Larger brains have been linked with weaker immune systems in a new study published in the Proceedings of the Royal Society B.
It is among the laws of nature that being endowed with one special ability will come with a cost — basically, we can’t have it all. This is so because resources have to be pooled to the different organs, and if one body part is receiving a considerable supply of energy, other organs will need to be restricted. This is why scientists have theorised that larger-brained animals will otherwise have reductions elsewhere. For instance, primates like humans having big brains have relatively small alimentary canals. Maybe, big brains whose performance will require much energy also imply weaker immune systems (which will also need considerable investment)?
The team of researchers who wanted to test this hypothesis analysed the Trindadian guppies; the guppy is commonly known as millionfish and rainbow fish. They had been artificially selected for large or small brains. Each of the fish ‘participant’ had an ‘implantation’ of scales obtained from another guppy. The grafting procedure was done to determine the extent of rejection response which would indicate the quality of an innate immune system.
The results unsurprisingly show that fish with larger brains displayed a less robust rejection response as opposed to those with smaller brains; the small-brained fish showed a significantly stronger rejection response than the large-brained ones.
Going one step further, testing the acquired immunity of the fish, they were made to go through another scale grafting procedure two weeks later. For the second grafting, all the fish had the same response, suggesting that big brains do not affect acquired immunity responses.
To conclude, large brains appear to be linked with lower innate immunity.
But, worry not, humans! The researchers explain that their findings do suggest that larger brains come with weaker immune systems. But, what is also true is that larger brains also mean more intelligence, thus allowing humans to make up for the disadvantage such that we can either change our environment to protect from infections or take to remedies when infected.