Climbing around the tree of life

/

Quercus rubra

I’m systematically studying systematics—how all living things on Earth are related—so herewith begins a series inspired by exploring the tree of life.

Yes, I claim to be approaching this exploration with a system, but it might be useful to know that my systems rarely involve sticking to recipes. Rather than gearing up to ascend the tree in an orderly fashion, expect to backtrack and change directions, jump squirrel-like to distant branches, and frequently fall off. The real plan is to spend much more time on tangents than actual taxonomy.

But we know the tree is there; we can come back to it. It’s a guidepost, a framework. It keeps contained and organized a vast realm of biological inquiry that would otherwise be completely overwhelming. It’s a lot like my 3,400-item hierarchical to-do list, which I edit and reshuffle ad nauseam while only occasionally completing an actual task. As mighty as my Workflowy list undoubtedly is, the tree of life has it beat with something like 1.8 million species described and 10 million estimated—or maybe 3 trillion, if that makes a difference—not counting untold oodles of extinct ones.

Something I find exciting about this tree is that it’s a new way to orient oneself as a naturalist, despite the fact that the biodiversity it encapsulates is 4 billion years in the making. We may have been identifying and categorizing living things for the entirety of human existence, but we have only had the concept of an evolutionary tree since around the time of Darwin. And the tree itself has evolved dramatically as taxonomists hone the ability to compare organisms at a molecular level. Only within my lifetime has it grown into its current triadic shape, dividing life on earth into three major superkingdoms or domains or whatever you want to call them: Eubacteria, Archaea, and Eukarya. (I’ll start with Eubacteria in the next post, if I stick to the recipe, at least.)

Tamiasciurus hudsonicus

This very moment, phylogeneticists in our midst are pooling information from 4,185 studies and 148,876 species (and counting) in the effort to refine not only the branching patterns of the tree but also the timing of those splits between lineages, some of which diverged hundreds of millions of years ago. Regardless of how accurate all of that is at this point, I like having such a tree to think about. It lends an expansive dimension of time to the landscapes and living things I see spread out over global space. It gives me a sense of the family relationships that intersect with the ecological ones I can observe myself. It’s a Y axis to my X axis of wandering around outside sketching stuff. Lest we fall out of the tree prematurely, I’ll stop here.

Islands of domestication

/

I drew this to illustrate another Forum paper for the scientific journal Oikos. Here is a summary of the study, “Insularity and early domestication: anthropogenic ecosystems as habitat islands” (by Robert N. Spengler III):

Maybe humans take too much credit for domesticating plants and animals. This Forum paper argues that the human-friendly qualities of our pets, livestock, and crops could have arisen without selective breeding or other human-centric mechanisms that are usually assumed. Instead, it explores an ecological mechanism: the island syndrome.

Think of early farms and villages as islands. The author draws parallels between the processes of domestication and island evolution, suggesting that the same ecological forces may be responsible for both. Both island plants and cultivated crops tend to have bigger and less dispersible seeds than their ancestors. Animals on islands and in human habitats can lose flight ability, fear responses, and patches of pigmentation, among other changes.

Why such parallel patterns of evolution? It could be that when plants and animals find their way to islands or other insular habitats—ranging from early villages to modern cities—they are released from predation and competition pressures. Domestication scholars and island biogeographers would benefit from comparing notes, the author concludes.