Last week, we trotted out early to gather our bulls and march them down to the southernmost pasture on the ranch where they will patiently endure the final few weeks before what I can only assume is their favorite two months of the year: breeding season. After a storm brought three welcome inches of rain a few days prior, the southern end of the ranch, at times desiccated save a few hanging springs and creeks, had become a desert oasis, punctuated with patches of soft clay, wetlands, and ephemeral ponds–the type of terrain that grabs at the hoof with every step of your horse and is reluctant to let go.

We meandered the bulls across the Chico Creek, now swollen with upstream drainage that, having carved its way through an impossible maze of arroyos, was finally beginning its obligatory quest for the Arkansas River. After pausing to give our horses and the bulls a few much-needed sips, we slowly worked the herd out of the creek–always an uphill battle–allowing the creek bed to resume its ancient task of making rain into rivers. Nudging the herd along the road through scrubby patches of rabbitbrush, greasewood, and four-wing saltbrush as tall as our horses, with the first brave blooms of prickly pear splashing yellow and pink up at our stirrups, we finally made it across the road and into the Little Chico pasture, completing the eight-mile trek just as dusk set in.

While being moved from pasture to pasture, our seed stock herd of purebred Beefmaster bulls fluctuates periodically between elegance and chaos. The bulls walk single file, head to tail, along a road or fence or cattle trail for hours, then seemingly for no reason whatsoever, the entire herd erupts into brawls. They remain quiet and orderly for so long, then one of the older bulls, perhaps encouraged by an overly energetic yearling pestering him, turns and faces his neighbor, tongue hanging out, snorting, pawing the ground.

Clouds of menacing dust rise up all around as head-butts lead to chases, and the instinctive ritual of competition for mates is rehearsed, this time before the cows are truly on the line. Smaller fights among yearlings can be broken up quite easily from horseback, but when the three-year-olds (most of which weigh well over a thousand pounds) begin to tussle, it’s usually best just to step aside and wait for them to work it out on their own. At times, the whole herd of bulls will continue trailing out while a single pair is left far behind, locked head to head for ten minutes or more, both too exhausted from the fight to move, but too full of hormonal pride to give up first. Then, just as abruptly as it began, with nothing more than the slight application of pressure to get the front of the herd moving, the chaos is smothered to a murmur, and eventually quieted to silence, as the bulls not-so-reluctantly return to the order of the single-file march. Slow but steady, they saunter on.

This is the way of the Beefmaster bull, who after years of natural selection has come to be known for his masculinity and libido. Massive, yet gentle. Tender one moment, quarrelsome the next. The Beefmaster bull is a symbol of strength and resilience in a herd that is built for production, endurance, and efficiency. The bulls are left largely to their own devices for ten months out of the year, yet still reach the optimal (and impressive) size with none of the nutritional supplements the cows, heifers, and yearlings receive (neither salt nor mineral). They carry out their work of breeding tirelessly, and take care of themselves otherwise.

Marching our bulls down south to the bull paddocks, and later back north to be turned out to breed, is somewhat of a ritual here, punctuating the rhythm of the cattle work year as summer comes and goes. The breeding season is bounded on either end by this habitual migration, when the bulls return from the isolation of winter to once again catch the scent of cycling cows carried by the wind.

The bulls had been in the pasture outside my front door for the last few weeks before their journey south. I frequently sat and watched them amble around the springs and flats from my porch. The behavioral patterns repeat themselves: a group of ten yearling bulls all lined out and following a handsomely large three-year-old wherever he went (he might be the closest thing they can find to a mother, or at least someone who knows where to go); two bulls resting in the heat of the day side by side, one’s head atop the other’s shoulder, one licking the other tenderly across the face. The very next moment, the fleeting display of fraternal affection erupts into a brawl once again, their deep bellows following the contours of the creek south.

The yearling Beefmaster bulls who this year will go into service here on the Chico are the product of a breeding program that began nearly a century ago. The philosophy upon which the Beefmaster breeding program is based grew out of identifying the role these unique cattle are playing in the larger ecosystem, and trying to understand how to optimize their ability to serve that role. In the case of bulls, aside from the ecological impacts of their grazing and movement, their role revolves around reproduction. All of our females–be they purebred or commercial Beefmaster cross cattle–are serviced exclusively by our Beefmaster bulls. These bulls, all born and raised here on the ranch, are direct descendents of the original Foundation Beefmaster herd, created on the Lasater Ranch in Matheson, Colorado. In addition to allowing us to maintain a high standard of production in our cattle operations, the Beefmaster bull is part of a tradition and allows us to carry on the genetic and philosophical legacy of the Lasater herd.

In 1945, Tom Lasater began using multiple sire herds combined with a short breeding season to breed his Beefmaster cattle, and this is how they have been bred ever since, including here on the Chico. Rather than picking a single bull (sire) with presumably good conformation and genetics, as many seedstock producers still do, and trying to maximize his progeny by eliminating the need to compete with other bulls for cows within a single herd, using multiple sires allows natural selection for mating ability to do the work. Tom Lasater wrote of his breeding program: “The bulls most capable of actually settling cows under range conditions leave the most inheritance in the herd. Those least capable leave the least; the infertile leave no progeny.”

So, every fall at weaning time, we select the superior bull calves from that year’s crop, and they will join the bull herd until they are marched back up and sorted through in the summer to breed. Choosing the bull calves with the highest weaning weights allows us to perpetuate the heavy-milking traits and hardiness (cows that walk to the far reaches of the pasture where the best forage is) of that bull’s mother cow. When we sort through the bulls again before breeding, we are judging the bull’s individual conformation and disposition. The rest, however, is left up to natural selection.

Large cohorts of bulls of assorted age classes (yearlings, two, and three-year-olds) are turned out into the cow herds in June, and after a short breeding season, those that are most able to breed on their own leave the largest genetic signature within the herd. While evolution is a process that occurs over deep, geological periods of time, the environmental and social forces that drive natural selection on a molecular, daily scale are what shape the Ranchlands Beefmaster bull–not as an individual animal, but as a population of cattle, always adapting to their environment.