Adults may resist scientific facts because of childhood experiences. Yale University psychologists note that before children can even speak, they develop common-sense assumptions about the physical world that can persist into adulthood and clash with scientific discoveries. For instance, because objects fall down if not held up, kids may have trouble accepting the world is round, reasoning that things on the other side should naturally fall off. Intuitive notions concerning psychology also lead children to see everything as designed for some reason—for example, a cloud's purpose might be to rain—which can lead to opposition to evolution. In reporting their work in the May 18 Science, the researchers also note that when both adults and kids obtain knowledge from others, they judge claims based on how much they trust the source of an assertion. It suggests that science will meet exaggerated resistance in societies where alternative views are championed by trustworthy authorities, such as political or religious figures.