surprises from science -- 4/28/21
Today's selection -- from The Tangled Tree by David Quammen. We are not precisely who we thought we were:
"[From the study of] molecular phylogenetics … there have come three big surprises about who we are -- we multicellular animals, more particularly we humans -- and what we are, and how life on our planet has evolved.
"One of those three surprises involves an anomalous form of creature, a whole category of life, previously unsuspected and now known as the archaea. (Their name gets uppercased when used as a formal taxonomic category: Archaea.) Another is a mode of hereditary change that was also unsuspected, now called horizontal gene transfer. The third is a revelation, or anyway a strong likelihood, about our own deepest ancestry. We ourselves -- we humans -- probably come from creatures that, as recently as forty years ago, were unknown to exist.
"The discovery and identification of the archaea, which had long been mistaken for subgroups of bacteria, revealed that present-day life at the microbial scale is very different from what science had previously depicted, and that the early history of life was very different too. The recognition of horizontal gene transfer (HGT, in the alphabet soup of the experts) as a widespread phenomenon has overturned the traditional certitude that genes flow only vertically, from parents to offspring, and can't be traded sideways across species boundaries. The latest news on archaea is that all animals, all plants, all fungi, and all other complex creatures composed of cells bearing DNA within nuclei -- that list includes us -- have descended from these odd, ancient microbes. Maybe. It's a little like learning, with a jolt, that your great-great-great-grandfather came not from Lithuania but from Mars.
"Taken together, these three surprises raise deep new uncertainties and carry big implications about human identity, human individuality, human health. We are not precisely who we thought we were. We are composite creatures, and our ancestry seems to arise from a dark zone of the living world, a group of creatures about which science, until recent decades, was ignorant. Evolution is trickier, far more intricate, than we had realized. The tree of life is more tangled. Genes don't move just vertically. They can also pass laterally across species boundaries, across wider gaps, even between different kingdoms of life, and some have come sideways into our own lineage -- the primate lineage -- from unsuspected, nonprimate sources. It's the genetic equivalent of a blood transfusion or (different metaphor, preferred by some scientists) an infection that transforms identity. 'Infective heredity.'...
"And meanwhile, speaking of infection: another result of this sideways gene movement involves the global medical challenge of antibiotic-resistant bacteria, a quiet crisis destined to become noisier. Dangerous bugs such as MRSA (methicillin-resistant Staphylococcus aureus, which kills more than eleven thousand people annually in the United States and many more thousands around the world) can abruptly acquire whole kits of drug-resistance genes, from entirely different kinds of bacteria, by horizontal gene transfer. That's why the problem of multiple-drug-resistant superbugs -- unkillable bacteria -- has spread around the world so quickly. By such revelations, both practical and profound, we're suddenly challenged to adjust our basic understandings of who we humans are, what has gone into the making of us, and how the living world works."
Reprinted by permission of Simon & Schuster, Inc. All rights reserved.