Integrated different disciplines to study human evolution need to use multiple approaches anatomy molecular genetics study of fossils-taphonomy past environments comparisons with modern & fossil primates examination of behaviors among living people

Anatomy study of modern skeletons effects of activity growth disease age diet environmental effects compare with fossils

Molecular Evolution can help us understand divergence in new ways timing geographical spread traits that are linked in evolution

Fossils & Taphonomy modification of remains animal damage weathering crushing & distortion through burial chemical modification

Past Environments plant remains invertebrate remainslarge fauna geologic setting

Living & Fossil Primates Proconsul africanus Kenya,14-23 mya tarsier baboons diet locomotion behaviors anatomy sociality evolution

Living Humans dietary decisions sociality sexual strategies growth & development population dynamics

What were the ancestors like?What does it mean to be human? Homo habilis KNM ER-1813 Koobi Fora, Kenya 1.9 mya

Primates have grasping hands for locomotion and feeding pygmy marmoset baboon

tarsier Primates have large, forward facing eyes for stereo vision tamarin ring tail lemur slender loris chimpanzee male

tarsier, Tarsius sp., small prosimian, Indonesia, vertical clinger & leaper

Lemurs Madagascar terrestrial locomotion arboreal clingers & leapers climbers social group living

Vertical leaping crouched and clinging to a limb thigh muscles provide the force to produce a leap arms used mostly for balance stabilization land feet first Drawings by Luci Betti

sifaka, lemur

Baboons terrestrial locomotion

New World Monkeys capuchin monkey arboreal suspensory above limb walking mostly group living

Gibbons Asia brachiation underbranch suspension

Orangutan Sumatra & Borneo slow solitary suspensory locomotion

Gorilla Central Africa group living terrestrial knuckle- walker

chimpanzee, Pan troglodytes bonobo, Pan paniscus Chimpanzees & Bonobos Central Africa group living highly social terrestrial & arboreal adaptations last great ape line that the hominin lineage diverged from ~10-7 mya

chimpanzee, Pan troglodytes, west and central Africa, forest knuckle walker-terrestrial locomotion and climbing

Adaptive Radiations of Primates Paleocene~60 mya-earliest possible primates Eocene mya ~ mya Late Oligocene ~30-22 Miocene ~22-11 mya

tree shrews resemble primitive primates different ear bones have claws non-grasping hands eye orbits not closed

Ida” 47 mya adapiform, near Frankfurt, Germany lemur-like prosimian ancestor

Aegyptopithecus zeuxis Egyptian Fayum, 29 mya, Miocene

Proconsul africanus Rusinga Island, Kenya,14-23 mya, Miocene

Sivapithecus indicus Potwar Plateau, Pakistan, mya, Late Miocene, orangutan ancestor

Sivapithecines = ancestors of the Orangutan lineage

Sahelanthropus tchadensis Chad, 6-7 mya

Sociality

Brain size % fruit in diet Brain size Group size Findings from the “ecological” and “social” hypotheses Points reflect individual species: both are upheld Mountain gorilla

Look at relationship of “social part of brain”-neocortex- with respect to group size Data tend to support “social” hypothesis, since this relationship doesn’t hold for ecological factors Neocortex and group size

Human social organization Human social organization is a mosaic of traits that have deep roots. Different traits arose at different times in different circumstances

Grooming

Male Aggression

primate sexual dimorphism associated with distinct feeding, mating, and sociality gorilla female gorilla male

Tamarin reproductive biology Insights into patterns of male care-giving and male fitness. Tamarin groups 1-3 adult males and 1-3 adult females. After mating with all group males, the alpha female gives birth to dizygotic twins, other females often don’t reproduce. Each offspring weighs 8% of mom’s weight and grows rapidly (in humans, the equivalent to giving birth to two 9lbs infants) The alpha female can give birth to two sets of twins in a year

Number of adult males/females Ave. number of surviving offspring males females Offspring survival depends on male care in tamarins In one study group, males did 73% of all infant carrying. Adult males will also provision infants with food. Males will provision infants/juveniles for 50% of their growth period (long, relative to other primates)

Tamarin reproductive biology Main point: male investment in offspring is a fact of tamarin male behavior; it is a function of local ecology, life history patterns, and reproductive options. Tamarin males, like human males, have high potential reproductive rates, but the evolved tamarin mating system does not let males actualize their reproductive potential. Instead, they share matings/reproduction with other males.

Brain not just an increase in size differences in brain organization cognition thought emotions brain is a costly tissue affects dietary needs growth & development birth

Primates: Unusually large brain relative to body size. Monkeys and apes: Very large brain when compared to other mammals Humans: Carry this pattern to greater extreme Large brains are expensive to maintain: Brains ~2% of body weight, consume ~20% metabolic energy We wouldn’t expect natural selection to maintain this costly feature unless it was adaptive.

Neocortex very thick in humans and non-human primates 30-40% brain volume in non-primate mammals 50% brain volume in prosimians 80% brain volume in humans

Interspecific comparisons

EQ the ratio of brain size to body mass based on interspecific comparisons. “Encephalization” refers to the degree of “excess” brain mass relative to body size. EQ’s take into account body size, since-obviously, an elephant’s brain will weigh more than a mouse’s brain on an absolute scale. However, taking the ratio of brain size to body mass allows us to compare brains in diverse taxa. Encephalization Quotient (EQ): an to compare brain size across sepcies

EQ in humans the line shows expected brain size for a give body size points above the line indicates a larger than expected brain size for a given body size larger than expected

Encephalization Quotient (EQ): ratio of brain size to body mass based on a linear regression of interspecific data for primates. EQs for various catarrhine taxa: baboon1.1 gorilla (male)2.1 chimpanzee2.3 australopithecines2.5 H. habilis3.1 H. erectus3.5 H. sapiens 7.5

Hypothesis that primate intelligence evolved in order to solve social challenges Machiavellian intelligence hypothesis: The ability to use other individuals as tools; manipulating the social environment in order to meet preconceived goals: deception (groom as a means to steal food) alliance formation (grooming predicts future support)