Three million years ago, one of humanity's most well-known ancestorsÂ Australopithecus afarensisÂ lived in Eastern Africa. It walked upright, and was three to four feet tall.
Today's humans' brains are three times larger than that ofÂ Australopithecus.
A study published in 2016 shows that theÂ brainÂ changed in other ways besides just size. These other changes may have been just as important as the growth. The tissues of the brain greatly increased their rate of metabolism.
Despite brain tissue notÂ fossilizing, scientists were able to find other ways to determine that metabolic growth rate.
When cells increase their metabolic rate, they need more oxygen and nutrients, and so the brain needs a bigger supply ofÂ blood. The human brain is supplied with blood by the carotid arteries, which enter the brain through holes in the skull called foramina.
Scientists studied the fossil skulls of eleven different species ofÂ humanÂ ancestors and measured the size of the foramina. By knowing the sizes, they could estimate how much blood flowed to the brain.
They estimate that blood flow to brain tissue increased about six times. This might be because the cells were more densely connected to one another, and more active in signaling than in the brains of our ancestors or of other animals.
Sources And Further Reading:
- Seymour, Roger S., Vanya Bosiocic, and Edward P. Snelling. âFossil skulls reveal that blood flow rate to the brain increased faster than brain volume during human evolution.â Royal Society Open Science 3, no. 8 (August 31, 2016): 160305. Accessed January 25, 2017. doi:10.1098/rsos.160305.
- University of Witwatersrand. âBloodthirsty Brains: Study Challenges Evolutionary Development of the Human Brain.â (accessed September 1, 2016)
- âSmarter brains are blood-thirsty brains.â Phys.org â News and Articles on Science and Technology. August 30, 2016. Accessed January 25, 2017.