I found the following statement on Richard Dawkins book The Selfish Gene (1989):
"... there are some ten thousand million neurones in the human brain: you could pack only a few hundred transistors into a skull."
Is this statement still true today? Thanks.
It wasn't even true back then. Well, maybe that's why Dawkins is a biologist and not an engineer. :-)
Today's processors pack billions of transistors on a die a few square cm in area and less than a mm high. There would fit hundreds of them in a skull, maybe \$10^{12}\$ transistors.
Even if you look at discrete transistors there would fit more than just a few hundred. I guess SOT-23 already existed in 1989, and then you would get \$10^5\$-\$10^6\$ of them in a skull.
edit (2011-06-13)
I own a copy of The Selfish Gene, and was curious what Dawkins had in mind, so I looked into it. Her's more from that paragraph:
The basic unit of biological computers, the nerve cell or neurone, is really nothing like a transistor in its internal workings. Certainly the code in which neurones communicate with each other seems to be a little bit like the pulse codes of digital computers, but the individual neurone is a much more sophisticated data-processing unit than the transistor. Instead of just three connections with other components (sic), a single neurone may have tens of thousands. The neurone is slower than the transistor, but it has gone much further in the direction of miniaturization, a trend which has dominated the electronics industry over the past two decades. (The Selfish Gene, p.49)
Somebody must have told Dawkins that a transistor has 3 pins :-).
Anyway, he doesn't only compare the numbers of neurons (or neurones, BE?) to transistors, but also points out that the neuron is a lot more complex, partly because of its thousands of connections. My guesstimate is that you'd need \$10^5\$ to \$10^6\$ transistors to emulate one such neuron (maybe as an analog instead digital computer?). Which means that a skull stuffed with GPUs wouldn't still come close to the processing power of a brain.
And then there's the problem of all these connections. They're the real power, not just the large number of neurons. We don't have the technology to build such complex systems, and IMO won't for a long time. And then I'm not even talking about the dynamic nature of these connections: they can rearrange themselves, making new connections and breaking others.
To put all these AI suckers in perspective, take a look at our vision system. In a second we can process a stereoscopic image of \$10^8\$ pixels, create a virtual 3D model of the scene and identify objects in detail. Move half a meter to the right and you add lots of new data. There's still a long way to go...
Where neurons score over transistors and electronic devices is the vast number of connections they make to other neurons - 7,000 on average.
The 68K coincidentally had 68,000 transistors in it, and that chip was available in 1979. You could certainly fit several 68K dies in the same space as a brain, and thereby exceed "several hundred" by three orders of magnitude, with what would have been 10 year old technology at the time of the statement. Perhaps if you went with TO-92 packages, you might not quite get to 1,000 of them.
OTOH it should be pointed out that a decent model of a single neuron would probably involve more than a single transistor.
This is a misquotation! The Selfish Gene was not written in 1989. It was written in 1976!
What Richard Dawkins published in 1989 was the second edition of the book. Indeed, this second edition includes endnotes where he updated the data about transistors:
"...my remarks about [computers] have become [...] dated. [...] The number of transistor-equivalents that you could pack into a skull today must be up in the billions.".
Dawkins made his homework before writing about transistors, you didn't make yours before quoting him...
