Question

1- discuss the major anatomical differences between two separate species of early hominins from the Australopithecus genus. Compare and contrast the various anatomical and behavioral characteristics of the species you selected. Once you have done this, which of these two species is a more likely candidate as a direct ancestor to Anatomically Modern Humans?

2- identify three specific variables that YOU think drove early Hominin evolution. These variables can be related to anatomy but remember—behaviors are the precedent prior to widespread anatomical changes of any species. From the two to three variables you identified, select one that may be the most influential in human evolution, and explain why YOU think this variable is the most important.

Answer 1

1.Human evolution is complex.Over the past 4 million years several species of humans were known to have existed but homo sapiens are the only species that exists till now.

• "Hominid" = means the members of the human family hominidae.
• Humans have evolved from 2 species = Australopithecine species and Homo species.

The Australopithecine

• Refers to any species in the related genera - Australopithecus and Paranthropus.
• The genus homo(humans ) believed to be evolved from the australopithecine ancestors.

Australopithecus afarensis

• lived between 3.2 to 4 million years ago in eastern africa.(fossils were discovered from Tanzania and ethiopia).
• Believed to be one of the earliest of human ancestors.
• Characteristic features include -

a.small brain capacity ranging between 380 -430 cc

b.had a large face relative to rest of the cranium but very small forehead

c.long arms with long curved fingers relative to their length of legs

d.had a characteristically broad face due to the zygomatic arches flair to the side.

e.Marked prognathism ( protruding jaw) of the face.

f.Cranium attaches to the backbone in a relatively backward position when compared in relative to other humans.

g.Sagittal ridge where strong chewing muscles are attached

• Had a characteristic dentition status with features like - presence of primate spaces,larger molars when compared to molars of modern humans ,large pointed dimorphic upper canines and the arcade of omega shaped and this shape was an intermediate shape when compared to the box row in apes and parabolic curve in humans.

Australopithecus africanus

• Time period they lived was 2 .3 to 3 million years ago.
• Believed to be lived in South Africa but the fossil remains were discovered from some other places.
• Raymond Dart discovered them in 1925.
• Considered as the direct descendant of A.afarensis.
• Had following features -

a.Absence of sagittal ridge /crest.

b.cranial capacity ranging between 435 cc to 530 cc.

c.Zygomatic arch is less robust when compared to other australopithecine.

d.Have longer arms and shorter legs compared to A.afarensis.

e.Prognathism is less evident when compared with A.afarensis,and had a more rounded jaw with larger back teeth and canines.

• Dentition status - had specialized dentition than a.afarensis - rows of teeth were more parallel,molar teeth were relatively larger in size for powerfull chewing,larger teeth size,incisors were angled forward instead of being vertical.

On comparing the characteristic features of both A.afarensis and A.africanus - we can conclude that it is the A.africans have more chances to be the direct ancestor of modern humans anatomically.It is the features like improved cranial capacity and facial features as well as specialized dentition ,make them more similar to modern humans.

2.Major important changes  that led to human evolution include ;

• Mouth development
• Brain size
• Bipedalism hunting ( inventing fire ,using tools, building shelters,clothing ,language etc was the result of bipedalism hunting).
• changes in dentition.
• Reduced size differences between male and female.
• key changes in family structure.
• cultural evolutions including agricultural advances,use of tools,skills from communication and teaching,use of fire,cave paintings ,introduction of languages etc.

From the above changes the most important 3 variables that may be responsible and most influential in human evolution are ;

• Bipedalism - on considering different stages of human evolution humans always showed the need for upright walking and they improved in that in each stages of evolution.Bipedalism was needed for several reasons including energy efficient locomotion,food gathering,predator avoidance etc.
• Next important ones are language and cultural evolution - as the language developed cultural evolution started taking place,it is the passing of information from one generation to the other through instinctive behaviors and syntax ,which is very different compared to genetic transmission.It is possible only through language and transferred to the young ones from the old in the same species.This characteristic is very unique and specific to humans and played a greater role and contribution to our successful evolution as a species.This shifted the hunter gathering life style to domestication of plants and animals ,thereby the formation of civilizations.
• other features like evolution in brain size,tool making ,social relationships etc also had their own important roles leading to the human evolution.