Importantly, evolution is not about optimization in the abstract; it is about optimization relative to other genetic variants within and across species. While we are evolving, so too are our enemies (like the influenza virus) and our friends (including the microbiomes in our guts). To a large extent, evolution is about preparing for the unknown, be

That, Losos said, leads to the idea of an entire way of life without species. What if there were no hard boundaries between one animal and another, just “a smear of variation”?