Like a steady production line, not in bursts like punctuated equilibrium. This study does not take into account epigenetics, but relies on random mutation! Weird. the headline implies natural selection is active not passive. Also weird:-https://www.quantamagazine.org/20150505-a-surprise-for-evolution-in-giant-tree-of-life/-"This controversial proposal stems from efforts by Hedges and collaborators to build the world's most comprehensive tree of life — a chart plotting the connections among 50,000 species of Earth's vast menagerie. Their analysis suggests that speciation is essentially random. No matter what the life form — plant or animal, insect or mammal — it takes about 2 million years for a new species to form. Random genetic events, not natural selection, play the main role in speciation.-"One reason scientists are skeptical is that Hedges' clocklike pattern conflicts with the traditional picture of how evolution unfolds. “The classic view of evolution is that it happens in fits and starts,” Benton said. A change in the environment, such as a rise in temperatures after an ice age, might spark a burst of speciation as organisms adapt to their new surroundings. Alternatively, a single remarkable adaptation such as flight in the ancestors of birds or hair in mammals might trigger a massive expansion of animals with those characteristics.-"Hedges argues that while such bursts do occur, the vast majority of speciation is more prosaic and evenly timed. To start, two populations become separated, driven apart by geography or other factors. New species emerge every 2 million years, on average, in a metronomic rhythm tapped out by the random nature of genetic mutations. He likens the process to radioactive decay. It's impossible to predict when an individual radioactive nucleus will decay, but a clump of many atoms will decay at a highly predictable rate known as the material's half-life. Similarly, mutations strike the genome randomly, but over a long enough time the accumulation of mutations follows a pattern. “There is a kind of speciation clock ticking along,” Hedges said."-*****-"But Hedges contends that speciation and adaptation are two distinct processes, each proceeding along its own path. (A team led by Mark Pagel, an evolutionary biologist at the University of Reading in England, has made a similar proposal, though for different reasons.) According to Hedges' model, after about 2 million years the two groups of birds accrued so many random genetic differences that they became incompatible. It wasn't adaptive mutations that made it impossible for the birds to intermingle, but rather the accumulation of enough mutations overall, most of them neutral ones. Geographic isolation provided the necessary spark for speciation, but simple time drove the process to its conclusion."-He doesn't think adaptation leads to speciation! Weird.