human evolution
TRANSCRIPT
Introduction to the Human Evolution
AKUM PAUL SINGH
ROLL NO. 2084
Time of Origin of Man
Primates started evolving in Eocene of tertiary period around 75-60 million years ago
Evolution of man and ape started together from some tree-dwelling common ancestors about 25-30 million years ago
Evolution of genus homo started about 5 million years ago
Place of origin of Man
Man’s origin was probably in Asia, Africa and Europe More precisely man has originated in Central Asia
because: Oldest known fossils have been obtained from China, Java and India
Domesticated plants and animals is maximum in Asia
No. of migrations of animals have occurred in the past from Asia
Asian culture appears to be the oldest
Climatic conditions in Africa, Asia and nearby places is most conductive for human evolution
Rich fossil beds are discovered in Asia and Africa
Differences and Similarities between Man and Apes
1. Bipedal Locomotion Man Man walks on hindlimbs only
Forelimbs and hands are freed for manupulatory and other functions
Apes They walk on all the four arms
Apes are still tree dwellers
2. Upright Posture/ Musculo-skeleton Man Hindlimbs are longer than fore limbs
Abdominal region is short and thorax became broad and flat
Lumbar vertebrae are 4-5 in man (sacral vertebrae are fused)
Lumbar curve is present
Iliac bones of pelvic girdle are broad and expanded
Tail is absent
Skull is balanced straight on vertebral column
Apes Forelimbs are longer than hind limbs
Lumbar vertebrae are 6-7 in no.
Lumbar curve is absent
Skull is balanced at right angle to the vertebral column
2. FaceMan Orthognathous type Simian shelf absent Chin is present Eye brow ridges absent Occipital condyle and foramen magnum are directed downward Forehead is straight Canines small
Apes Prognathous type Simian shelf is present Chin is absent Heavy ridges of bone project over the eyes Occipital condyle and foramen magnum are directed backward Forehead is slanting Canines large and protruding
2. TeethMan Dental arch is rounded parabola
Canines not projecting
Incisors are small
Simian Gap is absent
Apes Dental arch is straight sided U
Canines are large and projecting forming tusks
Incisors are large
Simian gap(diastema) is present in upper jaw between incisors and canines
2. Brain and Cranial Cavity In man cranial cavity is more voluminous averaging 1350-2000cc or
even more whereas in apes it is 450-600 cc
3.Food Man is omnivorous whereas apes are herbivorous
4.Binocular vision Man has large forwardly directed eyes giving stereoscopic vision
Rod and Cone cells are present in retina
5.Olfactory lobes less developed in man as compared to apes
6.Hearing capacity less in man
7. Breeding capacity low in humans than apes
Early Human Fossils
Orrorin tugenensis Early species of Hominids, estimated
at 6.1 to 5.7 million years First fossil discovered in 2000 from Tugen
Hills in Kenya The 20 specimens found as of 2007
include: the posterior part of a mandible in two pieces; a symphysis and several isolated teeth; three fragments of femora; a partial humerus; a proximal phalanx; and a distal thumb phalanx.
Features of Orrorin
Orrorin had small teeth relative to its body size
Head is spherical and rotated anteriorly
Neck is elongated and oval in section
Lesser trochanter protrudes medially. While this suggests that Orrorin was bipedal, the rest of the postcranium indicates it climbed trees
Proximal phalanx is curved, the distal pollical phalanx is of human proportions
Orrorin lived in dry evergreen forest environment, not the savannah
How Orrorin is related to Human evolution?
Still not confirmed; debates going on
Its discovery was an argument against the hypothesis that Australopithecines are human ancestors
If Orrorin proves to be a direct human ancestor, then Australopithecines such as Australopithecus afarensis ("Lucy") may be considered a side branch of the hominid family tree
Orrorin is both earlier, by almost 3 million years, and more similar to modern humans than is A. afarensis. The main similarity is that the Orrorin femur is morphologically closer to that of H. sapiens than is Lucy's; there is, however, some debate over this point.
Sahelanthropus tchadensis
The fossils were discovered in the Djurab Desert of Chad
Found between July 2001 to March 2002
Existing fossils include a relatively small cranium known as Toumaï, fine pieces of jaw, and some teeth
Features
The braincase, being only 320 cm³ to 380 cm³ in volume, is similar to that of extant chimpanzees
Cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges
Because no postcranial remains (i.e., bones below the skull) have been discovered, it is not known definitively whether Sahelanthropus tchadensis was bipedal or not
Relation with humans and Chimpanzees
I. If Toumaï is a direct human ancestor, then its facial features bring into doubt the status of Australopithecus because its thickened brow ridges were reported to be similar to those of some later fossil hominids (notably Homo erectus), whereas this morphology differs from that observed in all australopithecines, most fossil hominids and extant humans.
II. Sahelanthropus may represent a common ancestor of humans and chimpanzees
III. Another possibility is that Toumaï is related to both humans and chimpanzees, but is the ancestor of neither. the discoverers suggested that the features of S. tchadensis are consistent with a female proto-gorilla.
Ardipithecus
Ardipithecus is a genus of an extinct hominine that lived during Late Miocene and Early Pliocene in Afar Depression, Ethiopia
One of the earliest ancestors of humans after they diverged from the main ape lineage
Two fossil species are described in the literature:
A. ramidus, which lived about 4.4 million years ago
A. kadabba, dated to approximately 5.6 million years ago
Behavioral analysis showed that Ardipithecus could be very similar to those of chimpanzees, indicating that the early human ancestors were very much like chimpanzees in behaviour
Autralopithecus (The first ape man)
First fossil was an unusual skull cap of a child from a Pleistocene lime quarry near village of Taung in South Africa
Discovered by Raymond A. Dart in 1924 Australo-pithecus means Southern-Ape These were fully bipedal hominids with
relatively small brain Lived from 4 to 15 million years ago
Characteristics
Short statured measuring 4-5 ft Walked nearly or completely straight on
two hind legs Lived in open and had given up arboreal
life Vertebral column have distinct lumbar
curve Thighs and hips well adapted for
standing, walking and running Pelvics broad and flattened
Characteristics
Big toes in feet were still adapted for grasping
Arms adapted for brachiation
Brain was small but more or less man-like in shape
Cranial cavity 450-600cc
Protruding jaws with larger teeth
Dental arch was smoothly rounded parabola
Simian gap between canines and premolars
Face was prognathous and chin absent
Eyebrow ridges projecred over eyes
A.africanus1.Also called gracile forms2. 1.2 m tall 3.Weighed 25-30 kg
4.Molars larger and stronger5. Chew food by grinding motion6. Were omnivorous
A.Robustus1.Also called robust forms2. 1.5 m tall3.Weighed almost twice the gracile form
4.Massive molars5. Chew food by grinding motion
6. Were herbivorous
Two distinct species of Australopithecus have been identified:
Lucy
Also knonw as AL 288-1
discovered in 1974 at Hadar in the Awash Valley of the Afar Triangle in Ethiopia
several hundred pieces of bone representing about 40% of the skeleton of a female Australopithecus afarensis
Lucy is estimated to have lived 3.2 million years ago
The skeleton shows evidence of small skull capacity akin to that of apes and of bipedal upright walk akin to that of humans, supporting the debated view that bipedalism preceded increase in brain size in human evolution