“… creation is never over. It had a beginning but it has no ending. Creation is always busy making new scenes, new things, new worlds” — Immanuel Kant

By DR. CAMERON BARROWS

Charles Darwin got so much right. He identified what he called “natural selection” as a process in nature that was akin to what farmers and animal breeders do in selecting characteristics to enhance the quality of their flock, what we call artificial or domestic selection. Natural selection is a process in which, rather than those farmers and animal breeders, nature weeds out those less fit in favor of those more fit. Fitness refers to being more able to deal with the challenges of life, finding food and shelter, avoiding being eaten, and most importantly producing offspring that are themselves more fit. Darwin believed natural selection to be a slow, methodical process that ultimately could give rise to new species, but was too slow to be observed on the scale of a human life.

On that last point he got it wrong.

Peter and Rosemary Grant, Princeton University scientists, spent decades studying finch species (collectively called “Darwin’s finches”) on a tiny isolated desert island in the center of the Galapagos archipelago. In any given year their island’s finches could number from barely a hundred to nearly a thousand individuals, comprised of a couple different species. The birds’ population swings were caused by differences in rainfall, which then catalyzed the composition, abundance, growth, and flowering of different plant life – aka finch food. Exactly like what happens here in our desert. Each year the Grants and their students caught every single finch, measuring wings, legs, and beaks, and then released them otherwise unharmed but adorned with muti-colored leg bands to allow them to keep track of each individual. Their objective was to try and measure Darwin’s natural selection process, to see just how fast or slow it was. They measured the reproductive success of each individual, and then their children, grandchildren, and so on. What they found was, at the multi decadal scale of their study, that the finch’s morphology seemed pretty stable – a finding that would support Darwin’s belief in the slow pace of natural selection. However, on the scale of just one or a few years there were relatively large swings especially in beak size. If rainfall pattens favored small-seeded plants, then finches with smaller beaks flourished and produced more offspring. But, in years when plants with large seeds with hard to break husks dominated, then there was strong selection for the survival and reproduction of finches with larger, stronger beaks. The different species of Darwin’s finches are most easily distinguished on the basis of their beak size and shape, but when the availability of seeds favored large billed individuals, the different species rapidly converged on nearly the same bill morphology. If not for those color bands and the detailed genealogies kept by the Grants, there was almost no way to distinguish the two species. Natural selection can quickly change the characteristics of a population, and just as quickly change it back again.

More recently, published in 2023, a group of scientists, including James Stroud, Michael Moore, and Jonathan Losos replicated the Grants’ study, but instead used wild Anolis lizards in Florida. Rather than measuring beaks, they measured head and leg lengths of all the lizards occupying a coastal forest. Similar to the finches, over long periods the lizards did not change. However, year to year variation, in response to rainfall, hurricanes, and other climatic vagaries, was quite large. If over long periods of time the mean climate and habitat did not change, neither did the lizards. But over shorter periods associated with climatic punctuation marks (drought, flooding, hurricanes) there were substantial changes in the lizards’ bodies.

Rather than short-term fluctuations around a long-term mean climate, modern climate change is altering the means, taking us toward an increasingly warmer planet. For our deserts, it also results in a drier climate on average. One of the alarms about this trajectory is that it might be happening too fast for plants to adapt to these changes, leaving extinction as the only alternative. These studies on finches and lizards indicate that they can keep up with changes, at least to a point, and so offer some hope. Hope is good, but we need to be clear that if and when it becomes too hot and too dry for plants to live, then there is nothing for insects and finches and lizards to eat, and no amount of natural selection will allow species to live on air and rocks alone.

When our intrepid naturalists are conducting our lizard surveys, I have noticed that the lizards we encounter and count are not distributed evenly across the desert landscapes. Rather, we often can walk a few hundred meters and not see a lizard, and then within the space of 20-30 meters see three, four, five, or six lizards in quick succession, only to be followed by another lizard-less expanse. This could reflect pockets of adaptation, of natural selection, where there are groups of interbreeding lizards that are so far keeping up with our climate’s trajectory. Supporting this hypothesis, at the lowest, hottest, and driest survey elevations the distance between lizards appears to be much greater and the lizards are more typically found in just ones or twos. At higher elevations, at least up to a point, the lizards seem more evenly distributed and when in groups, the groups seem larger. We are also seeing incremental movement to higher elevations for each lizard species. For those high elevation pioneers, rather than adapting to hotter and drier conditions at lower elevations, these lizards will need to adapt to cold winters with months of below freezing temperatures even if the summers are within their existing temperature preferences.

The finches and lizards are giving us some time to get things right, and at the same time, at what are now the lowest elevations, showing us just how bleak our future could be.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.