Anthr. Ch. 10
Homo habilis
larger brain and reduced chewing complex— made its appearance At that time, australopithecines were diverse, evolving, and a significant presence on the African landscape. This gracile hominin likely evolved from an australopithecine, and the ancestor may have been Au. garhi. *This point in human evolution is critically important because it is the earliest record of a remarkable adaptive radiation, leading to the most prolific and widespread species of primate: us* The earliest Homo species, a possible descendant of Au. garhi and an ancestor to H. erectus; showed the first substantial increase in brain size and was the first species definitively associated with the production and use of stone tools.
AUSTRALOPITHECUS KENYANTHROPUS) PLATYOPS (3.5 MYA)
lesser-known hominin from about the same time as Au. afarensis discovered by Meave Leakey and her colleagues at Lomekwi, on the western side of Kenya's Lake Turkana, in deposits that date to about 3.5 mya. Its habitat was mainly woodlands. Its face was unusually flat (platyops, from the Greek, means "flat face"), a derived feature in hominins, but retained some primitive characteristics. def. An australopithecine from East Africa that had a unique flat face and was contemporaneous with Au. afarensis.
The Australopithecines (4-1 mya)
represented by hundreds of fossils of as many as nine species from one genus, Australopithecus. Some of the species represent members of ancestral-descendant lineages For the other species, however, anthropologists are sorting out the lineage relationships. Compared with other mammals, australopithecines did not vary greatly. Their variation was mostly in size and robusticity—from relatively small and gracile to large and robust. as a group, they had a small brain, small canines, large premolars, and large molars; *the later australopithecines' face, jaws, and teeth were very large*
Australopithecus africanus
A gracile (slender build) australopithecine from South Africa that was contemporaneous with Au. aethiopicus, Au. garhi, and Au. boisei and was likely ancestral to Au. robustus. initially found at the Taung site dates to about 3-2 mya had larger teeth than those of Au. afarensis. After about 2 mya, there were at least two descendant species of australopithecines in South Africa, Australopithecus robustus (sometimes called Parathropus robustus) and Australopithecus sediba dating to 2.0-1.5 mya and 2.0 mya, respectively. Studies of microwear on tooth surfaces and stable carbon isotopes from fossils suggest, however, that while robust australopithecines in South and East Africa chewed tough foods, they were eating significant amounts of low-quality vegetation. Small brain (450 cc) Moderate-size teeth Equal-size cusps on third premolar Phalanges not curved Adult partial skeleton has apelike leg-to-arm ratio (short legs, long arms) Lived in open grasslands Parabolic tooth rows in upper jaw
AUSTRALOPITHECUS GARHI (2.5 MYA) (pgs. 276-277 for more info.)
A late australopithecine from East Africa that was contemporaneous with Au. africanus and Au. aethiopicus and was the likely ancestor to the Homo lineage. garhi= surprise in the Afar language Found in Bouri, in Ethiopia's Middle Awash region, represented by bones, teeth, a partial skeleton, and a skull teeth were larger than the earlier australopithecines'. Its third premolar's two cusps were almost equal in size. As in Au. afarensis, beneath the nose the face had a primitive projection, and the brain was small (450 cc). For the first time in hominin evolution, the ratio of arm (humerus) length to leg (femur) length was much more humanlike than apelike, resulting from the femur's lengthening. (indicates a decreased commitment to the arborealism of earlier australopithecines) These features combined—especially the chronological position at 2.5 mya and the cranial, dental, and postcranial features—suggest that Au. garhi was ancestral to Homo. evidence indicate that this hominin lived on a lakeshore, as was typical of later australopithecines and early Homo. evidence indicates that like Au. garhi used stone tools to process animal remains for food
Australopithecus sediba
A late species of australopithecine from South Africa that may have descended from Au. africanus, was a contemporary of Au. robustus, and expresses anatomical features found in Australopithecus and in Homo. cranial features are distinctively different from those of Au. robustus. face, jaws, and teeth are relatively small. cheekbones (zygomatics) do not flair outward, unlike those of Au. robustus. the broad pelvis and its overall shape are more Homo-like. small body and relatively long arms, however, are more like those of australopithecines. hand has fingers with large, powerful muscles for grasping in arboreal settings yet with a long thumb for precision gripping, perhaps for tool production and use. brain was tiny, only about 420 cc, considerably smaller than the brains in any early Homo. The presence of features associated with Homo suggests that this australopithecine might have played a part in the ancestry of our genus (genetic traits in the teeth of Au. sediba show strong affinities with other australopithecines in South Africa and with early and recent Homo) However, the presence of early Homo in East Africa well before Au. sediba indicates that the transition from Australopithecus to Homo first took place in East Africa. However, the lineage leading to Homo seems to have developed an increasingly flexible and generalized diet, whereas the later robust australopithecines' diets became less flexible and more specialized.
Ardipithecus ramidus
A later preaustralopithecine species from the late Miocene to the early Pliocene; shows evidence of both bipedalism and arboreal activity but no indication of the primitive perihoning complex. 2009, Science called this finding the "Breakthrough of the Year" Anthropologists called it the breakthrough of the century it is represented by a huge assemblage of fossils. These fossils include the most complete early hominin skeleton found to date, along with bones and teeth of at least 35 other individuals, all bracketed to a depositional period of less than 10,000 years, an eyeblink in human evolution the fossils provide us with a snapshot of the species: their behavior, their adaptation, and what life was like for them not long after the chimpanzee and human lineages had diverged from their common ancestor in the late Miocene. *The ecological context shows dramatically that these early hominins lived in a forest* (cool and wet) *This discovery provides compelling evidence that—contrary to the hypotheses of Darwin and other authorities and reaffirmed by most of the fossil record dating to the Pliocene and Pleistocene—the first hominins did not evolve in the open grasslands* *the 1st hominin ancestor WAS NOT chimpanzee like*
Australopithecus robustus
A robust australopithecine from South Africa that may have descended from Au. afarensis, was contemporaneous with Au. boisei, and had the robust cranial traits of large teeth, large face, and heavy muscle attachments. probably the longest-surviving species of the australopithecine lineage in South Africa, had large premolars, a big face, and a well-developed sagittal crest. were similar in many respects to their contemporary East African counterparts. *Australopithecines' greater robusticity in South Africa and East Africa indicates a widespread adaptation involving an increased focus on foods that required heavy chewing*
Ardipithecus kadabba (came before ramidus)
An early preaustralopithecine species from the late Miocene to the early Pliocene; shows evidence of a perihoning complex, a primitive trait intermediate between apes and modern humans. known mainly from teeth, and these fossils show that hominins' canines wore from the tips (not the sides) but had some honing or polishing on the sides of the third lower premolar
Australopithecus aethiopicus
An early robust (strong & healthy) australopithecine from East Africa, with the hallmark physical traits of large teeth, large face, and massive muscle attachments on the cranium. genus Parathropus from the west side of Lake Turkana, dates to about 2.5 mya and had a brain size of about 410 cc. Compared with earlier australopithecines, these remarkably robust australopithecines had smaller front teeth, larger back teeth, and larger faces. Their most visually striking characteristic was a massive attachment area, on the skull, for the temporalis muscle, resulting in a well-developed sagittal crest. Both their premolars and their molars were enormous. These big teeth with large chewing surfaces, combined with large chewing muscles, made robust australopithecines the ultimate grinders greater cranial robusticity after about 2.5 mya indicates that they were increasingly focused on acquiring and eating foods that required more powerful chewing muscles than before. (ate harder foods) (named for Ethiopia, the country where they were first found)
the first tools
At the Gona River site, in the Middle Awash region, tools have been found dating to around 2.6 mya. Though still extraordinarily primitive, the tools would have been effective at cutting, butchering, and other kinds of food processing. The dominant tools, "chopper" tools and flakes, discovered in these early hominin sites were used to remove the meat and process the meat from various animals, mostly herbivores. At least two activities were involved: use of flakes with sharp edges for cutting meat from bones and use of choppers and cobbles to break and smash the bones to access the protein-rich marrow. One of the sites best known for such findings is the FLK 22 site at Olduvai Gorge, where the Leakeys found the famous Australopithecus boisei cranium in the late 1950s. some tools have shown wear (South African caves) produced by digging in the ground esp. in termite mounds (supports the idea that early hominins ate insects in addition to meat (providing protein) -> they may have also been used for digging up edible roots before this time, tools may not have been found b/c they were made of ephemeral (lasting for a short time) materials such as wood and grass Other evidence suggests, however, that australopithecines used tools. (hand bones have anatomical features associated with finer manipulation than that used by living apes, and a flexor muscle that makes possible the finer precision use of the thumb and other fingers for tool production and use) = material culture for acquiring, preparing, and consuming animal sources of protein
earliest hominins "Australopithecus"
Australopithecus (known from this one genus) found mostly in two key areas of Africa: 1. in a series of limestone caves in South Africa 2. sedimentary basins and associated river drainages in the Eastern Rift Valley (part of the Great Rift Valley) in Ethiopia, Kenya, and Tanzania the crucial time period during which hominins and the last common ancestor with apes (chimpanzees) split into separate lineages has been an unknown because of the 4-millionyear gap in the fossil record (8-4 mya). hominins predating Australopithecus have been discovered in north-central and eastern Africa. (These hominins have closed the gap between late Miocene ape evolution and the first hominins, the pre-australopithecines)
Australopithecus boisei
Formerly known as Zinjanthropus boisei; a later robust australopithecine from East Africa that was contemporaneous with Au. robustus and Au. africanus and had the robust cranial traits, including large teeth, large face, and heavy muscle attachments. (named for a benefactor who supported the discoverer's research) genus Parathropus from Olduvai Gorge and around Lake Turkana, dates to 2.3-1.2 mya and had a brain size of about 510 cc. Compared with earlier australopithecines, these remarkably robust australopithecines had smaller front teeth, larger back teeth, and larger faces. Their most visually striking characteristic was a massive attachment area, on the skull, for the temporalis muscle, resulting in a well-developed sagittal crest. Both their premolars and their molars were enormous. These big teeth with large chewing surfaces, combined with large chewing muscles, made robust australopithecines the ultimate grinders greater cranial robusticity after about 2.5 mya indicates that they were increasingly focused on acquiring and eating foods that required more powerful chewing muscles than before. (ate harder foods) evidence from stable carbon isotope ratios indicates that Au. boisei mostly ate savanna (C4) grasses. In this way, Au. boisei was like other contemporary grass-consuming mammals (such as horses, pigs, and hippopotamuses) but strikingly different from all other hominins. This reliance on grasses—perhaps as much as 80% of their diet was grass—would have required heavy grinding by the jaws and teeth.
dentition of hominins vs. apes
Hominins place more emphasis on the front portion of these muscles, to provide greater vertical force in crushing food. Apes place more emphasis on the back portion of the masticatory muscles because slicing requires more horizontally oriented forces. As an additional aid in powerful crushing, hominins have evolved thick enamel on their teeth Living apes have evolved thin enamel, reflecting diets dominated by plants and soft fruit. Among the hominoids, the only exception is the orangutan, which has evolved thick enamel—its diet includes tough foods that require heavy crushing. the distinguishing features of the Homininae are located in the anatomical complexes associated with acquiring and transporting food (locomotion) and chewing food (mastication).
disadvantages of bipedalism
Standing upright yields a better view across the landscape, but it also brings exposure to predators. Standing or walking on two feet while simultaneously lifting or carrying heavy objects over long periods of time causes back injury, such as that associated with arthritis and with slipped intervertebral disks. places an enormous burden on the circulatory system as it moves blood from the legs to the heart. The result of this burden is the development of varicose veins, a condition in which overwork causes the veins to bulge. Lastly, if one of a biped's two feet is injured, then that biped's ability to walk can be severely reduced. (Unable to move about the landscape, an early hominin would have had limited chances of surviving and of reproducing) only rarely do adaptive shifts come w/o a cost...
Hominin
The morphological characteristics—and behaviors inferred from these characteristics—shared by living humans and their ancestors but not shared by apes reveal what is distinctive about hominins. we speak, use language, depend fully on material culture and have advanced cognition (living apes do not have these characteristics) Speech, advanced cognition, and complex material culture evolved in the human line long after the first hominins appeared in Africa, 7-6 mya, *so these characteristics do not define a hominin* a hominin is much better understood as having two obligate behaviors—bipedal locomotion and nonhoning chewing—and the suite of associated physical characteristics that manifest these behaviors. The evidence is very clear: bipedal locomotion and nonhoning chewing preceded speech and material culture by several million years. Like large brains, speech and material culture help define humans today but were not attributes of the earliest hominins.
AUSTRALOPITHECUS ANAMENSIS (4 MYA)
The oldest australopithecine species; from East Africa and a likely ancestor to Australopithecus afarensis. (anam means "lake" in the Turkana language), found within Allia Bay and Kanapoi, in, respectively, the eastern and southern ends of Lake Turkana, Kenya was broadly similar in physical appearance to Ardipithecus, enough to indicate a probable ancestral-descendant relationship between the two genera. Reflecting its relatively early place in australopithecine evolution, Au. anamensis has a number of primitive, apelike characteristics, including very large canines, parallel tooth rows in the upper jaw, and a lower third premolar with both a very large outer cusp and a very small inner cusp The fossils were created in woodland environments.
Lower Paleolithic
The oldest part of the period during which the first stone tools were created and used, beginning with the Oldowan Complex.
Oldowan Complex,
The stone tool culture associated with H. habilis and, possibly, Au. garhi, including primitive chopper tools. the first hominin culture and the earliest culture of the Lower Paleolithic, named by Louis and Mary Leakey from their work at Olduvai Gorge. The Leakeys concluded that these early stone tools must have been produced solely by the larger-brained early Homo found at the site, rather than by the contemporary smaller-brained australopithecines. discovery of animal bones w/ cut marks strongly suggests that the first tool makers and users were australopithecines prob. Au. afarensis (the only hominin known from this setting) The cutmarks are characteristic of those made by tools when cutting meat from bone and extracting the nutritious marrow inside. the actual presence of stone tools dating to 3.3 mya from Lomekwi, West Turkana, Kenya. Scores of in situ artifacts, including Oldowan-like cobble tools and various other implements used for processing animals for food, document the presence of a well-established tool technology (substantially pre-dating early Homo) Because Au. (Kenyanthropus) platyops was found in the same geographic location and time, it seems likely that this hominin made and used these tools.
Philip Reno and his associates have studied early hominin bones to determine relative sizes of females and of males.
Their analysis shows relatively little sexual dimorphism in body size, especially in comparison with apes. Such reduced sexual dimorphism suggests that males were cooperative, not competitive. This cooperative behavior could have included pair-bonding—one male paired with one female—a behavior pattern necessary for the kind of provisioning required in Lovejoy's hypothesis.
advantage of bipedalism
ability to see greater distances (thanks to upright posture), greater ease of transporting both food and children; ability to run long distances; freeing of the hands for skills and activities as tool manufacture and use
Of the three key Au. afarensis sites, Laetoli is especially extraordinary
because of its assemblage of fossil hominins and because of its spectacular preservation of thousands of footprints left by numerous species of animals, ranging from tiny insects to giant elephants. (due to a volcanic eruption) Physical anthropologists' study of these tracks reveals that the creatures were humanlike and had three key characteristics of bipedalism: round heels, double arches (front- to-back and side-to-side), and nondivergent big toes. (differing from living apes -> Au. afarensis) -> primarily in terrestrial locomotion
second diff. b/w living apes and humans & human ancestors
dentition processing of food Apes and humans have evolved different dental characteristics, reflecting how each uses the canine and postcanine teeth When apes grab on to food with their front teeth, the upper canines and lower third premolars cut and shred the food. (honing complex) *humans have non honing chewing* Through evolution, apes' upper canines have become large, pointed, and projecting, with a sharp edge on the back. When the jaws are fully closed, each canine fits snugly in the diastema (The sharp edge on the back of the upper canine hones, or rubs against, a sharp edge on the front of the lower third premolar, or sectorial premolar) this is essential in apes to slice up leaves and fruit before they are chewed by the back of the teeth and swallowed Apes' lower third premolar is also distinctive in having one large, dominant cusp on the cheek side of the tooth and a tiny cusp on the tongue side of the tooth. In contrast, living and past hominins have small, blunt, and nonprojecting canines and no diastema. Hominin canines wear on the tips instead of the backs The cusps on both sides of the lower third premolars are similar in size, or at least more similar in size than are apes' cusps. hominins do not hone their canines as they chew Hone = rub In humans, the temporalis muscle is vertically oriented, enabling a crushing ability. In nonhuman primates, this muscle is oriented horizontally, producing slicing motions. Apes' and humans' postcanine teeth have many similar anatomical characteristics. (3rd & 4th premolars, upper & lower, have 2 cusps each; the upper molars have 4 cusps; lower molars have 5 cusps; back teeth crush and slice food w/ a diff. emphasis: humans crush food more than apes do) -> apes use their molars more for slicing than crushing reflecting their plant- heavy diet In apes and humans, grinding and slicing are facilitated by powerful chewing, or masticatory, muscles, especially the temporalis, masseter, and pterygoid muscles
Charles Darwin offered the first serious hypothesis about the first appearance of hominins.
drew on Thomas Huxley's anatomical research on the living apes of Africa Darwin concluded that because of the remarkable anatomical similarity between humans and African apes, Africa was hominins' likely place of origin. The characteristics that distinguish living humans from living apes, Darwin reasoned, derive from one key evolutionary event in their common ancestor, namely, the shift from life in the trees to life on the ground. In Darwin's time, there were no recorded instances of apes' making or using tools, so tools appeared a uniquely human phenomenon (since then apes have been making and using tools) He observed four characteristics that set living humans and living apes apart: 1. Humans are bipedal, apes are quadrupedal 2. humans have tiny canines, apes have large canines 3. humans rely on tools in their adaptations, apes do not 4. humans have big brains, apes have small brains He concluded that bipedalism had freed the hands for carrying the weapons. To manufacture and use these tools, the early humans needed great intelligence. Once they had the tools, they did not need the big canines for hunting or for defense. Although he saw tool production and tool use as essential factors in the development of human intelligence, Darwin believed that humans' large brain resulted mainly from the presence of language in humans. scientists now know that tool use and increase in brain size began well after the appearance of bipedalism and the reduction in canine size *Darwin proposed that hunting was at the basis of the divergence* ( however archeological record suggests that hunting began much later in human evolution and the brain began to expand) -> hunting played an impt. role in LATER human evolution but NOT in hominin origins
SAHELANTHROPUS TCHADENSIS (7-6 MYA)
earliest pre-australopithecine is represented by most of a skull and other fossils found in central Africa, beginning in 2001, by the French paleontologist Michel Brunet and his colleagues (meaning "genus named for the region of the southern Sahara Desert known as the Sahel") many were surprised by its geographic location (Toros-Menalla locality of the Djurab Desert, in Chad) b/c it was far from the Eastern Rift Valley where all other early hominins in East Africa had been found for a majority of time In short, humans originated in Africa during the late Miocene and early Pliocene. brain size of about 350 cc. compared to Homo Sapiens (about 1,450 cc) this shows an increase in brain size Its brain was primitive and like that of apes. Moreover, this hominin had a massive browridge, larger than that of modern gorillas. likely bipedal and the canine- premolar chewing complex was non honing (This combination of primitive (more apelike) and derived (more humanlike) features is to be expected in the oldest hominin, especially in apes' and humans' common ancestor) Its great age and primitive characteristics indicate that Sahelanthropus existed very close—the closest of any fossil known—to the divergence of their common ancestor into apes and hominins. the nonprimate animals found around it indicates that it lived in a forest near a lake (ex.'s fish, crocodiles, horses, elephants, primates, and rodents associated w/ forests & grasslands)
1800s
entire human fossil record was a very small fraction of what it is today, numerous authorities believed that the beginning of bipedalism was not the hallmark event distinguishing humans from apes. these scientists believed that the most important initial evolutionary change was an increase in brain size, reflecting advanced (human) intelligence. They speculated that only with advanced intelligence would language, tool use, and the other behaviors that collectively define humanness have become possible. The focus on intelligence to the exclusion of other attributes helped bring about the rapid and uncritical acceptance of some purported early hominin ancestors that later turned out to be fake.-> Since then, the large early hominin fossil record has proven that bipedalism— and not human intelligence—was the foundational behavior of the Hominini, preceding most attributes associated with humans and with human behavior by millions of years.
ORRORIN TUGENENSIS (6 MYA)
fossils of at least 5 pre- australopithecines found in the Tugen Hills on the western side of Kenya's Lake Turkana The discoverers, paleoanthropologists Brigitte Senut and Martin Pickford, named these hominins Orrorin tugenensis (the genus means "original man" in Tugen's local language). Among the 20 remains were several partial femurs, each missing the knee but indicating that these hominins were bipedal. (For example, the femur's neck, the area that is at the top of the bone and articulates with the hip, was relatively long) A hand phalanx found at the site was curved like a living ape's, suggesting that Orrorin spent time in the trees. Like those of Sahelanthropus, the canines had wear on the tips and were nonhoning. The animal bones at the site indicated that Orrorin lived in a forest.
THE PRE-AUSTRALOPITHECINES
had a number of primitive attributes, and in some respects they were more apelike than humanlike. They represent the first recognizable ancestors of the lineage leading to humans.
sexual dimorphism and human beh.
had a unique focus on diff's on female and male body sizes and on the implications of beh. with a decidedly human bent (Lovejoy) some argue that early hominins were highly dimorphic in the case the competing males were likely not involved for caring for their offspring (only for sexual access to females -.-) However, if early hominins were not especially dimorphic, then male competition for mates probably was not part of early hominin social behavior.
AUSTRALOPITHECUS AFARENSIS (3.6-3.0 MYA)
have been found in four main sites: Laetoli, in Tanzania, and Hadar, Korsi Dora, and Dikika, all in Ethiopia (Afar is the name of the local tribe on whose land the fossils were found in Ethiopia). best-known australopithecine and is represented by dozens of individuals from Laetoli and Hadar and single individuals from Korsi Dora and Dikika, collectively dating to 3.6-3.0 mya. The most spectacular of the Au. afarensis fossils are three partial skeletons from Hadar, Korsi Dora, and Dikika. (they represent an adult female nicknamed Lucy, and adult male, and a 3 yr old child) Lucy stood only a little more than 1 m (about 3.5 ft) and had somewhat short legs relative to the length of the arms and body trunk. (short legs may have limited the stride in comparison w/ modern people) -> found in East Africa However, the male stood about 1.5-1.7 m (about 5-5.5 ft), and the features of the skeleton and limb bones indicate that the form of walking was likely quite similar to modern humans'. (shoulder was similar to modern human's) This similarity suggests that Lucy's legs were not short because it had some form of limited bipedality. *Rather, Lucy simply was short* the adult skeleton has changed little in overall plan since the time when Au. afarensis lived on the African landscape The phalanges from Lucy's skeleton are the same length as modern humans', but they are curved, like the pre-australopithecines'. (suggests some potential arboreal locomotion using the hands) shoulder joints (scapulae) indicate suspensory locomotion displays a combo of apelike and humanlike anatomical features Au. afarensis clearly was an efficient, habitual biped that spent most of its time on the ground. The cranial capacity of this creature and others from the taxon is about 430 cc, that of a small brain, the size of an ape's. The apelike characteristics of the bone associated with speech indicate the strong likelihood that this hominin did not have speech. canines are large in comparison with later hominins', the face below the nose projects like an ape's, and overall it looks primitive. Its many similarities with Au. anamensis indicate an ancestral-descendant link between the two. Au. afarensis is not as primitive as the earlier hominin in that the two cusps of the lower third premolars are more equal in size. canines are smaller than the earlier species', and the upper tooth rows are parabolic and not parallel—in other words, more like humans' than like apes'. mandibles are larger, perhaps reflecting an increased use of the jaws in chewing. In contrast to earlier hominins, which were mostly associated with some type of forested environment, Au. afarensis lived in various habitats, including forests, woodlands, and open country. (indicates that hominins became more successful at this time), even the tooth wear is more varied than earlier australopithecines enabling it to have a more diverse diet
PETER RODMAN AND HENRY MCHENRY'S PATCHY FOREST HYPOTHESIS
have proposed that human origins and bipedality in particular may be related to the greater efficiency, in certain habitats, of walking on two feet rather than four feet. suggest that bipedalism arose in areas where the forest was becoming fragmented (broken apart), a process that began toward the end of the Miocene Apes' quadrupedalism, they note, is not energy-efficient in Africa's patchy forests. As the forests became patchy and food became more dispersed, early hominins would have used their energy much more efficiently once bipedalism freed their hands to pick up food. The early hominins could then have fed in trees and on the ground, depending on the availability of resources.
OWEN LOVEJOY'S PROVISIONING HYPOTHESIS
hypothesized that freeing the early hominins' hands was important in initiating bipedal locomotion but not for the reasons Darwin cited. Lovejoy observes that in many species of monkeys and apes, males compete for sexual access to females. However, the young are cared for by the mother without any involvement of the father Owing to the obligations of caregiving, such as the acquisition of food for her infant (and herself), the mother theoretically is not able to care for more than one infant at a time. (she is unreceptive to mating until the infant is able to find food on its own) this can take very long, gives the males a reproductive disadvantage Lovejoy hypothesizes that if infants and mothers were provided with more food, they would not have to move around as much for resources. (If males provisioned mothers and their offspring, each mother, again theoretically, would be able to care for two or more infants at a time) = mother can have more births, time interval in b/w would be reduced Lovejoy makes the case that, for early hominins, a monogamous father enhanced the survival of the mother and offspring by providing both food and protection from predators (This habitual provisioning required the male to have free hands for carrying food, so bipedalism arose) This model focuses on the selective and simultaneous advantages of monogamy and of pair-bonding, of food provisioning, of cooperation, and of bipedalism, all rolled into one distinctively human behavioral package.
Mary Leakey
one morning in July 1959 She, along with her husband, the Kenyan anthropologist Louis Leakey (1903-1972), had searched high and low for early human bones in Olduvai Gorge, a side branch of the Rift Valley, 50 km (31 mi) long. they searched long and hard to find the remains of the people who made the tools and had eaten the animals; motivated by questions (who were the first humans?) 1959 bits of bones and teeth found to be impt. for the hominin skull this expanded our knowledge that early hominins were just from South Africa *these very early findings represented the pre- australopithecines (before the genus Australopithecus), which lived 7-4 mya, and the australopithecines, which lived 4-1 mya*
Seven distinguishing characteristics in the skeleton are associated with bipedalism
the foramen magnum is positioned on the bottom of the skull, the spine is S-shaped, the ilium is short from front to back, the legs are long relative to the body trunk and arms, the knees are angled inward, the foot has a longitudinal arch, and the big toe (hallux) is not opposable. The position of the foramen magnum reflects the fact that the (bipedal) hominin carries its head atop its body, in contrast to the (quadrupedal) ape, which carries its head on the front of the body. The shortened ilium and pelvis generally reflect anatomical changes that coincided with the shift from quadrupedalism to bipedalism. Especially important is the reconfiguring of the gluteal muscles for stabilizing the hip in walking on two legs. for bipeds: long legs provide the ability to walk with minimal energy, angling of the knees toward the midline of the body helps place the feet below the body's center of gravity helping to stabilize the biped when standing, walking, or running; loss of the opposability in the big toe reflects the use of it helping propel the body forward during walking and running; longitudinal arch acts as a shock absorber allowing the forces of the body weight to be sustained esp. during running and long distance walking
Middle Awash region (pg. 258)
yielded the longest continuous record of hominin evolution: more than 6 million years, dating from before the australopithecines through the appearance and evolution of early Homo to the first modern H. sapiens The scientists of the Middle Awash project predicted that fossils discovered by them from the Miocene and early Pliocene at Aramis would reveal hominin ancestors having a mosaic of apelike and humanlike characteristics. among their findings were two species of a new genus of hominin, Ardipithecus, including the earlier Ardipithecus kadabba and the later Ardipithecus ramidus (in the local Afar language, ardi means "ground" or "floor" and rami means "root") Unlike an ape's foot, however, Ardi's foot lacked the flexibility required for grasping tree limbs and moving through trees. (the foot was rigid) -> not flexible -> hominin adaptation for using the foot to propel itself forward when walking bipedally The phalanges of the feet and hands were curved, indicating grasping capabilities similar to apes'. In addition, Ardi's wrist lacked the articulations and specialized adaptations of today's suspensory, knuckle-walking great apes. These details show that Ardi was adapted to life in the trees and to life on the ground. (part time biped and part time quadruped) did not evolve from an ape that was suspensory in the trees and a knuckle walker on the ground Ardi moved on its palms and feet along tree branches and walked upright on the ground (the intermediate form of bipedality is part of the ancestry of later hominins which became fully committed to life on the ground)
