A science fiction novel where an experimenting scientist, an old man, studying evolution, picked a girl and her boyfriend as subjects and secretly injects them, the girl evolved to be most intelligent (Class 1 intelligence), the boy devolved and regressed to a monkey. Vampire like advanced intelligence humanoids travelling from world to world came to Earth becoming a problem to the human race. One of these, a woman, was so starved she consumed a lot of humans' life energy because of former starvation and fear of going hungry again. When they eat a person there will be a blue white flash, flashing from the human to the advanced humanoid consuming.
A black journalist also developed in intelligence to become a Class 1 intelligence and checked the liberty of the vampire advanced intelligence humanoids.
At the end of the novel the over gorged 'vampire' being attempted to eat/take the life energy of the black journalist turned advanced intelligence and the blue white flash reversed as she lost her life energy to the being assumed to be human! She barely got her life saved after she slumped when her mate returned to find her fainted and he had to kiss her to flash some life back into her.
The dramatic scenes were varied and compelling, example when the girl being injected the evolution serum was undergoing the evolution changes and she had to sleep it off in a dusty room floor somewhere, she woke up with her body all covered in dust and realized the enhanced and advanced level of intelligent thought and perception she was capable of.
I think I read this interesting SciFi novel/book in early or mid eighties, 1984? Maybe it was written in late 1970s? Would love to read it again as I enjoyed it like I did Miss Shumway Waves a Wand, which I read about the same time and which I just re-read.