1 Phenotypes and genotypes
Since the invention of DNA sequencers in the late 20th century, measuring very small differences between the genes of different organisms has become much easier and more precise than quantifying phenotypic variation. Synonymous mutations and changes to introns are examples of genetic changes that have no consequences for the phenotype. Natural selection acts only on phenotypes, so the relationship between genotypic changes and phenotype is clearly very important to understanding evolution. Discoveries about how and when genes act during the growth and development of animals, the consequences of developmental processes for adult structure, and observations on the relationship between behaviour, physiology and anatomy, have led to new insight into the origin and the evolution of phenotypic traits.