The Yellowstone Cutthroat Trout and Deep Evolutionary Time

There is a place high in the Rockies in Wyoming where waters part. Two-Ocean Pass is a national landmark. Here, a small stream called North Two Ocean Creak splits into two waterways on the Continental Divide. The waters of one branch, Pacific Creek, are destined for the Pacific Ocean. The other, Altantic Creek, for the Atlantic Ocean.

This geographic peculiarity, called a distributary (the opposite of a tributary), probably allowed the ancestors of today’s Yellowstone Cutthroat Trout to spread into waters on both sides of the Continental Divide. Long ago a few enterprising young trout explored up what we now call Pacific Creek and somehow ended up on the other side of the hill, in Atlantic Creek. From there they reproduced and a new species was propagated into a new territory.

It is the peculiarities of nature that enable the “butterfly effect” in deep evolutionary time. A landslide changes the course of a creek drainage and isolates a population. Over many thousands of years that population evolves into a distinct sub-species of the original. Two ponds separated by a few feet of flat mud. A fish with extra strong fins manages to flipper its way across that mud into the other pond. Its mutant DNA is passed down to its offspring, and a few million years down the road, the fins morph into legs and the gills turn to lungs.

We can put a number on an immense time scale and claim to understand it. But we as humans cannot actually comprehend the immensity of deep evolutionary time. We try. We do visual exercises where we draw time out on a road. Where a mile of roadway represents the life of Earth, at 4.6 billion years, one million years on that scale is about one foot. Recorded human history (5,000 years) is about one millimeter of that one-mile track.

These visualizations are interesting, but they still don’t really change our brains to perceive a million years of time or more. I hold a rock in my hand and say to my second-grade daughter, “this rock right here might be 500 MILLION years old! Can you believe that?” She seems interested and curious, but she has no personal point of reference to relate, and neither do I.

The trout is a species that seems to easily morph into subspecies based on its environment. Isolated populations living in waterways with light-colored bottoms may evolve lighter colors and fewer spots. Natural selection favors the slightest variation in color between individual trout—the lighter ones ever so slightly more likely to survive predation and pass on their genes.

Humans are in the process of replacing natural evolution with artificial evolution. Gene editing, artificial intelligence, and augmented reality may be the more obvious affronts to nature’s designs. But, what about cars, genetically modified foods (which is almost all food modern humans consume), and medicines that prevent otherwise natural causes of death? Will our evolutionary path be technological? And, if so, what will be our connection to nature as our species increasingly becomes one of human design?

 

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