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Of course, the presence of chimpanzee genes, or Neanderthal genes, isn’t the half of it. There’s also that viral DNA—including syncytin-2, a gene co-opted from a retrovirus, repurposed to enable human pregnancy. The fact that endogenous retroviruses constitute 8 percent of the human genome certainly complicates our sense of Homo sapiens as a species of primate.
other aspects of our physiology, some hundred trillion bacterial cells, representing thousands of different bacterial “species.” And so does the realization that within every one of our human cells reside captured bacteria, long since transmogrified into mitochondria, without which we couldn’t exist.
Portuguese man-o’-war is not. It too, like an ant hill or a termite community, is a colony of individual creatures (in this case, small multicellular forms known as zooids), aggregated for a common purpose and variously performing specialized functions. Likewise that very strange thing known as a cellular slime mold, which during one phase of its existence looks and behaves like a garden slug, but at another phase reveals itself to be a fine-tuned team of individual amoebae.
aspen trees in a grove. They may look like individuals, but, in fact, aspens grow as clonal eruptions from underground rootstock, all interconnected, all sharing the same genome, sometimes including hundreds of trees across a wide area. The grove is the individual. By one accounting, the largest organism on Earth may be a single aspen clone composed of thousands of trees spread across more than a hundred acres in Utah’s Fishlake National Forest. It weighs about thirteen million pounds, this aspen individual, and is roughly eighty thousand years old.
in his view, considering the past four billion years, there were three: Bacteria, Eukarya, Archaea. Those three diverged from the last universal common ancestor of all life as we know it—life on Earth, life using one common genetic code, life that began with the RNA-world and then yielded cells and passed through the Darwinian Threshold and became very complex.
