Adaptation: Usually Something Done To Us

When John Endler first studied guppies in the streams of Venezuela and Trinidad in the 1970s, he noticed an intriguing pattern: guppies in the pools at the boom of waterfalls tended to be rather drab, while those in pools further upstream were eye-catchingly gaudy. Endler suspected the likely cause of the difference: while guppies were able to swim upstream past the waterfalls, the voracious guppy-eating pike cichlid could not, so the upper pools were cichlid-free. The drab guppies were camouflaged because they had evolved in a dangerous environment. The brightly-coloured ones lived in Guppy Eden, safely separated from the cichlids by a waterfall, and their colours were simply useful for attracting the attentions of other amorous guppies.

Endler decided to test his hypothesis in a more controlled environment, and filled a large greenhouse with ten guppy pools. Some pools had pebbles on the bottom, other pools were lined with finer gravel. Endler released the dangerous pike cichlids into some of each type of pool, and other pools were stocked either with gentler predators or no predators at all. Within fourteen months, ten generations, the guppy population adapted. In the dangerous pools, only the most boring guppies survived to breed; what is more, the guppy camouflage fitted the lining of the pool, with larger patterning in the pebble-floored pool and smaller patterning in the gravel-floored pool. In the safer pools, it was the brightly-spotted guppies that bred more -- female guppies, it seems, have a taste for colourful polka dot males.

Professor Endler's guppy experiments are modern classic in evolutionary biology, and a striking example of how a population adapts to a new problem, such as the appearance of a pike cichlid. Not only was the adaptation fast, it was sensitive to context: the right response to a pike cichlid depends on what sort of material the pool is lined with. It was a decentralised process, because no guppy planned the response. And it was driven by failure: some guppies were eaten, while others went on to produce future generations of well-adapted baby guppies.


Adapting is not necessarily something we do. It may well be something that is done to us. We may think of ourselves as Professor Endler, but we're actually the guppies. No individual guppy adapted, but some guppies avoided being eaten and some did not. [...]

So let's first acknowledge a crucial difference: individuals, unlike populations, can succeed without adapting. The guppy population evolved pebble-camouflage through trial and error, but no individual guppy did: each was born either with good-enough camouflage, or not.


Fortunately we [humans] have something that guppies do not: the ability to adapt as we go along.

-- Tim Harford

from "Adapt: Why Success Always Starts with Failure"

Quoted on Sat Feb 11th, 2012