Biological evolution is the changes in genetic information as it is passed from one generation to the next.
Bipedalism, The Skull, The Hand
Comparison between apes and modern humans
Structural Adaptations
Skeletal changes linked to bipedalism (Adaptations)
Body size
- Humans- Little difference between the sexes
- Apes- Males much larger than females
Chest
Structure-
Structure-
- Humans- Rib cage has been flattened from front to back, so that chest centre of gravity is as closer to the spine, minimising tendency to fall forward and improving balance
- Apes- The chest is flattened from the sides- this creates a deeper chest.
Spine
Shape-
Shape-
- Humans- has an S-shaped curve to provide support and balance for the upright biped as weight of chest sits almost directly above the joint between spine and pelvis, rather than further forward. This improves both balance and it absorbs the shock of walking.
- Apes- C-shaped spine confers less strength but promotes quadrupedal locomotion
- Humans- cervical vertebrae have short neural spines as little muscle attachment is required to hold the head upright
- Apes- Cervical vertebrae have long neural spines as there is the need for a large surface area for muscle attachment to support the massive head held horizontally
Pelvis
Shape-
Shape-
- Humans- broader, shorter (bowl-shaped) pelvis supports an upright torso by giving greater stability. The stress of the weight of the trunk is reduced by having it transmitted directly to the legs. This improves balance, enables support of the upper body and enlarges the valgus angle. The strong bowl shaped pelvis bones also increases the surface area for the attachment of large buttock muscles (gluteus maximus). The pelvis also supports internal organs. The wide pelvis allows the birth of babies with large skulls
- Apes- Longer and narrower pelvis. The greater length provides greater attachment area for gluteus medius muscle facilitating the pelvic tilting in quadrupedal motion and gives greater support for abdominal organs
- Humans- The large gluteus maximus muscle is located at the rear of the hip (and forms the buttock) where it acts to pull the femur backwards during walking
- Apes- Has smaller gluteus maximus muscles which lie to the outside of the hip and acts to raise the leg sideways
- Humans- Relative distance between the hip and sacro-lilac joint is shorter in humans, strengthening the region, transmitting body weight between two joints.
- Apes- Longer distance as don't need to support above body weight.
Legs
Structure-
Structure-
- Humans- Legs are longer than arms. The femur is longer (to increase stride length), straighter (to ensure body weight centered down length of bone) and thinner (to make lighter structure as weigh distribution is better)
- Apes- Legs are shorter than arms. They are required for support of the parts of the body attached to the lower part of the curved spine. Femur is shorter and broader. Promoted quadrupedal movement.
Knee
Valgus angle-
Valgus angle-
- Humans- The human femur is longer and slants inwards from the hip. This brings the knee joints closer together and assists the upper body to be positioned above the centre of gravity for walking. This is called the valgus angle. Humans have an increased valgus angle, so better balanced when walking. Humans are able to fully extend legs.
- Apes- The femur descends vertically from the pelvis with no slant i.e the valgus angle = 0. This enables good swinging motion (brachiating) when moving through trees. Apes are unable to fully extend their legs.
- Humans- increased buttress of bone at the base of the femur (which prevents the sideways deflection of the leg and thigh muscles when walking)
- Apes- No increase in the buttress of bone
Feet
Carrying angle-
Carrying angle-
- Humans- Feet are placed under the spine so that walking is carried out without swaying
- Apes- Feet are below the outer side of the pelvis so there is a sideways swaying motion when walking
- Humans- The weight is placed on the outer edge with the inner side elevated into an arch. The convex arch under the foot to act like a spring under tension and allows for a transfer of weight down the foot to the big toe, providing a shock absorber effect and a spring that facilitates long distance travelling.
- Apes- Has no arch (i.e they are flat footed)
- Humans-The foot has changed to become a platform, with short toes alongside the big toe, which is forward thrusting (non-opposable) to provide the final thrust against the ground to propel the body forward. The foot has lost all grasping ability.
- Apes- is divergent (slightly opposed) to allow for grasping action and anchorage in toes
Changes is skull and endocranial features
Skull (cranium)
Shape of skull-
Shape of skull-
- Humans- rounded brain case (enlarged brain) with reduced sites for muscle attachment, especially those used for chewing and aggressive facial displays which are no longer called for
- Apes- Flatter brain case (smaller brain) which allows for greater muscle attachment sites needed for aggressive facial displays
- Humans- Have brains about 1350cc. Enlarged frontal lobes- gives rise to increased thinking capacity and abstract thought. Very large brain.
- Apes- Brains are 400- 500cc. Smaller capacity gives less scope for logical thought. Large brain.
- Humans- Majority of weight is now concentrated in the cranium. The muscles have reduced in size due to diet changes (cooking) so less muscle attachment sites are required
- Apes- Majority of weight is concentrated in the jaw for attachment of large muscles to chew a tough diet
- Humans- In the centre of the underside of skull. The skull can balance on top of the spine and less energy expenditure is required by the muscles in the neck to keep the skull upright. it allows for better balance for bipedalism.
- Apes- Is at the back of the skull- facilitates quadrupedalism
- Humans- Far forward (from back to middle)- facilitates bipedalism by keeping the head above the centre of gravity.
- Apes- Much further back- facilitates quadrupedalism
- Humans- Reduced muscles as centre of gravity id behind the vertebral column, therefore have a small nuchal crest
- Apes- Have large nuchal muscles. In conjunction with this they have a nuchal crest for the attachment of these large muscles. Cetre of gravity is in front of the vertebral column so nuchal muscles must be very large and powerful to support the quadrupedal head, preventing it from sagging forward
- Humans- No brow ridges and the face is short
- Apes- Have brow ridges and a longer face
Lower jaws and teeth
Jaw-
Jaw-
- Humans- Small in size as human teeth size is small (due to the eating of a softer diet). Less prognathous (shorter muzzle)
- Apes- Large in size as apes have large teeth (needed to eat the tough, fibrous diet)
- Humans- The teeth are arranged in a rounded V-like "arch" shape
- Apes- The teeth are shaped like a "U" with parallel sides
- Humans- Smaller overall and more uniform in size, suiting their omnivorous diet and softer cooked foods. They have no diastema. Both sexes have small canines.
- Apes- Larger specialised teeth for grinding and chewing. Canines are used for defence. They have a diastema. Large canines especially in males.
- Humans- Have smaller premolars and molars with a thin enamel coating
- Apes- Large premolars and molars and a thick enamel coating
Changes in the manipulative ability of the hand
Hand
Structure-
Structure-
- Humans- Thumb is long and fully opposable enabling precision grip. Used for making and using tools. Finger bones are straight.
- Apes- Thumb is short and fingers are long and curved so precision grip is impossible. The hands are suitable for using crude tools only. The curved bones aid brachiating.
Behavioral Adaptations
Food-
Food-
- Humans- Hunted, gathered, transported to other sites, prepared, shared with others
- Apes- Food eaten where found
- Humans- Performs fine, manipulative movements- precision grip
- Apes- Can only perform gross manipulative movements- power grip only
- Humans- Usually live in non-forested regions
- Apes- Live in forested regions
- Humans- Bipedal locomotion
- Apes- Knuckle walking and sometimes brachiation (swinging from branches)
- Humans- Sexual relationship is prolonged between partners/ stronger parent-offspring bonds
- Apes- Sexual relationships brief with no father-offspring bond
- Humans- Highly sophisticated tool making which are essential to survival
- Apes- Rudimentary tool making and are not essential to survival
- Humans- Speech as well as facial expressions
- Apes- Wide repertoire of facial expression but no speech
- Humans- Very long periods of juvenile dependence
- Apes- Infant becomes independent relatively early in comparison
Physiological Adaptations
Ovulation-
Reproduction- Only birthing one offspring
Ovulation-
- Humans- Ovulation concealed
- Apes- Ovulation advertised
- Humans- Produces a lot of sweat (abundant sweat glands)
- Apes- Produces very little sweat (few sweat glands)
- Humans- Relatively hairless (except on the top of the head). Hair short and fine over most of the body. It has been suggested that this has been an advantage in that the body has an efficient cooling mechanism (sweating) during the late stages of running down prey during hunting. Humans have retained hair on their head that helps reflect and radiate heat before it reaches the skin of the exposed part of the body. With reduction of body hair, control of parasites such as fleas and ticks would have been improved. This would have been particularly important when early humans began to use a home base rather than continually wandering. Sun would also cause adaptive loss of hair to promote cooling.
- Apes- Hairy, long ans coarse
Reproduction- Only birthing one offspring
Selection Pressures Changed: Theories on Bipedalism- The Environment (causes the change in selection pressures)
There are a number of possible theories relating to why human ancestors became primarily bipedal in their gait. These include:
- Starting around 6 million years ago climate changes occurred which resulted in rain forests greatly receding and grasslands forming. This forced hominids to forage in open country as primates moved out of the forests and onto the plains. There was selection for walking on two legs in this new environment.
- Bipedalism began to be developed while primates lived in the trees. They may have walked upright on large branches or collected fruit from overhead by standing on limbs while hanging with one arm onto higher branches. By the time the forests began to shrink, the forerunners of early hominins were probably bipedal, at least part of the time. The pre-hominins were probably more bipedal than chimps are today.
- As the primates were forced into new areas where trees were smaller it became more efficient for them to feed standing upright on the ground rather than trying to move through the branches from tree to tree., Once on the ground it would have taken less energy to shuffle on two legs from tree to tree than to raise the torso from a four-legged posture to feed, then lower it again to move on all fours to the next tree. That would have been a side benefit- it freed the hands to do other things.
- As the amount of shady habitat shrank, keeping the brain cool might have been another factor in the development of bipedalism. One way to reduce the risk of heat stroke is to stand upright. During the most stressful part of the day, a biped on the Savannah gets only one third of the solar heat load a quadruped does. Also, with more of the body exposed to cooling breezes, losing heat happens faster/easier as well as evaporative cooling (sweating)- requiring hominins to consume less water.
- Primates (during times of hunger) would have ventures onto the seashore. Finding clams in rock pools was one way to get food. Beach combing was another. At certain times of the year, storms can damage fish and cephalopods (molluscs) and wash them up on the shore. Often they would have been cut off by the rising tide and would have to wade ashore. Wading in rock pools for sea food may have contributed to the development of bipedalism.
Advantages of Bipedalism vs Disadvantages
Survival Advantages
- Efficient locomotion- Bipedalism provides an energy efficient method that favours low speed, long distance movement like walking so that Hominins can move distances while carrying objects and can change location, moving to more suitable areas when needed (e.g summer, winter) or when an area becomes over populated they are able to move further away in small groups in order to reduce competition. Having energy efficient locomotion also allows the Homonins to follow prey until it is run down due to the inablilty to move long distances/ inability to remain in the sun because it gets too hot.
- Seeing over tall grass- Being upright would have allowed humans to be able to see better over the tall grass. This may have helped them spot predators or locate carcasses at a distance so that they can quickly find/hunt food and can gain food quickly without expending large amounts of energy in searching for food, enhancing the ability or chance of survival. Being taller makes them look larger and more threatening to predators, as well as them being able to brandish sticks or throw stones at predators to keep them away from their family groups, or spot predators and be able to get away quickly before they get in harms way.
- Freeing the hands- This allowed Hominins to carry objects like tools, food (from where it was killed or gathered back to the home base), babies (as the mother became relatively hairless, the baby had nothing to cling onto, especially without opposable toes) so that the infant could be born at an earlier/more helpless stage, not in the womb as long, because the parents could keep the infant safer. This means that the infant can be exposed and more stimulated by their surroundings earlier, and are able to interact, increasing responses in the brain and brain development. It also allowed Hominins to use objects such as weapons and tools to use, being upright in wielding a stick as mentioned above, as well as encouraging the making of tools and weapons so that the Hominins could efficiently gather food, protect their families and home bases and hunt. This makes them more successful in guarding territory, killing predators and prey, increasing their survival ability.
- Decreasing the exposure of the body to direct sunlight (by about 70%)- This helps to keep the body cool in the hot climate of the African Savannah so that the body doesn't overheat and reduces dehydration. Because the upright body absorbs much less heat energy, the body is surrounded by cooler and rapidly flowing, drier air, speeding up the evaporation of sweat. This means that the Hominins have more time and energy to forage in the sun, so they can get more food. Elevated temperatures (above 4 degrees Celcius) cause heat stroke, which can be fatal.
Disadvantages
- Back pains- Humans are particularly prone to back aches because of our S-shaped spine and bowl-shaped pelvis
- Slipped disc-degenerative Lower back troubles usually caused by degenerative changes with age are combined by load carried by two limbs instead of four
- Foot problems- Feet sometimes suffer strain because the body rests on just two limbs. The arches of the feet collapse, producing flat footedness, distorted bones and even bunions.
- Varicose veins- Bipedal posture makes it difficult for blood to be returned to the heart from the legs, especially in people with sedatory occupations. This develops varicose veins
- Hernia- Because the gut is no longer hung from the spine by a broad ligament as in four legged animals, the intestines may bulge out through our weakened abdominal wall. This is called hernia.
- Birth canal- The birth canal is too small to accommodate the very large brain of the infant, and can cause death of both the mother and the infant.
Evolution of the Brain
As a general rule, all apes and humans share the same basic pattern of brain configuration.
The size of the brain is important for two reasons. A bigger brain has:
Fontal lobes-
Particularly well developed in humans. This is the seat of imagination, memory, creativity and abstract thought.
Speech-
Two areas of the brain work together to make human speech and language possible:
The cerebellum, responsible for balance and fine motor skills, would develop with bipedalism. Being able to interact more fully with objects could promote the development of the brain, resulting in a larger brain and more folding, as those that could make and use more complex tools were more likely to get enough food to survive.Brain development and food-
Although the brain makes up only 2% of our body weight, it demands about 20% of the body's metabolic energy at rest. In order for the brain to further develop in size, a more energy and nutrient rich diet is required. This required the ability to obtain a more reliable food source of meat (as meat is a better source of protein and energy than tough plant matter). Cooking food would have supplied a better quality of food, as well as hunting and tool development supplying a bigger quantity of meat.
The size of the brain is important for two reasons. A bigger brain has:
- Greater complexity of linkages between cells
- More brain cells
Fontal lobes-
Particularly well developed in humans. This is the seat of imagination, memory, creativity and abstract thought.
Speech-
Two areas of the brain work together to make human speech and language possible:
- Wernicke's area is the section of the human brain that is involved in the understanding and comprehension of spoken language
- Broca's area is the section of the human brain that is involved in language processing, speech production and comprehension.
The cerebellum, responsible for balance and fine motor skills, would develop with bipedalism. Being able to interact more fully with objects could promote the development of the brain, resulting in a larger brain and more folding, as those that could make and use more complex tools were more likely to get enough food to survive.Brain development and food-
Although the brain makes up only 2% of our body weight, it demands about 20% of the body's metabolic energy at rest. In order for the brain to further develop in size, a more energy and nutrient rich diet is required. This required the ability to obtain a more reliable food source of meat (as meat is a better source of protein and energy than tough plant matter). Cooking food would have supplied a better quality of food, as well as hunting and tool development supplying a bigger quantity of meat.
Trends in human lineage
Hominoids- all ape species (gibbons, orangutans, chimpanzees, gorillas) as well as humans
Hominids- chimpanzees, gorillas and humans Hominins- living or fossil species of human lineage |
Humans and African apes shared a common ancestor, which probably lived in the forest and moved by swinging from arms and climbing on all fours. At some point, thought to be 5-7 million years ago, the human line split from the other Hominids, becoming bipedal.
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Uncertainty about Human Evolution
- Very few human fossils especially of some species, and are often found in fragments
- Much of the fossil evidence has not been fully analysed yet
- Australopithecines show large amounts of variation. Even those regarded as belonging to the same species vary in size and other characteristics. Adding to the complications, males appear to be considerably larger then females, so it is not always clear if two sizes represent two species or two sexes.
- Considerable difference in opinion as to the meaning and importance of some anatomical features
- Search for human ancestors ha,s in recent years, become exciting and intensely competitive. Discoverers of a new fossil are understandably predisposed to claim it as something distinctive and unique.
The first bipeds
Sahelanthropus tchadensis- Controversy whether this is the oldest known Hominid or an ape. It has ape-like characteristics with wide spaced eyes and a small brain case, but then human features in the shape of the skull and teeth. No post-cranial bones have been located, so it is impossible to know whether it was bipedal or not. (to the right, top) Orrorin tugenesis- Some argue ancestor of modern apes because the arm and finger bones indicate adaptations to life ion trees, as well as having long, pointy canines which is more similar to apes than humans. Others argue it is a Hominin as the femur indicates likely bipedalism. Ardipithecus ramidus kadabba- Size of modern chimpanzees (122cm tall) and roughly the same size as Ardipithecus ramidus ramidus. The brain and relative arm proportions are more chimp-like than human. It was supposed as walking upright most of the time by the 2.5cm toe bone (some scientists argue this was from another species as it was 16km away and dated a few thousand years different). They had behaviours of modern chimps, including spending time in trees, living in large social groups that would include both sexes and males band together to defend the troop from predators, forage for food and hunt game. They lived in a well forested environment (significant because it was previously thought that one reason why Hominins became bipedal was to enable seeing over the tall savannah grass. Ardipithecus ramidus ramidus- Indirect evidence suggests bipedalism. Some individuals were around 120cm tall. This species was likely to have lived in the forest, and had teeth which were intermediate between those of earlier apes and Australopithecus afarensis. (to the right, bottom) |
The Australopithecines
- The foramen magnum is further forward than in apes but not as far forward as in humans
- Articulation of the jaw is similar to humans. This suggests that they could move the jaw from side to side (for chewing). Apes are unable to do this.
- The teeth are in a U-shaped curve- unlike humans.
- The pelvis indicates they could walk bipedally- it was shorter and more bowl shaped than in the apes.
- The skull has no nose bone or chin.
- Their legs are generally longer than their arms
- The knee has an increased valgus angle.
- The spine has an S-shaped curve.
- The skull has a heavy brow ridge and sloping forehead.
- They are thought to have lived in troops. They cared for their young and exhibited a form of social co-operation.
- Fossil footprints at Laetoli (Tanzania) show bipedal motion with arched feet and a larger great toe. The big toe points forward.
Australopithecus anamensis- Gracile (light and small in structure). This is the oldest AustraIopithecine. It has a mixture of primitive features in the skull and advanced features in the body. The teeth and jaws are very similar to those of older fossil apes. A partial tibia has been found which strongly suggests the species was bipedal. It lived in a mixture of open savannah and forest. (Top left)
Australopithecus afarensis (Lucy)- Gracile (light and small in structure). This species lived in a group, in forest and semiarid savannah. Operating selection pressures would have encouraged the development of bipedal locomotion (to evade predators on the open savannah). Running required them to adapt an efficient cooling system- sweating ability increased and their hair decreased. The freeing of the hands allowed objects to be carried for long distances. Anatomy: Their brain size was 400-500cc, weight 30kg, height 1.07-1.52m. They had an ape-like face with a low forehead, bony brow ridge, flat nose and no chin. They also had human-like teeth, their canines which were smaller than those of apes, but larger than a humans. They have large molars and thick enamel on their teeth. The reduced canines. thick enamel and wear patterns indicate a diet of seeds, grains and tubers. They have long arms relative to their legs, and an arched feet with a big toe partially aligned with the other toes (Laetoli footprints). Valgus angle increased and lateral condyle of the femur is enlarged at the knee. Controversy: There is a possibility that A. afarensis is two species rather than one. Single-species proponents say the large specimens are males and the smaller ones are female (showing sexual dimorphism). Proponents on two-species say the size range indicates two species, one small, the other larger (referred to as the "small Hadar species" and "large Hadar species". (Directly left) Australopithecus africanus- Gracile (light and small in structure). They were forest dwellers. Anatomy: Brain size 400-500cc, weight 20-40kg, height 1.1-1.4m. Their teeth and jaws were larger than modern humans, but was also arranged in a parabolic v-shape. On the teeth were found wear patterns that indicate they ate an omnivorous diet. The brow ridges were less prominent, and they had a higher forehead and shorter face. They had an upright posture with spinal curvature so the trunk was over the pelvis. (4th from bottom, left) Australopithecus robustus- Robust (heavier, stronger structure). Also known as Paranthropus robustus. They lived in open savannah. Anatomy: Brain size around 530cc, weight 50-70kg, height 1.1-1.3m. They had a very thick jaw with small incisors and canines, large molar-like premolars and very large molars. They also had thick enamel on the teeth. The wear pattern on the teeth indicate they ate a vegetarian diet. The sagittal crest enabled the attachment of large jaw muscles. They had upright, bipedal locomotion with a human-like pelvic girdle. (Direct to left) Australopithecus boisei- Robust (heavier, stronger structure). Also known as Paranthropus boisei. Anatomy: Brain size 410-530cc, weight 60-80kg, height 1.2-1.4m. Had a very prominent sagittal crest, a very large face and small brain case with a very large brow ridge. They had a very thick jaw with small incisors ans small canines, as well as large molar-like premolars and very large molars. The wear pattern on the teeth demonstrates they ate a vegetarian diet. They were fully bipedal. (2nd to bottom left) Australopithecus sediba- Gracile (light and small in structure). Had long legs so they could walk and run on two feet, long arms and powerful hands showing they also felt at home in the trees. Their teeth were about the same size as those of humans. Their brains were smaller than a humans but larger than an apes. (Bottom left) |
The Genus Homo
- increase in the size and complexity of the brain
- development of speech- the hyoid bone for the attachment of tongue muscles
- further development of the S-shaped curvature of the spine
- proportional lengthening of the legs in relation to the length of the trunk and arms
- teeth became smaller with thinner enamel
- smaller jaw with a definite chin
- more rounded cranium with a bulging forehead
- gradual development of group living and culture (including tool making)
- foramen magnum closer to the middle of the skull
Homo habilis- (top right) Open savannah in East Africa, same time as the Australopithecines
Controversy: Many scientists think “habilis” has too wide of a range of variation, especially brain size (500-800cc) to be considered a single species. Many think there are two species- “habilis” and “rudolphenis” Physical Characteristics: Average brain size- 650cc, considerably larger than Australopithecines. Overlaps Australopithecines at lower end of brain size (500cc) and overlapping H. erectus at higher end (800cc). They were bipedal walkers. The femur is long and relatively straight. Changes in the pelvis also gave a more upright posture. They began to show the first signs of a chin and their teeth began to look more like Homo sapiens sapiens (became more like that of an omnivore). Incisors remained fairly large indicating they had an important function- ripping and tearing meat. Their molars are smaller than the Australopithecines but they are still considerably larger than in modern humans. Increasingly human: This species was different from the previous Australopithecines in a number of ways:
Physical features: Like H. habilis, the face has a protruding jaw with large molars, thick brow ridges and a long low skull. Foreheads began to develop in the larger specimens in order to accommodate the increasing brain size. The brain size varies between 750 and 1225cc. Early H. erectus specimens average around 900cc while later ones average about 1100cc. The molars became smaller and the jaw lighter than the H. habilis. This trend can be explained by the fact that food was being prepared before eating, either by pounding and chopping or later on by fire. Those tools were now performing many of the difficult tasks that the teeth have previously been responsible for. The skeleton is more robust than those of modern humans, implying greater strength. They ,may have been better adapted for walking than modern humans (whose skeleton had to be adapted for giving birth to larger brained infants). Increasingly human: Homo erectus had several practices which would be described today as characteristically human doings. By this time hominins were becoming quite adept at hunting. We can assume that this is partly due to the increased brain size development making communication and therefore organisation and planning, more efficient. All parts of animals were used. The meat for food, bones for tools and weapons and the fur for clothing. This last innovation, the use of clothing, is just one discovery that allowed H. erectus to survive in the colder Ice Age temperatures of the Northern land masses, such as Europe and Asia. The second and possibly more crucial new technique that H. erectus "discovered" was fire, almost a necessity for survival during the long cold months. Fire also provided protection against other animals, it allowed food to be cooked and therefor made soft enough for young children and the elderly to eat, increasing chances of survival and lifespan. Also more nutrients could be extracted. It provided extra hours of light during which H. erectus could socialise or plan the next day's hunting expedition. Location: There is some debated over where this species originated from. It probably originated as a species of Africa. From the African savannahs of home, H. erectus spread to populate many new and diverse habitats e.e drylands, forests, riverbanks and mountains. This move probably occured in small increments in response to animal migrations and the need for food (NB some of this travel could have occured over land bridges that formed between land masses as a result of the ice ages). Also climate changes is Africa could have increased competition for food therefore they were driven to find new sources. H. erectus was probably the first species to leave Africa. In 1994 volcanic deposits containing the fossil skull of a Homo erectus child, dated at 1.8 million years old, were found in Java. If H. erectus originated in Africa, as most scientists believe, this early date suggests that the species left Africa and made its way to Java shortly after it evolved (some scientists suggest that an unknown predecessor of H. erectus left Africa much earlier than previously believed. If this is true, H. erectus might have evolved elsewhere and later migrated into both Java and Africa). Different races/species: Some scientists classify some African H. erectus specimens as belonging to a species, Homo ergaster, which means "working man". These differ from the Asian H. erectus in some details of the skull (e.g the brow ridges differ in shape and the Asian erectus has a larger brain capacity). Evidence (stone tools, skeletal remains etc) place early Homo in Europe over 1.8 million years ago. Homo neanderthalensis- (Third from top, right) Physical characteristics: Neanderthals had short limbs and stocky bodies (ideally suited to conserve heat in the cold climate of Europe where they lived). They were very robust, suggesting extraordinary physical strength and great endurance. Larger brained than humans today (approximately 1400-1500cc) but because Homo sapiens sapiens are smaller in physique, our brains are relatively larger. Some experts speculate that Neanderthals needed more brain cells to coordinate their extra body mass (therefore they were not actually as intelligent as H. s. sapiens. The face was generally much lower and longer than ours (with prognathism) Increasingly human:
Location: They inhabited western, central and south-eastern Europe and south-west Asia. From 230,000-27,000 years ago they lived in highly variable climate conditions- sometimes during periods similar to present, but most often during glacial conditions, when ice sheets covered much of Britain and Northern Europe. Sea levels were lower and available landscapes much colder and drier than at present. Cold transformed the landscape, on the uplands forests died and gave way to bleak moor land, but the more sheltered valleys grew small forests because they were less effected by wind and frost. Neanderthals followed game into forest valleys, withdrawing more and more into the valleys, spending less and less time in the highlands instead of adapting to the world outside. They became isolated in the valleys and were unable to reach their own kind. The places they were able to survive in were destroyed by the advancing cold. Because they were unable to adapt well or improve their adaption they died out. Homo floresiensis- (Third from bottom, right) A fossil of a Hominin dwarf species found on the Indonesian island Flores. Characteristics:
Controversy: Was similar to Homo erectus (brain size 800-900cc), but much smaller and lived much later. Current thoughts are that they are not a direct ancestor to us. H. floresiensis could be an evolutionary response to living on an island. Dwarfism and gigantism is an observed response to the pressures of island life. Animals smaller than rabbits tend to evolved to be larger whilst larger animals tend to get smaller. Dwarf elephant bones were also found as well as giant rabbits and rats. H. floresiensis probably evolved from H. erectus. Denisovans- (Supposive skull, second from bottom, right) Little is known about the physical size of these humans as only small fragments (finger and toe bones and tooth from different individuals) have been found to date. These samples yeild good DNA and analysis of this DNA suggests that:
In 2008 in a remote cave in Siberia (the Denisova cave) scientists discovered remains of a previously unknown member of the genus Homo. The remains represent a group referred to as the Denisovans. A toe bone, a finger bone and a tooth have been found to date. The tooth appears much later than a modern humans. It is likely that the Denisovans and other humans lived in the same area at the same time. It's possible that they co-existed with modern sapiens as well as Neanderthals. Homo sapiens (Modern humans)- Physical features:
Increasingly human:
Location: Europe, Asia and Africa |
Selection pressures on Human Ancestors
A. afarensis/A. africanus-
A. robustus/A. boisei-
H. habilis-
H. ergaster/H. erectus-
Archaic H. sapiens/H. heidelbergensis-
H. neanderthalensis-
H. sapiens-
- tough food- this led to the development of large teeth and jaws
- warmer climate and the need to escape predators (through long distance running) led to the development of an efficient cooling system with the reduction of body hair
- freeing the hands allowed objects to be carried and the development of crude, unsophisticated tools (similar to modern chimpanzees today)
- larger brain leading to better co-ordination
A. robustus/A. boisei-
- diet (tough plants) led to the development of the sagittal crest
- lots of competition (A. boisei, A. robustus, H. habilis) led to these species becoming over specialised, ultimately leading to their extinction
H. habilis-
- main changes are development of the brain, allowing for better communication and the development of the stone tool manufacturing
- upright walking was enhanced
- a reduction in sexual dimorphism (usually associated with competition between males for females), implying there may have been more co-operation between males therefore hunting of larger game became possiblr
- with more meat in the diet, changes in the skull began to take place (H. rudolphensis is very similar)
H. ergaster/H. erectus-
- marked increase in brain size and complexity
- controlled fire
- selection favoured increased intelligence which improved manual dexterity, leading to the development of better tools which gave this species a competitive advantage
Archaic H. sapiens/H. heidelbergensis-
- lots of climate changes
- human occupation is continuous, advanced northward during interglacial periods (lasted 10,000 to 30,000 years) and retreated during glacial or ice ages
H. neanderthalensis-
- adapted well in the last ice age, penetrated the equatorial forest for the first time, then replaced in Western Europe by fully modern humans
- may have been out-competed by H. sapiens and forced to less favoured hunting grounds, which would have led to a poor reproductive rate
- combining this with an ice age would have led to problems (less shelter, food etc)
H. sapiens-
- because of cultural advancement, natural selection favoured increased intelligence