The logic

Should "Because the force of spinning pulls larger things down first" be "Because the force of spinning pulls ligher things up first"? Because when spinning force is used, it would pull all things in a culture tube up; the lighter ones go up first; only when the force stops, the gravity of the Earth pulls the larger things down first.

Context:

Just ask William Ratcliff and his colleagues at the University of Minnesota. In a PNAS paper published online this week, they show how multicellular yeast can arise in less than two months in the lab. To achieve this leap, they took brewer’s yeast – a common, single celled lab organism – and grew them in a liquid medium. Once a day, they gently spun the yeast in the culture, starting the next batch with whichever cells ended up at the bottom of the tube. Because the force of spinning pulls larger things down first, clumps of cells were more likely to be at the bottom than single ones, thus setting up a strong selective pressure for multicellularity.

More:

http://blogs.scientificamerican.com/science-sushi/2012/01/16/evolution-the-rise-of-complexity/