Hominin Evolution

Classification – where do we fit?

Classification• Kingdom Animalia• Phylum Chordata• Class Mammalia

Who & (no. of living species)• All animals (1,000,000)• With spinal cord (50,000)• Mammals (4,000)

What is a mammal?

Classification – where do we fit?

Classification• Kingdom Animalia• Phylum Chordata• Class Mammalia• Sub-class Eutheria• Order Primates

Who & (no. of living species)• All animals (1,000,000)• With spinal cord (50,000)• Mammals (4,000)• Placental mammals (3750)• Lemurs, monkeys, apes &

humans (230)

Distinguishing features – Order Primates•retention of the collar bone in the pectoral girdle;•shoulder joints which allow high degrees of movement in all directions;•five digits on the fore and hind limbs with opposable thumbs and big toes;•nails on the fingers and toes (in most species);•a flat nail on the hallux (in all extant species);•sensitive tactile pads on the ends of the digits;•orbits encircled in bone;•a trend towards a reduced snout and flattened face, attributed to a reliance on vision at the expense of olfaction•a complex visual system with stereoscopic vision, high visual acuity and color vision•a brain having a well developed cerebellum with posterior lobe and a Calcarine fissure•a large brain in comparison to body size, especially in simians;•differentiation of an enlarged cerebral cortex;•reduced number of teeth compared to primitive mammals;•three kinds of teeth;•a well-developed cecum;•two pectoral mammary glands;•typically one young per pregnancy;•a pendulous penis and scrotal testes;•a long gestation and developmental period;•a trend towards holding the torso upright leading to bipedalism.

Classification – where do we fit?

Classification• Kingdom Animalia• Phylum Chordata• Class Mammalia• Sub-class Eutheria• Order Primates

.• Sub-order Anthropoidea

. • Superfamily Hominoidea

Who & (no. of living species)• All animals (1,000,000)• With spinal cord (50,000)• Mammals (4,000)• Placental mammals (3750)• Lemurs, monkeys, apes &

humans (363)• Monkeys, apes & humans

(145)• Apes & humans (20)

Humans are Hominoids

• We share this classification with the great and lesser apes

Classification – where do we fit?

Classification• Order Primates

.• Sub-order Anthropoidea

. • Superfamily Hominoidea• Family Hominidae• Subfamily Homininae• Tribe Hominini• Genus Homo• Species sapiens

Who & (no. of living species)• Lemurs, monkeys, apes &

humans (363)• Monkeys, apes & humans

(145)• Apes & humans (20)• Great apes & humans (7)• Chimps & humans (2)• Humans (1)• Humans (1)• Humans (1)

How long have we all been primates?

• ~ 65 mya lemurs and simians diverged• ~ 40 mya new world monkeys (those found in the

Americas) broke off• ~ 31 mya old world monkeys and apes went

separate ways• ~ 18 mya the lesser apes (such as gibbons) diverged• ~ 14 mya orang-utans diverged• ~ 6-7 mya early hominoids evolved from a common

ancestor shared with chimps, bonobos and gorillas

How long have we all been primates?

Using the molecular clock

• Comparisons are made between the various sequences of amino acids of primates.

• The calculated evolutionary distances are calibrated against the fossil record.

• Results indicated the divergence between humans and chimps to have occurred between 6 and 7 mya.

• Comparisons of DNA sequences have yielded similar results.

• These findings are not universally agreed upon.

Hominin Evolution

• In response to Darwin’s theory, people immediately wanted to find evidence of this “missing link”

• A supposedly transitional fossil between apes and humans

• Since this time we have not found a single missing link, but many ...

We have dated these finds to the best of our ability

What can we tell from these finds?

• We get an idea of the period during which the species existed.

• If two species co-existed – one cannot be ancestral to the other– They will not have been able to occupy the same niche, so

• They either existed in geographical areas or• They did not compete for the dame food / habitat / shelter

• We get some idea of ancestral relationships– A species can only be ancestral to one which it pre-dates

and with which it did not co-exist.

The Australopithescines• Species belonging to the Australopithecus genus– Were small brained, large toothed and walked erect– Can be loosely divided in to Graciles and Robusts

• The robusts displayed marked sexual dimorphism– Eg. Males were larger with a distinct saggital crest

Gracile

Robust

Sexual Dimorphism

• Sexual (between the sexes)• Di (two) morphism (forms)• When the male and female of a species have a

distinctly different appearance.

Sexual Dimorphism – the implications

• The presence of sexual dimorphism appears to have an impact on the social organisation of species.– Gibbons (no sexual dimorph) – monogamous– Chimps (some sexual dimorph) – harem controlled by

group of males– Gorillas (extreme sexual dimorph) – harem controlled

by a single male• Gracile Australopithacines are thought to have

been similar to chimps in this respect.

The Australopithescines

• The graciles are thought to have been the line from which the genus Homo evolved.

Inferring diets• From observation of teeth, tooth wear, jaw size and

jaw musculature we can infer diet.• The size of the zygomatic arch infers size of

masseter and temporal jaw muscles• We can see that robusts ate course vegetable

matter and grailes ate less fibrous vegetable matter.

Inferring diets• Herbivores require a

much longer and more complex digestive tract.

• We can see evidence of this in the “pot-bellied” appearance inferred by australopithecine skeletons (a) as compared to human skeletons (b).

Bipedal locomotion

• Locomotion was most likely bipedal as femur was at an angle, so legs positioned under weight of body.

• Weight falls on outside of locking knees

Human A. Afarensis Chimp

Bipedal locomotion – further evidence• The foramen magnum of bipedal species is located

further forward in the skull. The foramen magnum in A. Africanus is not as far forward as in modern H. Sapiens, but far more than in gorillas.

Bipedal locomotion – further evidence

• Bipedal species have a short hip bone and a bowl shaped pelvis.a) Chimpb) A. Africanusc) H. Sapiens

Australopithecines were intermediatesGorilla H. africanus Human

Intermediate featuresa) Chimpb) A. Africanusc) Human• Jaw is intermediate between box-shaped and rounded• Brain case also displays intermediate cranial capacitya) Chimp

b) A. Afarensisc) Human

Note intermediate size of diastema

Australopithecus afarensis

Australopithecus afarensis

• Fossils range from ~3.7-2.9 mya• Brain size – 400cc• Evidence of brachiation & bipedal locomotion• No evidence of tool manufacture (although

use of sticks / rocks as tools is highly likely)• One of the most important find was the 40%

complete skeleton of “Lucy”. Discovered in 1974 in the Afar Triangle in Ethiopia.

Deductions

• The fact that the Australopithecines were small-brained bipeds dispels the myth that the hominid brain development led to tool use

• It appears to be the other way around, bipedalism would have allowed us greater vision in the plains

• This freed up our hands to develop and explore tool use (a couple of million years later)

• Our brains developed in response to this new-found ability

The Earlier years

• The A. afarensis and A. africanus are two of the most well documented.

• Earlier notable finds include Ardipithecus ramidus (4.4mya)

• Earlier hominids in the fossil record date back 6 to 7 mya.

Genus Homo• First appeared in Africa ~2.4 mya• Notable developments: smaller teeth, larger

brain, flatter face• Note the gradual enlargement of the brain

case over time

Brain development

• Brain size is not as indicative of cognitive ability until compared with body mass

Homo habilis

Homo Habilis “Handy Man”

• Fossils range from ~2.4-1.6 mya• Brain size – 640cc• First evidence of tool manufacture – basic

scrapers, cutters and choppers• Most probably the first to include a substantial

amount of meat in their diet – most likely carrion

• Thought to have co-existed with H. rudolphensis

Homo erectus

Homo Erectus “Upright Man”

• Fossils range from ~1.8 mya – 300,000 ya• Brain size – 900cc• More elaborate tools – still one piece but more

skill in manufacture• Displayed systematic hunting and controlled

use of fire• Communication through grunts and hand

signals

H. erectus - communication• Probably communicated through grunts and hand

signals• Fossil evidence shows that there were insufficient nerves

running through the thoracic vertebrae for H. erectus to have the fine breathing muscles required for speech.

H. erectus H. sapiens

H. Erectus leave africa• Homo Erectus was the first hominid species to move

out of sub-Saharan Africa. This map shows some of the locations where fossils have been found.

Other members of genus Homo

H. Floresciensis “The Hobbit”• 94,000 – 13,000 ya• Brain size – 380 cc• Only 1m tall• Made tools & used fire• Evolved from H. erectus

H. heidelbergensis• 400,000 – 40,000 ya• Brain size – 1100-1200 cc• Immediate predecessor of

H. sapiens

Homo neanderthalensis

Homo neanderthalensis

• Fossils range from ~150,000 – 35,000 ya• Brain size – 1400cc• Made intricate tools, hunting systematically and

controlled fire• Buried dead, wore clothes & made shelters• Communication through grunts and hand

signals

Homo neanderthalensis

• Populations existed in Europe, the Middle East, Russia and North Africa.

• Co-existed with H. sapiens in these locations for some time.

• mtDNA indicates a common ancestor with H. sapiens 500,000 – 600,000 years ago.

• mtDNA also shows no evidence of interbreeding with H. sapiens.

• So why did they disappear? Was it disease or war or were they simply outcompeted for resources?

Homo sapiens

Homo Sapiens “Wise Man”

• Fossils range from ~130,000 ya – present• Brain size – 1300cc• As long as 30,000 ya H. Sapiens was burying

their dead with intricate decorations and carved figurines.

• Earliest fossils found outside Africa were discovered in the Middle East and date to ~100,000 ya

Conflicting models of human evolution

• Predictions 1 and 3 have been shown to support the Out-of-Africa hypothesis.

• There is debate over whether some finds outside Africa constitute transitional forms or distant cousins of modern Homo sapiens

The “Out-of-Africa” model

Change in Homo sapiens

• Hunter-gatherer populations usually cannot support groups of individuals larger than 25.

• 10-12,000 ya was the dawn of agriculture in an area of the Middle East known as the “Fertile Crescent”

• Early crops / livestock included wheat, barley, peas, sheep and goats.

• Agriculture is considered 100 x more efficient in obtaining food

Change in Homo sapiens

• Agriculture continued with further developments– 9000 ya in South America: corn and cotton– 7000 ya in China: soy beans, yams and pigs

• Permanent communities with a food surplus gave us the time for creative projects and technological advances

• We created better tools and practiced selective breeding

• Larger communities had to be more structured and with a recognised hierarchy.

Differences in human populations• Although we are all one species, through time and

separation, differences have emerged.• These have been due to natural selection, but also due to

gene flow (founder effect and bottlenecks)

• Mammals usually become intolerant to lactose shortly after birth.

• Due to the nutritional benefits, humans able to metabolise lactose had a selective advantage

• A mutation enabling this was perpetuated in populations with domestic cattle but not in those without.

Differences in human populations• A higher surface area to volume ratio is

advantageous in hotter climates.• Results in greater ability to disperse heat via

sweating• We can gauge this

evolutionary trait by comparing hip width to distance from the equator

Differences in human populations• So why, in a country so close to the equator

(the Congo) has a population such as the Mbuti pygmys evolved?

• The humidity in the jungle nullifies the advantages of sweating and makes long limbs a disadvantage

Cultural and Technologoical Evolution

• The passing of information socially rather than genetically.

• Much faster than genetic evolution and can sometimes be more powerful

• Humans living in cold climates today won’t develop more hair or change body shape.

• They will put on some clothes and turn on the heater

Cultural and Technological Evolution

• Can work in either direction with biological evolution

• Forwards– Biological: bipedal with opposable thumbs– Cultural: teach each other to make tools– Technological: better suit tools to our needs

• Backwards– Technological: Internet dating– Cultural: Communicate with people in other countries– Biological: Genetic traits enter the gene pool