village.

But on a Grand Mesa ranch, the once-in-a-million, genetically “impossible” occurrence of a mule giving birth has only drawn keen interest from the scientific world. That, and a stream of the locally curious driving up from the small town of Collbran to check out and snap pictures of a frisky, huge-eared, gangly-legged foal.

“No one has run away in fear yet,” laughed Laura Amos, the owner of the foal, along with her husband, Larry.

The foal is being called a miracle because mules aren’t supposed to give birth. Mules are a hybrid of two species – a female horse and a male donkey – so they end up with an odd number of chromosomes. A horse has 64 chromosomes and a donkey has 62. A mule inherits 63. An even number of chromosomes is needed to divide into pairs and reproduce.

But those numbers added up to implausibility in late April when the Amoses awoke to a braying and whinnying ruckus in the corral behind their house.

Running to the rescue

They spotted a foal peeking out from between the front legs of one of their favorite black mules, Kate. They tore outside to save the baby from the male mules – the johns – that were trying to stomp the little critter and the other female mules – the mollies – that were trying to steal it.

And then the Amoses began to ponder how the foal had fooled mule sterility, a phenomenon first noted by the Greek philosopher Aristotle.

The Amoses, who have about 100 horses and mules at their Winterhawk Outfitters business, knew that what they were seeing is considered scientifically impossible – as much so today as in ancient Greece. They began doing research and found that in the past two centuries about 50 cases of mules giving birth have been recorded. Only two of those were proved with genetic testing.

It’s an event so rare that the Romans had a saying, “cum mula peperit,” meaning “when a mule foals” – the equivalent of “when hell freezes over.”

Genetic testing at the University of Kentucky and the University of California at Davis confirmed that Kate is indeed a mule and that the still unnamed foal really is her offspring. That ruled out factors that have explained away some of the past births mistakenly attributed to mules. Those mules had stolen foals or they were not really mules themselves. They were donkeys or mulish-looking horses.

Now, the Amoses are waiting for chromosome testing from the University of California to determine exactly what is the fast-growing foal cavorting clumsily around their corral. He could be a smidgen of horse and a lot of donkey or mostly horse with just a bit of donkey genes.

“He’s got a donkey look now, but they all do at that age,” Larry Amos said.

Surprise findings

Dr. Oliver Ryder, associate director of the Conservation and Research of Endangered Species division at the San Diego Zoo, said the answer to how Kate could give birth could be surprising. There were very unexpected – and still unexplained – findings when a molly mule gave birth to two foals in Nebraska in the mid-1980s. The event prompted notice from the local pulpit and a flurry of scientific investigation, including the first genetic testing of a mule’s offspring.

Ryder said that tests in the Nebraska case showed there was no evidence the mother passed along any genetic markers from her father – a donkey that was also the father of the foals. The phenomenon is called “hemiclonal transmission,” which in simple terms means that the mare’s genes canceled out the male’s genes as if they didn’t even exist.

That phenomenon has been observed in amphibians but not in mammals.

“No recombinations took place. There was no reassortment. We looked at markers on every chromosome,” Ryder said. “This was an extremely unexpected finding.”

Another famous but scientifically undocumented case occurred at Texas A&M in the 1920s. A mule gave birth to a mule when the sire was a donkey and then to a horse when the sire was a stallion.

Ryder said he is “fascinated by this phenomenon” and is looking forward to learning more from the Amoses’ foal.

So is the mule publication “Mules and More,” which is running a contest to name the foal and has promised readers regular updates.

The Amoses are still scratching their heads. They didn’t know Kate was pregnant when they bought her and nine other mules from a breeder in Pleasant Plains, Ark., late last summer. She worked as a pack animal through the winter, and no one noticed when the animals were brought in this spring that she was pregnant. They were all fattened from a winter of good feed.

The Amoses are talking about breeding Kate again. They want to see if the “miracle” will occur twice. They say they have no fear that it will bring on the end of the world.

Staff writer Nancy Lofholm can be reached at 970-256-1957 or nlofholm@denverpost.com.