Similar body plans suggest common origins. Analogy - body parts with similar function , without regard to origin. Similar functions but different structures suggest different origins. Organic evolution refers to changes in populations. It is influenced by both genetics and environment.
All organisms go through changes in appearance during their lifespan.
This is called ontogeny . In each of these examples, no genetic change is involved. The genotype remains the same, but the phenotype varies dramatically . In other words, the series of changes that an individual goes through during the course of its lifetime mimics the stages that the organism has passed through during evolution. The early stages of descendants resemble the adult stages of the ancestors.