Chapter 9

6 Mya the first hominids split from African Apes but were similar enough that they may have been able to interbreed. Over time through small changes in various features they developed more human characteristics, losing the ability to interbreed. This provided a transition from apes to humans.

Some significant changes:

Bipedal –The earliest members developed the capability to walk on two feet while still having arms suited for tree climbing. By 3.9 Mya arm changes indicated that bipedality was the norm (A. afarensis)
Teeth and Jaws – By 3 Mya, the teeth had become less canine and the jaws were more parabolic, more noticeably human like (A. africanus)
Brain Size - The earliest brain size was very similar to a chimpanzee - about 350 cc. About 4 Mya, brain size was up to 420 cc and by 2.0 Mya to 530 cc (A. robustus)

“Lucy” is a famous skeleton of a female who lived 3.2 Mya.

2.4 Mya H. habilis appeared. Despite sharing many other characteristics of Australopithecus it has recently been classified as the first member of the Homo line because it showed several significant changes:

Tools – it is referred to as “Handyman” for its tool making abilities
Brain Size - increased from 500 cc to 800 cc
Speech – the Broca’s area of the brain, essential for speech, was developed enough for rudimentary speech

2 Mya - Chimpanzees and Bonobos split into two lines. Chimpanzees can also use tools, in a more limited way, and pass the information to descendants, a cultural trait.

All the hominid lines (Ardipithecus, Australopithecus and H. Habilis) and chimps were found only in Africa where frequent climate variation influenced development.

Notable Events

Time Mya Event

6 Apes & Hominid line split

4.5 Modern Camels, Bears & Pigs

4.2 Baboons, Australopithecines

3.7 Modern Horses

3.2 Famous “Lucy” fossil (A. afarensis)

3.2 Current Series of Ice Ages intensified

3.2 Cheetah

3.0 North and South America join, animals inter migrate

2.4 H. habilis, Stone Tools

2 Chimpanzees and Bonobos split into separate lines

Near hominids

From Family Brain Size (cc)

6 S. tchadensis 350

6 Orrorin tugenensis

Ardipithecus Lineage

From To Family Brain Size (cc)

5.8 5.2 A. kadabba

5.4 4.2 A. ramidus 410

Australopithecus Lineage

From To Family Brain Size (cc)

4.2 3.9 A. anamensis

3.9 2.7 A. afarensis 375 to 550

3.3 2.2 A. africanus 420 to 500

A. garhi

2.6 2.3 A. aethiopicus 410

2.0 1.5 A. robustus 530

2.1 1.1 A. boisei 530

Corresponding Geological Time

Phanerozoic Eon 543 Mya to present

Cenozoic Era 65 Mya to today

Tertiary 65 to 2 Mya (Obsolete Name)

Neogene 23 Mya to today

Pliocene 5 to 2 Mya

Author: Paul Raynault Email: Paul@StudentWorldAssembly.org