It would go through all the processes of the physical and mental evolution of humanity until it reached the highest of human attributes--the ability to think, and therefore to reason.

In other words, from a merely living organism it would, in the old Scriptural language, have become a living soul.

That is, obviously, what the words in Genesis were really intended to mean.
It would then become capable of development, of proceeding from the partly-known to the more fully known, until, granted perfect physical and mental health, it reached what are generally called the limits of human knowledge." The Professor's thumb and finger went up to his chin again.

He walked another two or three hundred yards in silence; then he recommenced his spoken argument with himself: "Limits of human knowledge?
Yes, that sounds all very well in ordinary language, but are there any?
Who was it said that a man trying to reach those limits was like the child who saw a rainbow for the first time, and started out to find the place where it rested?
The simile is not bad, not by any means.

Just in the same way, we try to imagine the limits of time and space, and we can't do it.