Human Evolution

Introduction to Human Evolution

Thinking about the evidence for human evolution?

Trends in human biological evolution

Bipedalism

Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped

Skeletal changes linked to bipedalism

What was driving it? Selection Pressures/ environment

As the climate became warmer and dryer in Africa around 6 mya, the forests were receding and became scattered woodland. Hominins at the time would have to have travelled longer distances to gather resources. Being able to brachiate would become less important than being able to walk efficiently, as walking would be the most common mode of travel.

But why?

Early hominins that were able to take advantage of available food most efficiently would be selected for. One way of taking advantage is by carrying more food away at one time. The individuals that could do this by moving on 2 legs and using both hands to carry food would be selected for.

Normally here the question compares a type of ape with a Homin/ H. sapiens. It will be looking at the overall skeleton or a section such as the limbs (legs and arms), feet/hand, or skull. You will have to discuss both species in relation to if they are bipedal or quadrupedal. For this you will have to learn/ memorize all the differences.

Important Bones to know

An awesome site can be found here where you can compare and contrast skeletons of the primates/ humans - Link

Foramen magnum - the large whole the spinal cord goes through in the bottom of the skull.

Occipital condyles - sides of the FM, smooth, rounded surfaces where the atlas vertebra rest. (these are rearward in quadrupeds and central in bipeds)

vertebral column - The backbone of chimps and gorillas is a simple curve. Bipedals have a S shaped backbone.

Hip girdle - Long hip bone in quadrupedal animals (to support abdominal organs). Humans have a bowl shaped girdle to reduce the stress on the part of the hip that transmits body weight.

Femur and knee - Knees directly underneath the centre of the hip girdle.

Below the feet, chest, hands and teeth/ jaw will be covered in more depth.

Great Apes vs. Hominin

Early Hominin vs. Current

• bipedal as foramen magnum underskull / more centralise• bipedal as reduced nuchal

crest.

• not bipedal as foramen magnum islocated at the rear.

More detailforamen magnum underskull /more centralised suggests that skull is balanced on top of vertical spinal column, implying bipedalism.

Note: Pivot and lever not accepted – must be thrust / push

Shape of skull (from http://humanevolutionb36.weebly.com/)

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 displaysCranial capacity

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.Structure-

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

The change to bipedalism

A fantastic podcast can be found here.

As the climate changed and less forest was available, Ardi would have had to walk further to gather food. Longer legs and straighter spine for bipedalism gave a height advantage, allowing Ardi to be able to see further, allowing her to find resources more easily. However, being taller might have made her more visible to predators. In addition having hands free means that she could carry items such as tools for gathering more food, or food from another place to consume at a later date. However, changes to bipedalism make Ardi less well adapted for arboreal life, potentially reducing protection and food gathering.

An excellent animation looking at the main areas.

Excellent animation covering bipedalism

What would be driving bipedalism to happen?

Environmental change brought new selection pressures. A Change of Environment

About 20 million years ago, the Indian plate collided with Asia and thrust up the Himalayan range. The climate became drier and the forests of what is now Africa and Asia contracted. – The result was an increased area of savanna habitat, with fewer trees.

Bipedalism freed the hands which enabled hominins to develop tools, which have in turn enabled them to access meat, which is rich in protein and energy needed to increase brain development and therefore endocranial capacity, leading to development of speech, understanding and conceptual thought (Broca’s, Wernickes and increased cerebrum)

Bipedalism also freed the hands to allow for tool development and learning of more complex skills, and therefore selection for larger brains, requiring increased endocranial capacity.

In both the savannah andforest bipedal hominins would have been upright allowing them to seepredators. In the savannah they would have been less susceptible to heat exhaustion as less of their body surface is directly in the sun and they would be more exposed to cooler air breezes. In the

forest it would have been easier to reach food.In both habitats movement is more efficient.

Why bipedality?

What are the main changes - a good comparision

•can cover more distance to gather more resources as bipedal locomotion is more efficient.

•height makes her more visible to predators(vulnerability implied)

• Upright: Less likelihood of overheating when walking in the open / doing other activities

•The changing climate means that the niche is diminished, forcing her to leave the trees.

• As bipedalism leaves her hands free, can carry resources from place to place, giving her a survival advantage.

Thermoregulation- The upright posture exposed less surface to the tropical sun.

Efficient Locomotion- It is more economical than knuckle walking used by the other great apes. In a more fragmented woodland the hominids would have to travel further per day for resources.

Child Birth

Most of the questions have related to the size of the pelvis opening.

Increased diameter of inlet in sapiens so modern infants are born with a proportionally larger

head (cranial capacity) than erectus infants.

Trade-off between +ve and –ve;

• Ability to give birth to largerbrained babies

• Impact on locomotion – more efficient with smaller pelvic inlet

Summary of Adaptations for Bipedalism

Changes in skull and endocranial features

A good animation

Fun activity on digging for fossils

Changes in the manipulative ability of the hand

Powerpoint from Nayland College (excellent resources)

Changes in skull/ endocranial (inside skull)

Use of tools (stone, wood, bone)

Hands

Examples of trends in tool manufacture

• length of cutting edge increases

• number of blows increases.

• more precise tools

• more refined tools

• more time taken making tools.

Tool periods

Mousterian – made from flakes, resharpened edges, Levallois method; scrapers & spears, attached stone tools to handles, flint.

Palaeolithic – specialised, made from several materials(flint & bone), precision / refined / intricate, fine blades & points; spear thrower, bone needles, fish hooks, wide range of uses

Tools have progressed from the basic removal of stone flakes to create tear-drop shaped hand axes in the Acheulean culture. Next was the Mousterian culture where the Levallois method was used to remove a sharp-edged flake of stone. Lastly came the finer detailed Palaeolithic tools such as needles and hooks made from bone and flint.

How does this relate to the hominins?

Simplest tools made by earlier species

Habilis and Oldowan tools; erectus and Acheulean culture; Mousterian of neandertals and early sapiens

extremely complex tool kits of later sapiens.

The ultimate website on this topic

Use of fire

H.erectus fossil sites show evidence of the use of fire. Fire would have encouraged groups to gather together and provided light at night for longer days where erectus could have spent more time in communication and thinking through the days problems. Fire allowed H. erectus to live in more northern communities affected by greater seasonal changes and colder nights and winters, improved longevity by killing microbes through cooking meat/fish, helped in cooperative hunting by herding animals away from fire.

Benefits of using fire

• at night/in colder areas
• anti-predator defences eg. fire scares away predators
• easier to digest/destroy parasites/access greater range of food / more palatable / preserve food
• for toolmaking/preparing food /planning
• to get more food
• harden points of wooden tools/weapons.
• able to keep warm in cooler regions
• Use of fire lead to better / stronger tools more successful hunting and increased food
• Use of fire to cook food / meat to access additional protein / energy
• Use of fire as protection from predatory animals.

clothing

abstract thought (communication, language, art)

Broca’s OR Wernicke’s area linked to development of language is important.

Communication

Facial expressions important

An excellent web story can be found here

Speech

Culture requires intelligence and communication

Areas of the brain essential for structure and sense of speech

Broca’s area – concerned with speech

Wernicke’s area – concerned with comprehension of language

The lower the voice box, the more sounds can be articulated.

Singing and chanting

Essential for remembering kinship lines and tribal history

Better hearing and listening skills as a result of speech

Art

drawings of pictures and symbols on cave walls, bone carvings, clay statues

food-gathering

(hunter-gatherer, domestication of plants and animals)

Domestication

• Domestication happened, using crops and animals from the local environment, and adapting them to provide regular food supply for a group of individuals.

•Climate warming meant that agriculture appeared suddenly in many places as crops could be grown there [change]. This meant that people did not need to move to gather food, so could conserve energy and support larger populations [advantage].

•With more food available, larger populations could be supported [advantage]. However, this meant that there was more waste to deal with, potentially bringing pests and diseases [disadvantage].

•With crops being harvested at one point in time, food supply would be erratic through the year [disadvantage]. New technologies such as pottery containers for food storage would have been one solution to this [solution].

•With domestication of crops came a reduction in the variety of food available compared to hunter gathering. {disadvantage}. Trading between different groups gave greater food variety {solution}

shelter

(caves, temporary settlement, permanent settlement).

What shelter brings

planning

• communication

• cooperative behaviour

• division of labour

• suggests a larger group (NOT just communities)

Home Base Theory

At some sites, concentrations of tools, stones from other areas and bones are found.

This suggests that early hominins were not just carrying things around, but were focusing on one site as a home base.

Adults hunted and left young behind, and then brought all produce back to be shared

Sharing of food lead to complex societies

Clearly defined by the time of Homo erectus

Spiritual / religious / afterlife beliefs

a concept of the afterlife is shown by the ivory beads left by the dead – a gift for them (in another life). the idea that death was not the end and the mammoth shoulder blade could be used for protection in the next life.

Being settled in one place

By being settled in one place only some people would be toolmakers which enabled better specialised tools for better hunting / opportunity for learning from specialists (specialisation of roles).

Hominin overview

Interactive timeline (excellent link!) - This covers many of the hominids

http://sci.waikato.ac.nz/evolution/HumanEvolution.shtml - Another great information link

Patterns of dispersal of hominins

An excellent into to this topic can be found here (animation).

A good PowerPoint can be found here

Hominins refers to living and fossil species belonging to the human lineage. This is a subgroup of hominids, a group which includes both humans and the great apes.

Lisa Matisoo-Smith presented a LENS seminar on 16 September 2011 focusing on using DNA to understand the settlement of the Pacific. For more details, seehttp://lens.auckland.ac.nz/index.php/Pacific_Migration

From the Alan Wilson Centre (direct link)

These presentations trace the story of how modern humans spread across the globe, beginning around 65,000 years ago with migrations out of Africa, and ending with the settlement of New Zealand 750 years ago. In part 1, students will learn how researchers are using genomics to address questions such as: How many migrations out of Africa were there? Did Homo Sapiens interbreed with Neanderthals and other ancient human lineages as they spread across Europe and Asia? What does “race” really mean? The PowerPoints are aimed at senior biology students (Years 12 and 13), and fit with the Nature of Science and Living World strands of the curriculum. The pdf file contains notes for teachers to accompany the presentation.

Africa to Aotearoa part 1 (5,829 KB)

Africa to Aotearoa part 1 - Note (1,627 KB)

Out of Africa hypothesis

A good image showing the process. (Click to see full size)

Intial migration of early Homo, such as H.erectus, H.heidelbergensis and H.neanderthalis, did not contribute to modern humans, but there was a second wave of new humans out of Africa approx 200 000 years ago. It was a fully modern H.sapiens that then replaced whatever populations then occupied Asia and Europe. Intial migration of early Homo, such as H.erectus, H.heidelbergensis and H.neanderthalis, did not contribute to modern humans, but there was a second wave of new humans out of Africa approx 200 000 years ago. It was a fully modern H.sapiens that then replaced whatever populations then occupied Asia and Europe. Transitional forms found mainly in Africa. Modern traits found first in Africa and then later elsewhere as they spread. Since the species is young there should be little diversity

Why would early Homo need to migrate away from Africa?

Habitat change with specific example of how this lead to greater survival, eg. new hunting / foraging areas to exploit

• Pressure to expand into new ranges; follow prey /food plants to reduce competition
• Potential for drop in sea level to expose new migration routes(land bridges)

Evidence

Multiregional (and others) a comparison.

Use of mitochondrial DNA

• mtDNA has been used because it is passed on from mother to child and is not changed due to meiosis.
• Mutations occur at a steady rate in mtDNA and can be used to estimate how long ago two species shared a common ancestor.

How could they migrate so rapidly?

It would be possible to reach many areas via land bridges asit means a shorter /safer route. Straits between islands could be narrower – more likely to use boats/rafting to cross straits. Coastal travel would be easier on newly-exposed continental shelf with ready food supplies in shallow coastal

waters.

Why was Europe slow to colonise?

Eropean climate much more severe than the more southerly coastal route, forcing more southerly travel /so harder to get food.

• Neandertals were already present

in Europe creating competition.

• Too cold in Europe as adapted to

warmer climates so migrated further south.

MultiRegional

• Asian fossils show a clear transition from older hominid to modern H.sapiens. The oldest H.sapiens fossils outside Africa were in Australia, and are 60 000yrs old. Northern china fossils show no evidence that African features ever replaced the ancient Chinese in this region. Instead there is a smooth transformation of ancient peoples into the present populations of East Asia and the Americas. Post-Neanderthal people in Europe show mixtures of modern and archaic African features. Mitochondrial DNA analysis is flawed because; Present-day patterns cannot show links that become extinct. Whenever no daughters are produced the mitochondrial line dies out.

Evidence

Out of Africa

• Mitochondrial DNA shows high degree of similarity between all modern human populations that most likely occurred with the past 150 000 – 200 000 years ago
• The oldest H.sapiens fossils have only been found in Africa, 80 000 – 120 000 years old
• Humans arrived in Europe late – about 80 000 years ago. Fossil evidence shows that moderns humans appeared in Africa before the Neanderthals had disappeared in Europe so could not be descendants of the Neanderthals

Evidence that H Erectus could survive outside of Africa and the conflicting evidence that they did not.

Could survive.

H. erectus skulls show increased cranial capacity and fossil sites a more advanced Acheulian tool culture, which would have been better for hunting and scavenging. H. erectus skulls show increased cranial capacity indicating better communication / planning / cooperation leading to improved chances of survival.H. erectus have more advanced Acheulian tools therefore would have had the ability to access meat as a supply of additional calories / energy.H erectus used fire – able to keep warm in cooler regions / spend time making tools for hunting or processing meat at a home base / Use of fire lead to better / stronger tools more successful hunting and increased food.

Conflicting evidence about being the first hominin to leave Africa comes from Georgia (Europe / Asia) where a species, named H. georgicus, dated earlier than H. erectus 1.6-1.7 mya), with a cranial capacity of only 600-780 cm and associated with Oldowan tools has been found. H. georgicus is not associated with fire or the ability to produce the more advanced tool culture for accessing high protein food, thought necessary to survive outside of Africa

Comparison

The greatest variability is found within African populations which are the oldest. There is less genetic diversity in Asian and European populations, which suggests they are not as old as African populations.

European / Asian populations

Conclusion

The real hobbit - Homo floresiensis

Dating Rocks, Fossils and Artefacts

The future of human evolution

An excellent podcast covering this idea.

Readings - Attached below