Dont worry nothing to do with Biological terminology here. According to what I see today, it is more of a psychological phenomena in society – where, one keeps on growing his/her thinking skills and keeps on enhancing his/her own area of Expertise.

More you think, More you learn
More you learn, More you know,
More you know, More you command
More you command , More you earn
More you earn, Better you survive (live) …

So, Enable your Thinking Gland!!!