The Rakshasa story begins with the Rakshasas Heti and Praheti.
Heti, Praheti = 100% Rakshasa.
Heti marries Bhaya, sister of Yama/Kaal. They have a son, Vidyutkesa.
Vidyutkesa = 50% Rakshasa + 50% Deva
Vidyutkesa was married to Salakatankata, daughter of Surya and Sandhya. They have a son, Sukesa.
Sukesa = 25% Rakshasa + 75% Deva.
Sukesa was married to Devavati, daughter of a Gandharva named Gramani. They have 3 sons: Mali, Sumali and Malyavan.
Mali, Sumali, Malyavan = 12.5% Rakshasa + 37.5% Deva + 50% Gandharva.
The 3 brothers were married to the 3 daughters of a Gandharva woman named Narmada. They have many children. I won't list them all because they are not all important for this analysis. Of Sumali's 10 sons and 4 daughters, the one important for this discussion is obviously Kaikesi.
Kaikesi = 6.25% Rakshasa + 18.75% Deva + 75% Gandharva.
Kaikesi married Rishi Vishrava. They had several children of whom the eldest and most important one is Ravana.
So, finally, Ravana = 3.125% Rakshasa + 9.375% Deva + 37.5% Gandharva + 50% Brahmana.
So, in terms of genetics, Ravana was actually only 3.125% Rakshasa! 😆 Not only that, he also had genetic relations to Devas and Gandharvas besides the obvious Brahmana connection. 😊