Other treatments have posited biological invasions Invasion of the Body Snatchers, or cultural invasion The Uplift Wars[?] by David Brin.
... 3.32. In the town the population is spread out with 24.7% under the age of 18, 7.4% from 18 to 24, 32.6% from 25 to 44, 23.2% from 45 to 64, and 12.2% who are 65 years of ...