COSTS & BENEFITS OF GROUND LIVING

COSTS & BENEFITS Major benefit – tree living = safety from predators. Major benefit – tree living = safety from predators.

COSTS & BENEFITS Major benefit – tree living = safety from predators. Major benefit – tree living = safety from predators. Cost – leaves and fruits aren’t as rich in protein or energy. Cost – leaves and fruits aren’t as rich in protein or energy.

COSTS & BENEFITS Major benefit – tree living = safety from predators. Major benefit – tree living = safety from predators. Cost – leaves and fruits aren’t as rich in protein or energy. Cost – leaves and fruits aren’t as rich in protein or energy. Life on ground = wider diet, yet predation risk is greater. Life on ground = wider diet, yet predation risk is greater.

BIPEDALISM EVOLVED QUICKLY The change from brachiation to bipedalism probably occurred within 2.5 million years. The change from brachiation to bipedalism probably occurred within 2.5 million years.

BIPEDALISM EVOLVED QUICKLY The change from brachiation to bipedalism probably occurred within 2.5 million years. The change from brachiation to bipedalism probably occurred within 2.5 million years. Extensive changes to hip and leg – fast evolution = strong selective pressure. Extensive changes to hip and leg – fast evolution = strong selective pressure.

CARRYING INFANTS Infants able to be born earlier and more helpless if carried. Infants able to be born earlier and more helpless if carried.

CARRYING INFANTS Infants able to be born earlier and more helpless if carried. Infants able to be born earlier and more helpless if carried. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe.

CARRYING INFANTS Infants able to be born earlier and more helpless if carried. Infants able to be born earlier and more helpless if carried. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking

CARRYING INFANTS Infants able to be born earlier and more helpless if carried. Infants able to be born earlier and more helpless if carried. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking = offspring having the same trait = less able to cling on = mother would have to hold onto the baby This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking = offspring having the same trait = less able to cling on = mother would have to hold onto the baby

CARRYING INFANTS Infants able to be born earlier and more helpless if carried. Infants able to be born earlier and more helpless if carried. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. Human babies can’t grasp fur (as it’s not there) because they don’t have an opposable toe. This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking = offspring having the same trait = less able to cling on = mother would have to hold onto the baby = increasing advantage of having a forward facing toe. This adaptation would accelerate quickly – a partially bipedal pre-human would have a big toe facing more directly forward for walking = offspring having the same trait = less able to cling on = mother would have to hold onto the baby = increasing advantage of having a forward facing toe.

CARRYING FOOD Enabled large food items to be carried back to safety = Enabled large food items to be carried back to safety =

CARRYING FOOD Enabled large food items to be carried back to safety = males could attract mates this way = Enabled large food items to be carried back to safety = males could attract mates this way =

CARRYING FOOD Enabled large food items to be carried back to safety = males could attract mates this way = females then choose the ‘best providers’ for their offspring. Enabled large food items to be carried back to safety = males could attract mates this way = females then choose the ‘best providers’ for their offspring.

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot.

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours.

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. Hair on heads = reduced heat absorption. Hair on heads = reduced heat absorption.

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. Hair on heads = reduced heat absorption. Hair on heads = reduced heat absorption. Raising the body = surrounding air cools it Raising the body = surrounding air cools it

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. Hair on heads = reduced heat absorption. Hair on heads = reduced heat absorption. Raising the body = surrounding air cools it Raising the body = surrounding air cools it This hypothesis links bipedalism with the high density of sweat glands and semi- naked skin. This hypothesis links bipedalism with the high density of sweat glands and semi- naked skin.

KEEPING COOL A popular theory – bipedalism evolved in order to avoid getting too hot. A popular theory – bipedalism evolved in order to avoid getting too hot. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. By being upright, a human body absorbs much less heat energy than it would if exposed to the sun on all fours. Hair on heads = reduced heat absorption. Hair on heads = reduced heat absorption. Raising the body = surrounding air cools it Raising the body = surrounding air cools it This hypothesis links bipedalism with the high density of sweat glands and semi- naked skin. This hypothesis links bipedalism with the high density of sweat glands and semi- naked skin. Overheating could be avoided by staying in shade = less foraging time = less food. Overheating could be avoided by staying in shade = less foraging time = less food.

OTHER ADVANTAGES Predators can be seen earlier when upright Predators can be seen earlier when upright

OTHER ADVANTAGES Predators can be seen earlier when upright Predators can be seen earlier when upright More effective at brandishing weapons More effective at brandishing weapons

OTHER ADVANTAGES Predators can be seen earlier when upright Predators can be seen earlier when upright More effective at brandishing weapons More effective at brandishing weapons Taller body may seem larger to predators. Taller body may seem larger to predators