Even with animals which unite for each birth, and which do not propagate rapidly, we must not assume that free intercrossing would always eliminate the effects of natural selection; for I can bring forward a considerable body of facts showing that within the same area two varieties of the same animal may long remain distinct, from haunting different stations, from breeding at slightly different seasons, or from the individuals of each variety preferring to pair together.
Kume bakoitzerako batu beharra duten eta azkar ugaltzen ez diren animalien artean ere, ez dugu onartu behar gurutzaketa libreak hautespen naturalaren ondorenak beti galarazi behar dituenik; honetan, egitate mordo ederra aurkez dezaket herrialde berean animalia beraren bi aldakik ezberdin izaten luzaro segi dezaketela frogatzeko, leku diferenteetan dabiltzalako, umeketa sasoi ezberdintsuetan dutelako, edo aldaki bakoitzeko banakoek elkar estali nahiago dutelako.