Week 2: The Earliest Hominids (our first 4 million years)
I. Climatic Overview of the Cenozoic Era
A. Epochs of the Tertiary Period
1. Paleocene: 65-53 mya: Angiosperm forests now
common for first time. Selection pressures for
efficient foraging in trees begin to differentiate
primates (only prosimian-like at this point)
from other mammals:
a. hands well suited for grasping &
b. enhanced vision (depth perception, acuity,
c. behavioral flexibility: learn & remember
identity & locations of edible plants: most
primates are selective feeders
2. Eocene: 53-38 mya. NW & OW monkeys share
last common ancestor.
3. Oligocene: 38-25 mya: Apes & OW monkeys
share last common ancestor towards end of
this period or early Miocene.
4. Miocene: 25-5 mya: Lesser & greater apes
differentiate  20 mya. Last common ancestor
between chimps and hominids lived between 8
& 6 mya: "a leggy Miocene midget" & arboreal
biped emphasizing vertical climbing & standing
on branches; probably had grasping feet; not a
knuckle-walker (Wolpoff). Humans and chimps
are "sister groups" meaning they share a more
recent common ancestor than either shares
with the gorilla. Earliest hominid fragment is a
bit of lower jaw from Lothagam (Kenya), at
about 5.7 mya.
5. Pliocene: 5-2 mya: Australopithecines, Homo.
General cooling. Stone tool use, division of
labor, & food sharing in Homo allow increased
dietary selectivity despite decreased floral
B. Quaternary Period
1. Pleistocene: 2 mya-12,000 ya (B. P.): repeated
glaciations over much of N. hemisphere. Weather report: 
cold, windy, dry & dusty, but highly variable! next 2 
million years
2. Holocene (Recent) 12,000-present: more stable & 
warmer conditions
II. How we differ from the apes
A. Walking (bipedalism): by 3.7 mya at Laetoli (& 4.4
mya at Aramis). Obligate bipedalism
B. Precision grip; A. afarensis intermediate between
chimps and Homo.
C. Hairlessness (+/-); by H. erectus times?
D. Dental
1. Reduction of canines (beginning with afarensis)
2. Loss of diastema
3. Thicker enamel on cheek teeth (molars)
E. Larger brains & handedness developing by 2 mya
(symptom of lateralization of brain?)
F. Tool use indispensable and complex (by 2.2-2.5
G. Language & speech highly developed (by 100,000-
35,000 ya?)
III. The Early Hominids. Dart, 1924. "Osteodontokeratic
culture." The Killer Ape?
A. Newest oldest hominids:
1. Ardipithecus ramidus: 4.4 mya. Aramis, Ethi-
opia. ('rami-' = 'root' in Afar. Smaller cheek
teeth and thinner enamel than later A. a.
suggest frugivory? (Modern chimps have thin
enamel). Cranial base suggests upright stance
and pelvis may indicate bipedalism. 17 individu-
als? Same size orsmaller than most other aus-
tralopithecines. Long forelimbs, big canines,
small premolars and small deciduous molars;
but overall size increase from late Miocene
precursor (?). (White, Suwa, & Asfaw 1994)
2. Australopithecus anamensis: 4.2 - 3.9 mya
(Meave Leakey, Tim White, Alan Walker),
from two sites near Kenya's Lake Turkana.
('anam' = 'lake' in Turkana. Tibia (shinbone)
articulation with knee indicates bipedalism.
Looks alot like later A. afarensis.
B. Australopithecus afarensis: 4.2-3.0 mya. Lucy
(1974); Laetoli; Hadar (skull, 1994). Known only
from E. Africa. Obligate biped.
1. contrast with modern Akka. Apelike in
skull form, premolar dentition, most limb
proportions, and may still have spent a sig-
nificant amount of time in trees; adept climber.
2. bipedalism & reduced canines (vs. enlarged
brain or technology) as leading the way
(along with probably size increase) to homin-
C. Australopithecus aethiopicus (2.5 mya), type
specimen WT 17000 ("Black Skull"; Walker &
Leakey 1988). 410 cc adult male (very small brain);
but most powerful chewing apparatus until later A.
boisei. "Dead end."
D. Later Australopithecines: Robust vs. gracile
1. Gracile line: A. africanus. Descendant of
afarensis? Known only from S. Africa (Trans-
vaal). Mean brain size 440 cc; less massive face,
smaller cheek teeth, beginnings of a forehead.
2. Robust line (A. [Paranthropus] robustus, A.
boisei): petite size, massive jaws & teeth,
specialized for low-quality tough (high fiber)
vegetable diet. Sagittal crest. (But not strict
vegetarians?) Coexisted with Homo for over 1
my (from  2.5 mya to 1.2 mya). Evolutionary
dead ends.
3. Social organization of Australopithecines
a. Females outnumber males
b. Females much smaller
c. Early hominids probably lived in large kin-
related multi-male groups with females who
were not kin-related. A social pattern like
that of lions, with females working comun-
ally to support a few, big, lazy, territory-
patrolling males, would fit what we know.
4. Roots of modern human male-female
differences in sexuality, including --
a. intrasexual competition generally much
stronger among males;
b. men incline towards polygyny
c. men experience almost universal sexual
jealousy toward their mates
d. men tend to be more aroused by the sight of
naked women than are women by the sight
of naked men
e. physical characteristics correlating with
youth are much stronger determinants of
sexual attractiveness in women than in men
f. men are more predisposed to desire a vari-
ety of sexual partners for the sake of variety