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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.

The book is Supermind by A. E. van Vogt.

It's a fixup novel that is really three separate stories. The story you remember about the scientist and the girl and boy is Research Alpha. This story forms the last third of the book, and it has previously been discussed in this question.

The book is built from two stories about the vampires, The Proxy Intelligence and Asylum. The vampire like beings are the Dreeghs who absorb people's life force (not blood), and as you recall there is a blue flash as they do so. They appear in the first two parts of the book.

The unifying idea behind the book is that of the Great Galactics, who are beings so advanced that they can alter reality itself just by the power of their minds. The story Asylum was originally about the Great Galactic saving the Earth from the Dreeghs, but in Supermind it is recast as part of the Great Galactics plans to cure the Dreeghs of their vampirism.

The idea behind the short story Research Alpha is that the Great Galactics have injected some of their own genes into the races they encounter, but during human evolution these genes have become unevenly distributed. The scientist Dr Gloge is working on a project called Point Omega Stimulation which aims to enhance human evolution. Gloge secretly injects two people, Barbara Ellington and Vincent Strather with the Omega serum. Barbara possesses an unusually favourable package of Great Galactic genes and the serum enhances these so she basically turns into a Great Galactic. In Vincent the serum enhances other genes and he becomes a goblin like figure - it's implied but not stated explicitly that he's become mentally subnormal.