john hawks weblog

paleoanthropology, genetics and evolution

behavior

  • The scope of bonobos

    Sat, 2013-02-16 16:26 -- John Hawks

    National Geographic has an excellent article by David Quammen about the science of bonobo behavior: "The Left Bank Ape: An Exclusive Look at Bonobo Behavior". Much has been made of the contrast between chimpanzee and bonobo behavior, often centered around the question of which of these two closest human relatives might be the better model for hominin origins. In reality, the Anthro 101 version of bonobo behavior radically oversimplifies their behavioral variation. As Quammen discusses, bonobo behavior in the wild holds some surprises for students enamored of the simplistic sex primate story.

    That afternoon Hohmann and I sat beneath one of the thatch roofs discussing bonobo behavior. Few other researchers have seen bonobos in the act of predation, and those few reports generally involve small prey such as anomalures (only at Wamba) or baby duikers. Animal protein, insofar as bonobos get any, had seemed to come mainly from insects and millipedes. But Fruth and Hohmann reported nine cases of hunting by bonobos at Lomako, seven of which involved sizable duikers, usually grabbed by one bonobo, ripped apart at the belly while still alive, with the entrails eaten first, and the meat shared. More recently, here at Lui Kotale, they have seen another 21 successful predations, among which eight of the victims were mature duikers, one was a bush baby, and three were monkeys. Bonobos preying on other primates: “This is a regular part of the bonobo diet,” Hohmann said.

    Sexiness, on the other hand, seemed to him less manifest than others, such as de Waal, had claimed. “I could show Frans some of the behaviors that he would not think are possible in bonobos,” Hohmann said. Infrequent sex, for instance. Yes, there’s a great diversity of sexual acts in the bonobo repertoire, but “a captive setting really amplifies all these behaviors. Bonobo behavior in the wild is different—must be different—because bonobos are very busy making their living, searching for food.”

    Understanding the behavioral flexibility of both bonobos and chimpanzees is hugely important to the science of human origins. Meanwhile the continuing habitat loss and bushmeat trade threaten these creatures survival. Bonobo numbers remain fewer than 20,000 today. Their present genetic diversity is more comparable to the pattern of human variation than are chimpanzees, gorillas or orangutans. In that respect, at least, they may be the best primate model for our recent evolution. Hopefully genomics will begin to yield insights about the basis of bonobo-chimpanzee behavioral variation, which might open new doors to understand the evolution of the human brain.

    Tags: 
    bonobos
    chimpanzees
    conservation
    behavior

  • Primate mating patterns

    Mon, 2013-02-04 00:38 -- John Hawks
    Synopsis: 
    Primate groups are shaped by the pattern of mating competition and interactions

    Ecology, diet, competition, and ease of movement all affect the size of primate groups. The structure of primate groups is primarily affected by the mating system. There are several elements of primate mating systems. In most species, individuals of either one sex or the other disperse from their natal group --- the one they were born in --- when they reach adulthood. This dispersal affects the structure of the groups by breaking some kinds of relationships and preserving others.

    For example, in primate species where maturing females transfer to a new group, males are often left within the group where they are born. This means that males can form relationships as juveniles that last their entire lives. The long-lasting male coalitions in chimpanzees are a side-effect of female dispersal, conditioned by large group sizes and other social factors. In contrast, male savanna baboons transfer to new groups when they reach adulthood. In baboon groups, the female associations are highly structured by kin relations, since mothers and daughters live in the same group as adults.

    Mating conflicts

    Mating is essential to reproduction, and is the contest through which individuals pass their genes into future generations. From an evolutionary perspective, individuals do whatever they can to promote their own chances to reproduce. Sometimes, individuals can promote their own reproduction by inhibiting the chances of others. In other instances, it may be in their best interest to cooperate with other individuals, or to bide their time waiting for higher-ranking individuals to die or lose status.

    The most basic conflict of interest in mating is between males and females. Because of their biological role in carrying and providing nutrition for their offspring, both before and after birth, females must make a large investment in reproduction. Considering the large cost of reproduction, an adaptive mating strategy for a female is to mate with the male whose genes will contribute to the best possible offspring. For this reason, females are typically choosy about which males they will mate with. This element of female choice can give rise to sexual selection, in which males are advantaged by the possession of features that females value.

    In contrast, males may have extreme levels of competition for mates. A single male may be able, through fighting, threat, or intimidation, to prevent other males from having mating access to females, or even to expel all other adult males from the group. If he is successful, the reproductive opportunities for such a male are tremendous. On the other hand, the opportunities of other males fall to zero. This places a tremendous genetic payoff on social competition for mating.

    The intensity and form of mating competition vary from species to species. Some kinds of primates have a sparse diet that is simply unable to sustain the caloric requirements of huge male body sizes. Other primates or may modify the conditions of combat through coordination of activity with other individuals, emphasis on advertising the risks of combat rather than pursuing combat itself, or other means.

    Sexual dimorphism is a difference in size or form between males and females.

    Males and females within a species often differ in size or morphology. For example, male primates almost always have larger canine teeth than females. The canine teeth are important in male mating competition --- males can display their canines as a threat to other males, and at an extreme they can injure or kill other males with these teeth. One indication of the importance of the canines in displays is that they tend to be more dimorphic in species that are active during the day, as opposed to nocturnal species (Leutenegger and Cheverud 1982).

    Sexual dimorphism in body size is very pronounced in many primate species. For example, orangutan males average around twice the body mass of females. The body mass dimorphism is even more extreme for gorillas than for orangutans. Many different factors influence the body size dimorphism in a primate species (Hedrick and Temeles 1989). One of these is mating competition between males --- intense male competition increases the value of male body size. Another factor can be food competition between the sexes --- when males are larger, they may be able to dominate a larger share of valued food resources. Additionally, males can take on important reproductive roles beyond mating, such as protecting young juveniles from predation or infanticide.

    Territorial primate groups maintain their home ranges against incursions by other groups or individuals.

    Mating competition in many primates involves territoriality, when males defend a home range against incursions from other males. Primate groups may be territorial as a result of a single male's action, or the coordinated activity of multiple males. For example, Males of some primate species dominate access to females by preventing other males from coming into their home range. These primate males are said to be territorial. Even small social groups, like the monogamous male-female pairs of gibbons, may be highly territorial. But chimpanzees provide one of the strongest instances of territoriality among primates. Groups of male chimpanzees walk the approximate perimeter of their territory, engaging in violent conflicts with any members of neighboring groups they might encounter (Wrangham 1999). As observed by Jane Goodall (1986) at Gombe in Tanzania, the males of one group of chimpanzees killed all of the adult males and several females and juveniles in a neighboring group over the course of several months.

    Kinds of groups in primates

    Group size, dispersal, and mating competition all contribute to the proportion of males and females found in any given group. Sometimes a single male and female form a group; sometimes a single male and multiple females; sometimes multiple males and females; and occasionally a single female and multiple males.

    Monogamous, or pair-bonded, species have long-lasting mating relationships between a single male and a single female.

    Gibbons tend to form long-lasting associations between a single adult male and a single adult female. These pair-bonded primates occupy territories that they defend against incursions from other individuals. Both males and females make long vocalizations, called songs, to establish their shared territory. They often vocalize together in duets, although in different contexts based on whether threats come from males or female intruders (Geissmann 2000, Mitani 1987). These groups of a single adult male and female and their offspring are called monogamous groups.

    Polygynous groups have a single dominant male and multiple females.

    In many kinds of primates, a single male may dominate a group with multiple females. This is a polygynous group --- a multifemale, single-male group. Polygyny results from strong mating competition among males. Only if a single adult male can repel other males from the group can he reap the powerful reward of mating with many females.

    A well-known species with polygynous groups is the gorilla. Gorilla groups generally have one adult male, up to eight or more females, and their dependent offspring. Solitary males live outside of these polygynous groups and sometimes manage extragroup matings with females. These groups are maintained by strong mating competition --- a dominant male in a group repels other males by threats, intimidation, or violence.

    Even so, there is variability in gorilla societies. In mountain gorillas, multimale groups are common (Robbins 1999). In such groups, the dominant males have a majority of matings, and often harass subordinate males that attempt to mate. But subordinates do have many mating opportunities, demonstrating a social flexibility among gorillas.

    Polyandrous groups have a single dominant female and multiple males.

    Marmosets and tamarins, called callitrichids, are the smallest of the New World monkeys. These monkeys are among the few primates for which twin births --- and sometimes triplets --- are common. This means that females tend to have high energetic requirements in pregnancy, lactation, and caring for young. Callitrichids therefore face unique challenges compared to other primates.

    One way that these monkeys adapt to caring for more young is that older offspring of a female may stay with her for a longer time instead of quickly going off on their own. These older offspring help to watch and sometimes provide food for their younger siblings (Bales et al. 2000).

    Another behavioral adaptation is for a single female to mate with and coexist with multiple males. This kind of mating system is called polyandry. Mating with multiple males reduces the paternity certainty of the males --- a male cannot know if a female conceived her offspring with him or another male. As long as mating opportunities are limited, males may cooperate in a group with a single female on the chance of having offspring with her. These males help to provide food and defense for the young juveniles in polyandrous groups. Polyandry is not universal among callitrichids; it is adopted more when resources and mating opportunities are rare (Goldizen 1988).

    Fission-fusion societies are large multimale, multifemale communities that spend much of their time divided into smaller units that combine in different combinations.

    Some primates coexist in large groups numbering 50 individuals or more. A group this large is always a multimale group --- there is no way for a single male to deter other males from twenty or more adult females. But multiple males sometimes coordinate their behavior to deter neighboring groups. A large multimale group may occupy and defend a large territory, especially where movement costs are relatively low.

    Large primates who live in large groups have a problem: there are very few food patches large enough to feed them all. So even though a large multimale, multifemale group may occupy a substantial territory, it may not be possible for them to feed together much of the time. Chimpanzees live in such large multimale, multifemale groups. Even though members of the group share a dominance hierarchy, social interactions, and relationships, they spend much of their time apart. Smaller groups of individuals --- sometimes a single female and her young, sometimes male-female pairs, and sometimes small groups of either sex --- split apart in order to forage for food. These small groups recombine and split in different combinations, and sometimes all of them come together, especially when food is plentiful. This kind of social organization is called a fission-fusion society. Individuals divide into small foraging groups and come back together into the full community for social interactions.

    Study terms: 
    polygynous
    fission-fusion
    monogamous
    polyandrous
    Tags: 
    Anthropology 105
    primates
    behavior
    mating

  • How do primates move around?

    Fri, 2013-02-01 09:29 -- John Hawks
    Synopsis: 
    Exploring the way that primate locomotion influences body plan and behavior.

    The diversification of the first primates from other early mammals took place partly because the ancestors of the primates came to inhabit a unique environment --- the trees. These early primates developed many features to allow them to move quickly in this arboreal habitat. Early primates evolved the ability to direct and focus both eyes on objects, called binocular vision, which allowed them to accurately judge distances to branches and other objects. They also developed grasping hands and feet, with opposable digits --- thumbs and big toes. The fingertips were broader in these early primates, to apply greater grip strength to branches, and instead of claws primates developed wide nails. All of these features helped primates to succeed as arboreal specialists.

    • Primate adaptations to arboreal environments include binocular vision, opposable digits, enlarged fingertips and nails.

    Many primates today continue this arboreal existence, spending large proportions of their time off the ground and in the trees. Moving in an arboreal environment has the obvious risk of falling out of the tree if everything does not go exactly right. Yet primates are virtual trapeze artists, masters of the arboreal environment. Smaller monkeys and lemurs can rush headlong from branch to branch, seemingly mindless of any risk of falling, because of their unrivaled arboreal skills. These primates bridge immense gaps by leaping from one tree to another, limited only by the acceleration of gravity. Even large primates like chimpanzees and orangutans can rapidly scale trees and move effectively from one tree to another. These arboreal skills are made possible by a large suite of adaptations, many of which originated very early in primate evolution.

    But even though all primates are climbers, some of them have developed more specialized adaptations to other kinds of movement, or locomotion. These specialized forms of movement are adapted to different kinds of environments. Some primates are excellent at moving terrestrially, on the ground. Others are good at climbing tall vertical trunks and branches, or at swinging from one branch to another. Species who use these special forms of locomotion have consequences in their skeletons and muscle configurations.

    Vertical clinging and leaping

    Many prosimians, including tarsiers and many lemurs, use a form of locomotion called vertical clinging and leaping. These kinds of primates live in habitats where they climb relatively small tree trunks or bamboo. Sometimes they leap between these vertical supports. Other times, especially for the larger lemurs like sifakas, they leap along the ground. Their legs are relatively long compared to their arms, so that terrestrial movement can be more effective by leaping than by running on all fours.

    This form of locomotion gives their bodies a very distinctive shape --- especially tarsiers, who are masters of this pattern. Tarsier legs are longer than their bodies and forelimbs put together, and they especially have very long foot bones. The name for these bones are tarsals, giving these unique little primates their name.

    Below-branch locomotion

    Some monkeys and all apes are adapted more to hanging beneath branches than running atop them. This suspensory style of locomotion is essential for larger arboreal primates, which can move above only the largest branches. Hanging below branches enables large primates to climb into the forest canopy, often on smaller branches than could support them from above.

    A skeletal adaptation to suspension includes relatively long arms with very mobile shoulder joints. In contrast to quadrupedal monkeys, whose arms are limited in their range of motion, apes can move their arms through nearly a complete 360 degree circle. Also, apes' trunks are relatively flat from front to back, with the shoulders mostly alongside rather than in front of the spine. Putting the arms at the side requires long and strong collarbones --- called clavicles --- that serve as a strut supporting the shoulder musculature. Also, apes have extremely long fingers, useful for hooking onto branches quickly. Their thumbs are quite small, as they do not usually grip with their thumbs onto branches while hanging from them.

    • Brachiation is arm-over-arm swinging.

    Sometimes apes swing arm over arm from one branch to the next, a locomotor pattern called brachiation. Gibbons and siamangs are a brachiation specialists, but all living hominoids have the skeletal anatomy to enable them to brachiate. Brachiation conserves the energy of forward movement by treating the body as a swinging pendulum. This is a very efficient way to travel for medium-sized primates, combining energetic conservation with speed, and working with gravity instead of against it.

    • Quadrumanous locomotion uses all four hands and feet to move among branches.

    Large-bodied hominoids brachate less than gibbons. Branches of sufficient size to support the entire weight of a large ape are rarely located close enough to brachiate between them. Also, the pendular motion is less efficient for larger primates, because their arms just cannot be as long in proportion to the size of their bodies. Instead, when in the trees, the living great apes grip branches with three or four of their hands and feet at once. This allows large apes to support their weight on relatively small branches in the canopy. The masters of this kind of locomotion are orangutans, who move through the forest canopy moving one hand or foot at a time to a new support branch. This kind of locomotion, as if an animal was using four hands equally, is called quadrumanous locomotion.

    Knuckle-walking and fist-walking

    • Knuckle-walking allows quadrupedal walking in chimpanzees and gorillas, whose hands are adapted to suspension.

    Chimpanzees and gorillas, when they are on the ground, walk quadrupedally using the proximal finger joints of their hands instead of the palms of their hands. They use this style of locomotion, called knuckle-walking, because of their unique forelimbs. These apes have long forelimbs relative to their hindlimbs, and their hands are very long with strong tendons for curling the long fingers into a powerful hook. These hands are very well adapted to suspension in the trees, but they are not capable of being extended with the palms toward the ground, which is the way most other primates walk quadrupedally. So instead of walking palm-down, they use their knuckles.

    A few skeletal features of living chimpanzees and gorillas appear to be adaptations to knuckle-walking. Because the arms are held in a locked position while supporting the body, unlike the somewhat flexed position usual in quadrupeds, the proximal end of the ulna is more U-shaped, built for supporting the humerus mainly from below. Likewise, the joints of the hands are more limited in motion, and relatively incapable of being extended backward at the wrist and knuckles. It is not clear whether these unique anatomical consequences of knuckle-walking evolved in parallel in chimpanzees and gorillas, or whether they represent homologies inherited from a knuckle-walking common ancestor of gorillas, chimpanzees, and humans.

    Although many orangutans spend little time on the ground in their natural habitat, they can walk quadrupedally. But unlike chimpanzees and gorillas, orangutans do not walk on their knuckles when they are on the ground. Instead, they curl their hands inward, walking on the outside of their fists. This fist-walking accomplishes the same goal as knuckle-walking --- it allows walking on all fours without facing the palms of the hands toward the ground.

    Study terms: 
    brachiation
    knuckle-walking
    quadrumanous
    vertical clinging and leaping
    Tags: 
    Anthropology 105
    primates
    anatomy
    behavior

  • A Neandertal mortuary in Spain?

    Tue, 2012-10-09 19:53 -- John Hawks

    El Pais has a fascinating story about the Paleolithic sites in the Lozoya river valley: "A Neanderthal trove in Madrid".

    It was on the floor of Des-Cubierta that the Neanderthal must have placed the dead body of a small child aged two-and-a-half to three years old. They placed two slabs of stone and an aurochs horn on top, and set the body on fire. [Enrique] Baquedano explains that they found some of the child's teeth - they call it a little girl, although they have no scientific evidence of its gender - as well as a piece of coal that turned up just a few days ago and which will enable precise dating. "Complete burials, with a clear structure that allows [researchers] to reconstruct behaviors, is a very rare thing in any part of the world," says [Juan-Luis] Arsuaga, who is also co-director of the excavations at the major prehistoric site of Atapuerca.

    This one sounds like an incredible context, if it really is as described.

    Arsuaga is author of The Neanderthal's Necklace.

    Tags: 
    Neandertals
    behavior
    Mousterian
    Spain

  • Quote: Jerison on animal intelligence

    Thu, 2012-10-04 14:20 -- John Hawks

    Harry Jerison, famous researcher of brain sizes across classes and orders of animals, commented on the relation of "encephalization" to the intelligence of animals by considering the problem one of multidimensional optimization [1]:

    The insight is that comparable amounts of intelligence in different species may not (and normally would not) reflect comparable kinds of intelligence. Many and various intelligences (in the plural) must have evolved in conjunction with evolving environments and with brains and behaviours adapted to those environments.

    That intelligences would be of various kinds is almost an axiom of evolutionary analysis, since adaptations evolve in the contexts of the environments in which they are effective, and species never occupy identical niches. The evolution of neural and sensorimotor adaptations provides many fine examples of uniqueness of species. The visual systems of deer and wolf, for example, may be similar in many ways, for example, in the structure of the sensory cells, neural networks of the retina, and the central nervous pathways and centres. Yet these systems are significantly different: the deer, like most ungulate 'prey' species, probably has panoramic vision whereas the wolf's visual field is more nearly like the primate's proscenium stage. The visual system encumbers significant amounts of nervous tissues and, thus, contributes to brain size and measured encephalization. Neural machinery associated with the sensory systems and motor control systems as a group determines a large fraction of the mass of the whole brain. Equality of encephalization of deer and wolf, thus, implies that the neural control systems for the specialized adaptations, though different in the two species, sum to approximately equal amounts relative to body size.

    References

    1. Jerison HJ. Animal intelligence as encephalization. Philos Trans R Soc Lond B Biol Sci. 1985;308(1135):21-35.
    Tags: 
    brain
    brain size
    intelligence
    behavior

  • Perils of talking to apes

    Fri, 2012-09-28 10:28 -- John Hawks

    Barbara King comments on Koko, Kanzi and Panbanisha, "Thoughts On Three Famous 'Language Apes'".

    For decades, the Gorilla Foundation, run by the scientist Penny Patterson, has maintained — based on Koko's own use of sign language — that Koko would like to have a baby. Recently the Foundation posted this video clip, in which Koko is presented, verbally and in diagram form, with four complicated choices about "family planning."

    Patterson, at the end of the clip, affirms her interpretation that Koko grasped all of the options presented to her. The idea is that Koko, by pointing to one of the four diagrammed choices, can and should help make decisions that involve the reproductive activities and the welfare of other gorillas. This raises ethical issues, to say the least.

    We haven't come to the apes in my Biology of Mind course yet, but we were discussing the nineteenth-century origins of ethology yesterday. The initial move toward a science of animal behavior was possible because anthropomorphic accounts of animal behavior were set aside. The apes pose a recurring challenge to the rejection of anthropomorphism, because some of their behavioral capabilities really are homologous with ours. The cognitive border between ape and human may be a no-mans land, with one or two traits occasionally crossing the frontier to the other side. King's last word is fitting -- an ape can never grasp the complexities of the human world...yet neither can we fully grasp the complexities of theirs.

    Tags: 
    apes
    chimpanzees
    gorillas
    cognition
    behavior
    language evolution

  • Neandertals lacked mental eminence

    Sun, 2012-09-23 18:11 -- John Hawks

    If you care about Neandertal behavior and haven't read this 2004 article by John Speth, you really should treat yourself: "News flash: Negative evidence convicts Neanderthals of gross mental incompetence" [1]. I'm using the paper as a reference in a new manuscript, and so re-reading and giggling along the way:

    Neanderthals didn’t make blades, or at least not as often, or maybe not as well, as moderns did (they didn’t make microliths either, or stainless steel for that matter, but they did make great triangles; unfortunately rectangles are ‘in’ these days, not triangles). They didn’t carve bone or ivory (nor did they work fiberglass, though they may have carved a lot of wood, judging by recent use-wear evidence). They didn’t paint the walls of their caves, despite ample opportunity to do so (but, then, painting cave walls, even in the Upper Paleolithic, was truly the exception, not the rule). They did have spears, we have some of them (this, no doubt, is what all of their woodworking was about), but try as they might they just couldn’t throw them (the points that somehow managed to find their way through hair and hide of sizeable prey to become squarely embedded in solid bone notwithstanding). They had no large formal fireplaces (what’s wrong with some of the hearths at Kebara?), so they couldn’t sit cozily face-to-face around the fire at night holding hands, roasting marshmallows and singing campfire songs, hence they must have lacked true language (and Girl Scouts; in fact, the conspicuous absence of marshmallows throughout the Upper Paleolithic clearly testifies to the lack of language as we know it until very late in the Holocene).

    If you haven't been following paleoanthropology for long, you may find it difficult to believe that Serious Scientists have proposed some of the nonsense that Speth skewers (for example, that Neandertals lived bison-like in cow-calf and bull groups who only joined when rutting). Speth's tour through bad ideas is a ribald pleasure.

    Yet there is an important point in the paper, which is why I'm citing it today: The material record of Neandertals is in many respects within the range of hunter-gatherers who are unquestionably modern humans:

    What is the relevance of the North American record to the question of Neanderthal’s mental hardware? Simply this: most sites that date to the Paleo-Indian and early Archaic periods – periods that together last some 5,000 to 6,000 years and represent nearly half of the known occupation span of the New World – have little or no evident internal structure (unless you want to count ‘patches’ or ‘scatters’ as structure; the rare high-resolution examples share the same humdrum ‘carnivore dichotomy’ that was used to torpedo the poor Neanderthal); there are few if any formal hearths (isolated patches and lenses of ash are much more the norm); burials are extremely rare or absent altogether, and those few that exist have little or nothing in the way of ornaments or grave accompaniments; huts are generally absent or very controversial; and art of any non-perishable sort is virtually non-existent (they certainly didn’t paint cave walls; in fact, we are hard put in most cases to find anything that even remotely smacks of symbolism). If we were to use the same criteria that we apply to Neanderthals, we would have to conclude that the inhabitants of North America up until only a few thousand years ago were – to put it in politically correct terms – ‘cognitively challenged’. The parallels with the record of the Middle Paleolithic are even more striking if we exclude from consideration the few dry caves in western North America and waterlogged sites in Florida of late Paleo-Indian and early Archaic age which have miraculously preserved tantalizing traces of perishable basketry, textiles and other unusual items.

    Then around 5,000 years ago, give or take a millennium, came North America’s counterpart to Eurasia’s Upper Paleolithic ‘revolution’. We suddenly see an explosion of art – intricately shaped or carved and sometimes engraved ‘exotica’ of shell, antler, bone, stone, tortoise shell and native copper, including cups, tubes, pendants, beads, pins, rattles, atlatl hooks, bannerstones and gorgets; there are also remnants of probable ‘medicine’ bags, traces of textiles, decorated baskets and ubiquitous red ochre – the whole nine yards. Many of the raw materials came from distant lands – marine shell from the Gulf of Mexico, shark’s teeth from the mid-Atlantic states, copper from Lake Superior, galena and mica from Illinois and the Appalachians. This is also the time when we begin to see burials clustered together in real cemeteries, not just peppered here and there over the archaeological landscape; and many of these burials are elaborately decked out with ornaments and other ‘exotica’, so much so at times that we begin to speculate about the beginnings of prestige enhancement and wealth display, about ‘big men’, about reduced mobility and increasing conflict, about the growing importance of inter-group exchange and political alliances, about the very seeds of societal inequality and hierarchy. This is the bread and butter of North American archaeology. And, while there is lots to disagree and argue about (particularly about what is ‘cause’ and what is ‘effect’), all seem to agree that in some form or other what we are seeing over the course of the Archaic is the playing out of gradually increasing populations that were slowly filling in the landscape, reducing people’s ability to ‘vote with their feet’ when things got tough, and thereby compelling them to begin playing with alternative economic, social and political strategies for maintaining the delicate balance between war and peace – in a word, social, technological, economic and political intensification. No one, of course, would believe for a nanosecond that in the artless and styleless silence of the early Archaic we are dealing with a cognitively impaired proto-human.

    The Paleo-Indian/Archaic period transition is obviously not a perfect analogy for the Upper Paleolithic transition in Europe. Speth himself is explicit that this example does not prove anything about Neandertals.

    But it does illustrate a double-standard. Recent archaeological peoples are prima facie "modern" in behavior without showing evidence for "symbolic" interactions. With Paleo-Indian sites, the subsistence strategy itself argues for a complex logistical organization, even though habitation sites, kill sites and artifacts comport with the lack of structural complexity of many hunter-gatherer groups in the ethnographic present. Some scientists have presented similar arguments for Neandertals.

    Personally, I think that "cognitive modernity" is a red herring. Today's people learn some kinds of technical and symbolic complexity that were never present in ancient peoples. Some people living today in Western cultures, despite all our educational efforts, fail to attain levels of technical knowledge that are regular outcomes for the majority of people in the same environment. Human performance varies continuously.

    I assert that it is unreasonable to suppose that Neandertals had a "stupid gene". If so, it should be just as unreasonable to suppose that a "smart gene" could explain the evolution of human cognition during the last 100,000 years. These unrealistic assumptions are widespread, and impede our understanding just as thoroughly as assumptions about the nature of biological species impeded our understanding of Neandertal ancestry of living human populations. Some archaeologists have concluded that Neandertal cognition is an either/or proposition. Some look at Neandertals, find a lack of evidence that they behave identically to later people, and conclude that the Neandertals were therefore unquestionably cognitive inferiors. Others look at Neandertals, find some signs of modern-like behaviors, and conclude that Neandertals were therefore unquestionably our cognitive equals.

    Cognition in modern humans varies continuously across many axes of variation. No two humans are cognitively identical in outcomes. Nor can we appeal to "cognitive capacity", a meaningless abstraction unless we are discussing a particular structured learning environment in which the outcomes are potentially measurable. Will we someday raise a Neandertal in a human society to see whether and how they attain the skills and abilities we consider essential?

    I suspect somewhere within the broad scope of human variation in learning, we already are.

    References

    1. Speth J. News flash: Negative evidence convicts Neanderthals of gross mental incompetence. World Archaeology. 2004;36(4):519 - 526.
    Tags: 
    Neandertals
    modern human behavior
    cognition
    behavior
    learning
    Synopsis: 
    Human variation in learning and cognition is wide. Does it encompass Neandertals?

  • Chimpanzee watching

    Thu, 2012-05-10 12:36 -- John Hawks

    Captive chimpanzees do clever things, but how deep is their planning? Michael Balter describes a research study following how one chimpanzee harasses zoo visitors: "Stone-throwing chimp plans ahead".

    The next day, Santino again threatened visitors with stones, but the group again backed away to avoid being hit. Santino was then observed pulling a heap of hay from inside his enclosure and placing it on the island close to where the visitors approached. He put several stones under the hay and waited until the group returned about an hour later. Then, without performing a dominance display, Santino pulled a stone from under the hay and threw it. Later, he pulled a stone that he had apparently hidden behind a log and tried to hit the visitors with that, as well.

    This kind of research is a response to Morgan's Canon, the principle that animal behavior should be explained by the lowest-level cognitive process possible. If you want to demonstrate some kind of intentional planning, you have to do very close ethological study of every step in the planning process. The principle is a way of countering anthropomorphism -- animals sometimes do complex-looking things that actually impose very simple cognitive requirements. But it's good to remind ourselves that chimpanzees aren't ants.

    Tags: 
    animal attacks
    chimpanzees
    behavior

  • Lost pregnancies in geladas after male takeovers

    Thu, 2012-02-23 19:21 -- John Hawks

    Ed Yong reports on new research from Eila Roberts, with Jacinta Beehner's research group at the University of Michigan, who was able to show that the rate of pregnancy loss among geladas (close baboon relatives) skyrockets when a new dominant male takes over a group "The Bruce effect – why some pregnant monkeys abort when new males arrive".

    Geladas live in units where a single dominant male lords over several related females, whom he monopolises as mates. It’s an enviable position, and males often have to fend off takeover bids by eager bachelors. If a newcomer ousts the chief monkey, it’s bad news for the group’s females. A wave of death sweeps through the unit, as the new male kills all the youngsters whom his predecessor fathered. Indeed, babies are 32 times more likely to die after a takeover than at any other time.

    But that’s not all. Eila Roberts from the University of Michigan has found that the new male’s arrival triggers a wave of spontaneous abortions. Within weeks, the vast majority of the local females terminate their pregnancies. It’s the first time that this strategy has been observed in the wild.

    It really adds a new perspective to the well-known examples of male infanticide in primates. Finding early enough evidence of pregnancies and tracking their progress takes painstaking work collecting and processing fecal samples for hormone levels -- where the hormone quantities may be known only long after the researcher returns from the field with observations. The study is in the early access section of Science, which makes it hard for me to give bibliographic information, but here's the abstract.

    Tags: 
    primates
    behavior
    infanticide
    geladas
    birth
    dominance

  • Testosterone, fatherhood,

    Fri, 2011-12-16 00:23 -- John Hawks

    Daniel Lende has done a nice interview with Northwestern University anthropologist Lee Gettler ("On Testosterone and Real Men: An Interview with Lee Gettler"). Gettler is a Ph.D. candidate in human biology and author of a recent paper that demonstrated a decline in testosterone levels in new fathers [1]. This paper got a lot of press attention and was a big topic of conversation at the recent AAA meetings. Lende takes the conversation deep into the science, and probes the relation of human biology to behavior.

    All of human behavior is mitigated physiologically- i.e. through the actions of neuronal pathways and neurotransmitters- so there’s really no way of divorcing biology and behavior, which are in constant “flux” and “conversation” with one another. One challenge for anthropologists and other scholars studying these domains is trying in some coherent way to disentangle “the chicken” and “the egg” in the transactional relationship between biology and behavior.

    I like the formulation, "All of human behavior is mitigated physiologically." See also my old post: "Allostasis in human evolution".

    References

    1. Gettler LT, McDade TW, Feranil AB, Kuzawa CW. Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences of the United States of America. 2011;108(39):16194-9.
    Tags: 
    behavior
    behavior genetics
    hormones

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