I disagree.  I think many non-genetic factors affect &quot;intelligence&quot;, even on a day to day basis.  I myself have been able to detect noticeable and substantial variations in my faculties over these time frames.  Brain-training exercises might not increase intelligence (I don&#x27;t know) but there was a period of time when I found them valuable as a evaluation tool- I would do some sudoku puzzles every morning to &quot;test&quot; my myself that day (a very specific and narrow definition of intelligence).  Even between days where I didn&#x27;t feel noticeably different, I would still sometimes see a large difference in average time to solving the puzzles ( ie. as much as ~1min 30sec vs. ~5min! ).<p>I found the &quot;fast&quot; days where usually better spent focusing on specific, hard problems that had been vexing me, whereas the &quot;slow&quot; days might be better spent multitasking, organizing and communicating with peers to explore new ideas.  I never quite pinned down how to influence these variations... though I suspect it was a combination of sleep, stress, caffeine, etc.   In the end, I just roll with it.  I haven&#x27;t done the daily testing in a while, but I still try to be hyper-aware of which &quot;mode&quot; I might be in.