Grow fast, learn slow

Professor Pat Monaghan of Glasgow University, said: “ If environmental conditions improve for animals that have previously experienced a poor quality diet, their growth can accelerate to catch up in body size. We have found that this very rapid growth can carry long term costs – in our study on birds the greater the growth spurt in the chick, the poorer the learning performance of the adult.”

The findings of this research, funded by the Natural Environment Research Council, appear to be common across other species. Studies of humans and early nutrition have also found that low birth weight babies who grow quickly when fed an enriched diet have a similarly lower performance when tested at nine months compared with babies given a normal diet. Unlike the finches ‘though, this effect seems not to be so long lasting in humans.

In the zebra finches study, the scientists provided siblings with unlimited amounts of different quality food for a short period after hatching. Those that got the lower quality diet, which had less protein and vitamins, were then switched to the normal food. To test the long-term effect on learning abilities, the scientists gave all the birds a simple learning task involving finding food behind colour screens once they reached adulthood. Although all the birds eventually learned the task, how fast they did so was related to the rate of compensatory growth they had undergone as chicks. Birds that had grown fastest when switched to the normal diet were slowest to learn the task

The results suggest that accelerating growth can have long lasting negative consequences for learning ability. What is not clear at this point is whether the learning defects stem from behavioural, hormonal or neural changes. It is possible that resources normally dedicated to these pathways are diverted to support the accelerated growth. But in the harsh competitive world of nature, being big may be more important than being bright.