BIPEDAL ADAPTATION AND OUR EARLIEST
ANCESTORS LAB
Objectives
After completing this lab you should be able to:
recognize and describe the six hallmark traits that we use to identify the members
of the Hominini;
identify and describe the skeletal modifications necessary for bipedal locomotion;
identify and describe the anatomical characteristics of the earliest hominins and
the gracile and robust australopithecines;
define Rift Valley, “Lucy,” Laetoli footprints, Taung child, the Black Skull;
compare and contrast the anatomical differences between an australopithecine and
a modern human or a chimp;
compare and contrast the anatomical differences between a gracile and a robust
australopithecine; and
recognize illustrations, photos, and casts (if available) of the different major
hominin groups.
Reading Questions
You should first read through the text of this lab. Then answer the following questions
before you start. Select the correct answer and change to “bold” font. Be sure to also type
in the correct letter option in the blank space next to the question number.
1. ____c____Which of the following traits characterizes the early hominins?
a. C/P3 hone
b. thin enamel
c. parabolic dental arch
d. sectorial premolar
2. ___a_____A femur that drops down on an angle to bring the knees together in
the midline of the body is called a:
a. valgus knee
b. hip stabilizer
c. verus knee
d. divergent hallux
3. ____D____Which of the following traits characterizes the bipedal human?
a. verus knee
b. long toes for grasping
c. divergent hallux
d. gluteal muscles acting as hip stabilizers
4. ___C_____Which of the following traits characterizes the quadrupedal ape?
, a. valgus knee
b. S-shaped vertebral column
c. divergent hallux
d. two arches in foot.
5. ____B____Which of the following genera is not one of the earliest hominins
dating from 4 to 7 million years ago?
a. Ardipithecus
b. Australopithecus
c. Sahelanthropus
d. Orrorin
e.
6. ____C____Which australopithecine species was the very first ever discovered?
a. Australopithecus afarensis
b. Australopithecus robustus
c. Australopithecus africanus
d. Australopithecus boisei
7. ____B____Elements of Lucy’s anatomy that suggest she may have spent some
time in the trees include:
a. short legs
b. long arms
c. broad pelvis
d. short, straight digits
8. ___D_____Which of the following traits does not represent the robust
australopithecines?
a. sagittal crest
b. dished face
c. nuchal crest
d. small molar teeth
9. ___A_____True or False: A C/P3 hone involves the upper canine sliding across
the lower first premolar.
a. True
b. False
10. ____B____True or False: Australopithecus robustus and A. boisei are
considered “robust” because they have a much larger body size and brain size
than the gracile specimens.
a. True
b. False
,Introduction: Recognizing the Hominini
At the end of the Miocene, between 5 and 7 million years ago (mya), a new taxon arose
within the primate order, the Hominini. Remember that there are alternate taxonomic
classifications for humans and our bipedal predecessors. The traditional classification
chart is based on anatomical comparisons and contains three families: the hylobatids
(lesser apes), the pongids (all great apes), and the hominids (humans and our bipedal
ancestors). This system emphasizes the morphological adaptations, such as bipedalism
and large brain size and advanced cultural adaptations of humans by placing them in their
own taxonomic family separate from the great apes. However, many paleoanthropologists
have begun to emphasize the genetic relationships, which better reflect evolutionary
history, when classifying the Hominoidea.
This modern genetic classification includes two families: hylobatids (lesser apes) and
hominids (great apes and humans). The hominid family includes three subfamilies: the
pongines (orangutans), gorillines (gorillas), and hominines (chimps, bonobos, and
humans). The hominines in turn are divided into tribes: panins (chimps/bonobos) and
hominins (humans). Thus, in this system, humans and our extinct ancestors since the
divergence from the last common ancestor with chimpanzees are referred to as hominins
instead of hominids (Figure 1). Some anthropologists prefer to use the traditional
taxonomic system because it allows a better understanding of human adaptations and
uniqueness, while others prefer the modern system which better reflects genetic and
evolutionary relationships. This course follows the modern convention and refers to
humans and our ancestors as hominins.
Figure 1 Traditional (anatomical) versus modern (genetic) taxonomies. (a) The traditional system
refers to humans and our ancestors as hominids, while (b) the genetic system refers to humans
and our ancestors as hominins.
, DNA evidence and protein studies indicate that the last common ancestor to the
chimpanzee and human lineages evolved during the late Miocene epoch, between 5 and 7
million years ago (ma) (Goodman, 1999; Goodman et al., 1998; Ruvolo, 1997; Sarich &
Wilson, 1967). However, the biochemical evidence does not tell us about what these early
ancestors looked like. The anatomical evidence gleaned from the study of fossil remains
allows us to interpret our morphological evolution. When this anatomical evidence is
added to the behavioral evidence we have from living primates, we can begin to put the
pieces of the puzzle together, developing a more complete picture of our ancestors. The
hominins may be divided into three broad groups based on the order of their appearance:
(1) the earliest possible hominins (before the genus Australopithecus), (2) the
australopithecines, and (3) the genus Homo. The first two of these groups are discussed in
more detail in the following pages.
Modern humans differ from the apes in several obvious behavioral ways: speech and the
highly advanced use of symbolic language, complex material culture, relaxation of the
estrous cycle and concealed ovulation, and advanced cognition. However, not all of our
fossil ancestors will exhibit these traits, which evolved more recently in the hominin
lineage; and many of these behavioral traits are difficult to distinguish in fossil remains,
so we must look to the anatomical evidence to recognize members of our evolving
lineage. Hominins may be distinguished from the apes by the following anatomical traits:
Larger brain size
Bipedal locomotion, with a striding gait
Parabolic dental arch
Reduced prognathism (facial projection)
No C/P3 hone
Thick molar enamel
It is important to realize that many of these traits evolved in a mosaic fashion. Many of
the earliest hominins, discussed in this chapter, will not show all these traits but a subset
of them. This can cause controversy in classification, as different researchers may
emphasize the importance of certain traits over others.
The cranial capacity of modern humans is estimated to be between 1,300 and 1,400
cubic centimeters (cc), with an average of about 1,350 cc. The common chimpanzee’s
cranial capacity is approximately 350 to 400 cc. Thus, if the chimpanzee’s brain size
reflects the primitive condition, we can expect to see an increase in brain size over time
along the hominin lineage. Over time in this lineage, the brain of humans is positioned
higher on the cranium, creating a high, rounded, globular cranium, eventually creating a
forehead, while the snout retreats and the face does not project forward as far as in the
apes. This reduced prognathism, or less facial projection, characterizes the hominins.
Numerous dental characteristics differ between apes and humans (Stanford et al., 2006).
Due to their diet consisting of softer fruits and tender leaves and shoots, the African apes
have thin molar enamel on their teeth. However, hominins evolved on a coarser diet,
ANCESTORS LAB
Objectives
After completing this lab you should be able to:
recognize and describe the six hallmark traits that we use to identify the members
of the Hominini;
identify and describe the skeletal modifications necessary for bipedal locomotion;
identify and describe the anatomical characteristics of the earliest hominins and
the gracile and robust australopithecines;
define Rift Valley, “Lucy,” Laetoli footprints, Taung child, the Black Skull;
compare and contrast the anatomical differences between an australopithecine and
a modern human or a chimp;
compare and contrast the anatomical differences between a gracile and a robust
australopithecine; and
recognize illustrations, photos, and casts (if available) of the different major
hominin groups.
Reading Questions
You should first read through the text of this lab. Then answer the following questions
before you start. Select the correct answer and change to “bold” font. Be sure to also type
in the correct letter option in the blank space next to the question number.
1. ____c____Which of the following traits characterizes the early hominins?
a. C/P3 hone
b. thin enamel
c. parabolic dental arch
d. sectorial premolar
2. ___a_____A femur that drops down on an angle to bring the knees together in
the midline of the body is called a:
a. valgus knee
b. hip stabilizer
c. verus knee
d. divergent hallux
3. ____D____Which of the following traits characterizes the bipedal human?
a. verus knee
b. long toes for grasping
c. divergent hallux
d. gluteal muscles acting as hip stabilizers
4. ___C_____Which of the following traits characterizes the quadrupedal ape?
, a. valgus knee
b. S-shaped vertebral column
c. divergent hallux
d. two arches in foot.
5. ____B____Which of the following genera is not one of the earliest hominins
dating from 4 to 7 million years ago?
a. Ardipithecus
b. Australopithecus
c. Sahelanthropus
d. Orrorin
e.
6. ____C____Which australopithecine species was the very first ever discovered?
a. Australopithecus afarensis
b. Australopithecus robustus
c. Australopithecus africanus
d. Australopithecus boisei
7. ____B____Elements of Lucy’s anatomy that suggest she may have spent some
time in the trees include:
a. short legs
b. long arms
c. broad pelvis
d. short, straight digits
8. ___D_____Which of the following traits does not represent the robust
australopithecines?
a. sagittal crest
b. dished face
c. nuchal crest
d. small molar teeth
9. ___A_____True or False: A C/P3 hone involves the upper canine sliding across
the lower first premolar.
a. True
b. False
10. ____B____True or False: Australopithecus robustus and A. boisei are
considered “robust” because they have a much larger body size and brain size
than the gracile specimens.
a. True
b. False
,Introduction: Recognizing the Hominini
At the end of the Miocene, between 5 and 7 million years ago (mya), a new taxon arose
within the primate order, the Hominini. Remember that there are alternate taxonomic
classifications for humans and our bipedal predecessors. The traditional classification
chart is based on anatomical comparisons and contains three families: the hylobatids
(lesser apes), the pongids (all great apes), and the hominids (humans and our bipedal
ancestors). This system emphasizes the morphological adaptations, such as bipedalism
and large brain size and advanced cultural adaptations of humans by placing them in their
own taxonomic family separate from the great apes. However, many paleoanthropologists
have begun to emphasize the genetic relationships, which better reflect evolutionary
history, when classifying the Hominoidea.
This modern genetic classification includes two families: hylobatids (lesser apes) and
hominids (great apes and humans). The hominid family includes three subfamilies: the
pongines (orangutans), gorillines (gorillas), and hominines (chimps, bonobos, and
humans). The hominines in turn are divided into tribes: panins (chimps/bonobos) and
hominins (humans). Thus, in this system, humans and our extinct ancestors since the
divergence from the last common ancestor with chimpanzees are referred to as hominins
instead of hominids (Figure 1). Some anthropologists prefer to use the traditional
taxonomic system because it allows a better understanding of human adaptations and
uniqueness, while others prefer the modern system which better reflects genetic and
evolutionary relationships. This course follows the modern convention and refers to
humans and our ancestors as hominins.
Figure 1 Traditional (anatomical) versus modern (genetic) taxonomies. (a) The traditional system
refers to humans and our ancestors as hominids, while (b) the genetic system refers to humans
and our ancestors as hominins.
, DNA evidence and protein studies indicate that the last common ancestor to the
chimpanzee and human lineages evolved during the late Miocene epoch, between 5 and 7
million years ago (ma) (Goodman, 1999; Goodman et al., 1998; Ruvolo, 1997; Sarich &
Wilson, 1967). However, the biochemical evidence does not tell us about what these early
ancestors looked like. The anatomical evidence gleaned from the study of fossil remains
allows us to interpret our morphological evolution. When this anatomical evidence is
added to the behavioral evidence we have from living primates, we can begin to put the
pieces of the puzzle together, developing a more complete picture of our ancestors. The
hominins may be divided into three broad groups based on the order of their appearance:
(1) the earliest possible hominins (before the genus Australopithecus), (2) the
australopithecines, and (3) the genus Homo. The first two of these groups are discussed in
more detail in the following pages.
Modern humans differ from the apes in several obvious behavioral ways: speech and the
highly advanced use of symbolic language, complex material culture, relaxation of the
estrous cycle and concealed ovulation, and advanced cognition. However, not all of our
fossil ancestors will exhibit these traits, which evolved more recently in the hominin
lineage; and many of these behavioral traits are difficult to distinguish in fossil remains,
so we must look to the anatomical evidence to recognize members of our evolving
lineage. Hominins may be distinguished from the apes by the following anatomical traits:
Larger brain size
Bipedal locomotion, with a striding gait
Parabolic dental arch
Reduced prognathism (facial projection)
No C/P3 hone
Thick molar enamel
It is important to realize that many of these traits evolved in a mosaic fashion. Many of
the earliest hominins, discussed in this chapter, will not show all these traits but a subset
of them. This can cause controversy in classification, as different researchers may
emphasize the importance of certain traits over others.
The cranial capacity of modern humans is estimated to be between 1,300 and 1,400
cubic centimeters (cc), with an average of about 1,350 cc. The common chimpanzee’s
cranial capacity is approximately 350 to 400 cc. Thus, if the chimpanzee’s brain size
reflects the primitive condition, we can expect to see an increase in brain size over time
along the hominin lineage. Over time in this lineage, the brain of humans is positioned
higher on the cranium, creating a high, rounded, globular cranium, eventually creating a
forehead, while the snout retreats and the face does not project forward as far as in the
apes. This reduced prognathism, or less facial projection, characterizes the hominins.
Numerous dental characteristics differ between apes and humans (Stanford et al., 2006).
Due to their diet consisting of softer fruits and tender leaves and shoots, the African apes
have thin molar enamel on their teeth. However, hominins evolved on a coarser diet,
