4.11 Primates

The 2 clades of catarrhines: CERCOPITHECOIDS (vs. Hominoids)

*Cercopithecoid = Old World monkeys -OWMs = 2 groups: colobines and cercopithecines. Colobines = Africa, Asia -colobus, langur, proboscis, golden monkeys -more folivorous than cercopithecines, primarily arboreal, long tails, and hind legs longer than forelegs. Cercopithecines= African radiation -include macaques, baboons, etc -more omnivorous and folivorous than are colobines are also more terrestrial than colobines, with short tails and forelimbs and hindlimbs of equal length. -Cercopithecines have cheek pouches in which they carry food -ischial callosities! (NOT in colobines).

The 2 clades of catarrhines: (Cercopithecoids vs.) HOMINOIDS

*Hominoids = gibbons, great apes, humans -distinguished morphologically from other recent anthropoids by a pronounced widening and dorsoventral flattening of the trunk relative to body length -the shoulders, thorax, and hips have become proportionately broader than in monkeys -In all hominoids the clavicles are elongated, the iliac blades of the pelvis are wide, and the sternum is broad -The shoulder blades of hominoids lie over a broad, flattened back in contrast to their lateral position next to a narrow chest in monkeys and most other quadrupeds. -The lumbar region of the vertebral column is short. The caudal vertebrae have become reduced to vestiges (called the coccyx) in all recent hominoids, and normally no free tail appears postnatally. -Balance in a bipedal pose is assisted by the flat thorax, which places the center of gravity near the vertebral column. -These and other anatomical specializations of the trunk are common to all hominoids and help to maintain the erect postures that these primates assume during sitting, vertical climbing, and bipedal walking.

Importance of mother-infant bond

*The foundation of social group --Longest, strongest of primate relationships *Infant completely dependent on mother for --Nourishment --Transportation --Protection *Opportunity for social learning (of cues) to function in group --Visual --Auditory --Reproductive

Climate fluctuations and brain size

-NS drove evolution of larger brains. -as environment became unpredictable, bigger brains helped our ancestors survive. -origin of bipedality and large brains. However, this graphic suggests bipedality evolved much sooner than the rapid increase seen in brain size of modern humans and relatives. It is certainly reasonable to suspect the beginning of brain expansion with bipedality, for reasons discussed in text (and see next slide). But it is interesting to consider the connections between human adaptability, brain size, and climate change too!

Extant primates:

-lemurs, lorises, bush babies -new world monkeys + old world monkeys -apes (lesser and greater) - includes humans -flexible limbs to move thru trees, coordination -grasping hands/feet vs. clawed feet of rodents -binocular vision -large cerebral cortex = movement timing, distance judgment, perception of environment

Brachiation = specialized arboreal locomotion

-the animals swing rapidly from the underside of one branch to the underside of the next using their hands to grasp the branches, and is seen today in gibbons and spider monkeys, where it has evolved independently -Numerous of the skeletal adaptations of hominoids (apes) are specific to this fore-limb suspensory type of locomotion.

Diversity and Distribution: 5 natural groups of extant primates

1) Lemurs on Madagascar (only primates there!) ---underwent a major adaptive radiation. In addition to the almost eighty species of lemur alive today, that array included around twenty mostly larger-bodied sub-fossil species — some almost as big as a gorilla — that died out during the last two thousand years or so, after the first humans colonized Madagascar. 2) Lorises, pottos, bushbabies in Africa, S/SE Asia --widely spread, but more limited adaptive radiation (only ~30 species) 3) Tarsiers in SE Asian archipelago --about 12 species, small array 4) New world monkeys in S and Central America (only extant primates in new world) --diversified extensively, ~130 known species ----2 groups: small, claw-bearing marmosets and tamarins vs. larger-bodied true monkeys 5) Old world monkeys and apes in S Africa, S/SE Asia --largest group, over 150 species, extensive overlap in geographical dist. ---old world monkeys = 2 distinct sister groups

Six basic social patterns:

1) single female and her offspring - this group pattern is rare for primates but common for other mammals. Found in orangutans and some small nocturnal prosimians (e.g., mouse lemurs and galagos). The adult males lead their lives mostly alone, but come together with females occasionally for mating. The males of these species generally have large territories that overlap those of several females. Both male and female children usually leave their mother when they reach sexual maturity. 2) monogamous family group - these groups consist of an adult male and female with their children. When they are grown, the children leave to create their own nuclear families. This pattern is rare for NHPs. It is found among the small Asian apes as well as some of the New World monkeys and prosimians. Specifically, monogamous family groups are the common pattern for gibbons, siamangs, titi monkeys, indris, tarsiers, and apparently some pottos. 3) polyandrous family group - The smallest New World monkeys, the marmosets and tamarins, form both monogamous and polyandrous family units. They generally start with a monogamous mating pair. Later, a second adult male may join the family and assist in child rearing. When this occurs, both adult males will potentially mate with the adult female. This arrangement is practical because these monkeys commonly have twins and the fathers carry the babies around on their backs most of the time. This polyandrous mating pattern is extremely rare among NHPs. 4) Harem groups - polygynous mating patterns. That is to say, one male regularly mates and lives with more than one female at a time. Polygyny is generally not a promiscuous mating pattern. Rather, the male and his female mates form a distinct mating and child rearing group. This pattern is found among hamadryas baboons, geladas, langurs, howler monkeys, gorillas and many human societies. There are some caveats here - it would be a mistake to automatically assume that NHP harem groups are dominated by males; one-male-several female groups may take a different form when predator pressure is a problem, yet this is not the case with gorillas who are rarely concerned with predator dangers. 5) multi-male, multi-female - this is the most common social group pattern among semi-terrestrial primates. There are no stable heterosexual bonds--both males and females have a number of different mates. This is characteristic of savanna baboons, macaques, as well as some colobus and New World monkey species. These groups commonly have a dominance hierarchy among both males and females. Each individual is ranked relative to all other community members of the same gender. A female's rank in the hierarchy stays with her throughout life. Advancing up the male dominance hierarchy, e.g., in baboon communities, this is comparatively less peaceful than among macaques. Adult male baboons must constantly face challenges from other males who would take away their mates. These confrontations are usually noisy and violent. The fights often result in serious injuries caused by their exceptionally long canine teeth. 6) A fission-fusion society is one in which the social group size and composition change throughout the year with different activities and situations. This is the social pattern typical of chimpanzees. Individuals enter and leave communities from time to time. Adult males occasionally wander off and forage alone or join a few other males in a hunting party. Females casually change membership from one group to the other. This occurs especially when females are in estrus and seeking mates. As a result, foraging and sleeping groups reform frequently. Male chimps are the relatively stable core of the community since they rarely join other troops. What allows for the generally loose relationship between chimpanzee communities is that they apparently recognize a wider range of social bonds than do monkeys.

Why do humans lack fur?

1) we lost our fur in order to control our body temperature when we adapted to life on the hot savannah...The body-cooling idea seems sensible, but even though lacking fur might have made it easier for us to lose heat during the day, we also would have lost more heat at night, when we needed to retain it 2) modern humans became naked as a means to reduce the prevalence of external parasites that routinely infest fur. A furry coat provides an attractive and safe haven for "ectoparasites." These creatures not only bring irritation and annoyance but carry viral, bacterial and protozoan-based diseases such as malaria, sleeping sickness, West Nile and Lyme disease, all of which can cause chronic medical problems and, in some cases, death. Humans, by virtue of being able to build fires, construct shelters and produce clothes, would have been able to lose their fur and thereby reduce the numbers of parasites they were carrying without suffering from the cold at night or in colder climates...Human lice infections, which are confined to the hairy areas of our bodies, seem to support the parasite hypothesis Once hairlessness had evolved this way, it may have become subject to sexual selection—being a feature in one sex that appealed to another. Smooth, clear skin may have become a signal of health, like a peacock's tail, and could explain why women are naturally less hairy than men and why they put more effort into removing body hair. Despite exposing us to head lice, humans probably retained head hair for protection from the sun and to provide warmth when the air is cold. Pubic hair may have been retained for its role in enhancing pheromones or the airborne odors of sexual attraction

(hominoids) how to distinguish apes (hominoids) vs. monkeys

Apes and monkeys can be distinguished by their teeth -Monkeys have lower molars with four cusps, whereas those of hominoids have five cusps. -the teeth of apes have flatter relief than those of monkeys, and the grooves between the posterior cusps form a distinct Y pattern.

Jaw and dentition differences b/t pongids and hominins

Apes have long jaws that are rectangular or U shaped, with the molar rows parallel to each other; the canines are large and pointed; and there is a gap between the canines and the incisors. Hominins have short jaws in association with the shortening of the entire muzzle. The human jaw is V shaped or bow shaped; the canines are small and blunt; and the entire dentition is relatively uniform in size and shape without any gaps between the teeth

Gorillas and Chimps (tropical forests of central Africa)

Both are more terrestrial than gibbons and orangutans -On the ground they move quadrupedally by knuckle walking, a derived mode of locomotion in which they support themselves on the dorsal surface of digits 3 and 4 with the hand making a fist -Gorillas are the largest and most terrestrial of the apes. Unlike orangutans, they are highly social and live in groups, but like orangutans, gorillas are highly sexually dimorphic in body size...and they are the most folivorous of the apes ---Three geographically isolate subspecies of gorilla have been described: the western lowland gorilla, the eastern lowland gorilla, and the mountain gorilla -Chimpanzees are more omnivorous than are the more strictly herbivorous gorillas; they are also more arboreal, exhibiting a greater degree of suspensory locomotion. They are only moderately sexually dimorphic and, like gorillas, live in groups. ---There are two (possibly three) species of chimpanzees. The larger and more widely distribute common chimpanzee (Pan troglodytes) lives primarily in Central and East Africa. The western subspecies (P. troglodytes verus), from Nigeria and the Cameroon, may be a separate species. ---There is also a smaller species of chimpanzee, the bonobo (P. paniscus), in Central Africa south of the Zaire River. ---Chimpanzees are more omnivorous than are the more strictly herbivorous gorillas; they are also more arboreal, exhibiting a greater degree of suspensory locomotion. They are only moderately sexually dimorphic and, like gorillas, live in groups.

Social Organization and Behavior of Primates

Did sociality and group-living promote increased intelligence? Advantages of social living -Safety in numbers -Defense against predators -Defense of resources -Shared knowledge base (food, skills, traditions) -Support in raising young -Readily available mates -Social bonds=group cohesion -many relatively primitive primates are nocturnal and commonly described as 'solitary' --BUT field studies have revealed that nocturnal primates also have well-established patterns of social interactions, so all primates are social The difference is that 'solitary' nocturnal primates do not move around in groups, whereas diurnal (day-active) primates are typically gregarious, living in recognizable social groups. Gregarious behavior is seemingly connected with increased brain size and, presumably, with intelligence Yet a shift from nocturnal to diurnal habits in primate evolution is also connected with increased importance of vision, itself a cause of brain expansion, so this may be a driving influence. In any event, the pronounced social tendency now documented for all primates is doubtless linked to heavy investment in individual offspring (including intensive parental care) and extended lifespans -mating system and/or mean group size are a function of relative neocortex volume in primates. This relationship suggests that the size of the neocortex imposes some kind of constraint on the number of social relationships that an individual animal can keep track of within its social group.

History of brain size:

During the first four million years of human evolution, brain size increased very slowly. Encephalization, or the evolutionary enlargement of the brain relative to body size, was especially pronounced over the past 800,000 years, coinciding with the period of strongest climate fluctuation worldwide Larger brains allowed hominins to process and store information, to plan ahead, and to solve abstract problems. A large brain able to produce versatile solutions to new and diverse survival challenges was, according to the variability selection hypothesis, favored with an increase in the range of environments hominins confronted over time and space.

Great ape and hominin comparisons (see pic)

Generally, we went from quadrupedal -> bipedal, shorter canines, rarer arboreality to none

Hominoids: Hylobates vs. Hominids

Hylobates = lesser apes (smaller), such as gibbon, incl. siamangs -monogamous, entirely bipedal when walking on ground Hominids = great apes and hominins -Orangutan (arboreal, climb more than swing, solitary) -Gorillas, chimps (more terrestrial, knuckle-walking, social groups) --gorillas herbivorous, chimpanzees omnivorous

Parasites and hair loss:

If we look at our parasites and the corresponding obligate parasites on the species with which we share a common ancestor, we should see the same genetic and morphological relationships between them as between us and our ancestors. And this is exactly what we see in the three human lice and those of our closest relatives: So, where did we pick up these unwanted blood suckers in the first place? All signs point to a human-ape connection, and "connection" may mean something more tangible than an evolutionary link. Some studies suggest interaction between early Homo species and gorillas, and also between early Homo species and us -basically,we share a genus w/ both chimps and gorllas

What sets humans apart?

Locomotion: we are only habitually bipedal primate (skeletal changes support bipedalism) Larger, more complex brains: capacity for spoken language, culture as means of adaptation Reproductive behavior: sexual activity for non-reproductive purposes Reduced body hair.

Orangutans

Orangutans are about the same size as humans but are extremely sexually dimorphic, with males weighing twice as much as females. They are generally solitary, with groups consisting of females and their offspring. Orangutans are arboreal but rarely swing by their arms, preferring slow climbing among the branches of trees. They usually hang with all four limbs below the branch but sometimes walk on their hindlimbs on top of the branch, supporting themselves by grasping tree limbs above them.

Modern anthropoids = Haplorrhines (Platyrrhines vs. Catarrhines)

Platyrrhines = new world monkeys (Capuchin, squirrel monkey, marmosets, tamarins, owl monkey) -nostrils side-facing, round, wide-spread -3 premolars -prehensile tail Catarrhines = old world monkeys + apes (Colobines, mandrills, macaques, baboons + apes) -nostrils downward-facing, oval, narrow-spaced -2 premolars -tail not prehensile Olfaction: all catarrhines have trichromatic color vision, which is also seen in a few platyrrhines, such as the howler monkeys.... Olfaction - while all anthropoids have small olfactory bulbs, platyrrhine primates seem to have retained a relatively good sense of smell, and the most of the genes associated with olfaction are still functional. In contrast, only 50 percent of the olfactory genes of catarrhines code for functional receptor proteins, and catarrhines have also lost a functional vomeronasal organ. Skulls, brains, teeth - platyrrines and catarrhines also differ in some details of the skull, especially in the ear region. Additionally, while all modern anthropoids have relatively large brains, the fossil record shows that enlargement of the brain from a prosimian-like condition occurred independently in the two groups. Furthermore, platyrrhines retain the generalized primate condition of having three premolars on each side of the jaw, whereas catarrhines have only two premolars.

Hominids: Pongids (great apes) and Hominins (humans)

Pongids have lower braincase/skull ratio, smaller brain size, large canines, sexually dimorphic, sagittal crest, more prognathic, long and flat pelvis w/ musles attached at back, opposable big toes Hominins have higher braincase/skull ratio, brain 4x as big as apes, canines greatly reduced, no sagittal crest, less prognathic, shorter bowl pelvis w/ muscles attached to outside, big toes not opposable. Anatomical differences between humans and apes appear I the skull and jaws, the trunk and pelvis, and, to a lesser extent, the limbs -Several evolutionary trends can be identified within the hominins. The points of articulation of the skull with the vertebral column (the occipital condyle) and the foramen magnum (the hole for the passage of the spinal cord through the skull) shifted from the ancestral position at the rear of the braincase to a position under the braincase. -This change balances the skull on top of the vertebral column and signals the appearance of an upright, vertical posture. The braincase itself became greatly enlarged in association with an increase in forebrain size.

Form, Function, and Evolution of Primates

Primates -prehensile hands -nails -flatter face -larger braincase/skull ratio -forward-facing eyes -increased vision, decreased smell -bony enclosure around orbits -clavicle -bunodont teeth imply originally frugivorous diet --primates today mainly herbivorous, with smaller forms eating insects and larger forms eating leaves. Other mammals -no prehensile hands -claws -prognathic (longer snout) -braincase not enlarged -lateral eyes -better smell than vision -no bony enclosure around orbits OR clavicle Some mammals retain clavicle, have similar teeth structure, ungulates/kangas have only single young per pregnancy BUT, most of these traits = for arboreal life (such as modifications of limbs), and arboreality is rare among placental mammals --haha Meissner's corpuscles enhance sense of tough

Learning how to behave

Primates rely heavily on visual signals to acquire info about social group Signals convey *Age (coats diff. in babys vs. adults, vulnerability wards off predators from aggressive mother) *Sex (sexual dichromatism, dimorphism, divocalism *Rank (silver-back gorilla) *Reproductive status (females only sexually receptive during estrus = bright pink/red swollen genitals (OWMs, bonobos).

Prosimians (bush baby) vs. Anthropoids (tamarin)

Prosims = lorises, lemurs, potto, bush babies, tarsiers, etc -more prognathic, smaller braincase/skull ratio, toothcomb (thin incisors, forward-projecting), post-orbital bar, short snout w/ dry nose (exclude tarsiers bc they have dry nose?) -Prosimians are in general small, nocturnal, long snouted, and relatively small brained compared with the more derived anthropoids -Anthropoids lack the grooming claw on the second toe that is seen in modern prosimians. Anthropoids = monkeys, apes -less prognathic, greater braincase/skull ratio, no toothcomb, color vision, post-orbital bar + plate, include tarsiers if strepsirrhines vs. haplorrhines (simple nose) -Modern anthropoids are mostly larger than prosimians, with larger brains housing relatively small olfactory lobes, and they are frugivorous or folivorous rather than omnivorous or insectivorous. They also are usually diurnal, with complex social systems. -large brain size, fibrous diet w/ lots of chewing -bony post-orbital septum is an important distinguishing anthropoid feature. --significance of this character is related to the evolution of large, forwardly oriented orbits and the need to prevent mechanical disturbance of the eye when the temporalis muscle contracts

Dominance Hierarchies

Ranking system of dominant -> subordinates -Based on ability to displace, intimidate, or defeat through contests (Dominance = preferential access to food and mates) Rank varies w/ sex, age, time in group, aggression, intelligence, mother's social position. while violence can be used to maintain one's position, dominance hierarchies also serve to reduce the overall violence in the troop Access to reproduction and survival of offspring are most likely the key to dominance hierarchies. Among Gombe chimpanzees, the offspring of higher ranked females were more likely to survive; they also produced more offspring during their lifetimes as they matured faster. In most primate groups where multiple females are present, the males dominate them. There is a separate dominance hierarchy among the females (chimpanzees are one example). In species where there is pair bonding, the two partners are co-dominant (Gibbons are an example).

Maximizing reproductive success

Reproductive strategies vary for M vs. F Females = mate choice, multiple partners -> decreases infanticide (paternity confusion) Infanticide is individualistic strategy for males (e.g. langurs) -harem, bachelor males raid group, fight dominant male, new one takes over, infants killed, females resume estrus

Catarrhines origins - include the Old World monkeys, apes, and humans

The split between apes and monkeys has been estimated from molecular studies to have occurred about 28 mya Catarrhines have nostrils that are close together and open forward and downward, and they have a smaller bony nasal opening from the skull than do platyrrhines Catarrhines' tails are often short or absent, and they never evolved prehensile tails.

Biological continuum

The term biological continnum refers to the fact that organisms are related through common ancestry and that behaviors and traits seen in one species are seen also in others to varying degrees. The differences between human and other primates (especially chimpanzees) are more quantitative and not qualitative. This has also been described as "a matter of degree and not kind". A few human features to acknowledge on the continuum (and for which we are more similar than different): -Human brains are larger than primate brains, but the neurological processes are functionally the same. -The necessity of close bonding with at least one parent -Need for physical contact -Developmental stages and dependence on learning -Capacity for cruelty, aggression, compassion, altruism (with humans having the capability to reflect on behavior) But, we are also different (here just a few suggested examples): -Humans are better at symbolic communication and may be only species capable of true language (though this is open to debate!) -Humans are interested in teaching others for the purpose of shared goals -Human women go through menopause decades before they die, which is not true of other primate species - is this really true or not?

Dominance hierarchies contd

They impose order (reduce violence) (displaying, mounting) Submissive behavior = grooming higher ranked individuals, presenting hindquarters, crouching Grooming - time-consuming, essential -social solidarity -most imp activity ---Pleasure of physical contact, reinforces social bonds and status, helps with hygiene

Variations in social structure

While there is considerable variation in social group structure or composition among the primates, there is very little variability within each species -Solitary (mostly prosimians, but also orangutan) -Monogamous pairs (rare) -Large, permanent or semi-permanent groups --Fusion-fission society - groups/individuals come and go (e.g., chimps) --Harem - single male, multi-female ----Dominant male has exclusive mating access (e.g., gorilla) --Multi-male, multi-female ----Dominance hierarchy ----Males compete for females (e.g., baboon troops, common chimps)

Sexual dimorphism in cercopithecines

adult males are often twice as large as females and much more aggressive (powerful jaws and canines) -The cercopithecines share two other identifiable anatomical characteristics--ischial callosities [see definition below] and cheek pouches ---Ischial callosities are specialised regions of skin and subdermal tissue in the form of fibro-fatty cushions with a tough, non-slip surface, firmly bound to the underlying ischial tuberosity ------They occur in primates of the families Cercopithecidae and Hylobatidae

Euprimates = direct fossil relatives of primates

date back to Eocene, 55 mya -earliest euprimates adapted for arboreal life, possessed many key features of skull, teeth that characterize modern primates Inferred relationships within the mammalian superorder Euarchontoglires (supertree w/ molecular data).

Primate ancestors:

insectivorous, tree-dwelling, likely nocturnal -tree shrew possibly closest relative to all primates This ancestral primate lineage split into two lineages, one of which gave rise to lemurs and lorises; and the other, to tarsiers, monkeys, and apes Traditionally lemurs, lorises, and tarsiers have been called prosimians, a paraphyletic group, and apes and monkeys have been called simians or anthropoids. Prosimians and many simians are arboreal (tree-dwellers), which is probably the ancestral lifestyle for both groups

Platyrrhines origins - exclusively New World radiation

presumed to have rafted from Africa across the Atlantic Ocean....Marmosets and tamarins are small and squirrel-like and have secondarily clawlike nails on all digits except for the big toe They are also unusual among anthropoid primates, and more like the prosimians, in producing twins. The owl monkeys are the only nocturnal anthropoids....[Howler, spider and titi monkeys] are distinguished by their prehensile tail

Determinants of group composition

primate socioecological theory in line with the basic premise that, for most species, female behavior is affected by ecological variables and food competition, while males are primarily affected by mating competition and the distribution of receptive females Female food competition, as the ultimate evolutionary force influencing primate social organization, has provided the fundamental starting point for all subsequent models females will live in groups when the benefits of cooperative resource defense outweigh the costs of within-group feeding competition. Females will form bonds with their relatives to cooperatively defend access to food resources. Large groups will out-compete smaller groups and obtain greater fitness by excluding neighboring groups from food sources SO: these female-bonded species, between-group competition will select for group formation and create a selective advantage for larger groups, while within-group competition (in non-territorial species) or the ability to defend a home range of appropriate size (in territorial species) will ultimately constrain group size Wrangham's model suggests that predation risk was the ultimate factor forcing females to live in groups despite the costs imposed by feeding competition van Schaik argued that the costs of within-group competition far outweigh any advantages resulting from communal resource defense and that resource defense cannot be invoked as the primary selective force for grouping. Rather, the threat of predation puts a lower limit on group size, while within group food competition sets the upper limit."

insectivore-primate boundary

smooth gradient from insectivores (archetypal primitive mammals) to primates -tree shrews were seen as intermediate BUT, this is FALSE -because "frozen ancestor" approach is not true...extant species are NOT models for evolutionary stages -there is no evolutionary sequence from hedgehogs through tree-shrews to lemurs. These extant species are all end-points on the phylogenetic tree of mammals, which must be painstakingly reconstructed through analysis of individual characters -Such reconstructions indicate that tree-shrews, at best, are only distantly related to primates.

Extant Apes: Asian gibbons (incl siamangs), orangutan, African chimps and gorilla

social learning (for example, of tool use) with distinct differences among different biogeographic regions, has been observed in both chimps and orangutans -chimpanzees have been shown to be capable of foresight and planning for future events All of the great apes are critically endangered.

Gibbons (smallest apes)

they differ from other apes (and, indeed, the great majority of mammals) in their monogamous social system. Gibbons move through the trees most frequently by brachiation. They become entirely bipedal when moving on the ground, holding their arms outstretched for balance like a tightrope walker using a pole...

Old hominoid classification:

used to be Hylobatidae (gibbons/siamangs), Pongidae (other apes, or "great apes", and Hominidae (humans) -hylobatidae is only valid family remaining molecular data show that chimpanzees are more closely related to humans than are the gorilla and the orangutan, and in turn the gorilla is more closely related to the human and chimps than is the orangutan. -Many researchers now consider that the great apes and humans belong in a single family, and the term "Hominidae" now includes these apes as well as ourselves....Thus, what was called a hominid in fossil studies only a few years ago (and in earlier editions of this book), meaning a fossil human, is now called a hominin