All life came into existence approx 3.5bya. From that point mutations introduced variation, a key requirement for evoluation
Comparative analysis techniques including DNA : DNA hybridisation and DNA sequencing can be used to determine the genetic distance between two species (or individuals)
Within a species alleles can be tracked through analysis of pedigrees and specific test crosses
More modern projects such as genome mapping and tech identifying SNPS can form the basis of GWAS which link genetic variations to specific phenotype
