Hominid Studies and Evolution in present times

1. Hominid Studies:
Hominid – group consisting of all modern and extinct great Apes (that is
modern humans) e.g. chimp, gorillas, and orangutans.
Hominin – the group consisting of modern humans, extinct human species and
all our immediate ancestors (including members of the
genera Homo, Australopithecus, Paranthropus and Ardipithecus).


What evidence is there that primates have a common
ancestor?
 Biogeographical evidence of a common ancestor as all wild primates are found
in lands that previously were part of southern continent, Gondwanaland.
 Primates originated 85 mya. Then continental drift, which broke up the super
continent Gondwanaland.  geographical subdivisions within primates.
 Present-day primates are arboreal, i.e. living in trees; this characteristic
suggests that they evolved from an ancestor that was arboreal. Then diversified
into habitats.

Primates have many characteristics that are adaptations to this
arboreal way of life:
 Kept the clavicle or collarbone- important part of shoulder joint. Stabilizes
shoulder, allowing a primate to support its weight by hanging from its arms
alone.
 Have long, slender limbs that rotate freely at the shoulders and hips – helps
movement in trees.
 Many have mobile opposable thumbs.

Other characteristics that all primates share:
 Enlarged and complex brain relative to body size.
 Flattened face and reduced snout with reduced sense of smell.
 Eyes that face forward so that the eyes’ visual fields overlap to give
stereoscopic vison.
 Digits with flat nails (not claws, or hooves.
 Molar and premolar teeth with cusps that are low and rounded.
 Complex social behaviour, usually only one offspring at a time and extended
care for the young.

Genetic evidence of a common ancestor for primates is slowly
emerging. Primates:
 Share large percentage of DNA. Humans share 98.5% of DNA with
chimpanzees and 93% with rhesus monkeys.
 Have a larger number of olfactory-receptor pseudo-genes than non-primates.
Pseudo-genes – remnants of genes that are no longer functional

 Have full trichromatic colour vision, which is found only in primate order.

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Evidence for a common ancestor for living hominids:
 Living hominids  African apes and humans
 If there’s 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.
 Scientists use fossil record and genetics

African apes and humans – compared:
 Physical and genetic similarities show that the modern human species,
Homo sapiens, very closely resembles the African apes, i.e. chimpanzee,
bonobos, and gorillas.
 Humans did not evolve from a common ancestor.

What are their anatomical similarities?
All living hominins:
1) Have an upright posture
2) Lack external tails
3) Have freely rotating arms
4) Have hands with an opposable thumb – grasp and handle objects.
5) Have digits with flat nails.
6) Have eyes that face forward so eyes’ visual fields overlap to give
stereoscopic vision.
7) Have molar and premolar teeth with low and rounded cusps.
8) Have eyes with cones for colour vision.
9) Are sexually dimorphic (some physical differences) e.g. male – larger and
more built.

What are their anatomical differences?
 Humans experienced different selection pressures, such as climate change,
different diet, and effect of bipedal locomotion.
 These pressures  various differences developing.

Skeletal differences
 Anatomical difference between humans and African apes are largely related to
evolution of habitual bipedalism in humans.
Bipedalism is the ability to walk upright on two legs.