Nature has taken millions of years for coming to the stage of so called present human being .
This statement does not really mean very much to me. I could have accepted 'nature has taken billions of years', or 'nature has taken tens of thousands of years', but 'millions of years' seems to be the wrong order of magnitude either way.
Life arose on the Earth (or drifted in from interstellar space) around four billion years ago. So it has taken nature billions of years to produce
homo sapiens.
Homo sapiens evolved from his predecessor around 150,000 to 200,000 years ago.
I am also intrigued by your phrase
'so called present' human being. What on Earth does that mean? Who is doing the calling?
And I have an underlying unease in your use of the word
stage that you are thinking of evolution as having a
direction, of man being the
pinnacle of evolution: that kind of thing. Please tell me it isn't so.
What is the most likely immediate development after the human being?
More of the same.
Intelligence will likely increase: The world has been made sufficiently complex that high intelligence is required to fill in tax forms and operate the remote controls.
But once we start tailoring our own genetic structure, then almost anything is possible.