A letter written by George Washington to his mother about the latest developments in the Revolutionary war. is it a primary or secondary source?

Natural selection involves changes in the genetic makeup of a population over a period of time. the random change of dna from parent to offspring, called mutations, can produce variations in offspring. some mutations can be , while others can be harmful. in this experiment, students modeled random mutations. data was collected to determine if the mutations were or harmful when trying to collect and eat food.