Reader questions

A reader wrote us to share the following quote from University of Zurich scientists: 

  . . . 
"Compared to our closest living relatives, the chimpanzees, we have a peculiar style of development. Our newborns have an exceptionally large brain (400 cubic centimeters, like an adult chimp), which makes birth a difficult process," University of Zurich scientists Marcia Ponce de León and Christoph Zollikofer said in notes accompanying a paper published today in the Proceedings of the National Academies of Science.
"Brain size reduction in modern humans over the past 40,000 years is well-documented," the researchers said in their notes. "We hypothesize that growing smaller but similarly efficient brains might have represented an energetic advantage, which paid off in faster reproductive rates in modern [humans] compared to Pleistocene people. Reducing brain size thus might represent an evolutionary advantage." 

Our reply: 


Thanks for your email, and for your helpful pointers to the recent literature.  There have been some very surprising comments about the book, Big Brain, and its explorations of our large brains and those of our recent ancestors. 


A fundamental misunderstanding has rapidly arisen.  One reader even suggested that “archeological acceptance of Boskops is non-existent.”  Umm: archeological acceptance of what?  Skulls from the town of Boskop, Africa?  Actually these are very well accepted.  (See, e.g., Schwartz & Tattersall, 2003 for a comprehensive review).  The other large skulls the book discusses, from all over africa, europe, asia?  All are near the large end of the human scale, and all are from roughly 10,000 to 30,000 years ago.  All are solidly documented and pretty much universally accepted.  (Again see S&T 2003).  What’s going on then?  Aha:  an insidious notion, from many decades ago, that there was something called a “Boskop race” with supposed racial implications for todays populations?  This one is widely rejected, including in our book!  


Real Boskop Skulls vs Imaginary “Boskop Race”

Boskop is a place in South Africa, where these skulls were found.  But many decades ago, in an unsavory episode in the annals of anthropology, there was an attempt to lump these Boskop skulls and others into a groundless notion of a separate “race” of peoples, and worse: they attempted to use these to make implications about the separateness of races in the modern population.  This has nothing whatever to do with the book.  The terms “Boskop race” and “Boskop man” never even appear in Big Brain!  And when the (interesting) scientific topics of species and gene pools arise (mostly in Chapter 10), the book actually debunks the entire popular notion of purported “races” within species, and cites modern support for this rejection of old-fashioned “race” concepts (e.g., Brace 2005; Schwartz 2006).  In sum, it is pretty unfortunate that a long-discredited notion of a Boskop “race” is being brought up, and it is not due in any way to this book.  Of course we did all the searches, and of course we were thoroughly acquainted with the literature on these topics in various fields; and the book contains extensive end-notes and a substantial scholarly bibliography including all the relevant references.  It is not possible to read Big Brain and conclude that the authors believe in any way in this notional “Boskop race”, nor that we have in any way somehow mistakenly adopted decades-old, long-rejected interpretations of these skulls.  


Whew.  Ok then, what the heck?  Why does this book refer to these Boskop skulls at all?  Clearly one shouldn’t throw out the real skulls with the false-race-controversy bathwater, but if it’s not about this old, discredited anthropology argument, then what is it about?  Good; now we’re on to facts, and scholarly analysis, i.e., the kinds of discussions that actually occur in the book.  Let’s take a look.  


Our Brains Are Smaller Than Those From 10,000 Years Ago

First, what are the facts — those that are not particularly controversial?  (You may be surprised).  A quick precis: 

  * The book focuses on a set of many recent (mostly 10,000 - 30,000 year old) skulls: from Boskop, Africa (our particular "poster child", but just one of many), from Skhul, from Fish Hoek, from Qafzeh, from Border Cave, from Brno, from Tuinplaas, and many others, all of which are near the high end of hominid (more specifically, hominin) skull sizes ( > 1550 cc’s).  

  * That is, these skulls represent a slight statistical anomaly:  from locations all over africa, europe, asia; all from a limited time span; all above current average size.  (These skulls, and their documented size and age, are listed at the beginning of the book’s Appendix.) 

  * These large hominid calvaria contained comparably large brains (i.e., independent of bone thickness and other considerations, it is accepted that the brains, not just the skulls, were also likely near the high end of hominid size).  Again, they weren’t ridiculously large, but were at the large end of the distribution.     

  * In other words:  Hominid brain size has been shrinking for perhaps 10,000 to 30,000 years.  


Yes, various versions of that premise are almost universally agreed upon, and find extensive current support in the scholarly literature:  Hominids from 10,000 to 30,000 years ago tended to have bigger brains.  (Again, one can go straight to the raw data, all present and measured in the recent comprehensive compendium of hominid skulls by Schwartz & Tattersall (2003); many further references appear therein.)


Whoa.  Those facts are widely agreed upon?  Yes indeed (as in the references listed in your email message).  Why don’t we hear more about this?  Surely there are disputes about it! 


There’s plenty of dispute about what the facts mean, but not about the facts themselves.  The facts could be taken as disturbing: bigger brains 10,000 years ago; our brains smaller than theirs.  Where then did they go?  Why are we here while they’re not?  Were these two separate groups, one of which supplanted the other, or ancestors absorbed by us?  The data are insufficient to support any solid answers at all.  But meanwhile researchers hasten to make hypotheses about how big brains may have arisen.  These include the well documented metabolic expense of brains, the pre- and post-natal developmental growth patterns of brains, and nutrition issues such as dietary changes in hominid history.  Any or all of these important points may indeed affect brain size (and all discussed to various extents in Big Brain).  Of course, we still lack explanations of how bigger brains arose at all, especially in light of these hypothetical forces working to shrink brains.  This problem too is discussed at some length in the book.  


Brain Differences and Mind Differences

But let’s remind ourselves that, altough brains are indeed organs, shrinking or expanding in response to evolutionary and environmental effects, brains are unique in their effects: unlike livers and stomachs, size change in a brain may alter the way the resulting animal thinks and acts.  So in addition to questions of brain nutrition and metabolism, let’s ask a question relating to what brains uniquely do, to wit: Would there be any cognitive effects of different sized brains?  Extremely precarious territory.  The very notion of brain size and cognition is laden with innuendo, and indeed has an often-ugly history.  As a particularly loathsome example, some researchers to this day doggedly suggest links between brain size and intellect in humans; and again many of these attempt to make links to racial issues.  So let us point out the facts right at the outset: there is absolutely no good evidence that has ever been presented that brain size within a species is correlated with intellect.  Many publications exist on this highly controversial topic, and even the most pugnacious of them turn out to be arguing over tiny statistical effects: figures that, even were they true, would at best account for a miniscule fraction of the statistical variance among individuals.  Indeed, it has convincingly been shown, time and again, that individual differences crushingly overwhelm any purported human brain-size effect.  And this makes eminent sense in the context of gene pool correlations within species (all discussed in the book).  Anecdotally, it is useful to remember that Einstein’s brain was in the low range of normal human brain sizes.  


So much for differences within species.  What of comparisons among different species?  Here, the literature is replete with scientific support for correlations between average brain size on one hand and cognitive and behavioral repertoire on the other.  (Note that most of the discussion is actually about brain size per body size, i.e., brain-body ratio.  Absolute brain size is also a factor.  Again, all discussed in the book.)  (See, e.g., the seminal studies by Finlay & Darlington 1995).  Mammals with larger brains for their body size tend to have capabilities beyond those with smaller brains; the trend is true even for bird species (crows, parrots) with big brains (see, e.g., excellent references and review in Striedter 2005).  


But these are highly variable findings.  What about highly similar mammals with different brain sizes, such as dogs and wolves?  Are dogs really stupider than wolves, and if so, in what definable ways?  They’re almost apples and oranges; both are highly competent, exhibiting differences in kind (domesticity, flight distance) rather than in any unidimensional measure of intellect.  Related questions can arise (cautiously) with primates.  Do our big brains give us greater mental powers than chimpanzees?  Do chimps’ relatively big brains give them additional mental powers over gibbons?  Did homo sapiens’ brain size correspond to different cognitive faculties from those of homo heidelbergensis, or of homo erectus?  Could anything be predicted of mental proficiencies of a species with an average brain size just 20% smaller than ours?  Or 20% larger?  These comparative biology topics are among the most intriguing unanswered questions of neuroscience; Big Brain gives a brief history of mammalian brains, and attempts to marshal arguments from state-of-the-art neuroscience, genetics, evolution, physical anthropology, population biology, and computational modeling to propose potential answers.  There is lots of hard scientific fact, and lots of probing speculation; and both are clearly labeled.  We provide extensive scientific “end notes”, expansive discussions of multiple views, and a copious list of references and pointers to further studies.  


To summarize: It would have been egregious to have unlearnedly adopted old, discredited theories.  There is none of this whatever in Big Brain.  The Boskop (and Fish Hoek, and Skhul, and Tuinplaas, and many other) recent large skulls are very real indeed, and lead to intriguing scientific questions; questions that are highly current and still unanswered:  How do different species’ brains give rise to different mental faculties?  What findings from a multiple disciplines can be brought to bear on such questions?  How did our brains — larger than apes, but smaller than many from 20,000 years ago — get they way they are?  What are the consequences?  What differences might arise as a result? 


The answers are not known, and they will not be simple.  We hope that engaging these questions will help inform broad explorations of our own human brains, and of our own human nature.  


I’d be glad of course to discuss these points (or others) further with you.  


- Rick Granger


(A few of the references mentioned here:)

Brace CL (2005). “Race”is a four-letter word: The genesis of the concept. Oxford University Press. 

Finlay B, Darlington R (1995). Linked regularities in the development and evolution of mammalian brains.  Science, 268: 1578–1584. 

Lynch G, Granger R (2008).  Big Brain.  Palgrave Macmillan.  

Schwartz,J., Tattersall,I. (2003). The Human Fossil Record, Vols 1–4. Wiley.

Schwartz J (2006) Race and the odd history of human paleontology. The Anatomical Record, 289B: 225–240. 

Striedter G (2005). Principles of Brain Evolution. Sinauer. 

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Jan 1, 2009, 2:28 PM
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