I presume that lowness here means that the several parts of the organisation have been but little specialised for particular functions; and as long as the same part has to perform diversified work, we can perhaps see why it should remain variable, that is, why natural selection should not have preserved or rejected each little deviation of form so carefully as when the part has to serve for some one special purpose. In the same way that a knife which has to cut all sorts of things may be of almost any shape; whilst a tool for some particular purpose must be of some particular shape.
Suposatzen dut hemen behe-mailan egoteak, organismoaren atal ezberdinak funtzio partikularretarako gutxi espezialdurik egotea esan nahi duela; eta, atal berak lan ezberdinak egin behar dituenean, agian uler genezake zergatik iraun behar duen aldagarri, hau da, zergatik hautespen naturalak ez duen kontserbatu edo arbuiatzen forma-aldakuntza txiki bakoitza, atalak helburu berezi bat bete behar duenean bezainbateko arduraz. Edozer ebakitzeko den ganibeta ia edozein tankeratakoa izan daitekeen moduan, xede partikular baterako den lanabesak, ostera, tankera partikularra eduki behar du.