23.1. Humans
are Primates
A. Primate Characteristics
1. Primates differ from other mammals by being adapted for
arboreal life (life in trees).
2. Mobile Forelimbs and Hindlimbs
a. Primate
limbs are mobile and hands and feet each have five digits each.
b. Flat
nails replaced claws and sensitive pads developed under fingers and toes.
c. Primate
hands have an opposable thumb; many also have an opposable big toe.
d. These
features allow free grasping of tree limbs and easy harvest of fruit.
3. Binocular Vision
a. Primates
have a reduced snout and the face is relatively flat.
b. The sense
of smell is generally reduced.
c. The eyes
are moved to the front of the face for overlap and stereoscopic vision.
d. Cone
cells provide greater visual acuity and color vision but require bright light.
4. Large Complex Brain
a. Better
senses requires both sense organs and a more complex brain.
b. More of
the brain becomes devoted to processing information received from hands and
thumb.
5. Reduced Reproductive Rate
a. Primates
have more single births, which reduces need for care for several offspring and
allows
forebrain development.
b. Period of
parental care is extended with an emphasis on learned behavior and complex
social interactions.
B. Evolution of Major Groups
1. The primate order contains two suborders: prosimians and anthropoids.
2. Prosimians
a. Prosimians
diverged first and are most closely related to the original primate.
b.
Prosimians include the lemurs, tarsiers, and lorises.
c. Lemurs are
squirrel-like fruit eaters confined largely to the island of Madagascar.
d. Lorises
and bushbabies are nocturnal and live in Africa and Asia and resemble lemurs.
e. Tarsiers
are small, nocturnal, mouse-sized insectivores found in Philippines and East
Indies.
f. Evolution
of prosimians followed spread of forests.
3. Anthropoids
a. Surviving
anthropoids are classified into three superfamilies: New World
monkeys, Old World
monkeys and hominoids.
b. New World
monkeys reside in South America and diverged first.
1) Therefore, New World monkeys are less closely related to Old World monkeys
than they are to apes.
2) New World monkeys (e.g., spider monkey and capuchin) have long prehensile
tails and flat noses.
c. Old World
monkeys (e.g., baboon and rhesus monkey) lack prehensile tails and have
protruding noses.
d. Hominoids
include all the apes and the humans.
1) Proconsul was one of several ape species prevalent in Africa
during the Miocene and is believed
ancestral to apes and humans.
2) At the end of the Miocene epoch, Africa joined with Asia, and the hominoids
migrated into Europe.
3) The two ancestral groups included dryomorphs and ramamorphs that were
ancestral to orangutans.
4) Dryopithecus was a tree-dweller that moved similar to
orangutans and did not walk along tree limbs
as did Pronconsul.
4. Hominoids
a. Humans
and apes are closely related and placed in the same superfamily, Hominoidea.
b. Four
types of apes exist: gibbons and orangutans (Asia) and gorillas and chimpanzees
(Africa).
c. Amino
acid and DNA base pair changes act as a molecular clock; humans
are most closely related to
African apes.
d. The
orangutan line diverged about 14 million years ago.
e. The ancestors
of African apes and hominids diverged about 8 million years ago during the
early Pliocene epoch.
f. Hominids
differ from modern apes such as the gorilla.
1) Type of locomotion changed, which is dependent on the spine, the pelvis, and
the bones of the appendages.
2) The shape of the jaw is related to the size and the shape of the teeth, and
was adaptive to a new diet.
3) The brain size grew larger.
g. Until
now, science thought that the climate changed forests into savannas; there is
little evidence of a
shift in vegetation at this time.
h. While
still living in trees, the first hominids may have walked upright to collect
overhead fruit.
i.
Additional advantages of bipedalism include reduction of heat stroke and
carrying food back to females.
23.2.
Evolution of Australopithecines
A. Mosaic Evolution of Early Hominids
1. Australopithecines belong to the genus Australopithecus,
and contain the first generally recognized hominids.
2. Expanding fossil record shows it
is not an orderly sequence between forms.
3. Several hominids existed at the
same time; the phylogeny resembles a bush rather than a line.
4. Characteristics did not evolve as
same rate; in some the legs lengthened but forearms remained long.
5. "Mosaic evolution"
refers to this variation in resemblance to humans.
6. Australopithecines evolved and
diversified in Africa with gracile and robust forms with varied diets.
B. South Africa
1. Australopithecus africanus described by Raymond Dart in the
1920's is a gracile type from southern Africa.
2. Abundant fossils of A.
africanus date from 2.4 to 3 MYA.
3. Australopithecus robustus
was a robust type, it had a brain size of 500 cc similar to A. africanus.
4. Both had forelimbs longer than
hindlimbs and probably walked upright.
5. A. africanus is
best candidate as ancestor to early Homo.
C. Eastern Africa
1. Australopithecus ramidus is based on bone fragments dated at
4.4 MYA.
a. Name was
later changed to Ardipithecus ramidus.
b. Compared
to later australopithecines, its cheek teeth were smaller, canine teeth larger,
and skull more
like that of a chimpanzee.
c. Upright
stance is yet to be determined.
2. Australopithecus anamensis
was discovered in 1995 and dated to about 4 MYA; jaws were ape-like but
legs were
human-like and it probably walked upright.
3. Australopithecus afarensis
is based on many skeletal fragments (Lucy) dated at 3.18 MYA.
a. Brain was
small at 400 cc.
b. May have
been ancestral to the robust types, A.aethiopicus and A.
Boisei that later died out.
c. May (or
may not) be species that left Laetoli footprints in volcanic ash 3.7 MYA.
d. Thought
to have stood upright and walked bipedally.
e. They are
sexually dimorphic: females are 4 feet tall and about 30 kg, males are 5 feet
tall and up to 45 kg.
4. Australopithecus garhi
is possible alternate candidate intermediate between A. afarensis
and Homo;
nearby
fossils show butchering of other animals for bone marrow.
D. Evolutionary Relationships Between Australopithecines
1. There was extensive overlap with as many as six or seven species of hominids
living in Africa at same time.
2. Australopithecus africanus
described by Raymond Dart in the 1920's is a gracile type from southern Africa.
3. Australopithecus boisei
is robust form from eastern Africa that probably fed on tougher foods than
gracile forms.
4. Australopithecus robustus
had jaws, teeth, and habitat similar to A. boisei but may not be
closely related.
23.3.
Evolution of Humans
A. Early Homo
1. Oldest fossils to be classified in the genus Homo are known as
Homo habilis dated between 2.0 and 1.9 MYA;
to be in the
genus Homo, the following traits are used:
a. brain
size 600 cc or greater;
b. jaw and
teeth are human-like;
c. face is
smaller and more flat as in humans; and
d. tool
manufacture and use seems evident.
2. H. habilis warrants
classification as Homo because of brain size related to speech,
posture, and dentition.
3. Cut marks on bones suggest the
use of tools to prepare meat and possible scavenging.
4. Oldowan Tools associated with H.
habilis includes fakes used to scrape away hide or remove meat.
5. A large brain (700 cc) indicates
that this hominid may have had speech to help in cooperation and sharing.
6. What has been considered Homo
habilis may be two species with Homo rudolfensis is
taller, broad-faced,
larger-brained species.
B. Homo ergaster and Homo erectus
1. Eugene DuBois was a Dutch anatomist who unearthed the first H. erectus
bones in Java in 1891.
2. Fossils were found in Africa,
Asia, and Europe and date between 1.9 and 0.5 million years ago.
3. African types are now called Homo
ergaster.
4. H. ergaster had a
large brain capacity of 900 cc, was taller than H. habilis, and
had a striding gait.
5. H. erectus fossils
found in Java and the Republic of Georgia at 1.9 MYA and 1.6 MYA indicates an
early
migration of H. ergaster from Africa, followed by H.
erectus evolving in Asia and spreading to other areas.
6. These are the first hominids
to use fire, to be systematic game hunters, and possibly to use home bases.
C. Evolution of Modern Humans
1. The archaic species Homo sapiens, now called Homo
heidelbergensis, were present in Europe, Asia and Africa.
2. Two contradicting hypotheses are
suggested about the origin of modern humans.
a. The multiregional
continuity hypothesis proposes that modern humans originated separately
in Asia,
Europe, and Africa.
1) If valid, then a distinctive continuity in anatomy and genetic variation is
expected in each location.
2) A more recent DNA analysis done in 1999 supports the multiregional
hypothesis; it compared variation
in a gene on the X chromosome from worldwide samples and pointed to two
ancestral versions.
b. The out-of-Africa
hypothesis states that modern humans originated only in Africa and
after migrating into
Europe and Asia, they replaced the archaic Homo species found
there.
1) All extant humans are descended from a few individuals from about 100,000
years ago.
2) Mitochondrial DNA analyses indicate a close genetic relationship among all
Europeans; although the
first analysis was flawed, the data tend to support the out-of-Africa
hypothesis.
D. Neanderthals
1. Neanderthals were named for Neander Valley where skeletons
were dated 50,000 years ago.
2. Neanderthals are classified
as H. sapiens neanderthalensis.
3. Classical Neanderthal anatomy
includes massive brow ridges; a nose, jaws, and teeth that protruded forward;
a low
sloping forehead; a lower jaw sloping back without a chin; a longer pubic bone;
a slightly larger brain
than that of
modern humans; shorter and thicker limb bones; and heavier muscles in shoulder
and neck.
4. It is speculated that a larger
brain than that of modern humans was required to control the extra musculature.
5. Sturdy build of Neanderthals was
likely adaptation to cold climate; they lived in Eurasia during last Ice Age.
6. The Neanderthals give evidence of
being culturally advanced.
a. Most
lived in caves, but those who lived in the open may have build houses.
b. They
manufactured a variety of stone tools, including spear points, scrapers, and
knives.
c. They used
and could control fire, which probably helped in cooking frozen meat and in
keeping warm.
d. They
buried their dead with flowers and tools and may have had a religion.
e. Fragments
for 30,000 years ago indicate classic features and therefore no interbreeding
with humans.
E. Cro-Magnons Were Modern Humans
1. Cro-Magnons are modern humans (H. sapiens) found
in Eurasia 100,000 years ago.
2. Cro-Magnons are named for a
fossil location in France and had a thoroughly modern appearance.
3. They had advanced Aurignacian
stone tools and may have been the first to throw spears.
4. Cro-Magnons hunted cooperatively,
and perhaps were the first to have had a language.
5. Cro-Magnons may have been
responsible for extinction of large mammals during the late Pleistocene.
6. Cro-Magnon culture included
figurines carved out of bone and antler and cave paintings.