female - gatherer of vegetable matter
What do these two types of foraging strategies require, and what
genetically-based behaviors might confer a selective advantage to
Our Favorite Ape: Homo sapiens
Paleoanthropology is the study of human origins and evolution. Because
humans and chimpanzees have existed as separate species for only a few
million years, this branch of science examines only a very small, recent
portion of the fossil record.
Terms to know:
REMEMBER: HUMANS DID NOT EVOLVE FROM MONKEYS OR APES! No
scientist would ever say that!
- anthropoid - of or pertaining to monkeys and apes
- hominoid - of or pertaining to the great apes (including humans)
- hominid - member of family Hominidae
It is correct to say only that humans, apes, and monkeys all diverged from
a common anthropoid ancestor, evolving into different species due to
natural selection and the other factors that can drive macroevolution.
The earliest fossil members of our genus (Homo) range in age from
about 2.5 to 1.6 million years, and are classified as Homo
Homo erectus shared common ancestry with H. habilis, and
shows up in the fossil record from about 1.8 million to 0.5 million years
Homo sapiens neanderthalensis , named for the Neander Valley in
Germany where its fossils were first found, may have arisen from an H.
erectus-like ancestor, as H. erectus is known to have migrated into both Europe
and Asia (timing uncertain).
There's a good deal of argument about how anatomically modern Homo sapiens
sapiens came onto the scene, but it's generally agreed that we
originated in Africa, where all the oldest hominid fossils are found.
Here's a nice
overview of our hominid relatives, for those who would like to delve a
- Multiregional Hypothesis:
Homo sapiens evolved in each of the
regions where its fossils are now found from ancestral Homo
erectus that migrated out of Africa about 1.5 million years ago.
Advocates of this hypothesis consider H. erectus to be an early
version of H. sapiens, and not a different species.
Constant interbreeding between neighboring populations of this "archaic"
may have prevented reproductive isolation, resulting in our
present-day races of Homo
rather than multiple species of Homo.
- "Out of Africa" Hypothesis:
All H. sapiens now living evolved from a second major migration out of
Africa that occurred about 100,000 years ago, and not from wandering Homo
erectus. These later migrants replaced the descendants of the
earlier H. erectus migrants.
So far, DNA analyses have supported the "Out of Africa" ("Replacement")
hypothesis. But as any hypothesis, this one is subject to further
testing as new analytic methods become available.
What makes humans different from the other great apes?
- Brain size
Hominoids of 6 million years ago had brains of about 400 -
450cm2. This is about the same as modern chimpanzees. Modern
humans' average brain volume is 1300cm2. This threefold
increase in volume is associated with cultural trends such as development
of complex language
- Jaw shape
Anthropoids and ancient hominoids have prognathic jaws: the
upper and lower jaws protrude beyond the nose. Recall that the human
face is paedomorphic with respect to that of other modern apes. The
face is flatter, the prognathous jaws lost. Changes in dentition
accompanied this change in jaw shape.
- Bipedal posture
Ancestral anthropoids and some of the earliest hominoids walked on all
fours, though--like modern apes--they could probably walk on their hind
legs with some degree of balance and skill. Humans are different from
all other apes in that the body posture is fully upright and
locomotion is entirely bipedal. A number of skeletal and muscular
modifications make this possible, but there is still a great deal of
academic argument about why humans became bipedal.
- Reduced sexually dimorphic size differences
In orangutans and gorillas, the male weighs about twice as much as the
female. In chimpanzees and Bonobos, males weigh about 1.4 times as much
as females. In humans, the difference is still less, with males
averaging 1.2 the body weight of females. (Why do you suppose this is the
case? HINT: social structure is a major selective factor here.)
- Key changes in family and other social structures
- Gibbons are social, with a dominant male defending a group of
females from other male rivals.
- Orangutans are solitary and do not form permanent social groups
- Gorillas are social, with a single "silverback" dominant male
getting all the mating opportunities with the females in his band.
Immature and subordinate males are allowed to stay in the group, but
do not get many mating opportunities.
- Chimpanzees are social and promiscuous. When a female comes into
estrus, all males will attempt to mate with her, and she will mate
with multiple males.
- Bonobos will have sex with anyone who holds still long enough.
- Hunter-gatherer human societies may be polygamous or
polyandrous. But in most human societies, monogamy is the norm.
(But is it biologically programmed?)
- Young are even more altricial than other great apes' young.
Newborn humans are exceptionally dependent on their mothers, and parental
care lasts longer after birth than in other ape species. This extended
period, coupled with the enlarged brain, enhances learning and is one
factor that contributes to the behavioral complexity of the human
Let's talk about some of that behavior right now.