Heredity refers to the similarity between parents and children. Variation refers to the difference between parents and children. The phrase "one mother gives birth to nine children, even ten mothers" means that there are differences among different children, thus embodying the universality of variation. The sentence "As you sow, you reap" means that the offspring of beans are beans and the offspring of melons are melons, which means that parents and children have the same characteristics, thus reflecting the genetic phenomenon of organisms. Some variations are caused by changes in genetic material, while others are caused by environmental factors during biological development. Heredity and variation are achieved through reproduction and development.

So, the answer is: heredity and variation; Reproduction and development