Humans have noted, in mapping human genes, that a number of DNA links that are dormant. The number casually noted by humans in no way reflect the vast span of dormant portions in the human physiology. Think merely of the many human brains, in where there are frontal lobes where the conscious resides and a rear brain where the subconscious lies that in essence do not speak to each other or are reluctant to speak to each other. How would this evolve in normal evolution? This was forced upon humankind. There are many, many portions of the human body which are remnants or leftovers, unused. The appendix is one. Your DNA is rift with genes which if allowed to express would horrify and surprise humans.
The hybrids that we are creating will have many dormant genes in them. A clear example is the violent nature of humans, which evolved to allow humans to live on a planet where large predators exist. Were it not for your violent nature, you would not have survived past a couple of generations. We suppress that violent nature in our hybrids, yet those genes exist. Just as you would be horrified to develop tentacles, or a gaping mouth in the center of your stomach, with smacking lips ready to take in whatever might float by, in the future the new hybrids would be horrified to find their dormant violent nature expressing from hidden genes.