The Compendium of Caraka 4.3.17

4.3.17

yaccoktaṃ---yadi ca manuṣyo manuṣyaprabhavaḥ, kasmānna jaḍādibhyo jātāḥ pitṛsadṛśarūpā bhavantīti; tatrocyate---yasya yasya hyaṅgāvayavasya bīje bījabhāga upatapto bhavati, tasya tasyāṅgāvayavasya vikṛtirupajāyate, nopajāyate cānupatāpāt; tasmādubhayopapattirapyatra/

And as to what was said: 'If a human originates from a human, why are those born from the dull and the like not similar in form to their parents?' It is said in reply: whichever part of the seed representing an organ or limb is afflicted in the seed, a deformity arises in that organ or limb; and it does not arise when there is no affliction; therefore both possibilities are accounted for here.