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