Thus to adapt a species to new habits of life, many co-ordinated modifications are almost indispensable, and it may often have happened that the requisite parts did not vary in the right manner or to the right degree.
Horrela, espezie bat bizi-baldintza berrietara egokitzeko, ia ezinbestekoa da eraldaketa koordinatu asko izatea, eta maiz gerta zitekeen beharrezko atalak behar zen moduan edo behar zen mailaraino aldatu ez izana.