(p. 460)
21.1 The Evolutionary Path to Humans (p. 460; Fig. 21.1)
A.
About 65 million years ago, a small group of arboreal, nocturnal animals called Archonta underwent adaptive radiation and out of this group evolved the bats, tree shrews, and primates.
B.
The Earliest Primates
1.
Two adaptive features were seen in the earliest primates: grasping fingers and toes, and binocular vision.
2.
Both traits enabled the early primates to better move through the trees and capture their insect food.
C.
The Evolution of Prosimians and Anthropoids
1.
Around 40 million years ago, the earliest primates split into two groups, giving rise to the prosimians and the anthropoids.
2.
Most prosimians, such as tarsiers and lemurs, are nocturnal and eat plant material.
3.
The anthropoids, or higher primates, include monkeys, apes, and humans.
4.
The early anthropoids, now extinct, arose in Africa and gave rise to the monkeys.
5.
Some early anthropoids migrated to South America and gave rise to the New World, which are arboreal and have prehensile tails.
7.
About 25 million years ago, anthropoids in Africa gave rise to both the Old World monkeys and to the hominoids, the group containing to humans.
8.
Old World monkeys include both ground-dwellers and arboreal species, and they do not have prehensile tails.
21.2 How the Apes Evolved (p. 461, Fig. 21.2)
A.
From their anthropoid ancestors, the hominoids evolved and include apes and hominids, humans and their ancestors.
B.
Living apes include the gibbon, orangutan, gorilla, and chimpanzee.
C.
Apes have larger brains than monkeys, and they lack tails.
D.
Apes were once widespread in Asia and Africa, but their distribution is limited today.
E.
Which Ape Is Our Closest Relative?
1.
Studies of DNA indicate that the Asian apes evolved first; neither orangutans nor gibbons are closely related to humans.
2.
African apes evolved more recently, around 6 to 10 million years ago.
3.
Chimpanzees are more closely related to humans than gorillas are, with humans and chimps sharing 98.6% of the same nuclear DNA.
4.
Chimpanzees and humans diverged about 6 million years ago.
5.
The greater genetic difference between gorillas and humans indicate a split between these two groups about 8 million years ago.
F.
Comparing Apes to Hominids
1.
The common ancestor to apes and humans is thought to have been an arboreal climber.
2.
Hominids became bipedal, while the apes evolved knuckle-walking.
3.
Humans have an S-shaped spinal curvature, while apes have a straighter spine needed for knuckle-walking.
4.
The human pelvis is bowl-shaped and broader, shaped to support body weight over the legs.
5.
Upper limbs of humans are shorter than those of apes, but legs are considerably longer.

(p. 462)
21.3 Walking Upright (p. 462; Figs. 21.3, 21.4)
A.
The climate cooled some 5 to 10 million years ago, and the vast forests receded, giving way to open savannas.
B.
A new kind of ape was evolving, one that was bipedal.
C.
The hominids include species of Homo and Australopithecus , and several older lineages.
D.
Hominid fossils extending back to 4 million years ago demonstrate bipedalism.
E.
Brain expansion did not appear until about 2 million years ago, indicating that bipedalism preceded larger brains.
21.4 The Hominid Family Tree (p. 463; Fig. 21.5)
A.
In recent years, many different kinds of early hominid fossils have been discovered, some dating back to 6–7 million years ago.
B.
More information is needed before scientists can determine how the early hominids are related to australopithecines and humans.
C.
The First Australopithecine
A.
In 1995, 4.2-million-year-old hominid fossils were found and were named
Australopithecus anamensis.
B.
Most researchers believe A. anamensis represent the base of our family tree.
C.
Several other species of Australopithecus existed, including A.
afarensis
D.
Differing Views of the Hominid Family Tree
1.
Scientists have taken two different approaches in classifying the species of Homo and characterizing the hominid family tree.
2.
“Lumpers” recognize three species of Homo, focusing on common elements among fossils and attributing the differences to diversity within the group.
3.
“Splitters” recognize at least seven species of Homo.
(p. 464)
21.5 African Origin: Early Homo (p. 464; Figs. 21.6, 21.7)
A.
The first humans evolved from australopithecine ancestors around 2 million years ago.
B.
The exact ancestor is not known, but is thought to be Australopithecus afarensis .
C.
Within recent years, numerous fossils have been found, which will eventually shed more light on the exact sequence of the evolution of early humans.
D.
Homo habilis
1.
Fossils of Homo habilis indicate that this species was short-statured like the australopithecines, but its brain was larger.
2.
This species is sometimes called “handy man” because of its association with tools.
E.
Homo rudolfensis
1.
In 1972, Richard Leakey unearthed a virtually complete 1.6 million-year-old skull of
Homo habilis in Africa.
2.
Some anthropologists assign this specimen to Homo rudolfensis because of its large brain case.
F.
Homo ergaster
1.
Some other early Homo specimens have even larger brain cases and also have small cheek teeth, similar to those of modern humans.
2.
These specimens are assigned by some to the species Homo ergaster.
G.
How Diverse Was Early Homo ?
1.
There is still debate as to whether all early Homo specimens should be grouped into one or split into two species.
2.
Because of its modern skeleton, Homo ergaster is thought to be the most likely ancestor to later species of Homo and is often lumped with Homo erectus.
21.6 Out of Africa: Homo erectus (p. 465; Fig. 21.8)
A.
Although doubt exists about early species of Homo , it is quite obvious that Homo erectus was a true human.

B.
Java Man
1.
Eugene Dubois found a fossil of Homo erectus in 1891 that he called Java man, although few scientists at the time were willing to accept that this was an ancient type of human.
C.
Peking Man
1.
In the 1920s, excavation in the Peking region of China unearthed many fossils that disappeared during World War II.
2.
Since 1949, many more examples of Peking man have been excavated.
D.
A Very Successful Species
1.
Java man and Peking man are now known to be species of Homo erectus.
2.
Homo erectus was larger than H. habilis and had a larger brain size.
3.
This species, too, came out of Africa and spread throughout Asia and Europe.
4.
Homo erectus survived for over a million years, longer than any other species of human.
5.
Homo erectus disappeared about 500,000 years ago in Africa, but the species survived even longer in Asia.
(p. 466)
21.7 Our Own Species also Evolved in Africa (p. 466; Fig. 21.9)
A.
Around 600,000 years ago, the first modern humans appeared in Africa.
B.
Some scientists describe three species of modern humans: Homo heidelbergensis, H. neanderthalensis, and H. sapiens.
C.
The oldest modern human, Homo heidelbergensis, is known from a 600,000-year-old fossil found in Africa.
D.
H. heidelbergensis coexisted with H. erectus in Africa but had several more advanced anatomical features.
E.
H. heidelbergensis spread to several areas in Africa, Europe, and western Asia.
F.
As Homo erectus became rarer about 130,000 years ago, another species of human appeared in Europe, Neanderthal man ( Homo neanderthalensis ).
G.
Neanderthals were short, stocky, and powerfully built .
H.
Out of Africa—Again?
1.
The oldest fossils of Homo sapiens are from Africa and are about 130,000 years old.
2.
Fossils of H. sapiens from other areas are only about 40,000 years old.
3.
Human mitochondrial DNA (mtDNA) and nuclear chromosomal DNA evidence suggests that Homo sapiens evolved first in Africa then migrated to other areas of the world.
I. A Fourth Species of Recent Human
J. A Fifth?
21.8 The Only Surviving Hominid (p. 468; Fig. 21.10)
A.
The Neanderthals (classified by some as Homo neanderthalensis ) were named after the
Neander Valley of Germany, where their fossils were first discovered.
B.
They became common in Europe and Asia by 70,000 years ago, made diverse tools, and lived in huts or caves.
C.
Molecular analyses of Neanderthal bones over 30,000 years old reveal that their DNA was quite different than the DNA of Homo sapiens.
D.
Fossils of H. neanderthalensis disappear from the record about 34,000 years ago and are replaced by fossils of H. sapiens called the Cro-Magnons.
E.
Cro-Magnons were sophisticated tool users, had social organization, and probably had full language capabilities.
F.
Humans eventually spread across Siberia to North America about 13,000 years ago.
G.
Homo sapiens Are Unique
1.
Human evolution has been characterized by an increase in brain size and the ability for conceptual thought.