Human nature or human natures

Human nature or human natures? Peter Frost * a/s Bernard Saladin d’Anglure, De´partement d’anthropologie, Universite´ Laval, Que´bec G1V 0A6, Canada 1. The current model In evolutionary psychology, one key concept has been the ‘environment of evolutionary adaptedness’ (EEA). This is the ancestral environment that presumably made us what we are today. It is usually placed in the African savannah of the Pleistocene, long before modern humans began to spread to other continents some fifty thousand years ago. Proponents notably include John Tooby and Leda Cosmides: It is nomore plausible to believe that whole newmental organs could evolve since the Pleistocene—i.e., over historical time—than it is to believe that whole new physical organs such as eyes would evolve over brief spans. It is easily imaginable that such things as the population mean retinal sensitivity might modestly shift over historical time, and similarly minor modifications might have been made in various psychological mechanisms. However, major and intricate changes in innately specified information-processing procedures present in human psychological mechanisms do not seem likely to have taken place over brief spans of historical time. Futures 43 (2011) 740–748 A R T I C L E I N F O Article history: Available online 24 May 2011 A B S T R A C T Most evolutionary psychologists share a belief in one key concept: the environment of evolutionary adaptedness (EEA), i.e., the ancestral environment that shaped the heritable mental and behavioral traits of present-day humans. It is usually placed in the African savannah of the Pleistocene, long before our ancestors began to spread to other continents some fifty thousand years ago. Thus, later environments have not given rise to new traits through genetic evolution. This belief rests on two arguments: 1) such traits are complex and therefore evolve too slowly to have substantially changed over the past fifty thousand years; 2) because the same time frame has seen our species diversify into many environments, recent traits should tend to be environment-specific and hence population-specific, yet such specificity seems inconsistent with the high genetic overlap among human populations. Both arguments are weaker than they seem. New complex traits can arise over a relatively short time through additions, deletions, or modifications to existing complex traits, and genetic overlap can be considerable even between species that are morphologically, behaviorally, and physiologically distinct. There is thus no conceptual barrier to the existence of EEAs in post-Pleistocene times. Such a paradigm could shed light on such research topics as the visual word form area, reproductive strategy, predisposition to violence among young men, and personality traits. Eventually, a multi-EEA model may dominate evolutionary psychology, perhaps after an interim period of accommodation with the current model. � 2011 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +1 418 683 1740. E-mail address: peter_frost61z@globetrotter.qc.ca. Contents lists available at ScienceDirect Futures journa l homepage: www.e lsev ier .com/ locate / fu tures 0016-3287/$ – see front matter � 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.futures.2011.05.017 . . . For these and other reasons, the complex architecture of the human psyche can be expected to have assumed approximately modern form during the Pleistocene, in the process of adapting to Pleistocene conditions, and to have undergone only minor modifications since then [1, p. 34]. Recently, Tooby and Cosmides have softened their stand: ‘‘Although the hominid line is thought to have originated on edges of the African savannahs, the EEA is not a particular place or time’’ [2, p. 22]. It is a composite of whichever selection pressures brought each adaptation into existence [2]. There are thus potentially as many EEAs as there are adaptations, and some may be later than others. 1.1. Problem of complexity How much later? Tooby and Cosmides consider one limiting factor to be complexity. The more complex the adaptation, the more genes it involves, and the more time needed to make all of the right changes to all of the right genes. Therefore, recent evolution has created only simple traits, and certainly nothing as complex as mental or behavioral ones [1]. This argument assumes that complex traits evolve directly from simple origins. Actually, they almost always arise through additions, deletions, or modifications to existing complex traits. As Henry Harpending and Gregory Cochran point out: Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted [3, p. 10–11]. 1.2. Problem of apparent panmixia There is another argument against recent evolution of mental or behavioral traits. Because the past fifty thousand years have seen our species diversify into a wide range of environments, recent traits would tend to be adaptive in some environments but not in others. And their underlying genetic variants would tend to proliferate in some populations but not in others. Yet such population specificity seems impossible. At almost any genetic marker (blood types, serum proteins, enzymes, mtDNA, etc.), a typical gene varies much more within than between human populations. And this is true not only for large continental populations but also for small local ones. The geneticist Richard Lewontin concluded that 85% of our genetic variation exists only among individuals and not between ‘races’ [4]. For Tooby and Cosmides, these findings render ‘‘implausible the notion that different humans have fundamentally different and competing cognitive programs’’ [5, p. 30]: Human groups do not differ substantially in the types of genes found, but instead only in the relative proportions of those alleles. . . .What thismeans is that the average genetic difference between one Peruvian farmer and his neighbor, or one Bornean horticulturist and her best friend, or one Swiss villager and his neighbor, is 12 times greater than the difference between the ‘‘average genotype’’ of the Swiss population and the ‘‘average genotype’’ of the Peruvian population (i.e., the within-group variance is 12 times greater than the between-group variance) [5, p. 35]. This is true but does notmeanwhat onemight think. The same genetic overlap exists not only between populations of one species, like our own, but also between related species, like canids. ‘‘[U]sing genetic and biochemical methods, researchers have shown domestic dogs to be virtually identical in many respects to other members of the genus. . . . there is less mtDNA difference between dogs, wolves and coyotes than there is between the various ethnic groups of human beings, which are recognized as belonging to a single species’’ [6, p. 32–33]. Many other examples could be cited. In the deer family, we seemore genetic variability within some species than between somegenera [7]. Somemasked shrewpopulations are genetically closer toprairie shrews than they are toothermasked shrews [8].Onlyaminorityofmallardscluster togetheronanmtDNAtree, the restbeingscatteredamongblackducks [9].All six species of Darwin’s ground finches seem to form a genetically homogeneous genus with very little concordance between mtDNA, nuclear DNA, andmorphology [10]. In terms of genetic distance, redpoll finches fromone species are not significantly closer to each other than are redpolls from different species [11]. Among the haplochromine cichlids of Lake Victoria, it is extremely difficult to find interspecies differences in either nuclear or mitochondrial genes, even though these fishes are well differentiated morphologically and behaviorally [12]. Neither mtDNA nor allozyme alleles distinguish the various species of Lycaedis butterflies, despite cleardifferences inmorphology [13]. Anextremeexample is adog tumor that spreads tootherdogs through sexual contact: canine transmissible venereal sarcoma (CTVS). It looks and acts like an infectiousmicrobe, yet its genes would reveal a canid and conceivably some beagles may be genetically closer to it than to Great Danes [14]. In sum, total genetic variation poorly mirrors genetic variation in adaptive traits, be they morphological, behavioral, or physiological. Keep in mind that a new species typically arises when a founder group buds off from a parent population and enters a new environment with new selection pressures. The new selection pressures, however, will leave most of its genome unchanged. In some cases, this is because the gene itself has little adaptive value (e.g., most genetic markers), often P. Frost / Futures 43 (2011) 740–748 741 being nomore than ‘junk DNA’. In other cases, the gene’s variants are equally adaptive in a variety of organisms. Many blood polymorphisms span not only different species but even different genera. In terms of the ABO system, for instance, a person may have more in common with some apes than with other people [12]. Of course, once the two populations have become reproductively isolated, they no longer accumulate the same mutations and will drift apart at all gene loci, including the many that weakly respond to natural selection. But this process is slow. For example, redpoll finches diverged into two species some fifty thousand years ago and have distinct phenotypes, yet their mitochondrial DNA shows a single undifferentiated gene pool [11]. The past ten thousand years have seen dogs diverge into distinct breeds, which nonetheless cannot be told apart by genetic markers. In fact, greater mtDNA differences exist within the single breeds of Doberman pinscher or poodle than between dogs and wolves [6]. One might argue that humans have artificially created dog breeds by using limited criteria that involve a small set of genes. This objection is not wholly true. Many breeds, such as dingoes, originated in prehistory long before kennel clubs. More to the point, if one argues that artificial selection acts on relatively few genes, it does not follow that natural selection acts on thewhole genome. In fact, we are still looking at a small set of genes, a larger one thanwhat dog breeders use, but still much smaller than the genome. It is no surprise, then, that human populations overlap so much genetically. They began to move apart only some fifty thousand years ago. 2. Building a new model: gene-culture coevolution So let us reframe the question. How much do human populations differ from each other because of real adaptive differences due to natural selection? The jury is still out but an answer is taking shape. A team led by anthropologist John Hawks estimates that natural selection has altered at least 7% of our genome over the last forty thousand years. This period saw modern humans spread from Africa to other continents, thus forming the different populations we know today. Furthermore, again according to Hawks et al., natural selection has been altering our genome at an accelerating rate, particularly after agriculture replaced hunting and gathering less than ten thousand years ago. The rate of genetic change may have then risen over a hundred-fold [15]. We still poorly understand these recent changes to the genome. John Hawks sees adaptations to new ecological and cultural environments, specifically to colder climates, to an agricultural diet (cereals, milk, etc.), to diseases associated with the spread of agriculture (smallpox, malaria, yellow fever, typhus, cholera), and to forms of ‘‘communication, social interactions, and creativity’’ [15]. Indeed, given that the human genome has changed mainly over the past ten thousand years, we are probably looking at adaptations to new cultural environments. JohnHawks is not the first to give culture a role in human evolution. So have such people as Pierre van den Berghe, Charles Lumsden, E.O. Wilson, Robert Boyd, and Peter J. Richardson [16–18]. This paradigm, usually called gene-culture coevolution, has nonetheless remained marginal partly because of the influence of John Tooby and Leda Cosmides and partly because of two obstacles to research: 1. The linkages between genes and culture tend to be remote, indirect, multiple, and complex. Some are fairly straightforward, like the one between lactose tolerance and milk consumption, but such linkages are atypical. 2. With a few minor exceptions, gene-culture coevolution is specific to humans. Cross-species comparisons, so common elsewhere in evolutionary study, are of little help [16]. These obstacles are not insuperable. To some degree, they reflect awish to study humanswith the same research tools we use to study other species. But there is no reason why we cannot develop other tools or borrow them from psychology, sociology, and anthropology. Methodology alone should be no barrier. There remains, however, a conceptual barrier: the single-EEA model and its dominant status within evolutionary psychology. This barrier can be negotiated at some cost of theoretical dissonance, for example by claiming to believe in a single EEA while arguing for population-specific ‘fine-tuning.’ Such dissonance could settle into a relatively stable regime of data interpretation, at least over the short term. Over the longer term, however, efforts to reconcile data with theory will likely become more and more perfunctory and eventually cease altogether. Only then, and long after it has ceased to guide research, will the single-EEA model disappear from scientific discourse. Only then will its theoretical impossibility become apparent to many researchers and most educated laypeople. For now, this conceptual shift will be driven not somuch by overt changes in scientific discourse as by an accumulation of data that cannot easily fit the single-EEAmodel. Such data are accumulating in several fields of research, including four to be discussed here: a) ASPM and the visual word form area; b) reproductive strategy; c) predisposition to violence among young men; and d) personality traits. In all four fields, the data increasingly challenge the existence of a single species-wide human nature. 2.1. ASPM and the visual word form area (VWFA) ASPM is a gene implicated in the regulation of primate brain growth. In humans, a new variant arose some six thousand years ago, apparently somewhere in the Middle East. It then spread outward, becoming more prevalent in the Middle East (37–52% incidence) and Europe (38–50%) than in East Asia (0–25%) [19]. P. Frost / Futures 43 (2011) 740–748742 This pattern matches the spread of alphabetical writing [20]. Writing emerged near the end of the fourth millennium BC in the Middle East, initially with pictorial characters that represented ideas rather than sounds. This ideographic system gradually became phonetic in the third to second millennia BC and ultimately developed into an alphabet that spread to Europe, North Africa, and the Indian subcontinent. An ideographic system independently emerged in East Asia, perhaps in the second millennium BC, but never gave way to an alphabet, except in Korea some six hundred years ago. Although an alphabet has fewer characters and is easier to learn, it demands more from short-term memory. Longer character strings must be remembered and more transformations performed in mental space. In contrast, ideographic systems seem to evoke meaning faster, apparently because the mind encodes the characters visually and maps them onto meanings directly [21–24]. Inantiquity, alphabetical scriptdemandedevenmorementaleffort. Readingwould cause fatiguebecause characters formed a continuous streamwith little or nopunctuation.Writingwasno less tiresomebecause speech had tobe transcribedmanually in real time. Texts also needed frequent copying, likewise by hand, given the deterioration of parchment and papyrus inwarm climates. Today, all of these tasks aremuch easier or simply unneeded. Reading is facilitated byword, sentence, and paragraph breaks. Stenography is seldomdone in real time, thanks todictaphones andother recordingmachines. Copyinghasbeen largely automated by printers, scanners, photocopiers, fax machines, cut-and-paste functions, and so forth. Thus, ancient reading and writing tested the limits of human ability, particularly for the various scribes who processed texts day in and day out, i.e., clerks, stenographers, copyists, secretaries, notaries, and calligraphers. Their skillswere honored in the eulogy ‘Praise of the scribe’ (Book of Sirach, 2nd century BC): Many will praise his understanding; it will never be blotted out. His memory will not disappear, and his name will live through all generations. Nations will speak of his wisdom, and the congregation will proclaim his praise. If he lives long, he will leave a name greater than a thousand [25]. In the ancient world, ‘leaving a great name’ did not mean being written about by historians but rather having many illustrious children to carry on the family name long after death. Scribes thus seem to have enjoyed high reproductive success. In addition, their offspring often entered the same profession, thereby creating a quasi-hereditary caste as seen in the many Mesopotamian scribes who claimed descent from the editor of the Epic of Gilgamesh [26]. Such individuals may have been vectors for genetic factors that facilitate reading and writing, including perhaps the new ASPM variant. Of course, not all offspring could become scribes, given the limited number of positions in the public administration and as personal secretaries to the wealthy. Their talents were put to other uses, thereby raising the intellectual tenor of society. Indeed, ancient philosophers used analytical tools that scribes had earlier developed for legal and administrative texts: statement of the problem; presentation of the argument and counter-argument; review of the literature and inventory of relevant facts; quotations from authorities; and so on [27]. All of this assumes the existence of heritable aptitudes for reading and writing. Such an assumption is at odds with the view, held by many psychologists, that cognition displays heritable variation only for general intelligence (commonly referred to as g). This view helped dry up interest in ASPM when its variants showed no significant correlation with IQ or brain size [28,29]. Recently, however, it has been found that ASPM variants correlate not with total brain size but with growth of specific brain tissues, especiallywithin the cerebral cortex. After examining ASPM variants in different primate species, the authors of a comparative study concluded: ‘‘different brain parts still have their own evolutionary and functional differentiation with unique genetic bases’’ [30, p. 6]. Researchers have also found a specific brain region for processing of alphabetical characters. Named the visual word form area, it seems to be a patchy population of neurons in the left posterior occipitotemporal sulcus [31]. Its very existence raises a question: . . . why is there a reproducible cortical site responsive to visual words? Reading is a recent cultural activity of the human species. The 5400 years that have elapsed since its invention are too short to permit the evolution of dedicated biological mechanisms for learning to read [31, p. 473]. Howdid this specializedbrain area evolve so rapidly? Thiswould bepuzzling if adaptations came together fromscratch, but evolution sel