No one knows why willpower can grow with practice but it must reflect some biological change in the brain.
The evolutionary biologist Stephen Jay Gould put it like this: "There's been no biological change in humans in 40,000 or 50,000 years.
That is 'selection.' " Later, he would get to the touchier part, about how the minute changes in organisms that drive biological change arise spontaneously, without direction.
The natural environment was rapidly replaced by an artificial one, composed of new chemical and physical agents, many of which possessed powerful capacities for inducing biological change.
Is everything we find in an animal an adaptation, or does simple genetic drift and accident account for some part of biological change?
Shoemaker's studies of meteorites and astrogeology changed the way people did planetary science and helped open the path for big-event theories of biological change, most notably the theory of species extinction associated with the Chicxulub crater.
Professor Boris Worm, who co-authored the study, said in shock: "I've been trying to think of a biological change that's bigger than this and I can't think of one".
On a bright, blue-skied day in April or May, it can feel as if you're standing in a river of biological change, whether you're in Central Park or out in the country.
It was Spencer's wide-ranging attempts to apply the concept of organic evolution to society, rather than Darwin's more cautious and narrow theories of biological change, that caught fire in the competitive, by-your-own bootstraps atmosphere of post-Civil War America.
Biological change questions used in closed-ended instrument.
Nonetheless, visitors continued to use mixed reasoning (endorsing all three reasoning patterns) in explaining biological change.
