Some evidence suggests that sympatric speciation is occurring . Hawthorn flies mature later in the season and take longer to mature than apple flies ; and there is little evidence of interbreeding ( researchers have documented a 4-6 % hybridization rate ) . Some evidence , such as the fact that six out of thirteen allozyme loci are different , that hawthorn flies mature later in the season and take longer to mature than apple flies ; and that there is little evidence of interbreeding ( researchers have documented a 4-6 % hybridization rate ) suggests that sympatric speciation is occurring .