I am not pointing out anyone in particular as this appears to concern all of us. We are part of the genus Homo which has been around for about two million years. We split off from our common ancestor about 200,000 years ago when we became a species named Homo sapiens. From this point and probably for longer, our brains have increased in size. We know this because we can compare fossils of skulls from different eras. The change in size over this period is from 1,500 cubic centimetres to 1,350 cubic centimetres. That is quite a serious proportion. And before you ask, male and female brains have shrunk roughly in the same proportion.
However, for the last 10% of our time as Homo sapiens, the previous 20,000 years, there has been a small but steady reduction in our cranial size and brains. There are several theories as to why this might be so. But it may very well be a combination of factors.
It is reported that our body size is also reducing. If this is so, then our nervous system would also decrease in size, and since our nervous system is controlled by the brain, then perhaps it needs less brain to maintain its control. This makes sense but I am not sure if it is the whole story.
Another likely reason is that although the brain size overall is reducing, some parts of our brains are increasing in size at the expense of others. From an evolutionary viewpoint, this makes a lot of sense to me. We live in a technological age and if our ancient ancestors saw it, they would think it is magic or that we are gods of some sort. One part that has increased in size is the cerebellum which is responsible for motor activity and coordination.
Perhaps allied to this is the fact that in some ways we do not have to remember as much knowledge in certain areas because we can easily retrieve it from databanks such as our computer hard drives or the internet. Yes, we need the knowledge to run and operate these devices but this is small compared with trying to remember all the data.
Two further reasons which I think may at best, only contribute a small part to the solution is the increase in obesity in the world. It uses a process called encephalisation which is a projected ratio of brain size to body size. This does appear to distort the first reason we discussed. A further theory says that if we have smaller bodies and brains, then we need less energy and therefore the need for producing food will also decrease. I can see some advantage to that but I do not think it contributes much to the answer.
Finally, someone has put up their theory. And that is, we are all getting stupider!
John Pullen 