3.1a The processes of sexual reproduction and mutation have given rise to a variety of
traits within a species.
3.1b Changes in environmental conditions can affect the survival of individual organ-
isms with a particular trait. Small differences between parents and offspring can accu-
mulate in successive generations so that descendants are very different from their ances-
tors. Individual organisms with certain traits are more likely to survive and have
offspring than individuals without those traits.
3.1c Human activities such as selective breeding and advances in genetic engineering
may affect the variations of species.