How Many Friends does One Person Need: Dunbar’s Number and other Evolutionary Quirks,

Robin Dunbar, “How Many Friends does One Person Need: Dunbar’s Number and other Evolutionary Quirks,”  Harvard Univ. Press, 2010, 292 pgs.

A fairly interesting book that repeats nuggets I have read before in other books that deal with evolution.  Nothing new, but entertaining.

Pg. 4 We have lived in villages only for the last ten thousand years, and cities of over a million people only for the last century at most.  Yet, at the same time, our social world is still what it was several hundred thousand years ago.  The number of people we know personally, whom we can trust, whom we feel some emotional affinity for, is no more than 150, Dunbar’s Number.  And it is 150 because our minds lack the capacity to make it any larger.  We are as much the product of our evolutionary history as any other species is.

Pg. 11:  Our brains are massively expensive, consuming about twenty percent of our total energy intake even though they only account for about two percent of our total body weight.  It seems that it is pair-bonding that is the real drain on the brain.  Among the birds and mammals in general, the species with the biggest brains relative to body size are precisely those that are monogamous. Those that live in large anonymous flocks or herds and mate promiscuously have much smaller brains.  (Only about five percent of mammals mate monogamously).

Pg. 93:  The modern human pelvis has been with us for the better part of the last two million years, ever since the first members of our genus, Homo erectus, developed their upright striding walk and the capacity to migrate over long distances.  However, to get the benefits of long-distance striding we have a weak lower back.  Then when the brain became bigger, we had to reduce dramatically the length of time for which the mother carries the baby before birth…from the twenty-one months we ought to have, to the nine we finally settled for.  But this came at a cost: giving birth to a baby whose brain is only half-developed means a very vulnerable baby.  Whereas monkey and ape babies are active and busy within a few hours, human babies take a full year – the missing twelve months – to reach that stage.

Pg. 100:  An analysis of 335 major new disease outbreaks that have occurred since 1940 has shown that the frequency of new diseases has increased steadily with time.  The number of new diseases that have hit us each decade has increased three- to four-fold in the last half century alone.  Among the more familiar ones are the likes of MRSA and the various new strains of ‘superbug’ that are resistant to antibiotics, SARS, HIV, and drug-resistant strains of malaria. 

Pg. 120:  In 2008, Harvard University scientist carried out the first successful extraction of DNA from a sixty-five-million-year-old fossil Tyrannosaurus rex—the archetypal dinosaur proving that birds do belong to the dinosaur family.

Pg. 127:  Our history is a long one, stretching back some six million years to the point at which our ancestors parted company with the other members of the African great apes, the biological family to which we humans belong.  The passage from then to now, however, has been far from simple.  There were many blind alleys that led nowhere in the end, even though some of them prospered for many hundreds of thousands of years before going extinct—the many australopithecines (the apemen that diversified into more than a dozen different species between six and two million years ago), the early Homo erectus species that migrated out of Africa and colonized Asia as far east as modern Beijing, the iconic Neanderthals of Europe.  There were, equally, many moments when the fragile lineage that eventually gave rise to us teetered on the brink of extinction.  The genetic evidence now indicates that all modern humans are descended from as few as five thousand breeding women who lived around two hundred thousand years ago in Africa.

Pg. 128:  For the first time in our lineage’s six-million-year history, this is the first time Homo sapiens are the only one of our species alive: prior to that, there have always been several, sometimes as many as six.  Many of these now-extinct species survived a great deal longer than we humans have done so far.  The last Neanderthals died out in Europe only twenty-eight thousand years ago.  The last erectus hominids died out in China sometime after sixty thousand years ago.  And on the Indonesian island of Flores, a diminutive member of this group may have survived until as recently as twelve thousand years ago.

Pg. 143:  Sixty-five million years ago, a massive asteroid smashed into the Yucatan peninsula.  The resulting nuclear winter wiped out the dinosaurs that had dominated the planet for the previous 250 million years.  This dramatic turnover in the world’s fauna was the fifth massive bout of extinction in the five-hundred-million-year history of life on earth.  Most of these mass extinctions seem to have occurred at intervals of about sixty-five million years. 

Pg. 171:  The jury system was introduced in England in 1215 to protect the nobles from the King and allowing them to be tried by their fellow peers.  It was only centuries later that this right was extended to all, i.e., us peasants.

Pg. 191:  The great markers that set us apart from the brute beasts are culture and language.  Animals continue to face one crucial stumbling block: the ability to engage in the higher forms of culture that we associate with religious ritual, literature and even science which depends on the ability to step outside oneself to see the world from an independent perspective.  Children begin to possess this capacity at around four years of age and is evidenced by their persistent “Why?” to everything.  However, some humans (such as autistic people) never acquire it. 

Pg. 276:  What makes us human has to do with the ability to understand the mind of another individual.  Prior to the age of four, children do not realize that other individuals can hold a belief about the world that is different from their own.  But eventually they come to realize that others can hold beliefs which they know to be false. 

Pg. 282:  We can identify at least four ways in which religion might be of benefit in terms of evolutionary fitness.  The first is to provide sufficient explanatory structure to the universe; this is use of religion as a form of primitive, albeit flawed science that allows us to predict and control the future better.  The second is to make us feel better about life, or at least more resigned to its vagaries.  A third is the provision of a moral code for keeping social order.  And finally, religion might bring a sense of communality, of group membership.  Religion does seem to work, at least on the intimate social scale.  Its real benefits seem to be in creating closely knit communities.  It is only when religion is taken over by the state and becomes large-scale that problems arise.  It seems that the psychological forces it can call on are so powerful as to be able to turn perfectly rational individuals into bigoted mobs.