The hybrids were created when unseen aliens sent SETI a message explaining how to combine human and alien DNA. (Ignoring the scientific illiteracy and contradictions in the films) Under the constraints of real science, how could an engineered alien-human hybrid organism approximate the traits of the hybrids in the films?
These traits, off the top of my head, include:
- accelerated growth and aging: Sil grew to adulthood in under a month, Miranda was dying of old age after a few years of life.
- shape shifting: the hybrids look like Giger monsters with claws and spines and tentacles but may assume an externally human appearance.
- excel at observational learning: Sil learned to speak conversational English in a few days, Sara and Miranda could instantly read books in a few seconds.
- sense genetic abnormalities in potential partners: Sil could determine a man had type 1 diabetes, Eve could determine a man was a carrier for sickle cell anemia, Miranda could determine another hybrid was sterile.
- heightened and unusual senses: Sil in the novel mentally perceived toxic gases, good smells and pheromone signals as colors.
EDIT: additional traits after some researching:
- genetic message in a bottle: Sil would experience dreams that included subliminal messages from whoever provided the alien DNA that impelled her to reproduce, Eve broke out of containment to seek another hybrid partner after learning of his presence, Miranda experienced psychotic episodes as she began dying of old age and then became murderously horny after receiving stem cells to reverse her aging.
- no innate conscience: Sil was raised in a glass box with little human contact and killed anyone who got in her way, Eve was taught morality and attempted to stop a mass murdering psychopath, Sara was taught morality and refrained from killing except when under sexual assault, Miranda was taught morality and only committed murder while experiencing abnormal psychotic episodes.