The elements to answer your question are contained in previous messages. You give me opportunity for putting them together and I thank you for this. My model works as follows:
1
God created Humanity in His Image by endowing human-like animals with capacity to freely love Him, which as a consequence includes also the possibility of rejecting Him and sinning.
This creation happened in several moments:
God first created a little population of Image-Bearers. This corresponds to the creation referred to in Genesis 1:26-28 and 2:22-24. Thus, at this moment only a little percentage of the whole population of human-like animals (individuals of Homo sapiens) becomes Image-Bearers. The descendants of these Image-Bearers were Image-Bearers as well.
Thereafter, and in addition to these descendants, God still created other Image-Bearers from human-like animals, according to Genesis 6:1-4, so that the percentage of Image-Bearers increased.
Finally, at a later moment God made the resting human-like animals (a large population living all over the world) to Image-Bearers. This corresponds to the God’s Decree referred to in Genesis 9:6. Since this moment and till the end of times all human-like animals on earth are Image-Bearers. In fact it is Humanity that prompts us to define the species “modern humans”.
2
The transmission of “humanity” (i.e.: the quality of Being Image-Bearer) to the next generations happens at the instant when God creates a spiritual principle (“soul”) to animate a piece of “flesh” (a fertilized egg or equivalent cell consisting in biological stuff originating through evolution) and a human personal body appears.
Accordingly, “humanity” (the quality of Being Image-Bearer) emerges at the very moment of the generation of each new person, and thus is transmitted through both by physical means (including DNA) and Godly ones.
The transformation of adult human-like animals into Image-Bearers is a purely spiritual transformation and happens without any observable genetic or anatomical change. The signs of such a transformation are rather achievements of Humanity demonstrating sense of law and accountability as we found at the dawn of civilizations.
Similarly the emergence of a human being in God’s image at the moment of fertilization or equivalent process does not involve any physical change other than the usual growth through cell cleavage and metabolism.
An important point in this respect is that Humanity as community of Image-Bearers is called to live according to moral rules and law, mainly the “Golden Rule”. And at the moment of implement this rule and assign rights the “observable Golden Basis” is the specific human body, the sign for belonging to Humanity. A human individual shares the status of a person, and personhood is inseparably united to Humanity. This principle means that the fundamental rights of a person cannot be established by belonging to a subgroup of humankind, be it by race, religion, stage of development, nation, or political class. Neither can one reduce the rights of humankind to the rights of the present-day generation. [see M&M, 16-1 (2013) 85]
Please let me know whether I have answered your queries or you would like further clarifications.