Made in the Image and Likeness
Genesis 1: 26 states, “Then God said, 'Let us make humankind in our image, according to our likeness.'” Since God is ultimately free, humanity must also have freedom. God placed the Tree of Knowledge of Good and Evil within the garden in order that He protect humanity's freedom — to choose to follow God or to turn away from God. Even in humanity's fallen state, God provides for our freedom. The Devil is allowed to work in the world so that humanity may continue to have the freedom to accept or reject God. For God to abolish evil in the fallen world would be to destroy our freedom to choose evil, and thus God would destroy the image and likeness of God within humanity — something He declared very good (Gen 1:31). To destroy the image and likeness in humanity would make God a coercive and evil being. He has revealed to us His goodness and His longsuffering love by sending His Only-Begotten Son to take on our humanity, so that by willingly going to the cross and to the tomb, Christ might raise us up with Him in resurrection and to ascend to sit at the right hand of the Father. Our very nature, in the person of Jesus Christ, can now participate in the very being of God. Our choice to follow God allows us to tap into the power of the Holy Spirit, which allows us to overcome anything the Devil might throw at us.
To insist upon a scientific and genetic understanding of humanity severely limits what it means to be human. Historically these limitations have been used as excuses for racism, slavery, murder and genocide. The human person is not determined by DNA. We know this, because identical twins with identical DNA are unique and unrepeatable human persons. They may look alike, they may share many of the same interests, but each one is their own person. If DNA were determinative of the human person, then a twin could murder their identical sibling with no consequences, because they would be the same person.
In terms of the Planar Cosmology of D&D, the term “humanity” must be understood in context of the image and likeness, and not race (another word for DNA and genes). Even if we don't fully embrace the concept of the image and likeness, in a multiverse where magic exists, our scientific understanding of evolution becomes irrelevant. Any sentient being with the freedom to choose should be considered “human” in terms of their relationship with God. Elves, Dwarves, Halflings, Orcs, Goblins, Celestials, Abyssals, etc. are all created in the image and likeness of God.
In my own world-building, the origin of all these various races is in the Fall. Influenced by magic and the various conditions found in the environments of all the various planes, each race came into being from their human progenitors. Regardless of origin, however, no one race is inherently better than any other in the eyes of God, because they are all made in His image and likeness. When Christ came, He did so in order to save all of humanity and all of creation. That means every sentient race in the multiverse, and the entire multiverse itself.