Human Evolution        1. Describe primate origins and characteristics         2. Discuss the development of Hominids         3. Compare the two models for the origin of modern Homo Sapiens

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Hominid characteristics: there are certain features that place a species in the Hominidae family.  The more advanced they appear, the closer the species is to modern humans. 
     - Bipedalism - walking upright; evidence for this includes a change in the femure/pelvis structure, the foramen magnum placed under the cranium, and shorter arms; early australopithecenes seem to show that they were starting to walk upright part of the time
     - Brain size - modern humans average about 1350cc in brain size; increasing brain size of hominids may indicate evolution towards H. sapiens; a more vertical forehead indicates the development of the frontal lobe of the brain
     - Speech - the ability to speak is a hominid characteristic; measuring brain casts tells us which hominids may have been able to speak; the first words may have begin with H. habilis
     - Tools - hominids are thought to be the first animal to make and use tools; the first tools were thought to have been made by H.habilis

     NOTE: both Sahelanthropus tchadensis and Orrorin tugenensis predate A. ramidus, but their discovery is so recent that there is not much written on how they may fit into the hominid family tree.
 

Ardipithecus ramidus      There is only one species in this genus, A. ramidus (sometimes A. ramidus kadabba).  Fossil evidence dates back to about 4.5 mya.  This, perhaps the earliest hominid, was identified from fossils found around Aramis, Ethiopia in the 1990s.  This individual was probably part of a radiation that included other hominids.  Because of its recent discovery, not much has been written about it.   If you take a look at the fossils recovered thus far [picture], you can see how difficult it might be to speculate as to it's skull characteristics.       The specimen’s hominid characteristics suggest that it was 'on the road ' to being bipedal.  The characteristics include a valgus knee angle, anteriorly placed foramen magnum and most importantly, a short, broad pelvis.

     Australopithecenes are considered to be the progenitors of the Homo genus.  There are two main types: gracile and robust. 
     Gracile australopithecenes: Their skeletons are less "bony."  For example, they do not have bony crests on their skulls to support large chewing muscles.  Their overall size was less than the robusts.  They started to appear about 4 million years ago and lasted till about 2 million years ago.  Gracile species include A. afarensis, A. africanus, and A. anamensis.
     Robust australopithecenes: An overall larger bone structure gives these species the robust title.  Their large molars and jawbones may mean that their diet required  tough chewing.    They started to appear about 4 million years ago and lasted till about 1 million years ago.  Robust species include A. aethiopicus, A. boisei and A. robustus.  Some scientists think that they are different enough from australopithecenes that they deserve their own genus, Paranthropus.

Australopithecus afarensis       Australopithecus afarensis lived 3.9-3.0 million years ago in East Africa (Ethiopia, Tanzania, Kenya.).  Their skeletons were still quite similar to early Pliocene apes.  For example, their legs were shorter than the later australopithecines.  They had large canines.  Some of the males had small sagittal crests. Afarensis had slender curved fingers like modern chimpanzees.  Because of these features, they may have been more adapted to tree climbing than bipedalism.  They were under 5 feet tall and weight about 100 pounds.  The females were significantly smaller (weighed 64% as much as males and were 70%  of the males' height).  Their slender structure also has led to the australopithecenes being known as gracile species.

     The first member of the Homo genus is commonly thought to be Homo habilis (and/or Homo rudolfensis).  There is some disagreement as to how things evolved afterwards.  Homo ergaster and Homo erectus are thought to follow H. habilis. H. ergaster stayed in Africa, while H. erectus moved to the Asia about 2 million years ago.  While we know that modern humans are classified as Homo sapiens, the exact lineage is uncertain.  For a long time, it was assumed that we came from H. erectus.  Neanderthals (H. neanderthalensis) is thought to be a 'cousin' of H. sapiens.  Recent thought is that Homo heidelbergensis may be a common ancestor to H. sapiens and Neanderthals. 
     It is thought that H. habilis may have been the first tool makers. H. erectus advanced the art of toolmaking and was the first to utilize fire. 
 

Homo habilis / Homo rudolfensis      Though many paleoanthropologists classify Homo habilis ("handy man") as a Homo sapiens ancestor, the exact bridge from one species to another has been debated since the Leakeys found the first specimen (OH 7) in 1960.      Homo habilis is thought to be the first hominid to use simple tools. Its brain size is bigger than that of the australopithecenes.  Experts can't even agree on exactly which specimens should be definitely considered Homo habilis.      Adding to the confusion over Homo habilis, some specimens have sufficient differences that another species has been proposed.  V.P. Alexeev, using thee KNM-ER 1470 as a type specimen, suggested the species Homo rudolfensis in 1986. Homo rudolfensis may have been the ancestor to the Homo habilis.  Perhaps they were two separate species.  Some even believe it should be classified as an australopithecene.

H. habilis

H. erectus

Homo erectus / Homo ergaster      The Leakeys have long proposed that Homo erectus was the ancestor of modern Homo sapiens.  Other opinions do exist (see Homo sapiens below).  One theory is the Homo erectus left Africa to populate Asia and perhaps Europe, but Homo ergastor stayed in Africa and evolved into Homo sapiens who then replaced Homo erectus.  Of course, if you believe in the multiregional theory of H. sapiens origins, then you might say that H. ergaster evolved into a form of H. erectus and then into H. sapiens in Africa, while H. erectus evolved into H. sapiens in other parts of the world.      Homo erectus is thought to have advanced the art of tool making.  They are also thought to be the first hominids to use fire.  Their brain capacity averaged over 1000cc (while H. habilis averaged 750cc).

H. sapiens

Homo sapiens      This is "us."  The modern traits of today's human started appearing about 100,000 years ago (though recent discoveries may push that back another 50,000 years).  The earliest fossil record of Homo sapiens is from Africa.  Sometimes early Homo sapiens is known as archaic or Cro-Magnon man.       Brain size is about 1350cc and we are fully bipedal.  Although we have hair over most of our bodies, at some point we lost the thick coat we once had. [see Why Humans and Their Fur Parted Ways]  Theories range from the idea that humans went through a semi-aquatic phase and lost it ... to the idea that it was lost through natural selection (more hair = more parasites & diseases).

Australopithecus africanus      Until 1925, it was thought that human ancestors would only be found in Europe.  But that year, Raymond Dart labeled his find (the Taung child) as a hominid because it was partially bipedal and created the genus australopithecus ("southern ape").       Australopithecus africanus lived about 3.0-2.5 million years ago in East and South Africa.  Their bone structure was less ape-like than earlier species of australopithecines.  Their skeletons were still small and lightweight ... even smaller than a.afarensis.  Unlike a. afarensis, their canines did not project beyond the other teeth.

A. africanus

A. robustus

Some scientists give the larger australopithecenes their own category (paranthropus), though some paleoanthropologists still call them australopithecenes.      Paranthropus or A. aethiopicus - the earliest robust species; lived about 2.5 million years ago; found only in East Africa; smaller brain than the other robust species; large sagittal crest.       Paranthropus or A. boisei - the largest of the three Paranthropes; found in East Africa; lived about 2.3-1.4 million years ago; large canines and grinding teeth       Paranthropus or A. robustus - lived about 1.9-1.0 million years ago in South Africa; smaller version of the p. boisei

Homo sapeins neanderthalensis or Homo neanderthalensis       Neanderthals started appearing about 130,000 years ago, and they seem to have died out about 30,000 years ago.  Their fossil evidence is mainly in western Europe.  Some people think that rather than becoming extinct, surviving Neanderthals mixed in with the Homo sapien population.

H. neanderthalensis

The Hominid Family Tree      Here is one of the more commonly accepted views of the hominid family tree.       Other versions can be found at the Hominid Family Tree page.