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Why Are Our Brains Smaller Than Our Ancestors'?

According to a study published in the journal Karger, the size of brain mass has significantly reduced over the past 50000 years between hominids (great apes) and modern humans. [1]

Another study talks about the decrease in the brain size in both males (9.9 per cent) and females (17.4 per cent) over the past 20000 years. [2]

Many studies have proven that there has been a reduction in the size of the brain as humans have evolved. But the question is why and when did these changes take place? Also, do changes in brain size affect our cognition?

Why Are Our Brains Getting Smaller?

1. No need for bigger brains

According to the Kerger study, brain size reduction could possibly be due to evolutionary pressure that looks forward to a smaller body size. This could be because ancient humans were required to be muscular to hunt their food, protect themselves from wild animals and survive in the forest. They may have required larger bodies and larger brains to sustain them in those times.

However, the development of societies, advancement in science and technology, changes in diets, shifting from hunting to farming and other better survival options have completely changed the overall way of living of the humans. As the demand for being muscular has reduced, there have been changes in body sizes. Also, the need for bigger brains has become less as humans have started relying more on collective intelligence rather than survival intelligence.

2. Environmental factors

The encephalization levels (the ratio between observed and predicted brain mass) have remained largely steady over the past 50,000 years, however as humans have evolved, there have been changes in their physiology, such as an increase in the body mass index (BMI).

It is likely that an increase in fatty body mass has improperly lowered encephalization in modern humans compared to ancient ones, given that in the latter, brain mass contributes to physical function rather than the development of fatty tissue. Therefore, an increase in body fat may have anatomically affected the relationship between body and brain mass and caused a reduction in the modern brain size compared to homo sapiens.

Also, there is a development in the nervous system due to changes in genes such as NOVAI, along with the normal development of language and speech. All these changes may have affected brain morphology. [3]

Are There Changes In Cognitive Functions?

Our brain size is getting smaller; does it mean that there is also a decrease in our cognitive functions, or as we say in layman's terms, are humans getting less intelligent than their ancestors?

In a study, 30 Holocene and 25 Late Pleistocene AM Homo skeletals were tested for both cranial and post-cranial nerves, along with 11 Caucasians and 8 Australians deceased between 1980 and 1982.

The test was done to find changes in the brain nerves between homo sapiens and modern humans.

Due to the limited availability of prehistoric remains and limitations such as the absence of certain brain parts like neuronal density, neuronal count and axonal conduction velocity that determine cognitive ability, the comparison was limited.

However, after utilising the genetic details along with various surveys of educational attainment of the sapeins, it was suggested that there has been a genetic decrease in cognitive ability, considerably due to an evolutionary decline in the size of the brain.

Despite the changes in brain size, general intelligence has risen due to many environmental factors like advancements in education, health and the introduction of technologies that may cause long-term genetic changes in modern humans. [4]

Also, the general intelligence of a person is not determined by their genetic intelligence and brain size, as environmental factors like better education and technology can help improve the cognitive functions of a person.

To Conclude

Our brains have evolved to be useful in the modern environment. Every part of the brain is significant and facilitates our integration into this modern human society. However, this was not the condition tens of thousands of years ago. Conditions were different for our ancestors to survive.

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