Evolution of humankind Sequence of human evolution - Humans belong to the order Primates – divided into two subfamilies Prosimians – meaning “before apes” Hominoidea – “great apes” – which typically have large brains when compared to body size –Monkeys, African apes and humans belong to this family The Hominoidea group gave rise to the Hominidae family. – Which in turn gave rise to the sub-families, Homininae and Ponginae. Homininae has been divided into two tribes Gorillini – gorillas Hominini- Hominins – living humans and their extinct ancestors and Pan – chimpanzee and bonobos Genetic analysis combined with fossil evidence indicates that: - Hominidae family split into the sub families, Homininae and Ponginae about 15 million years ago (mya) Homininae subfamily split into two tribes, Hominini and Gorillini about 7 mya Hominini tribe split into the genera, Homo, Australopithecines and Pan about 6 mya. - A phylogenetic tree depicts a hypothesis about evolutionary relationships among organisms. Evidence for a common ancestor for living hominids - Living hominids include the African apes and humans If there is a common ancestor we will be able to trace the evolution of humans from this ancestor through the series of early hominin species to today’s humans To find the common ancestor, scientists use the fossil record Knowing the similarities and differences of African apes and humans will give us a starting point when looking at fossils of early man and enable us to follow the trend in human evolution. African apes and humans- compared - Physical and genetic similarities show that the modern human species, Homo sapiens, resemble the African apes Human however did not evolve from African apes The two groups evolved from a common ancestor – existed 6 million years ago Both groups have gone 6 million years with separate evolution. What are their anatomical similarities? All living hominins: - - Have a upright posture Lack external tails Have freely rotating arms Have hands with an opposable thumb that, with the other fingers, allows them to grasp and handle objects Have digits (fingers and toes) with flat nails. All other mammals have claws or hooves on their digits. Nails probably allowed for manipulation that is more sensitive Have eyes that face forward so that the eyes’ visual field overlap to give stereoscopic vision Have molar and premolar teeth with low and rounded cusps. This feature makes it easy to identity if it is a hominin or not Have yes with cones for colour vision Are sexually dimorphic Have large brains compared to their body size What are their anatomical differences? Skeletal differences - Differences are related to the evolution of habitual bipedalism in humans The African apes are tree climbers, but when on the ground, they are quadrupedal knuckle-walkers Apes can, walk shortly on two legs but humans do it naturally Bipedalism= ability to walk upright on two legs - Habitual bipedalism is was started humans on their evolutionary path It resulted in the differences in skeleton between African apes and humans Apes have: - - Arms that are usually longer than the legs Fingers and toes that are long and curved for grasping branches Big toes that are divergent Ilia (hipbones) that is large, elongated and parallel to the spinal column. This is to support the legs and trunk in the bent-over posture necessary for quadrupedal knuckle-walking A bow shaped spine Humans have: - Arms that are shorter and weaker than the legs – if long arms were no longer needed for climbing they would not have been selected - Fingers and toes that are short and straight - Thumbs that can grasp objects precisely and firmly between the tips of the fingers and thumb This has greatly increased humans ability to manipulate objects. The African apes do not have this advanced manipulatory ability. They can only grasp between the thumb and sides of the other fingers - A shorter, broader and more bowl shaped pelvis, which supports the legs and trunk in an upright position. Thus provides greater stability for walking and running - Longer femurs (thighbones) that are set farther apart at the hips than they are at the knees close together. The femur arrangement makes walking and running more efficient From L to R, hip bones and femur of chimpanzee, early human and modern human Notice in the two humans how the femur increases in length and slants towards midline, and how the pelvis changes in shape in all of these hominids - Feet have: A large strong heel Tiny toes with the large big toe moved into line with the others – it is converged Longer feet with a stable arch, which supports the body better The foot is adapted to support the whole weight of the body and for walking or running - A spine curvature that has two major curves, the thoracic (where the back curves away from the chest) and the lumbar (where the spine curves towards the stomach) - These “S” shaped curves keep the trunk of the body, and the weight of it, centred above the pelvis, which is crucial for walking upright. Brain differences - Humans have a much larger brain than that of the African ape, especially the cerebral cortex - The average capacity of an adult chimpanzee is 395 cc while that of a human is 1350 cc – humans have far more white matter in the cortex than chimpanzees, this means that there are more connections between nerve cells and a greater ability to process information - The larger more complex brain is responsible for the development of the unique behavioural qualities of humans which include: Using their hands with greater dexterity to make simple tools. After bipedalism, toolmaking was the next major evolutionary step in human development The use and control of fire The use of a highly developed language Skull differences - Humans do not have the pronounced brow ridges of an African ape The foramen magnum in humans is found centrally under the skull, unlike African apes that have it at the rear of the skull Therefore the spine of a human connects with the skull underneath and near the centre so that the head is held firmly upright and the body’s centre of gravity is directly over the legs. This reduces the energy needed to balance. However the spine of an African ape connects with the skull at the back to allow for the attachment of strong neck muscles and to place the head at an angle, the proper position for walking on all fours - Humans have a large braincase, small jaws, a nearly vertical face and chin, but African apes have a small braincase, large jaws, a sloping face but no chin These features suggest that the cranial capacity of the African apes is smaller than of humans and that their diet is different - The canine teeth of humans are small Those of apes are large and pointed and project beyond the other teeth Human evolution from ape-like ancestors What is the evidence? - - The story of human evolution began in Africa about 6 mya and continued until about 2 mya The forces of natural selection have directed it Environmental factors such as climate change caused alterations in habitat and food supply, as well as fast-running prey and fierce predators, acted on the gene pool Those hominins with adaptions that allowed them to survive to breed successfully over time formed new species For much of the first 4 million years there were more than one hominin species living in Africa at the same time Over time, with the exception of the human species, Homo sapiens, they all became extinct The main sources of evidence to show humans have evolved from ape-like ancestors are: A. Fossil evidence, fossil record of early hominins B. Genetic evidence, analysis of mitochondrial DNA (mtDNA) C. Cultural evidence such as tool-making A. Fossil Evidence - About 7000 hominin fossils have been found worldwide – these represent about 6 million years of evolution - The most common fossils are teeth and lower jaws, and the facial and upper cranial bones of the skull - Skulls are almost never found intact but can be reconstructed from fragments - Femurs are the next most common, while remains of the feet, hands, pelvis or spine are very rare - By studying fossilised bones, scientists learn about the physical appearance - Bone size, shape and markings left by muscles show how hominins moved around and held tools - Although the hominin fossil record is far from complete, there is enough evidence to give a good outline of the evolutionary history of Homo sapiens - To try and work this out, palaeontologists look at the following key features of the fossils: 1. Bipedalism 2. 3. 4. 5. 6. Brain size Teeth – dentition Prognathism- having a jaw that sticks out markedly Palate shape – roof of mouth Cranial (sagittal) and brow ridges 1. Bipedalism - Habitual bipedalism – walking upright was the most important adaptation that started humans on their evolutionary path - It is therefore very important to be able to trace the transition from walking on four legs to walking on two legs - Some of the early hominids (hominins and African apes) were pre-adapted to bipedalism; they had freed arms that they used for climbing trees and stretching for fruit. - 10 mya, when the climate changed and Africa was drying up, the habitat changed from near continuous forest to wooded savannah – this affected human evolution as our ancestors would have been forced to move across open ground to find new sources of food - With time those early hominids that could move about upright on the ground, survived to breed and formed a new species – NATURAL SELECTION TAKING PLACE - Bipedalism therefore gave them a crucial advantage in the struggle for survival. - It enabled early hominids to: Live in a greater variety of areas, e.g. forested areas, open savannah, deserts and coastal areas See danger from predators Gather food and make and use tools with their completely free arms and more erect stance Reduce the risk of over-heating as a large surface area is exposed for losing heat to the surroundings How do we know if a fossil was bipedal? - A foramen magnum that is positioned further forward; the skull weight is born by the shoulders while walking upright with the skull balanced on a vertical spine A shorter, broader pelvis; allows for efficient weight distribution in an upright position An “S”- shaped spine; this acts like a spring enabling an upright posture to be easily maintained 2. Brain size - Throughout human evolution there were drastic climate changes – this caused the environment to alter and be unpredictable - To enable our ancestors to survive, a larger, more complex brain, capable of processing new information, was selected - This trend of an increase in braincase size over time can be observed in fossils - The average brain capacity of African apes is 395 cc which is close to that of early hominins 435 cc - Brain size continued to increase in the later hominins 700 cc then 850 cc and finally - Homo sapiens 1360 cc Note: The larger brain made the following possible: - Better co-ordination of movement Large amount of information could be processed The development of speech and a written language for communication 3. Teeth - Fossil teeth are important as they give an indication of which specific hominin species and what environment they might have lived in - The tooth remains show a general decrease in size – mostly the molars and the canines - There is an exception, paranthropus robutus that has massive grinding teeth (premolars and molars) in its lower jaw when compared to the incisors and canines – this would indicate that its diet probably would have been mostly coarse, tough food that needed a lot of chewing - The tooth enamel, thin in African apes, gradually thickens in early and later hominins until in humans it is thick - In African apes and early hominins, the canines are larger and project above the tooth row. – over time they gradually got smaller until, in humans they are the same size as the other teeth and no longer stick out above then others - The canines of the African apes are so large that a gap (the diastema) develops between the canine and incisors to make room for the opposing canine so the jaw can close 4. Prognathism - African apes have large and prognathous jaws, .i.e jaws stick out beyond the upper part of the face - This condition is still seen in the early hominins, the Australopithecines. - Partly because the teeth and the muscles for chewing become smaller the trend is towards a smaller and less sloping face until finally in humans the face is small and flat 5. Palate shape - The palate, dental arch, is the bone separating the mouth and nasal cavities - The chewing trend is away from crushing and tearing to crushing and grinding - For this to happen, the palate shape changed from a roughly rectangular palate in African apes to u-shaped in early hominins (australopithecine) and finally, in Homo sapiens, to a parabolic curve. 6. Cranial and brow ridges - Cranial ridge (sagittal crest), found on the top of the skull, can be seen in hominids that have protruding (prognathous) jaws and well- developed chewing muscles, e.g gorillas - Brow ridges, ie bony ridges over the eye sockets, are very big in African apes and are well developed in some early hominins - They get smaller in later hominins until in humans they are greatly reduced or usually absent How does the change in teeth and skull show a change in diet? - Another trend evident in human evolution is the change in diet from raw food to cooked food - The following suggests that the ape-like beings ate raw food, plant matter and meat, which required a great deal of processing, ie tearing, biting and chewing The teeth, especially the canines, were larger Jaws were large and protruding Cranial and brow ridges served as attachment for large chewing muscles - Early homo species used tools to cut and grind food before eating - Therefore large teeth became unnecessary - In addition the later hominin species began to cook their food, which meant that it did not need the same amount of processing. - Teeth were needed to only bite and crush food - This is seen by: Smaller teeth, including the canines Smaller jaws and a less prognathous skull The absence of cranial and brow ridges, which that were not needed for muscle attachment, as the muscles for chewing were much smaller - Therefore the reduction in cranial and brow ridges, jaw size, tooth size show a change in diet form raw to cooked food. B. Genetic evidence - The strong similarities between humans and the African great apes led Charles Darwin in 1871 to predict that Africa was the likely place where the common ancestor of African apes and humans came from - As will be explained, both chromosomal DNA and mitochondrial DNA (mtDNA) evidence supports this daring prediction made almost 150 years, as do the fossils - The comparison of nuclear DNA (or genes) shared by two hominids shows how related they are. - The more genes they share the more closely they are related All humans share about 99,9% of the same genes, showing their obvious close relationship Humans and apes share between 96,9% and 98,8% of the same genes Of the apes, the chimpanzee (African ape) shares the most genes with humans (98,8%), making them the closet relative to humans - This close relationship shows that humans and apes must not only have had a common ancestor, but that this ancestor must have been ape-like - Comparison of hominid mtDNA of two species tells scientists not only how related the species are but how long ago they separated. - If there are few differences, the species separated recently. - If there are many differences, the species separated long ago. - The preceding cladogram shows that the common ancestors for all apes and humans lived about 15 mya, and the common ancestor of humans and chimpanzees lived about 6 mya, - From that common ancestor, African apes and hominins diverged along two separate lineages To sum up: - Genetics are providing invaluable in gaining a better understanding of human evolution - Geneticist can, by comparing : Nuclear DNA of hominids see how related they are mtDNA of hominids: - that humans evolved from ape-like ancestors - the approximate age when the evolutionary paths of the various hominids diverged C. Cultural evidence - Fossils and genetic evidence are not the only evidence of human evolution - Early hominins very gradually began to control their environment; to use it to alter their way of life because of the unique combination of: A larger brain, especially the cortical area Specialised physical features such as more dexterous hands - This non- genetic means of adaption, called cultural evolution, improved the success of early hominins Tool-making - African apes use objects such as stones and thin sticks This behaviour is learnt from their parents and it is likely that the common ancestor of chimpanzees and humans used tools similarly - However they did not make tools - Therefore, the remains of manufactured tools are evidence of human cultural evolution - After the evolution of bipedalism (4.2 mya) in the earliest genus of hominins, Ardipithecus, tool-making was the next major step in human evolution - It marks the first trait that is unique to the genus Homo. - Hominin hands are well adapted for tool-making as they are capable of fine manipulation and coordination - Tool-making and the use of the tools lead to: New ways of getting food, eg the ability to crack open long bones and get at the marrow, to dig and to sharpen or shape wooden implements Efficient hunting in organised groups with the later more sophisticated tools. Hunting also required the development of good communication - Gradually as the learned skills and behaviours were passed on to offspring cultural evolution occurred. - By dating stone tools, a clear pattern of tool evolution can be seen - The earliest tools were large, simple and crude while the most recent were small, complex and elegant - Much less skill was needed to make the early tools than that the later tools - The greater the evidence of skill the more the brain, particularly the cerebral cortex and thus the species, must have evolved Stone tool evolution 1. Beginning 2.5 mya to 0.2 mya – very static over a very long period of time - The first evidence of the intentional manufacture of any stone-tool comes 2.5 mya from the Ethiopian Rift Valley - The early humans, probably Homo habilis, used hammer stones to strike stone cores and produce sharp flakes - These large simple tools represent the simplest form of stone tool technology and are known as Oldowan tools - They show little if any control over the end design - None-the-less they are evidence that the early humans had intellectually evolved beyond their earlier hominin ancestors, the australopithecines, who did not appear to make tools - Paranthropus robustus might have made bone tools for gathering plant foods - For more than 2 million years, early humans used these tools to cut, pound, crush and access new foods- including meat from large animals - There were two groups of tools Choppers (the remains of the core), which were for crushing nuts and seeds, or bones to get the marrow and for softening vegetable material Scrapers (the flakes chipped off the core), which being sharp could cut the meat off a carcass killed by other animals - These unsophisticated tools suggest that the early Homo species, Homo habilis, were scavenger and not hunters 2. From 1.5 mya until about 250 kya- basically static - At about the same time as Homo ergaster appeared archaeologists found that there was a major change in the stone- tool industry - These more advanced tools of the Archeulian industry showed a preconceived design, not just a random hammering of a core stone. - This provides evidence of the intellectual evolution of their probable makers, H ergaster - These large tools had a central core of a stone with larger flakes chipped off and edges that were sharpened all round and had a more regular “tear-drop” shape. - For well over a million years these double- faced hand-axes, cleavers and picks were made and used - During this time they showed little variation - With these multi-purpose sharper tools H.ergaster became an efficient hunter of small mammals, and was able to live on a mixed diet of meat and plants 3. Beginning 250 kya to recent times- not static, pieces of art - The Acheulian tool industry ended only about 250 000 years ago, which may be associated with the rise of Homo heidelbergensis (archaic Homo sapiens) - Technological and cultural evolution really accelerated from about 250 kya - The stone tools became more diverse, smaller and more refined - Some tools has engravings with symbolic markings - These changes required thoughtful actions, fine motor control and coordination, all of which showed further cultural evolution - Bone tools dated to about 80 000 years ago have been found in Blombos Cave, on the southern cape coast of SA- showing more cultural evolution - By about 40 000 years ago, humans had learned to craft small flakes and blades that became part of a lightweight, sophisticated composite toolkit - The tools were used for an ever greater variety of specific tasks which allowed the hominins to catch fast and dangerous prey - All of this further evidence of hominin evolution - About 20 000 years ago the development of a far more complex tool kit, with microliths, bone and wooden tools with an infinite variety of uses, from stitching to harpooning fish, was further evidence of the evolution of modern human behaviour - These later tools were also things of beauty, something not seen in earlier tool cultures, which showed an aesthetic appreciation – a human trait - About 5000 years ago stone was replaced by copper, bronze and tin in toolmaking as more complex societies evolved Other indications of cultural evolution - There are other practices that showed the cultural evolution of hominins These include the following: Co-operative hunting, which enabled early hunters to catch large prey that otherwise would not have been possible Fire- making, this provided a means of keeping warm, deterred predators from the camp site and helped drive prey during a hunt. During the evenings, fires probably also encouraged socialization. All signs of cultural evolution What can the use of fires tell us about the lifestyle of H.erectus? The control and use of fire is highly significant as it enables anthropologists to determine a fair amount about the lifestyle of early hominins – H. erectus/ H. ergaster (African H.erectus) Fire could have: - Led to social behaviour with the warmth and extended “daylight” hours Encouraged conversation and teaching Offered more permanent (but still temporary) dwelling sites Given a measure of protection from predators at night Helped in cooperative hunting by herding animals away from fire Provided humans with roast meat making it more appetizing. This could have resulted in more protein being eaten, which may have aided brain development A wider choice of food, including smoked and dried fish and meat, and led to the invention of cooking Been a sign of intelligence, as keeping a fire going showed forward planning Enabled better, stronger tools to be made that would have led to more successful hunting Been a factor that enabled H.erectus to migrate out of Africa and into colder climates in Europe and Asia The controlled use of fire marked a crucial change in human behaviour as it showed they had the ability to adjust the environment to suit their needs Major phases in hominin evolution from 6 mya to the present - - As mentioned earlier fossil discoveries show that the first 4 million years or so of human evolutionary history took place exclusively on the African continent Over the passage of time, from the common ancestor of the hominids to modern evolution What caused these? A current hypothesis is that extreme shifts of climate where it swung wildly from hot and wet to dry and cold were a key factor in driving human evolution These dramatic changes presented powerful selection pressures for all living organisms Many plants and animals became extinct However, hominins survived mainly as nature selected for survival those variants with the ability to walk upright and with larger brains These hominins being more intelligent and physically adaptable could deal with different environments and changing food sources The successful hominins then bred to form populations of new species - The evolutionary trends in Tribe Hominini can be summed up as a transition from an arboreal, long-armed, short-legged, small-brained ancestor to a terrestrial one with short arms, long legs and a big brain What are the genera of Tribe Hominini? - The Tribe Hominini consists of the following genera: A. Orrorin and Ardipithecus, from Ethiopia B. Australopithecus, from East and SA C. Homo, from various sites in and out of Africa - Within these genera most scientists currently recognize 15 to 20 different species of early hominins. - While they do not all agree on how these species are related they agree that today there is only one living hominin species - The Tribe Hominini (humans and fossil hominins) and the African apes separated about 6 mya in Africa. - By comparison, the last dinosaurs died out 65 mya, the earth was formed about 4 600 mya and the universe was born about 14 000 mya.
