Regular readers of this blog will know that I've pointed out on several occasions that the late Julian Simon's principal message was that the human brain is the "ultimate resource." Here are two graphs that tend to illustrate that point. The first is a graph is of the annual world population growth rate from 1800 to 2005 (and extrapolated to 2025).
The second is a graph of world per-capita GDP growth rates from 1900 to 2000 (from Brad DeLong's paper on GDP from 1 million BC to present). The growth rate then has five predictions up to the year 2100.
The way I think these two graphs show the importance of human brains is that both the human population growth rate and the world per-capita GDP growth rate rose from circa 1940 to 1970, peaked circa 1970, and then declined from 1970 to 2000.
Arnold Kling and I both predict that the per-capita GDP growth rate will increase again (in fact, far exceeding any historical rates) as computer brains become much more plentiful.