Saturday 24 December 2011

No Limits to Intelligence

An article earlier in the year in Scientific American suggested that there may be inherent limits on human intelligence, far beyond those imposed by the process of birth.

One intriguing suggestion in the article is that functional specialisation in neuroanatomy may not be driven by algorithmic requirements (i.e. by partitioning the task being the “right way” to go about, for example, seeing), but by connectivity limitations: functions cluster together because it’s not possible to  maintain enough longer-distance connections. The article also pointed out that, by some measures at least, even across humans, intelligence is predicted by the speed of neural communication, controlled, roughly, by the number of neural links traversed by a signal: that long distance communication, when it is possible, is important.

The main point, however, of the article is that humans are unlikely to be able to evolve to get much more intelligent, but that social connections and technology, outside the brain, may have made that unimportant.

However, the evolutionary limit is a pretty specific thing: it’s a constraint on what a type of organism can become, given what it has been previously. For us as humans, it means where we could get to as a species,  given no
"non human" intermediate states, and large, but not astronomical, amounts of time.  But we are no longer constrained in the same ways. As a simple example, it seems likely that the maximisation of the size of the human birth canal is the result of a trade-off against the survival costs of birth earlier during brain growth. But that constraint is now released: infants can be safely born far earlier, after which their brains could grow as big as they like.

Many of the other constraints (transmission speed, neuron size, axon diameter) the article discusses could be also released if we needed them to be, since we no longer need to respect the path dependencies (e.g. we now use myelinated axons for rapid signalling, because we started with axons; but in the reachable future, we will almost certainly be able to engineer multiplexed metal paths, or even multiplexed optical paths (see the recent experiments on inducing lasing inside cells, under conditions that could probably be made to hold "naturally")). This would simultaneously reduce the limitations on wiring density (since theses “neoaxons” could be far thinner than the current  hundreds to thousands of nanometres ( IC transistors are around 20 nm), and increase transmission speed (by around 2million times).

Networking is also badly limited, as you have heard me say, by our IO  channel bandwidth. My guess is that advancement will come both by optimising networking and by reengineering brains, using both biology and non-biological techniques. Imagine, forSketch24613245 example, the architecture I’ve sketched at the right, in which a simplified brain, reduced to two sheets of neurons is provided with a laser optical interconnect instead of axons. The sheets in question (if wolfram alpha and I are correct) would be roughly 5 meters on a side. Assuming that they’re on two sides of a five metre cube, that gives an worst case interconnect delay of 58ns. The worst case delay in a brain, even if there were a directly connected myelinated axon, is more like 2ms. This one (somewhat ungainly – we are talking about putting your brain in a 5m cube) change provides a transmission speed up of about 35000 times.

In short, even for human-like intelligence, it isn’t clear that natural human evolution matters any more. It's certainly happening, but it's so slow that it won't have any appreciable effect compared with the much faster processes of brain augmentation that are now just beginning to occur. The same argument, on a faster timescale, is also why we (and our computer collaborators) are simply going to win against disease-causing organisms, within the next 50 years.