Brain Size and Evolution: Is There a Valid Correlation?

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For many years a dogma within evolutionary biology has been that as organisms evolved from mouse to chimp to human their brain size increased (even relative to body weight). The assumption being that an increase in brain size meant an increase in intelligence. Recent news articles1,2 reporting on findings presented in an article in an August 16 Nature advance online publication3 claim that a gene responsible for this increase in brain size in humans may have been found.

Biased Research

The scientists began by looking for regions of the genome that were conserved among mice, rats, chimps and humans (due to being mammalian and the assumption of shared ancestry).3 Regions of the genomes that showed the greatest differences between chimps (our closet living relative-in the minds of evolutionists) and humans were identified as “human accelerated regions” or HARs (49 were found).1 The most active region, with 18 differences among 118 bases, was named HAR1. HAR1F, an RNA gene that HAR1 is a part of, is expressed in specific brain neurons during 7-19 weeks of gestation in humans.1

The scientists reason that since human brains are triple the size of chimp brains, HAR1 may be at least partially responsible for the size difference. This is a huge assumption, considering the following statement made by David Haussler, team leader of the research: “Right now we have very suggestive evidence it might be involved at a critical step in brain development, but we still need to prove that it really makes a difference.”1 (emphasis added). A news article also states, “The scientists still don’t know specifically what the gene does.”2

There is a lot of circular reasoning going on here: because of the many differences in HAR1 between humans and chimps it may be responsible for larger brain size in humans; as humans evolved from chimps brain size increased and this must have been accomplished via changes in the genome, like the HAR1 region. This leads nowhere.

The Importance of Non-Coding DNA

One interesting thing about the HARs is that 96% of them were found in non-coding regions of the genome (areas that don’t code for proteins). For years scientists have ignored this region of the genome, affectionately called “junk” DNA. Due to their presuppositional bias they believed that the many differences observed in these regions between organisms meant these areas don’t have an important function, could accumulate mutations without ill effects to the organism and are thus not conserved. Chris Pointing, a scientist at Oxford University, wrote, “Now it would seem that searches within the functional non-coding ‘dark matter’ might be more enlightening.”1 Notice the change to calling the non-coding regions “dark matter,” implying they have functions that we do not yet understand, from “junk” DNA, implying no function.

From a creationist viewpoint, differences between organisms in non-coding DNA makes logical sense. If a particular protein serves a function in one organism and the function was needed in another organism, wouldn’t we expect to find the same protein? The differences would be expected in regions regulating the expression of the genes, which are now commonly believed to be in the non-coding regions of DNA. This is exactly what is found time and again. Human and chimp coding regions share 99% similarity, but overall the genomes are considered to be less than 80% similar. The genome will most likely be found to be nearly 100% functional, confirming that differences in non-coding regions are highly significant.4

Anatomy of Brain Size Differences

Inferred from the scientists’ discussion about brain evolution is that bigger is better or more intelligent, since humans have bigger brains and are smarter than chimps. This inference has been proven false many times over. Douglas Jue states, “Because man’s cranial capacity is so variable today, it has been shown that there is very little relationship between cranial capacity and human intelligence.”5 Jue quotes Ralph Holloway, professor of anthropology at Columbia University, as saying, “One cc of chimpanzee cortex [location of many neurons involved in higher brain functions] is not equivalent of human cortex, nor is it likely that any equivalent measure can be found.”5 This indicates that it’s not just size, but complexity that contributes to intelligence.

Some evolutionists have decided body size must also be taken into account when looking at evolutionary relationships based on brain size. This number is called the brain-body ratio (BBR).5 Since humans have a small ratio (1:38-40) and chimpanzees have a much larger one (1:129), this seems reasonable.5 However, many animals (such as the house mouse, 1:40) have been found with a BBR the same as humans or smaller.5

In addition, what about women and people of small stature? Their brain sizes are typically smaller than that of an average-sized man, but no one would dare say they are not as intelligent (or at least I hope not, speaking from the female viewpoint!). Even some geniuses have been found to have average-sized or even smaller-than-average brains.

A recently discovered “humanlike” fossil named Homo floresiensis (nicknamed “Hobbit”) is believed to have a very small brain size, based on a cast of the endocranial (inner cranial) cavity. A news article summarizes the “problems” as shared by a scientist on the project: “The primary problem, clashing directly with the tiny brain size, is the sophisticated nature of the stone tools found in the same cave deposits where the fossils were discovered. Based on their size, style, and workmanship, these tools belong to types that are consistently associated with modern humans, or Homo sapiens.”6 This finding provides evidence that brain size and intelligence should not be linked and is a blow to assumptions about increased intelligence due to evolution, since H. floresiensis pre-dates H. sapiens (according to evolutionary dating methods).6

Jue suggests that the differences in configuration of gyri (ridges) and sulci (depressions) may be key to understanding the differences between human and chimp brains.5 However, these differences would be hard to study on fossils, since this information is not “recorded” on the fossil.5 Close examination of Albert Einstein’s brain showed that, even though his brain was average-sized, the area involved in spatial relationships, math, etc., was 15% larger than average.7 Although the cortex where HAR1 is apparently functional is an important part of the brain, it is useless without the other parts of the brain with which it connects. It would appear there are many aspects more relevant than size that need to be studied to understand differences between human and animal brains.


So are HARs and, specifically, is HAR1 of any real importance? If (as evolutionists assume) humans evolved recently from chimps, the HAR1 gene must have changed rather rapidly. A news article states, “… [T]he gene [HAR1] changed so fast that Clark [professor of molecular biology at Cornell University] said that he has a hard time believing it unless something unusual happened in a mutation. It’s not part of the normal evolution, he said.”2 We as creationists have a hard time believing it too! Research team leader Haussler, “attributed the dramatic change [in HAR1] to the stress of man getting out of the trees and walking on two feet.”2 The better and reliable explanation is found in the Word of God. God created chimps and humans separately. The differences in these regions of the DNA, like HAR1, reflect designed differences between humans and chimps.


  1. Jeremy Lovell, DNA hints at roots of brain evolution.
  2. Seth Borenstein, Scientists Find Brain Evolution Gene.
  3. Katherine Pollard, et al., An RNA gene expressed during cortical development evolved rapidly in humans, Nature, August 16, 2006.
  4. J.C. Sanford, Genetic Entropy and The Mystery of the Genome, Ivan Press, 2006.
  5. Douglas Jue, Cranial Capacity and Endocranial Casts, TJ 4(1):56–65, 1990.
  6. AAAS EurekAlert!, Scientists scuttle claims that “Hobbit” fossil from Flores, Indonesia, is a new hominid.
  7. BBC News, Why size mattered for Einstein.


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