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doi 10.4436/jass.94034 JASs Proceeding Paper Journal of Anthropological Sciences Vol. 94 (2016), pp. 183-192

Why human should be a basic science for medicine and psychology students

Paola Palanza & Stefano Parmigiani

Department of Neuroscience, Unit of Behavioral Biology, University of Parma, Viale delle Scienze 11A, 43100 Parma, Italy e-mail: [email protected]

Summary - Based on our teaching experience in medicine and psychology degree programs, we examine different aspects of that can help students to understand how the human body and mind work and why they are vulnerable to certain diseases. Three main issues are discussed: 1) the necessity to consider not only the mechanisms, i.e. the “proximate causations”, implicated in biological processes but also why these mechanisms have evolved, i.e. the “ultimate causations” or “adaptive significance”, to understand the functioning and malfunctioning of human body and mind; 2) examples of how human vulnerabilities to disease are caused by phylogenetic constraints, evolutionary tradeoffs reflecting the combined actions of natural and , and/or mismatch between past and present environment (i.e., evolution of the , teeth and diets, erect posture and their consequences); 3) human pair-bonding and parent-offspring relationships as the result of socio-sexual selection and evolutionary compromises between cooperation and conflict. These psychobiological mechanisms are interwoven with our brain developmental plasticity and the effects of culture in shaping our behavior and mind, and allow a better understanding of functional (normal) and dysfunctional (pathological) behaviors. Thus, because the study of human evolution offers a powerful framework for clinical practice and research, the curriculum studiorum of medical and psychology students should include and human phylogeny.

Keywords - Science education, , Sexual selection, Ultimate causation, Human health, Darwinian medicine.

Introduction the focus is on understanding how the body or the mind works and on detailed descriptions of Since publication of Darwin’s book “the pathophysiology. This proximate approach is the descent of man and sexual selection” in 1871 over- prevalent conceptual and cognitive framework whelming evidence from different disciplines, for the current models of learning, practice and ranging from to molecular biol- research in medicine (including psychiatry) and ogy, genetics, comparative anatomy, embryol- psychology. From an evolutionary perspective ogy, neuroscience and behaviour, clearly shows for understanding the functioning and malfunc- that what made us human is the process of evo- tioning of human body and mind, it is neces- lution by natural and sexual selection, which sary to consider not only the mechanisms, i.e. operated to increase individual’s reproductive the “proximate causations”, implicated in the fitness. It follows that human body and mind processes but also why these mechanisms have are a product of biological evolution. Although evolved, i.e. the “ultimate causations” or “adap- this concept should be obvious for all biological tive significance”. These so-called “how and disciplines it is foreign to many physicians and why questions” were originally proposed by the psychologists. Commonly, in these disciplines ethologist Niko Tinbergen, recipient of the 1973

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Nobel Prize for Physiology and Medicine, as include evolutionary topics in their curriculum the four questions that need to be answered to in the USA. In our experience, the same holds fully understand a behavioral trait (Tinbergen, for Italy and other European country. 1963), namely: 1. How does a behavior come We are behavioral biologists who teach to be expressed (i.e., the mechanisms underly- biology at the schools of Medicine, Dentistry, ing a certain behavior)? 2. Why does a certain Obstetrics, and Psychology, both for under- behavior come to be expressed (i.e., adaptive graduate and graduate students. The longer we significance)? 3. How does the behavior develop teach, the more our programs focus on evolu- in individuals (i.e., ontogeny)? 4. What is the tionary biology and, more specifically, evolutionary history of the behavior in related and human evolution. Human evolution deals species (i.e., phylogeny)? This classic ethological with all aspects of evolutionary change in Homo approach on proximal (questions 1 and 3) and sapiens and its descent from other hominins, as ultimate (questions 2 and 4) causations of animal well as with vertebrate evolution and the concept behavior, which can and should be applied to the of the common ancestry of living beings. It also study of any biological trait (a , a cell, an concerns the evolutionary changes in human , a system, a behaviour), radically changed physiology and morphology and has important the way in which biologists ask questions about implications for understanding human behav- any phenotype, including disease (Mayr, 1982). ior, health and disease. In this paper we describe Evolution is the foundation for biology and some practical examples that illustrate why biology the foundation for medicine, it follows medical and psychology students have much to that evolution ought to be a foundation for med- gain including evolution and human phylogeny icine. In 1991 George Williams and Randolph in their curriculum studiorum and understand- Nesse published a seminal paper, and few years ing how evolutionary principles affects human later a book, that defined the new science of health and disease (Nesse et al., 2010). Darwinian Medicine (Nesse & Williams, 1991, 1994). Darwinian medicine explains the impor- tance of asking: why in order to understand how, Human evolution and medicine e.g., asking why the body is designed in a way that makes us vulnerable to infections, cancer, chok- The study of pathologies has often been key ing, depression, hypertension, ulcers, diarrhea, for understanding the underlying normal physi- back pain, prenatal complications, etc. It recog- ology of organs and systems. Despite the obvious nizes that the body is a bundle of compromises human vulnerability to pathologies, during the and is far from perfect and provides explanations first years of medical school students focus on for the body’s flaws and vulnerabilities that fall basic sciences and learn how perfect the associa- into just a few categories, and explains how dis- tion is between structure and function of various criminating between them can help the under- parts of the healthy human body, including the standing of health and disease. Understanding skeleton and muscles, the eye, the nephron, the the evolutionary origins of disease vulnerability heart, the teeth, the brain, etc. In the last 3 years is not alternative to understanding proximate of medical school students study clinical sciences causes of disease; both levels of analysis offer and suddenly learn how the human body is tre- synergetic explanations that together can ame- mendously imperfect, flawed, and prone to dis- liorate the search for causes and cures. Although eases, such as backache, pain of the neck, fragil- medicine uses some evolutionary concepts, such ity of hips, knees and ankles, myopia, presbyopia as the evolution of antibiotic resistance in bac- and cataract, heart failure, dental cavities, obesity teria or the phylogeny of viral infections, evolu- and diabetes, depression, and so on (Fig. 1). tion is poorly studied in medical school. Nesse This apparent contradiction reveals a lack & Shiffman (2000) have shown that few courses of knowledge about biological and human P. Palanza & S. Parmigiani 185

1.Inverted eye: is 7. Cervical and Lombar backwards, blind spot. Vertebraes are compressed (neck-pain, back-ache).

2. Non functional wisdom. 8. Small Pelvi: painful and - teeth threatening parturition for (3rd molar). women and babies!

3.Risk of choking. 9. Inguinal hernia, adhesions, haemorrhoids – (intestines hung down compressed)

4. Male nipples: embryonal / 10. Easily damaged knees, developmental vestigium. ankles, feet.

5. Appendix: remnant of 11. Varicose veins, swelling. caecum intestinum.

6. Coccyx: caudal vertebrae- the remnant of a lost tail.

Fig. 1 - Homo vitruvianus, the “perfect human body”…or not ? N. 1, 3: trade offs and evolutionary constraints; n. 2,4,5,6: vestigial stuctures; n. 7-11: consequences of erect, bipedal posture. Image credit: Luc Viatour (www.Lucnix.be). The colour version of this figure is available at the JASs website. evolution because attention is focused on proxi- reflecting the combined actions of natural and mal mechanisms of normal and pathological sexual selection offers a powerful framework function. Physicians in training and in their for clinical practice and research. This means subsequent professional practice learn to iden- that physicians should know when and how the tify illnesses by recognizing patterns of signs and species of Homo sapiens developed from other symptoms. However, vulnerability to disease can species and spread over the world in order to partly be explained by common ancestry, phy- understand that the anatomy, physiology and logenetic relationships, constraints and selec- behavior of humans is constrained by evolution tion. Understanding how human vulnerabilities and that the human evolutionary past and pre- to disease are caused by evolutionary tradeoffs sent are mismatched.

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Below we provide specific examples of such sophisticated. It looks and works like the verte- apparent contradictions and flaws of the human brate eye (, , , and retina) but the body which can only be understood by taking retina is not inverted. Instead the photoreceptors our evolutionary history into account. are at the front of the retina and the supply sys- tems are stored beneath the visual cells, i.e. there A ‘perfect’ eye is no blind spot. The flawed structure shared by “To suppose that the eye, with all its inimitable all is most likely the result of evolu- contrivances for adjusting the focus to different tionary developmental constraints and/or trade distances, for admitting different amounts of offs between costs and benefits. Thus the evolu- light, and for the correction of spherical and tion of an inverted retina depended on contin- chromatic aberration, could have been formed gencies and on possible selective advantages out- by natural selection, seems, I freely confess, weighing the costs of having a blind spot, such as absurd in the highest possible degree…” the need of increased oxygen supply and/or long C. Darwin 1859, chapter VI, The origin of lasting functionality of the retina photorecep- species by means of natural selection. tors (Nesse & Williams, 1994). An evolutionary approach not only allows one to understand why The eye is often reported as a great example of these “flaws” exist, it also allows us to understand a human organ that has been exquisitely shaped; the frequent eye pathologies we suffer today, Darwin himself confessed that it was absurd to such as: myopia, presbyopia, cataracts, glau- propose that the must have evolved coma, iritis, retinal detachment etc. According through spontaneous and natural to the Darwinian medicine perspective, all these selection because of its perfection. However, he diseases arise from a mismatch between evolved then explained how this was possible, through a eye functionality during phylogenesis and mod- gradation of changes from “an optic nerve merely ern environments. Our did not evolve to coated with “ to “a moderately high read books, watch TV or look at smartphone stage of perfection” (Darwin, 1859, chapter VI). screens. Neither were we supposed to age and Darwin’s hypothesis has been demonstrated to be thus develop cataracts or presbyopia, as we live correct by recent scientific evidence; for instance, much longer today than in the past. Many mod- comparative analysis indicates that the vertebrate ern diseases are indeed related to aging and the eye most likely evolved from ancient population consequent senescence of structures and organs of light-sensitive cells that were initially located (Nesse & Williams, 1994). in the brain, as now can be observed in the living worm, (Urbilateria; Teeth and diets Arendt et al., 2004). The inimitable human eye “Tell me what you eat, and I will tell you who is, however, far from perfect, and has a subopti- you are” mal design. In the vertebrate eye, including ours, Jean Anthelme Brillat-Savarin. the nerves and blood vessels run across the top of the retina and cast a network of shadowed areas This famous quotation could be rephrased across it. Furthermore, where the optic nerve for mammals as “Show me your teeth, and I passes through the retina there is a blind spot will tell you what you eat”. Teeth of different (students can experience it by closing one eye forms and size (heterodontia) are a characteris- and watching a point on a piece of paper that is tic feature of mammals. Heterodontia is accom- moving forward). The Vertebrate retina is there- panied by the occlusion of teeth and the ability fore inverted, in that cones and rods sit at the to chew that in turn affects the jaws joint and back of the retina and light must pass through relative muscles. Mammalian teeth became dif- the layers of the supply systems to reach them. ferentiated during evolution to enable animals By contrast, the eye is extremely to obtain food more efficiently and to extract P. Palanza & S. Parmigiani 187

nutrients more quickly and thoroughly. Teeth the human diet, food preparation, and technol- are also used as weapons in defense against ogy. The combined effects of improved cutting, predators and in fighting conspecifics, usu- pounding, and grinding tools and techniques, ally of the same sex. Their diversity of uses is the use of fire for cooking and an increased con- reflected in their morphology. One can look at sumption of meat surely have contributed to the the teeth of any unknown mammal and make a process (Wrangham, 2009). In addition, brain very good guess about what it eats and its life- volume constantly increased during hominin style. It is thus not surprising that mammalo- evolution and a large brain needs energy. The gists are obsessed with teeth and that teeth are human brain consumes 25% of our energy when one of the most important taxonomic tools for resting and thus there is need for energy-rich mammalian classification, including primates food (Wrangham, 2009). Humans have indeed and hominin . evolved a strong preference – a craving - for Some of the most noticeable changes in the sweet and fat food but we move less than our evolution of the genus Homo and its antecedents ancestors. Consequently, in our modern envi- (australopithecines) have indeed been in the den- ronment, many adults (and children) suffer from tition and the jaws which support them. More obesity and related diseases, such as cardiovascu- specifically, the overall constant trend in human lar diseases and diabetes mellitus. According to evolution was toward smaller teeth and a reduced Darwinian medicine, the mismatch between our splacnocranium together with a parallel increase evolved dietary needs and modern diet explains of the neurocranium and larger brain size (Jones many modern diseases. et al., 1992). From Australopithecus spp. to Homo The evolution of the masticatory complex habilis, H. erectus, H. neanderthalensis and finally is related to other anatomical features such as H. sapiens, the architecture of the head has bipedal posture and brain size, which led to changed dramatically. The australopithecines important anatomical modifications that facili- had large molars and premolars, prominent jaws tated the emergence of speech and language. In and receding mandibular symphysis, but slightly association with the emergence of spoken lan- reduced canines and a chimpanzee-size brain. guage, a reduced prognatic face and the rela- Since about 2.5 million years ago, successive spe- tive reduced oral cavity were accompanied by a cies of the genus Homo reduced the size of their re-organization of the throat with an elongated jaws and teeth and the mandibular symphysis pharynx and a lower larynx. This creates a reso- became more vertical and eventually protruded nating chamber in which the tongue can move as a chin in H. sapiens. Such a reduction of the and articulate sounds. The low position of the prognatic face resulted in a regular curved shape larynx, however, does not allow the epiglottis of the dental arcade typical of our species and to lock behind the soft palate, which makes it in crowded teeth, with no space between them possible to choke while eating or drinking. This and not enough space for the eruption of the of the human throat for speech is, third molars. Indeed most modern humans have thus, a flaw, resulting from a trade off between non-functional wisdom teeth, which are easily the selective advantage of a complex language impacted in about 70% of people. Wisdom teeth for social communication (see the paper by are the third permanent molars, which emerge Liebermann in this issue) and the need of swal- between 17-25 years of age and have lost their lowing. From an evolutionary point of view, the function. This is clearly a flaw, because we main- advantages of talking outweighted the risk of tain a structure that not only is not functional choking. This is a good example of the concept anymore but also creates medical problems that of changing morphologies and changing behav- need odontoiatric treatment. ior over time and the close link between behav- The main causes for such a decrease in the ioral and morphological changes in evolutionary masticatory complex appear to be changes in processes (Mayr, 1982).

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The importance of being erect brain and most likely the behavior were ape-like. “Man alone has become a biped; and we can, Bipedalism thus appeared far earlier than the large I think, partly see how he has come to assume brains that we consider to be a crucial human his erect attitude, which forms one of his most characteristic. Many hypotheses about why conspicuous characters” bipedal locomotion evolved are debated, from the Darwin 1872, p.434. “patchy environment” hypothesis to the energetic advantage for running (Jones et al., 1992). Human beings walk upright as the only liv- Many of the recognized flaws in our body ing bipedal mammals. Erect posture and loco- design arise primarily from the evolutionary motion require small changes to turn a compromises that occurred when our ances- four-footed animal into a two-footed animal tors became biped (Fig. 1, n. 7-11). By standing walking upright. This process entails upright the weight of the head and top of the in the entire skeleton from head to toe for tak- body greatly compresses the vertebrae in the neck ing the weight on the hind legs and balancing it and in the lower spine, which necessitates more on one leg when each stride is taken. The head muscular effort to maintain a bipedal than a quad- becomes balanced on the spinal column with the rupedal stance. Pain of the neck and backache are foramen magnum opening centrally at the base highly common medical problems in our species, of the skull; the vertebral column, which was ranging from being a minor annoyance to becom- originally designed as a weight bearing arch with ing a serious disability. Knees, ankles and feet are one backward thoracic curve (kyphosis), evolved fragile and easily injured as they bear all the action a series of S curves (i.e., two lordosis and two of body weight that was originally distributed on kyphosis) to bring the body’s centre of gravity four legs. The abdominal viscera of mammals are directly over the feet. The rib-cage becomes bar- enclosed in the peritoneum and hang loosely in the rel shaped (rather that an inverted funnel-shape); abdominal cavity. On the other hand, the upright the pelvis is remodelled into a bowled shape, posture in humans presses the viscera towards the which is lower and broader compared to apes and vertical wall of the cavity thus causing problems also its muscles are remodelled. Because of these such as digestive blockages, hemorroids, visceral changes, femurs elongate and are angled inwards, adhesions, inguinal hernia. Also the mammalian thus assuming a carrying angle that ensures that circulatory system is affected by upright posture, the knees are brought under the body and bear which increases the hydrostatic pressure in the its weight. The feet are thus placed under the lower limbs and can cause varicose veins and swol- body and the allux is not opposed to the other len feet and ankles. On the opposite side, towards toes (non-abductible), making the foot strong the brain, decreased blood pressure can result and suited for powerful push-offs during the in dizziness and fainting, for instance when one last point of contact with the ground during the abruptly stands up. None of these defects exist in stride (Jones et al., 1992). other primate or mammalian species, all of which Bipedalism was the initial adaptation, the are quadruped. The flaws due to the evolution first step in the long path to becoming human. of biped locomotion have only recently become This change took place at least four million years pathologies as indicated by the fact that they ago, probably much earlier. In fact, the pelvis generally arise with senescence due to aging. But and femurs of Australopitecus afarensis, “Lucy”, when bipedalism evolved, aging was not a problem together with the footprints embossed in a bed of because individuals died long before senescence. volcanic ash found near Laetoli in Tanzania clearly The same can be said for many contemporary indicate habitual bipedalism 3.0 to 3.5 mya (Jones diseases which are related to aging. Evolution is et al., 1992). However, the head (skull, brain size not about increasing longevity but reproduction, and the prognatic face) was still similar to that of as stated by Nesse & Williams (1993): “we did not apes. While the body was already human-like, the evolve to live long but to reproduce”. P. Palanza & S. Parmigiani 189

However, the most striking cost of becom- women (Hrdy, 1999). The obstetrician is indeed ing bipedal appears to be related to the conse- one of the oldest jobs described in the first histori- quences of a reduced pelvis for parturition. cal documents and social support during birth is a “To the woman He said, «I will greatly multiply near universal feature of human cultures – a con- your pain in childbirth, in pain you will bring forth dition that is not considered enough in hospitals’ children»” (Genesis 3,16). delivery rooms (Trevathan & Rosenberg, 2002). In our species giving birth conveys a great The second effect of this evolutionary com- health risk for mothers and newborns due to promise is that in order to pass through the pel- the evolutionary constraints imposed by having vic canal, human babies are born underdeveloped a small pelvis and a big brain. Reproduction is compared with other primates; their brains are crucial in evolution and it is puzzling that such around 25 percent of their adult size at birth, com- flawed features reducing reproductive success pared with around 45 percent for chimpanzees, could have evolved in humans. As noted, how- our closest living ape relative. In fact, it would take ever, the reduced pelvis was an early adaptation a gestation length of 18 to 21 months instead of for upright walking that was established before nine months for human babies to reach a level of 4 million years ago in australopithecines, when development comparable with that of a newborn brains were relatively small and ape-sized (about chimpanzee (Portmann, 1990). Thus the human 450 cc). It follows that bibedalism alone did not infant is the least neurologically mature primate at introduce into the process of childbirth enough birth and experiences the longest delays in both difficulty for mothers to make it too disadvanta- social and biological maturation -a fact that can be geous (Rosenberg & Trevathan, 2002), but the appreciated only through a comparative analysis expanding size of the hominin brain certainly did. of primate evolution and development. As a con- The conflict of function between the size of the sequence of its immaturity, the human infant is birth canal and the baby’s head arose later with forced to rely on external regulation and support, the rapid size that started especially in the first year of life (Trevathan, 2011). around 2.5 million years ago and more than tri- All of these lead to human infants depending on pled the brain volume in H. sapiens. The evolu- their mothers much more and for much longer tionary result of this conflict was the remodelling than other primates. These needy babies and of the female pelvis and the birth of a premature infants imply high energetic costs for the moth- baby with an underdeveloped brain. The female ers and most likely constituted a selective pressure pelvis has become larger and broader than the for the evolution of paternal support and care and male pelvis to respond to the requirements of the the consequent change in the mating system dur- diverse selective forces for efficient bipedalism and ing human evolution. Accordingly, sexual dimor- parturition (the so called “obstetrical dilemma” phism, that is a strong index of the mating system - Trevathan & Rosenberg, 2002). In addition, of a species, decreased constantly during human sexual selection has made this sexual dimorphism evolution suggesting a constant trend towards even more pronounced, with males being more reduced polygyny in favour of monogamy (Ridley, attracted by females with larger hips and females 1993). This also implies the evolution of strong preferring males with narrow hips (Buss, 1989). emotional bonding between mother and child Despite these structural adjustments, childbirth is (even between father and child) and also between painful and dangerous and can result in signifi- male and female (pair bonding), which can be cant infant and maternal mortality and morbidity. considered the biological root of our enlarged This helps to explain why assistance during labor social brain (Dunbar & Schultz, 2007), as dis- and delivery is a common feature of human socie- cussed in the next section. Again, changes in mor- ties, as laboring women and their babies benefit phology always cause (or are caused by) changes in by lower rates of mortality, injury and anxiety behavior, but changing behavior implies changing with the assistance of others, specifically of other the brain and thus the mind and the psyche.

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Human evolution and psychology same neuro-endocrine substrates, i.e. oxytocin and vasopressin in association with dopaminergic system, that are also involved in social “Psychology will be based on a new foundation, (Insel & Young, 2001). This strongly suggests that of the necessary acquirement of each mental that the biological substrates of the social brain power and capacity by gradation. Light will be (i.e., pairbonding, altruism, cooperation, empa- thrown on the origin of Man and his history” thy) most likely originated as an of the , 1859, p.458 maternal-infant attachment process. It is notewor- thy that the understanding of the importance of The difference in the brain-size between our a critical period in social behavior development species and our closest living relatives, the chim- started with the discovery of the imprinting phe- panzees, mostly reflects the evolutionary expan- nomenon in geese by K. Lorenz (Lorenz, 1935), sion of association cortex, a group of regions was subsequently reinforced by Harlow’s studies that supports human-specialized functions as on long-term effects of maternal deprivation in language, tool making, reasoning, social cogni- macaques (Harlow, 1958), and finally led to the tion and self-awareness. Seventy-five percent of fundamental psychological Theory of Attachment human brain growth occurs post-natally, more that emphasizes the importance of early experi- than any other placental mammal, and this fact ences on the development of social behavior in probably accounts for the developmental com- humans (Bowlby, 1969). It follows that the com- plexity of its neuronal connections and high plas- parative analysis of brain and behavior in an evo- ticity. During human evolution patterns of gene lutionary perspective is essential to understand expression in the brain have changed, in associa- human social behavior and that these prosocial tion with higher brain and greater mechanisms belong to all mammals and existed levels of neuronal activity and plasticity across long before the appearance of primates, including much of the lifespan. These changes may account Homo sapiens. Understanding evolution would for our increased cognitive capacity but may also help psychologists to understand the human mind have influenced the unique human susceptibility and behavior, because evolutionary processes to neurodegenerative disease, such as Alzheimer’s forged the brain that controls human behavior, disease, and to neuropsychiatric diseases such as just as they forged the brain of other species. autism and schizophrenia (Preuss, 2012). An evolutionary perspective can help psy- The puzzle is why primates, the hominin line- chologists to understand, for instance, the age and, in particular, Homo sapiens evolved such a ambivalence of feelings and behavior in mother- large, highly wired brain? The traditional hypoth- child relationships and male-female pairbond- esis focused on the importance of technical skills ing, which although crucial for individual fitness, and ecological problem-solving, while the more are far from the harmonious ideals celebrated by recent evidence emphasizes the role of complex our symbolic brain in poetries, romances, arts social relationships as the main selective force for and songs. Instead, these behaviors are a com- the evolution of a large brain, the so called “social promise between cooperation and conflict as brain hypothesis” (reviewed in Dunbar & Schultz, explained by the theory of Sexual selection and 2007). Sharing food, caring for infants, develop- Parental Investment (Darwin, 1871; Trivers, ing pair bonds and building social networks 1972). Parental investment is “any investment by helped our ancestors to meet the daily challenges the parent in an individual offspring that increases of their environments and increased individuals’ the offspring’s chance of surviving (and hence repro- reproductive success (Fletcher et al., 2015). In ductive success) at the cost of the parent’s ability to this view, maternal care and pair bonding seem invest in other offspring” (Trivers, 1972, p.138). to have played a crucial role in setting the social As a general rule, males and females have diver- capability of a species and, indeed, they share the gent reproductive strategies that originate from P. Palanza & S. Parmigiani 191

the asymmetric investment in the production of Nature is expressed via nurture (Ridley, 2006). gametes (many tiny sperms and few large eggs) Most likely our brain structure has not changed and the care of offspring, with females sustaining too much since the appearance of Homo sapiens higher costs than males in most cases. In humans, (Barash, 1986). However, because of long postna- this asymmetry is extremely pronounced because tal brain development, plasticity and culture, this the females sustain all the physical costs of preg- is not entirely true. This concept is well expressed nancy, delivery and lactation for a long period of by David Barash (1986): “There would be little if time due to their immature and underdeveloped any difficulty exchanging a Cro-Magnon and a mod- infants. A clear implication of this asymmetry is ern infant, but great incongruity in making the same that men and women have different mating strat- switch amongst adults of both cultures” . egies and men are notoriously less choosy than women (Buss, 1989), as demonstrated by cross- cultural studies that show that sex differences in Conclusions sociosexual behavior are consistent and universal (Buss, 1989; Schmitt, 2005). Although cultural “Origin of man now proved. – Metaphysics must variations exist in human socio-sexual behaviors, flourish. – He who understands baboon would these studies show that biological sex is the largest do more towards metaphysics than Locke” and strongest predictor of human mating strate- Charles Darwin, M Notebook, 16 August 1838. gies across different cultures (Schmitt, 2005). Additionally, the most harmonious relation of We have reviewed different aspects of human all, the mother-child bond, suffers the burden of evolution that help to understand how human potential conflict. In a seminal paper on the evo- bodies and minds work and why they are vulner- lution of parent–offspring conflict, Trivers (1974) able to certain diseases. There are, of course, many argued that offspring are selected to demand more more examples of evolutionary principles of medi- investment than parents are selected to give. This cal and psychological significance, but the point genetic conflict starts in utero (mother-fetus con- is that an evolutionary perspective is necessary to flict: Haig, 1993) and then continues over the understand vulnerability to diseases and behavio- termination of parental investment with offspring ral disorders. Based on a long teaching experience demanding a longer investment period and/or a in medicine and psychology, we are convinced larger amount of investment at any time during that the curriculum studiorum of medical and the period of offspring dependence. psychology students should include evolution- As seen for the bundle of compromises and ary biology and human phylogeny. In addition to flaws in design of the human body, the same is the fact that a humanistic culture is important for true for human behavior and mind. To acknowl- scientists, understanding how natural and sexual edge that human social behaviors, such as sexual selection and other evolutionary processes shaped and parent-offspring relationships, are a result the human species is indeed relevant for all of of evolutionary compromises between coopera- the academic disciplines that are concerned with tion and conflict allows a better understanding human beings (i.e., medicine, psychology, social of functional (normal) and dysfunctional (patho- sciences and even the humanities). logical) psychological mechanisms. This evolutionary approach to psychology does not mean to underestimate the plasticity of References our brain and the effects of culture in shaping human behaviour and mind. The recent epigenet- Arendt D., Tessmar-Raible K., Snyman H., ics revolution has clearly revealed how genes com- Dorresteijn A.W. & Wittbrodt J. 2004. Ciliary bine with environment in determining the devel- photoreceptors with a vertebrate-type in opment of brain, neural mechanisms and behavior. an invertebrate brain. Science, 306: 869-871.

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