Reasons to Believe

Blood Flow to Brain Contributes to Human Exceptionalism

Are human beings exceptional? Are we unique, as the Bible teaches?

Recent work by paleoanthropologists from Australia adds to the mounting scientific evidence for human exceptionalism. These scientists demonstrate that modern humans have an unusually high rate of blood flow to our brains compared to other primates, including the hominids represented in the fossil record.1 They argue that the increased blood flow to the human brain reflects an unusually high level of (1) neuron-neuron connectivity, and (2) synaptic activity. Ultimately, these enhanced capabilities support the uniquely advanced cognitive capacity displayed by modern humans. To put it differently, the increased blood flow to the modern human brain helps account for the cognitive differences between humans and the other hominids, including Neanderthals.

This research helps support a key prediction of RTB’s human origins model (derived from the biblical text) by demonstrating a fundamental difference between humans and Neanderthals.

Measuring Blood Flow to Hominid Brains

To establish the relative blood flow to the brains of modern humans and hominids, the researchers measured the radius of the opening of two holes at the base of the skull that serve as the entryway for the internal carotid arteries. These blood vessels accommodate about 85 percent of the blood flow to the human brain. These arteries also give rise to the middle cerebral arteries (which supply the lateral portions of the frontal, parietal, and temporal lobes) and the anterior cerebral arteries (which supply the medial parts of the frontal and parietal lobes).

 

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Image: Internal Carotid Artery
Image credit: Wikipedia

These holes in the skull exclusively provide the conduits for the internal carotid arteries. No accompanying nerves or veins pass through these openings. Blood flow and blood pressure control the radius and the wall thickness of the arteries, making the size of these openings a reasonable proxy for blood flow to the brain.

Performing measurements only on complete and undamaged skull openings, the researchers determined the radius of the carotid openings for 34 hominid specimens, representing 12 species:

  • Australopithecus africanus (8 specimens)
  • A. afarensis (3 specimens)
  • A. boisei (1 specimen)
  • Homo habilis (1 specimen)
  • H. naledi (1 specimen)
  • H. rudolfensis (1 specimen)
  • H. georgicus (1 specimen)
  • H. erectus (5 specimens)
  • H. heidelbergensis (2 specimens)
  • H. neanderthalensis (5 specimens)
  • H. floresiensis (1 specimen)
  • archaic H. sapiens (5 specimens)

Brain Blood Flow in Hominids

In lower primates, neuron numbers increase with brain mass in a linear manner (because neurons occupy a constant volume). Measurements made in a previous study for 34 haplorhine primates saw brain blood flow scaling with brain volume.

But the researchers observed something different for the hominids. While the blood flow to the brain scaled with increases in brain volume for the australopithecines and early Homo species, a different pattern was observed for H. erectus, H. heidelbergensis, and Neanderthals. Increases in cerebral blood grew at a faster pace than expected based on increases in brain size.

For modern humans, the increase in cerebral blood flow maxes out, even departing further from the trend line observed for the late appearing Homo species. To put it another way, modern humans (H. sapiens sapiens) stand as an outlier, with an unusually high cerebral blood flow, even compared to Neanderthals.

Differences in Brain Blood Flow between Humans and Neanderthals

The primate brain possesses an extremely high aerobic demand, requiring prodigious amounts of oxygen. For modern humans, the brain is responsible for 25 percent of our resting metabolic activity. The brain needs a constant supply of oxygen and nutrients (such as glucose). The disproportionate blood flow to the human brain reflects the high level of interneuronal activity and synaptic transmissions between nerve cells.

Even though Neanderthals had roughly the same brain size as modern humans, the cerebral blood flow to their brain was significantly lower. This observation implies that these hominids inherently lacked the capacity to support the same high level of interneuronal connectivity and synaptic activity as modern humans. This result lines up with a wide range of other findings (detailed in the expanded and updated edition of Who Was Adam?) indicating Neanderthals had limited cognitive capacity compared to modern humans. Collectively, these results justify skepticism regarding claims that these creatures possessed symbolic capability (language, art, music, body ornamentation, etc.).

Brain Blood Flow and Implications for Human Uniqueness

This research helps support a key prediction of RTB’s human origins model (derived from the biblical text) by demonstrating a fundamental difference between humans and Neanderthals. Instead of viewing hominids as evolutionary transitional forms, RTB’s biblical model holds that hominids, including Neanderthals, were animals made by God. They possessed intelligence and emotional capacity but lacked the image of God—a quality associated only with anatomically modern humans (Genesis 1:26–27). Therefore, we expect that Neanderthals would have displayed behavior that is qualitatively different from, and inferior to, that of modern humans. This study provides confirmation of this expectation.

This study also provides scientific support for the biblical teaching that human beings are uniquely made in God’s image. If human beings truly are image bearers, then we should expect that scientific data would emerge for human exceptionalism, and it has in a way that aligns with the biblical perspective of humanity’s unique cognitive and behavioral capacities.

Resources

Endnotes

  1. Roger Seymour, Vanya Bosiocic, and Edward Snelling, “Fossil Skulls Reveal That Blood Flow Rate to the Brain Increased Faster than Brain Volume during Human Evolution,” Royal Society Open Science 3 (August 2016): id. 160305, doi:10.1089/rsos.160305.

 

Subjects: Adam & Eve, Human Uniqueness