|PREHISTORIC LIFE HOME||PREHISTORIC LIFE TABLE OF CONTENTS||OBL HOME||OBL REFERENCES|
DATES: to 1.6 million years ago
Homo habilis differs from Australopithecus at the base of the skull. The foramen magnum (the opening for the spinal chord) is closer to the middle of the skull and the skull base is reduced in length but increased in width. The face decreased in width and the nasal opening was more sharply defined. The postcanine teeth were smaller than in Australopithecus.
Its cranial capacity was 500 to 800 cc. and values increase from the earliest specimens to latest ones. This range overlaps with Australopithecus at the low end and Homo erectus at the high end. It can be debated (indeed, there has been a debate several decades long) on whether early H. habilis should be classified as Australopithecus and late H. habilis should be called Homo erectus. H. habilis stood approximately 5 foot tall and weighed 100 pounds with females being smaller than males (Leakey, 1973b; Wood, 1987; Leakey, 1971b; Hughes, 1977; Johansen, 1987; Bilsburough, 1988; Tobias, 1972). Early Homo populations coexisted with australopithecines (Johanson, 1976).
In one brain endocast, there is a bulge corresponding to Broca’s area (an important speech center) in modern human brains. Two aspects of wrist bones (the scaphoid tubercle and the articular surface of the trapezium) were chimp-like. The thumb was similar to humans in the carpo-metacarpal joint and the flattened metacarpal surface. The foot was less flexible than in chimps and its degree of possible abduction was limited. Some characteristics of the lower leg were primitive and others were advanced, not found in any ape (Susman, 1982; Skelton, 1986).
| Homo habilis is translated as “handy man”
referring to the simple stone tools found at many sites (Toth,
1985; Leakey, 1970). Some feel that
the variation in skulls is too great to accommodate in one species and classify
some Homo habilis skulls as Homo rudolfensis (Wood,
1992; Wood, 1999)
Although humans are not speedy sprinters compared to quadrupeds and running is metabolically twice as expensive as it is for many other animals, humans are the only primates and one of the few mammals which practices endurance running. (Dogs, hyenas, wildebeest, and horses are also capable of endurance running.) It is thought that endurance running evolved with the genus Homo given that some of the specializations which allow endurance running (such as short toes, an adducted big toe, a more balanced head, neck ligaments, and an enlarged calcaneus) evolved in Homo habilis, other features (such as enlarged semicircular canals, shorter forearms, and larger hip, leg, and back muscle attachment sites, longer legs, and a stronger sacroiliac joint) evolved in Homo erectus, and several other features (a head which was more independent from the shoulder, a narrow pelvis, an arched foot, and a long calcaneal tendon) evolved early in the Homo lineage although the precise point is not known (Bramble, 2004).
| Hominids seemingly intermediate between Homo habilis
and Homo erectus traveled outside
The following image compares a Homo habilis skull to that of a female bonobo chimp.
The following image compares a Homo habilis skull to that of a female bonobo chimp.
DATES: 1.8 million years ago to as late as10 to 27 thousand years ago (have been dated with K/Ar, Ar/Ar, U series, ESR, and faunal dating methods)
The cranial capacities range from 750 to
1225 cc; early forms average 900 cc; later forms average 1100 cc. The depth and robusticity of the zygomatic bone
differs from modern humans. H. erectus is similar to H. habilis in its protruding jaws, large
molars, lack of a prominent chin, thick brow, and the long, low skull. H. erectus
had human limb proportions and human body shape (it was the first hominid
to have this). Homo erectus increased the length of its thighs and the hips became more human-like (McHenry, 2006). Its skeleton more robust than modern
humans, suggesting considerable strength (Rightmire,
1981; Brown, 1985; Leakey, 1973; Walker, 1981; Day, 1971; Clark, 1976;
Leakey, 1976; Wolpoff, 1984. There was some sexual dimorphism in the skeleton
and one specimen shows signs of hypervitaminosis A (
The assemblages of tools found with Homo erectus are more sophisticated than
earlier tools and 2 sites are associated with fire. In
Fossil specimens dating from about 1.75 million years ago discovered at Dmanisi, in the Republic of Georgia have been tentatively identified as the most primitive known Homo erectus/Homo ergaster. Although the most primitive skull whose classification as a member of Homo is not in dispute, it resembles Homo habilis. It appears that early hominids similar to Homo habilis migrated from Africa prior to the evolution of the more typical Homo erectus form (Vekua, 2002).
erectus is considered to be the first hominid to travel out of
Homo erectus is known in Java as early as 1.8 million years
ago and as late as 50,000 years ago. The
combination of very thick crania and evidence of healed skull fractures
and head trauma have caused some to propose that male Homo erectus fought
with each other using clubs (Boaz, 2004).
The last Homo erectus
populations existed in Java between 27 and 53 thousand years ago dates
which overlap with the existence of Homo
sapiens sapiens in the region (Gibbons, 1996; Thorne, 1972; Swisher,
1996). The earliest African forms of Homo erectus have smaller and more projecting
noses. Some researchers classify
these specimens as Homo ergaster
and feel that Homo ergaster
or some pre-erectus population
A skull similar to the Dmanisi skull (considered an early Homo erectus) has been found representing a toothless individual. This suggests that the diet of these hominids included soft food items and perhaps that the social structure of this hominid allowed for support from other members of the group (Lordkipanidze, 2005).
The skeleton of an infant Homo erectus indicates that the endocranial volume was within variations for Homo sapiens and distinct from the chimpanzee range (Leigh, 2006).
Homo fossils are known in the Caucasus since about 1.8 million years ago, Spain and Italy from 800,000 years ago and northern Europe from 700,000 years ago (Parfitt, 2005).
Homo floriensis inhabited Indonesia at least for the period from 95-74 to 12 thousand years ago. Heights of two individuals have been estimated at 1.06 and 1.09 meters. The structure of the brain is most similar to Homo erectus but the size of brain relative to the body is comparable to australopithecines and chimps. It lacked a chin. While facial and dental features justify its classification in the genus Homo, it may not be a species of Homo erectus that evolved a shorter stature (Morwood, 2005).
ARCHAIC Homo sapiens/ Homo heidelbergensis
DATES: 500 thousand years ago to 200 thousand years ago
The earliest specimens classified as archaic Homo sapiens or Homo heidelbergensis have features of both H. erectus and H. sapiens sapiens with robust skeletons and teeth. Some specimens have brow ridges, receding foreheads, and receding chins. Some specimens already display some neanderthal facial characteristics (morphology of the eye sockets, cheekbones, and nasal bones) suggesting that neanderthals may have diverged from other lineages quite early. There is an advanced expansion of the cranial vault and the average cranial capacity was 1200 cc (Brauer, 1993; Howell, 1952; Trinkaus, 1997; Stringer, 1988; Stringer 1993; Arsuaga, 1997).
One significant change that occurred between
the archaic and modern humans was a shortening of the sphenoid bone in
the braincase. Externally, this
change resulted in jaws, which did not protrude to the same degree. Internally, the change could have had a much
more profound effect: it would have affected the dimensions of the oropharynx
and the variety of sounds that humans could have made in speech. (Chimps and gorillas are capable of large vocabularies
when using sign language and their use of signs suggests a degree of complex
thought which they were previously thought to be incapable of. Apes do not speak because they do not have the
anatomy for it. Thus changes in
the vocal tract could have had a much larger impact on language than increases
in brain size.) (Hublin, 1996;
Rightmire, 1997; Rightmire, 1976;
|THE PIT OF BONES: In
Homo antecessor displays a mosaic of traits, such as primitive dental features and advanced aspects of the midfacial region, which indicate that it could represent the common ancestor of Neanderthals and modern humans (De Castro, 1997). Some have suggested that Homo erectus was not directly ancestral to modern humans and hominids such as Homo antecessor represent the common ancestor of Neanderthals and modern humans (De Castro, 1997). Homo antecessor possessed a styloid process (De Castro, 1997).
DATES: 230 to 30 thousand years ago
Although some neanderthal
characteristics are found in modern humans or earlier Homo species, the combination of these characteristics in neanderthals
is unique. These characteristics
increased in frequency as later neanderthals evolved.
As a result, there are differences between the robust “classic”
Neanderthals had a long trunk, short legs, and a robust skeleton. The size of muscle attachment sites imply considerable muscle power. A diastema (gap) exists between the jaw and lower wisdom teeth. The skull and face were long, the forehead low, there were protruding brow ridges, the rear of the braincase was round (not pentagonal as in modern humans), there was a large nasal cavity, the floor of the eye socket was flat or even receding laterally, there was a strong mandible lacking a chin, a protruding midface, the cheekbones were weak and oriented obliquely, the occipital bone bulges posteriorly (the occipital bun, a trait which very rarely can still occur in modern humans), and the occipital bone has a conspicuous depression known as the sura-iniac fossa. Hand bones indicate that Neanderthals may not have been as dextrous as modern humans (Musgrave, 1971; Trinkhaus, 1982). Although neanderthal faces seem abnormally long, they are actually similar to earlier specimens of Homo. Modern human faces are much shorter, including the region of the pharynx which affects the ability to produce the sounds of human speech (Trinkhaus, 2003).
Males averaged 5’6” in height but because of their robustness, they may have averaged 30% larger than modern humans. The average brain capacity was 1450 cc (a little larger than that of moderns) and one young male specimen had a capacity of 1750 cc (Kappelman, 1997). While some concluded that neanderthal nasal specializations make them unique among hominids, others have refuted this (Schwartz, 1996; Laitman, 1996; Franciscus, 1999).. Some neanderthal hand characteristics are unique. Neanderthal hip morphology suggests that they were more active as children. Some analyze this as a potential culture difference between neanderthals and the modern humans that replaced them (how active/mobile the young members of a group were).
Between 300 and 127 thousand years ago there
were two periods of glacial advance separated by a cool interglacial period
and many features of the Neanderthal body are adaptations to cold temperatures.
Neanderthals have provided the first evidence of burying the dead
100 thousand years ago and later burials include animal bones and flint.
One 47,600-year-old cave has an impressive 4-meter x 5-meter structure
built of stalagtites and stalagmites. Neanderthals arrived in
| The craniofacial differences between
Neanderthals and modern Europeans are greater than those observed between
the two species of chimpanzee and between all modern human populations. This suggests that Neanderthals were a separate
species (Harvati, 2003; Harvati, 2004). Genetic evidence
also supports this conclusion. Mitochondrial DNA was successfully isolated from neanderthal bone and the sequence was unlike any living human.
Its variation from modern humans is roughly half of the difference
between humans and chimps. A second lab repeated this with identical results.
Analysis of Cro-Magnon DNA of about the same age identified a sequence which
was well within the variations of modern humans.
The conclusion drawn from this genetic evidence is that neanderthals
are not related to living humans. An analysis of a fossil modern human mitochondrial
genome indicated that it also went extinct-- if this one human’s mitochondrial
genes are absent today, it is possible that neanderthals
interbred with modern humans and their mitochondrial lineages disappeared
as well. Although mitochondrial DNA from several Neanderthals
has identified DNA sequences which predate the origin of the mitochondrial
strains which are known in modern living humans, anatomically modern humans
from about 60 thousand years ago possessed a DNA segment on their mitochondrial
chromosomes which now exists in the nucleus of modern human populations.
Some feel that neanderthals
and modern humans did interbreed and that neanderthals
helped to contribute to European lineages (Caramelli, 2003; Adcook, 2001; Ward,
1997; Kahn, 1997; Mellars, 1998). There is one fossil find of a young human from
The oldest remains of Homo sapiens sapiens are known from Ethiopia and have been dated at 195,000 years old (Wilford, 2005). East Africa underwent severe drought during the period of 135 to 75 thousand years ago. Lake Malawi, for example, seems to have been reduced to 95% of its original extent. This may have been a factor in the migration of some humans out of Africa (Scholz, 2007). Modern humans became lighter and more gracile. (Gibbons, 1997). The sphenoid bone shortened, meaning that the face did not project quite as far. The skull became higher and rounder in contrast to the low, long skulls of Homo erectus and Neanderthals (Lieberman, 1998). How did modern humans evolve? There are two different models.
In the replacement model, it is thought that
somewhere between 1 million and 100,000 years ago, modern humans left
Africa, migrated throughout the continents, and completely replaced all
other hominids (such as Homo erectus,
Homo neanderthalis) so that they alone were ancestral to all modern
human groups. Proponents of this
model vary on the timing, often due to discipline; paleontologists favor
older dates, geneticists favor younger dates. One strong piece of evidence that is frequently
observed is that the greatest genetic difference in
human populations occur between African populations. The evidence for some of the oldest branches
of humanity exist in
--Regional Continuity Model:
Although modern humans did leave
In comparing the microsatellite
DNA in the human genome, the most divergent patterns are observed in some
African populations, suggesting an African origin of humanity (Goldstein,
1995). Comparisons can be made between mitochondrial genomes (which
are primarily passed from women to their children) and Y-chromosome sequences
(which are passed from men to their sons).
These comparisons tentatively
indicate that women have actually been more mobile than men (in that they
did not necessarily stay in the areas in which they were raised) and thus
were greater agents of gene dispersal (Pennisi,
2001). The gene microcephalin (MCPH1) and its surrounding genes can exist in various forms, known as haplotypes. One form, known as haplotype D, is found in 70% modern humans. Although the haplotype seems to have spread through human populations several tens of thousands of years ago, the degree of nucleotide divergence between members of the same haplotype is far greater than what would be expected. One explanation is that interbreeding between archaic humans and modern Homo sapiens resulted in a beneficial set of alleles which were then positively selected for (Evans, 2006).
The gene microcephalin (MCPH1) and its surrounding genes can exist in various forms, known as haplotypes. One form, known as haplotype D, is found in 70% modern humans. Although the haplotype seems to have spread through human populations several tens of thousands of years ago, the degree of nucleotide divergence between members of the same haplotype is far greater than what would be expected. One explanation is that interbreeding between archaic humans and modern Homo sapiens resulted in a beneficial set of alleles which were then positively selected for (Evans, 2006).
Modern humans arrived in
Molecular analyses point to three groups of aboriginal Americans: Amer-Ind, Na-Dene, and Eskimo. The Na-Dene and Eskimo might not represent separate migrations but rather early offshoots of the Amer-Ind group which were isolated in northern regions by changing climates (Bonatto, 1997).