Environmental conditions could be said to be the occasions of change in the activities of the organism; but the decisive thrust of evolutionary change was internal process of a sort. (religion-online.org)
Check for rashes or spots on your baby's body and beware of changes in activity level and mood. (apartmentbaby.com)
A relatively new area is to look at the developing nervous system by scanning infants, children, and adults at rest, to chart changes in activity patterns as the brain matures. (sciencemag.org)