The Human Story – Biology

Classification: General classification hierarchy from phylum to species

Phylum, class, order, family, genus and species. Phylum is the most general category, and species is the most specific

What is a species, and its criteria: A species can be defined as a group of actually or potentially interbreeding

natural populations that is reproductively isolated from other groups. The criteria used to identify a species are that members of a species can

interbreed and produce fertile offspring, as well as sharing a common gene pool.

Features that classify humans as: Mammal: hair, mammary glands, three separate bones in the inner ear, four-

chambered heart and a lower jaw consisting of one bone Primate: fingernails and toenails, an opposable thumb, binocular vision, a

relatively large brain, a flattened face with a reduced sense of smell and forward facing eyes, prolonged period of care for young

Hominid: relatively large brain, lack of a tail Hominin: bipedal upright gait (walk), shorter arms than legs, larger brain size

relative to brain size The classification process:Classification level Name of group CharacteristicsKingdom Animalia Heterotrophic organismsPhylum Chordata Have a notochord and

hollow dorsal nerve tubeClass Mammalia Hair, mammary glands,

four chambered heartOrder Primate Opposable thumbs, nails,

binocular visionFamily Hominidae No tail, upright stanceGenus Homo Bipedal gait, S-shaped

spine, foramen magnum centred under the skull

Species Sapiens Large brain, complex social system, capacity for speech and abstract thought

Hominin/hominid; arbitrary nature of classification systems: The use of the groups hominid and hominin in undergoing change, as new

evidence becomes available fro biochemical and genetic sources. The definition of the term hominid has broadened from humans and their

immediate ancestors to now include the modern and extinct greater apes.

This is because classification has been revised, with being sufficiently similar to belong to the one family, hominidae.

The term hominin now refers to the groups belonging to the tribe considered to be direct human ancestors including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus, as well as the chimpanzee.

Primate characteristics:Hand/foot structure Pentadactyl limbs, opposable toes and

thumbs, nails instead of clawsSkull shape/function Enlarged skull to protect the relatively

large brain, flatter face with shorter nose better depth perception but poorer sense of smell

Brain size relative to body size Well developed brains, larger relative brain size to body size

Arrangement of the vertebral column Upright stance, S-shaped spine, foramen magnum centred under the skull

Vision Large forward facing eyes good view of overlap, stereoscopic vision (good for living in trees), good colour vision (important adaptation in finding food, especially with reduced sense of smell)

Reproductive features Long gestation period (length of pregnancy), usually produce one baby. Restricted breeding period and two nipples

Parenting/group bonding Dependent for long periods of time long learning time for the young to develop social skills. Living in groups is a form of protection against predators, increases chances in finding food. Many primate groups are well organized, clear hierarchy of position

Advances that have changed opinions about classification of primates: There are a lot of different ideas about the details of primate classification.

Several taxonomic systems exist and these have changed over time. As more fossil primate-like animals were discovered, more disagreement

arose about how to classify them and how they evolved. There is still disagreement about prosimians and anthropoids and what fits

where. An example is that some people believe that tarsiers fit somewhere in between due to the evident primate characteristics.

Another example involves DNA-DNA hybridization, showing that chimpanzees and humans are closer than gorillas.

Primate characteristics in: Prosimians: belong to the suborder Prosimii. Prosimians have an elongated

snout, large olfactory bulbs and rhinarium (wet nose) and rely to a large extent on their sense of smell. They lack bony eye sockets and colour visions, may have claws instead of nails. Sometimes nocturnal, with eyes adapted for night vision. Mostly arboreal, move by vertical clinging and leaping. Examples include lemurs and lorises.

New world monkeys: range from southern Mexico through to Central America to southern Brazil. Usually smaller, slimmer monkeys. Flat nose, nostrils open to the side. Arboreal, have long limbs and walk on all four legs but some brachiate (swing from hand to hand). Curved nails, some have a prehensile tail. Examples are the spider and howler monkeys.

Old world monkeys: range from northwest Africa through to southern Arabia, South-East Asia, Japan, Indonesia, Timor and the Philippines. Nostrils are closer together and open downwards; skull is often robust and heavily ridged. All fingers have nails, some old world monkeys are arboreal, and some are terrestrial. None have a prehensile tail. Examples include mandrills and baboons.

Apes: include gibbons and the great apes (Pongids) – the chimpanzees, orangutans and gorillas. Most divergent from humans. Small and move mostly by brachiating. Closest living relatives to humans. Pongids have no tails. They are terrestrial; their forelimbs are longer than the hind limbs. Hands and feet are similar to humans. One significant difference between apes and humans is bipedalism.

Humans: characterized by the large size of the brain, completely upright stance, bipedalism, a highly opposable thumb and the development of complex patterns of language.

Similarities and differences between: Features - Prosimians HumansShape of face Pointed with long snout Very flatTail Usually possesses tail No tailDigits At least one with a claw,

used for grooming, others have nails, thumb less opposable

All digits with nails, thumbs very opposable, toe not opposable

Locomotion/body stance/limbs

Arboreal, vertical clinging and leaping

Striding bipedal gait, arms shorter than legs

Nostrils/nose Rhinarium present Rhinarium absentVision/eyes Eyes face forward but

more widely spaced than other primates, possess tapetum lucidum for nocturnal vision

Eyes face forward, encased in bony socket, diurnal

Hair covering Thick hair over body Fine hair over body except head. Hair can indicate sexual maturity.

Size Small Large

Biological evidence for human evolution:Formal formation:

Conditions under which fossils may form include:o Quick burial before decomposition can occuro Burial in soft sediments such as sand, mud and volcanic asho Minimal disturbance of the sediments, such as in still lakes or ocean

bedso The organism possessing hard parts such as bones, exoskeleton, teeth

or shells.

Age of the Earth and geological time: The age of the Earth is estimated to be 4500 million years old. Geological

time is described as a time scale. The details of the time scale start about 570 million years ago. The main eras

included in this time include the Palaeozoic Era (570-250mya), the Mesozoic Era (250-65mya) and the Cenozoic Era (65mya-present). This is the time during which plants and animals developed ‘hard’ parts and so have left a fairly good fossil record.

The oldest evidence of life on Earth is 3500 million years old.

Relative and absolute dating techniques: Relative dating techniques involve comparing fossil sequences in strata

(layers) of sedimentary rocks. Layers of sedimentary rock containing the same fossil sets are thought to be of the same age. This technique is also based on the law of superposition that states that the older rock layers and below the top layers. Some fossils have become the indicators and their presence can assist in dating fossils found with them, above them or below them.

o Stratigraphic correlation: study of rock layers or stratao Palaeomagnetism: based on the periodic reversals of the magnetic

field that Earth experienceso Faunal dating: uses common fossils to date other fossils

Absolute dating techniques were developed after the discovery of radioactivity in 1896. The method is based on the radioactive decay of certain elements such as carbon and argon. When igneous rocks form by solidification, the minerals contain a certain proportion of radioisotopes. By determining the relative proportion of the parent material (potassium-40) to the daughter material (argon-40), a determination of the age of the rock can be made (conventional K/Ar dating).

o Dendrochronology: study of tree ringso Radiocarbon dating: using the amount of radioactive carbon that is

found in fossils such as charcoal or bones. Scientists can also date the actual organic material is fossils using the half-life (5730 years) of the carbon-14 radioisotope.

o Thermoluminescence: uses the property of minerals such as quarts, feldspar and calcite to emit light when they are heated

Relative dating techniques using fossil sequence in strata: Stratigraphic correlation Relative dating techniques involve making comparisons between rock layers

that contain fossils. Those at the bottom are believed to have been around earlier and are therefore older.

By comparing similar strata, the relative ages of different groups of organisms represented by fossils can be deduced.

The rate at which sediments are deposited is far from uniform, so this method gives an estimate and cannot be related to a time scale.

Difficulty of interpreting the past from the fossil record: Conflicting dates based on different technologies: new evidence and

techniques become available at different times. The different technologies will each have a different margin of accuracy. Therefore each method can lead to a different interpretation of the fossil age.

The paucity of the fossil record: there are gaps in the fossil record and the fossil record is heavily weighted towards the organisms that have hard parts. Fossils tend to be incomplete and this can make it difficult to interpret some features of a fossil or a species.

Different interpretations of the same evidence: different scientists may specialise in different areas and therefore interpret the evidence differently. Different people/scientists have different pre-conceived ideas that can affect their interpretations. If the only evidence you have for a species is limited, then the rest of the anatomy and physiology of the fossil is open to the interpretation of each of the people working on it.

Model karyotype analysis: In traditional karyotype analysis, dye is added to the set of chromosomes.

This creates a banding pattern. Each chromosome can be identified by its banding pattern and compared with other chromosomes. Current genetic engineering technologies use fluorescent markers that now make it possible to recognise crossing over and translocations.

Results of this experiment: o Humans have 23 pairs of chromosomes; apes have 24. Of the 23 pairs

of chromosomes that are common to humans and chimpanzees, 13 are identical. The other 10 are arranged differently. Some segments are completely reversed.

o Chromosomes 6, 13, 19, 21, 22 and X have identical patterns in humans, chimpanzees, gorillas and orangutans. Chromosomes 4 and 17 are different amongst all four species.

DNA-DNA Hybridisation model: DNA hybridisation uses one bit of the DNA to find out whether a

complementary bit of DNA is present. The process works because DNA is made of double strands that can be unzipped.

Example: to determine the relationship between humans and chimpanzees, DNA is extracted from human and chimpanzee tissue. The DNA is purified and

fragmented by ultrasound. Parts of the chimpanzee’s DNA is ‘labelled’ with radioactive iodine and then combined (hybridised) with human DNA.

DNA-DNA hybridisation studies show that the difference between the human nucleotide sequence and that of the chimpanzee is 0.7%. Humans are more closely related to chimpanzees than either species is to the gorilla.

Evidence from living primates to hypothesis about past relationships: Karyotype analysis: refers to the characteristics of the set of chromosomes

of a somatic cell. Humans and apes are extremely genetically similar – they share almost 99% of their genetic material

DNA-DNA Hybridisation: refers to a genetic engineering technique that takes DNA from organisms of the same species or different species and splices them together to make a hybrid. The more closely related the species are, the more similar is their DNA. The DNA hybrid is a measure of the evolutionary closeness of the two organisms. The use of heating and cooling separate the DNA and tell us how close the match is between the hybrid strands.

o 1% difference in nucleotide sequence results in a temperature change of 1 degree

o Species of the same genus: 4 degreeso Different genera of the same family: 4 – 11 degreeso Different families, same order: 11 – 20 degrees

Comparison of haemoglobin: in the 1970s, scientists began studying the similarities between blood proteins of humans, chimpanzees and gorillas. If two species have similar haemoglobin, their DNA must be similar and they have shared a common ancestor. Recent studies of blood molecules and immune responses indicate that there is a much closer evolutionary relationship between humans and chimpanzees than originally thought.

DNA sequencing: the order of bases along a DNA strand is called its sequence. If the sequences are similar then the two organisms have shared a common ancestor.

Mitochondrial DNA as a molecular clock: Mitochondrial DNA (mtDNA) is a single, double-stranded loop that codes for only 13 proteins. Mitochondrial DNA is only inherited from the mother. By comparing the mitochondrial DNA from living primates, it is possible to calculate a molecular clock based on a constant rate of mutation. Depending on how different the mtDNA is, it’s an indication of how many years has passed since two organisms shared a common ancestor.

The importance of maternal inheritance of mitochondrial DNA in tracing human evolution:

In 1991, a study involving maternal inheritance using mitochondrial DNA challenged scientific thinking about the origins of modern human beings.

The study suggests that Homo sapiens developed from early hominids in Africa between 166,000-249,000ya and that all mitochondria in people living today can be traced back to a single mitochondrion from a woman who lived in Africa about 200,000 years ago (Eve hypothesis).

The study, which involved comparing the differences in mtDNA of 189 people globally and using it as a molecular clock, decided that it would’ve taken about 200,000yrs for the largest differences in mtDNA to accumulate.

The conclusion is that African populations have been separated from one another the longest.

The hominid debate:Two alternative views of human evolutionary relationships:

Johanson’s theory: his theory is that Australopithecus afarensis is the ancestor of the Australopithecines and the genus Homo. The other Australopithecines and Paranthropus species do not lead directly to humans.

Richard Leakey’s theory: his theory is that the Australopithecines and the Homo line are both separate and have a different ancestor that is yet to be discovered. This common ancestor would be further back in time.

Similarities and differences in tracing evolutionary differences: Australopithecus afarensis and Homo habilis

Features Australopithecus Afarensis

Homo Habilis

Body structure Pronounced ridge above eyes, no chin, strong upper body, smallish brain

Much smaller, flatter looking face (more human-like), upper limbs still strong, more primitive than other Homo species

Cranial capacity 380-450ml 700mlAge 3.7-2.8mya 2.3-1.44myaCulture “Lucy” – hunters of small

game, occasional meat eaters

Worked with stone tools, mostly made of pebbles. One of the first groups to use stone tools

A. Afarensis provides evidence that hominins walked upright (with a small brain capacity).

H. Habilis provides evidence of the use of first stone tools. For a long time, it was hypothesized that the upright stance and bipedalism in hominins freed the hands for making tools.

It is now clear that 2-3mil years separate bipedalism from the first worked tools. The development of the brain had to occur for at least 3mil years to allow the capacity to make tools from stone.

Comparison of hominid groups (body structure/cranial capacity/fossil age/inferred culture):

Hominid Body structure Cranial capacity (cc)

Fossil age and locations

Inferred culture

Ardipithecus ramidus

Ape-like body Unknown Eastern Africa and Ethiopia 4.5 to 4.4 million years ago

Lived on flat plains with woods and forests

Australopithecus afarensis

Bipedal upright posture, S-shaped spine, foramen magnum is centred under the skull

420-490 Eastern Africa 4 to 3 million years ago.

“Lucy” – hunters of small game and occasional meat eaters

Paranthropus robustus

Height 1.75m. Bony crest on skull, robust

450-550 Southern Africa 3 to 1 million years ago.

Sticks and stones were most likely used to gather food

Paranthropus boisei

Robust, short but heavily built, sagittal crest, short legs, long arms

500-545 East Africa 1.75 to 1.4 million years ago.

Australopithecus africanus

Slender built 420 to 490

Southern and East Africa 3.2 to 2.5 million years ago

Vegetarian, probably used teeth to break hard seeds

Homo habilis Rounder head and smaller molars

500-800 Africa 2.2 to 1.6 million years ago

Stone tools.

Homo ergaster Projecting brow ridge, long limbs, tall

848-908 Africa 1.7 to 1.4 million years ago.

Stone flakes used for chopping and cutting

Home erectus Stocky, less protruding face

900-1200 Africa, Asia, Europe, 1.7 million to 250 000 years ago

Used ore sophisticated stone tools, thought to be peaceful hunter-gatherers

Homo heidelbergensis

Slender build, double arched brow ridge, slight mid-face projection

1100-1300

Europe, western Asia 500 000–125 000 years ago

More sophisticated acheulian tools

Homo neanderthalensis

1.6 m tall, smaller forehead, large eyebrow ridge, little or no chin

1400-1750

Europe, western Asia 200 000–30 000 years ago

Adapted to cold climates of Ice Age Europe, the first to bury their dead, refined stone tool making

Homo sapiens Well developed chin

1350-1500

All over the world 130 000 to present day.

Complicated tools and social structure

Increasing understanding of hominid evolution:Goodall’s contribution to our increasing understanding of human evolution:

Rejected early definitions of human through studying chimpanzees. She showed that they make and use tools in a regular way, which

contradicted the early definition of humans, being ‘the stage of primate evolution when the creature beings to make tools to a regular pattern’

Evidence for two different models of human evolution:1. Whether or not Neanderthals are human ancestors It was once thought that H. sapiens were related to Neanderthals. Now many

see Neanderthals as a separate species. DNA extracted from Neanderthal bones supports the theory that they were a

distinct species that did not contribute to the human gene pool. It is now thought that we descended from H. erectus, out of Africa

2. Whether H. habilis evolved into H. erectus Recent finds near Lake Turkana suggest they coexisted for a considerable

period. Because their populations were small and they had different diets, it is

believed there was little interaction between the species. This suggests there is a new ‘missing link’, the ancestor of H. erectus

Evidence for the patter of human migration:The ‘Out of Africa’ model:

More commonly held model Proposed by Christopher Stringer from London’s Natural History Museum States that there was a second wave of migration out of Africa of modern

humans (H. sapiens), who evolved from H. erectus 130,000-200,000 years ago and spread from there less than 10,000 years ago.

The model states that modern humans replaced all archaic populations, such as Neanderthals, all over the world.

Evidence comes from mitochondrial DNA taken from the arm bone of a Neanderthal fossil

The theory of regional continuity (multi-regional hypothesis):

Proposed by Milford Wolpol. In this model, there is no second wave of migration.

Proposed H. erectus moved out of Africa about 2 mya. It states that humans arose in Africa and evolved as a single widespread species, with multiple populations interconnected by genetic and cultural interactions and exchanges.

H. erectus gradually evolved, resulting in divergence, but continued to interbreed enough to remain one species. Different divergence in areas, e.g. China, Java/Australia, Europe

The strongest evidence comes from Australian Aborigines who first migrated to Australia 60,000yrs ago from Indonesia. The evidence suggests that Aborigines have traits reminiscent of the H. erectus found in Java. Many scientists still remain skeptical of this theory.

Human adaptation to their environment:Mechanisms that led to human diversity:

Migration, adaptation and isolation

The differences between polymorphism and clinal gradation: Polymorphism: the presence of two or more distinct forms of a genetically

determined character. Humans are polymorphic for skin colour, body stature, sickle-cell anaemia, blood groups and the epicanthic eye-fold. Polymorphic differences occur as selective adaptations to different environments.

Clinal gradation: occurs as a result of interbreeding and intermediate environments. Clinal gradation is seen in skin colour, eye colour and body stature. A cline is a gradual change in gene frequency in a population. This produces a gradual change in the phenotype characteristics of a species over a geographical range.

An example of polymorphism and clinal gradation in humans is the gradual increase in the frequency of blonde haired, blue-eyed people as you move from the Mediterranean to the countries of Scandinavia. Eye colour and skin colour are both polymorphic. The clinal gradation that occurs is because of the existence of intermediate environments where different genetic factors

have an advantage. The presence of these clines make it difficult to maintain the concept of a race.

Polymorphism in humans: Ancestral stock from Asia have phenotypic features, such as epicanthic eye-

folds, a flattened face, fat-padded cheekbones and a low, small nose. These features give an evolutionary advantage because they are adaptations to cold conditions. The eye folds are formed from fat and protect eyes in snow conditions. The shape of the cheeks and nose helps to prevent the occurrence of frostbite.

Ancestral stock from central and southern Africa have phenotypic features characterized by very heavy skin pigmentation. This phenotype can be an evolutionary advantage in tropical conditions as the skin provides protection from skin cancer. Other features, such as thick fibrous pads on the soles of feet, also protect from the heat. There is a high presence of the gene for sickle-cell anaemia, which helps provide a degree of resistance to malaria, despite having a deleterious effect, particularly when homozygous.

Cultural development as a significant feature of human evolution:Cultural changes in human society:

Human cultural development dates back to over 2mil years ago. The predominant view today is that human differences come from cultural variations, not biological variations

The manufacture of tools and the development and diversity of rituals, ceremonies and lifestyle illustrate cultural development.

Evidence of cultural development over the past 40,000yrs include:o The development of a more rigid, complex social structureo The development of greater dietary flexibility from seed-eaters to

hunters and so the development of cooperative behaviour for hunting and distribution of the ‘kill’

o Increased length of infancy, childhood and adolescence because of the need to learn more, and more complex culture

o The development of more complex behaviouro The development of language and the ability to communicateo The ability to travel long distanceso The development of permanent settlements which permitted greater

specialisation of activityo The development of increasingly complex tools; from stone tools to

pottery to metals, to the complex electronics and machinery of today

Impacts of cultural development: Cultural development gave humans an evolutionary advantage. The different

cultures that succeeded one another have helped to create a belief in the adaptability of humans.

Specialisation of roles occurred and humans developed more permanent shelters. The continued development of tools and weapons used in hunting

would lead to population increase and eventually to the agricultural revolution and urbanisation.

As population increased, populations of some prey species could decline. Increased population could lead to epidemics of disease and the need for better sanitation and medicine.

Comparing humans with other primates:

Primate Care of young Length of juvenile period

Social group Tools Communication

Lemur Mothers care for young for 5 to 6 months, gestation 2-5 months

2 years Some lead solitary lives, some have large stable groups, some in fluid associations, and others in small grouping. Most lemurs show female dominance, unique in non-human primates.

No Scent markings and body language including tail waving

Orangutan Close relationship, gestation 8.5 months

Female 10 years, male 11-13 years

Noyau -can also be referred to as dispersed polygyny with one male having a range that overlaps that of several female ranges

Little Vocal signals

Gorilla Very close- other females may assist, gestation 8.3 months

Female 10 years, male 11-13 years

Polygynous- one male mates with several females

Little Complex vocal signals

Chimpanzee Very close-older sisters often help with care of the infant, gestation 8.5

4-5 years Fission/fusion Yes Complex vocal signals and can learn symbols

months

Human Very close- both parents look after young and other family members usually also help, gestation 9 months

12 years Family Yes Complex language and complex thought-therefore complex toolmaker and user

Evolutionary significance of the similarities and differences identified: All primates care for their young. This is very important because, as they only

tend to have one offspring at a time, their reproductive capacity compared to other groups is limited. Caring for young helps to increase the chances of successful raising of the offspring.

Social groups are fairly common among primates, although the nature and flexibility of the group differs. Groups tend to provide some help with obtaining food, controlling territory or rearing young, so generally provide an evolutionary advantage.

A difference between primate groups occurs in the use of tools. Some groups of apes (chimpanzees) make use of tools but humans have taken this to a much higher level and it has given them significant advantage. Similarly, the development of vocal signals to the level where humans have complex language has also given great advantage in social cooperation, problem solving and abstract thought.

Current and future trends in biological evolution and cultural development:Possible effects of key factors on human evolution:

Increased population mobility: clinal degradations should decline as increased mobility leads to more interbreeding between cross-cultural groups. From an optimistic viewpoint, cultural development will probably result in less sectionalism, with cultural groups becoming more flexible and tolerant of differences.

Modern medicine: may almost eliminate the ‘survival of the fittest’, in physical terms. Vaccines may be further developed to eliminate major infectious diseases. Alternatively, the overuse of antibiotics may lead to the development of new strains of virulent microorganisms. Risk factors associated with disease will be understood and public education programs will reach more people. As a result, more people will have the opportunity of living a healthy lifestyle and living longer or reproducing more.

Genetic engineering: many genetic diseases will be treated but this may lead to an increase in the number of deleterious genes in the population. Genetic engineers may further develop the technologies to carry out modification in gametic or embryonic cells and therefore eliminate genetic defects. Genetic engineering may lead to increased agricultural and industrial productivity and

therefore better and more varied foods. It could also enhance our ability to produce renewable energy sources that burn cleanlier. Alternatively, genetic engineering could lead to the development of resistance in pests and a decline in productivity. Misuse of genetic engineering could facilitate biological warfare and wreak devastation and instability. It also offers the potential for abuse in the form of eugenics. The whole meaning of being human could be devalued if genetic engineering and reproductive technologies, such as cloning, are applied to humans.

Changes in human population numbers: Some ideas to explain the dramatic growth in human population in the last

10,000 years include:o The impact of agricultural, industrial and technological revolutionso Improvements in medical knowledge, treatments and preventative

care The potential impact of modern technologies on future populations may

include:o A population in which people live longer, with a resultant dramatic

increase in the number of older people. Scientists may be successful in identifying and manipulating the gene(s) for ageing. People may live longer without ageing.

o An increasingly healthy population with even genetic diseases being cured.

The purpose and implications of the Human Genome Project: The Human Genome Project (HGP) was completed in 2003, although the

implications will continue to be felt for some time. It mapped the location of 20,000 to 25,000 genes on the human chromosomes and decoded the 3 billion DNA base pair sequences that make up the human genome.

It has implications for our understanding of diversity among human groups and clines, as well as human evolution. It has great potential to help manage human disease and predict the chances of the onset of certain conditions that may have a genetic component.