It is commonly assumed, perhaps from monstrosities affecting the embryo at a very early period, that slight variations or individual differences necessarily appear at an equally early period.
Guztiek onartzen dute eskuarki, enbrioiari hasiera-hasierako fasean gertatzen zaizkion munstrotasunengatik beharbada, banakoaren ezberdintasun edo aldakuntza arinak nahitaez fase goiztiar berdintsuan agertzen direla.