or by having adapted them during past periods of time: the adaptations being aided in many cases by the increased use or disuse of parts, being affected by the direct action of external conditions of life, and subjected in all cases to the several laws of growth and variation.
Ihardun ere, hautespen naturalak, edo izaki bakoitzaren atal aldakorrak haien bizi-baldintza organiko eta ezorganikoetara gaur egun moldatuz, edo lehenagoko garaietan moldatu izanaz iharduten du; moldaerok, berriz, kasu askotan erabilera edo erabilerarik ez hazkorraren laguntza hartzen dute, baita kanpoko bizi-baldintzen eragina ere, eta hazkunde eta aldakuntza legeen pean daude.