It may even be doubted whether the varieties of any of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock (crossing being prevented) could be kept up for half-a-dozen generations, if they were allowed to struggle together, in the same manner as beings in a state of nature, and if the seed or young were not annually preserved in due proportion.
Dudatan jar liteke, halaber, etxe-landare eta animali aldaki batzuek indar, aztura eta osaera berdin-berdina ote luketen, dozenerdi belaunalditan multzo nahasi baten hasierako proportzioak (gurutzaketa ekidinik) mantentzeko gai izateko modukoa, baldin natur egoerako izakiak bezala elkarrekin borrokan egiten utziko balitzaie, eta haziak edo kumeak urtero proportzio egokian zaindu ezean.