Were australopithecines ape--human intermediates or just apes? a test of both hypotheses using the "Lucy" skeleton.
Abstract: Mainstream scientists often claim that australopithecines such as the specimen nicknamed "Lucy" exhibit anatomy intermediate between that of apes and that of humans and use this as evidence that humans evolved from australopithecines, which evolved from apes. On the other hand, creationists reject evolution and claim that australopithecines are "just apes." Here, a point-by-point visual comparison with the skeletons of a chimpanzee, "Lucy," and a human is presented in order to evaluate both claims, treating them as testable hypotheses. The results support the hypothesis that australopithecines are anatomically intermediate between apes and humans. Classroom applications of this test of hypotheses are also discussed.

Key Words: Human evolution; comparison of human and chimpanzee skeletons; australopithecines.
Article Type: Report
Subject: Human evolution (Research)
Human evolution (Study and teaching)
Apes (Research)
Apes (Study and teaching)
Australopithecines (Study and teaching)
Australopithecines (Research)
Author: Senter, Phil
Pub Date: 02/01/2010
Publication: Name: The American Biology Teacher Publisher: National Association of Biology Teachers Audience: Academic; Professional Format: Magazine/Journal Subject: Biological sciences; Education Copyright: COPYRIGHT 2010 National Association of Biology Teachers ISSN: 0002-7685
Issue: Date: Feb, 2010 Source Volume: 72 Source Issue: 2
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: United States Geographic Code: 1USA United States
Accession Number: 245037742
Full Text: [ILLUSTRATION OMITTED]

To effectively introduce the evidence for evolution, it is important that a biology teacher have a basic grasp of the anatomy of australopithecines. This is because the presence of evolutionary sequences in the fossil record is one of the main lines of evidence for evolution, and no fossil evolutionary lineage generates more interest than our own. As evolutionary intermediates between apes and humans, the australopithecines form a prominent part of that lineage, and their anatomy is a beautiful illustration of the anatomical transition from ape to human.

A good way to become familiar with australopithecine anatomy would be to use a point-by-point comparison of their skeletons with those of apes and humans. Unfortunately, such is lacking in most biology textbooks (e.g., Starr & Taggart, 2004; Campbell et al., 2009), including those on evolution (e.g., Volpe & Rosenbaum, 2000; Barton et al., 2007). This makes it difficult for the biology teacher to illustrate exactly how australopithecines are intermediate between apes and humans. Here, I compare an australopithecine skeleton with those of the chimpanzee (Pan troglodytes) and the modern human species (Homo sapiens).

A point-by-point comparison of ape, australopithecine, and human anatomy presents another opportunity that should be seized. Such a comparison can be used to test two competing claims that can be treated as testable hypotheses: (1) the consensus among mainstream scientists that australopithecine anatomy is intermediate between those of apes and humans and (2) the young-earth creationist claim that australopithecines are "just apes," unrelated to humans (Mehlert, 2000; Line, 2005; Murdock, 2006). In a time of rampant creationism (Mazur, 2005; Miller et al., 2006), it is important not to dismiss the latter claim out of hand but to explicitly put it to the test.

Hundreds of australopithecine specimens are known, but to keep this study simple and to avoid overwhelming the nonspecialist reader, I chose to use a single australopithecine specimen: AL 288-1, nicknamed "Lucy." Discovered in Ethiopia in 1974 (Johanson et al., 1982), AL 288-1 is particularly appropriate to use for this test of hypotheses, for several reasons. First, at 40% complete (Johanson et al., 1982), it is one of the most complete australopithecine skeletons known to date; most of the skull is missing, but the preserved portions of the jaw, dentition, vertebral column, pelvis, and limbs are sufficient to test the two hypotheses with traits from a variety of skeletal regions. Second, cast replicas of the entire known skeleton of Lucy are commercially available--as are those of chimpanzees and humans--so this test of hypotheses can be repeated by any academic or other entity with an appropriate budget without having to travel to see the fossil itself. Third, AL 288-1 represents a species, Australopithecus afarensis, with important phylogenetic significance. It predates both our own genus (Homo) and the later australopithecines with which early Homo coexisted, and it is possibly ancestral to both (Stein & Rowe, 2006). Other specimens of A. afarensis show that AL 288-1 is similar enough to its conspecifics to serve as an exemplar of the species (Drapeau et al., 2005). Fourth, it is a particularly famous fossil, and the public's familiarity with it continues to increase as a result of publicity generated by its current tour through the United States.

The hypothesis that Lucy is anatomically intermediate between apes and humans predicts that a point-by-point comparison will reveal a mixture of apelike features and humanlike features in the specimen. The hypothesis that Lucy is just an ape predicts that such a comparison will only reveal apelike features in the specimen. Some proponents of the latter hypothesis recognize that australopithecines had upright bipedal locomotion but do not consider this a feature linking australopithecines with humans (Mehlert, 2000; Murdock, 2006). To satisfy such strict interpreters of the "just an ape" hypothesis, the predictions can be modified: the hypothesis that Lucy is anatomically intermediate between apes and humans predicts that a point-by-point comparison will reveal in Lucy a mixture of apelike features and humanlike features in which some of the humanlike features are not necessary for upright bipedal locomotion. The hypothesis that Lucy is just an ape predicts that the comparison will reveal no humanlike features in Lucy that are unnecessary for upright bipedal locomotion.

* Materials & Methods

To test the hypotheses, I compiled a list of skeletal differences between chimpanzee and human skeletons, using direct examination of several chimpanzee skeletons at the U.S. National Museum and human skeletons at Fayetteville State University and the U.S. National Museum. I examined the australopithecine skeleton AL 288-1, which was on temporary display in Seattle, and tabulated which characters in the list exhibit the apelike state and which exhibit the humanlike state (Figures 1 and 2, Table 1). For features that I could not make out on AL 288-1 because of the position of the specimen as it was laid out for display, I used a cast of the specimen.

[FIGURE 1 OMITTED]

* Results & Conclusion

Of 36 anatomical characters examined on AL 288-1, 14 (39%) exhibit the apelike state and 22 (61%) exhibit the humanlike state. Of the 22 characters for which AL 288-1 exhibits the humanlike state, 12 (55%) are found on the vertebral column, pelvis, and lower limb and could therefore be construed as related to upright bipedal locomotion, whereas 10 (45%) are found on the jaw, teeth, and upper limb and are therefore unrelated to upright bipedal locomotion. The data therefore support the hypothesis that Lucy is anatomically intermediate between apes and humans and falsify the hypothesis that Lucy is just an ape.

* Discussion

This study can be adapted as a classroom exercise using commercially available casts of the Lucy skeleton in conjunction with chimp and human skeletons or commercially available casts thereof (Table 2). For schools with lower budgets, pictures could be used instead of casts. Free images of human and chimpanzee bones in various views are available at http://www.eskeletons.org. Bone Clones (http://www.boneclones.com) sells a 14" x 11" poster of the Lucy skeleton for $10.00, although it shows the bones in only one view.

[FIGURE 2 OMITTED]

One way to adapt this study to the classroom is for a teacher to instruct students to come up with their own lists of differences between chimp and human skeletons and then run down the list with the Lucy skeleton to tabulate traits for which it exhibits the apelike state and those for which it exhibits the humanlike state. Alternatively, the teacher could instruct students to focus their attention on the traits used here (Table 1). Either way, at the end of the exercise, students can be asked to make up their own minds about whether Lucy is anatomically intermediate between apes and humans or not.

A potential criticism of such an exercise is that it does not employ a cladistic approach. Cladistics, the preferred method for determining relationships, uses shared, derived characters (traits) to determine which taxa are most closely related to which, ignoring shared ancestral characters. It treats all taxa as endpoints on an evolutionary tree rather than treating any taxon as ancestral to any other. By contrast, the approach used here treats "apes" (exemplified by the chimpanzee) as an ancestral grade from which "australopithecines" evolved and treats "australopithecines" (exemplified by Lucy) as an ancestral evolutionary grade from which humans evolved. Such a way of looking at things is accurate but may confuse students that have been taught in a strictly cladistic manner. It is therefore important for the teacher to note that the results of this exercise do not show that the chimp is the ancestor of Lucy and that Lucy is the ancestor of humans. Instead, the results show that a representative of the australopithecine grade (Lucy) has too many anatomical traits in common with humans--and in contrast with apes--to support a conclusion that the creature is a mere ape.

A classroom exercise such as this can be taken a step further by noting functional implications of Lucy's anatomy as well as the anatomy of the chimp and the human. Table 3 lists functional hypotheses associated with locomotion and predictions that are testable with the Lucy material. For this, students should be instructed to compare each specimen's anatomy with the predictions of each hypothesis to determine which hypotheses are falsified (or not) by anatomical data. Such an exercise not only elucidates australopithecine locomotion but also involves the use of hypothesis testing, an important scientific tool.

Exercises such as these are not likely to change the mind of anyone who is strongly influenced by the religious dogmas that keep young-earth creationism alive. Nevertheless, they are potentially useful for students on both sides of the fence. For those who accept that humans evolved from apelike precursors, such exercises provide clarification of the evidence. For those who do not accept the evolution of humans from nonhumans, such exercises at least show that the idea is not just a baseless atheistic conspiracy, as is often falsely claimed (Gish, 1995; Sarfati, 2002), but is instead based on observable physical data.

DOI: 10.1525/abt.2010.72.2.4

* Acknowledgments

Linda Gordon and Jennifer Clark of the U.S. National Museum deserve thanks for access to chimpanzee skeletons and a cast of AL 288-1, respectively. I also thank Jennifer Muench for her assistance, Rick Johnson and Marilyn Jacobs for lodging in Seattle, and Scott and Lynn Rountree for lodging in Washington, DC. Finally, I thank two anonymous reviewers for constructive comments that improved the manuscript.

References

Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B. & Patel, N.H. (2007). Evolution. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.

Campbell, N.A., Reece, J.B., Taylor, M.R., Simon, E.J. & Dickey, J.L. (2009). Biology: Concepts and Connections, 6th Ed. San Francisco, CA: Pearson Benjamin Cummings.

Drapeau, M.S.M., Ward, C.V., Kimbel, W.H., Johanson, D.C. & Rak, Y. (2005). Associated cranial and forelimb remains attributed to Australopithecus afarensis from Hadar, Ethiopia. Journal of Human Evolution, 48, 593-642.

Gish, D.T. (1995). Evolution: The Fossils Still Say NO! El Cajon, CA: Institute for Creation Research.

Johanson, D.C., Lovejoy, C.O., Kimbel, W.H., White, T.D., Ward, S.C., Bush, M.E., Latimer, B.M. & Coppens, Y. (1982). Morphology of the Pliocene partial hominid skeleton (A.L. 288-1) from the Hadar Formation, Ethiopia. American Journal of Physical Anthropology, 57, 403-451.

Line, P. (2005). Fossil evidence for alleged apemen--part 2: non-Homo hominids. TJ, 19, 33-42.

Mazur, A. (2005). Believers and disbelievers in evolution. Politics and the Life Sciences, 23, 55-61.

Mehlert, A.W. (2000). Australopithecines--the extinct southern apes of Africa: a fresh light on their status? Creation Ex Nihilo Technical Journal, 14, 91-99.

Miller, J.D., Scott, E.C. & Okamoto, S. (2006). Public acceptance of evolution. Science, 313, 765-766.

Murdock, M. (2006). These apes were made for walking: the pelves of Australopithecus afarensis and Australopithecus africanus. Journal of Creation, 20, 104-112.

Sarfati, J. (2002). Refuting Evolution 2. Green Forest, AR: Master Books. Starr, C. & Taggart, R. (2004). Biology: The Unity and Diversity of Life, 10th Ed.

London: Thomson-Brooks/Cole. Stein, P.L. & Rowe, B.M. (2006). Physical Anthropology, 9th Ed. Boston: McGraw Hill.

Volpe, E.P. & Rosenbaum, P.A. (2000). Understanding Evolution, 6th Ed. Boston: McGraw Hill.

PHIL SENTER is Associate Professor in the Department of Natural Sciences at Fayetteville State University, 1200 Murchison Road, Fayetteville, NC 28301; e-mail: psenter@uncfsu.edu.
Table 1. Comparison of chimpanzee (Pan troglodytes) and modern human
(Homo sapiens) skeletal anatomy. Underlining shows the condition in
"Lucy" (Australopithecus afarensis, specimen AL 288-1).

Anatomical Trait        Condition in            Condition in Modern
                        Chimpanzee              Human

1. Shape of mandible    V-shaped                parabolic

2. Simian shelf of      present                 absent
mandible

3. Slope of             strongly sloped         vertical
mandibular symphysis    (receding
in lateral view         inferiorly)

4. Protruding chin      absent                  present

5. Orientation of       parallel to each        posteriorly
left and right          other                   divergent
postcanine tooth
rows

6. Incisor size         about the same as       much smaller than
                        molar size              molars

7. Diastema             present                 absent
(toothless space)
between lower canine
and first lower
premolar

8. Lateral facet for    present                 absent
canine on first
lower premolar

9. Size of first        much larger than        about the same size
lower premolar          second premolar         as second premolar

10. Spinous process     angled                  angled
of 4th through 10th     20-45[degrees]          50-90[degrees]
thoracic vertebrae      toward tail             toward tail

11. Transverse          angled dorsally         angled dorsally
processes of 10th       about 30[degrees]       50-80[degrees]
through 12th
thoracic vertebrae

12. Displacement of
postzygapophyses        absent                  present
beyond caudal margin
of centrum on 11th
and 12th thoracic
vertebrae

13. Spinous process     angled toward tail;     not angled toward
of 2nd and 3rd          trapezoidal             tail; square
lumbar vertebrae

14. Transverse width    not much greater        much greater than
of centrum of 2nd       than length or          its length and
through 5th lumbar      height of centrum       height
vertebrae

15. Number of fused     six                     five
vertebrae in sacrum

16. Maximum             about 2/3 the length    about equal to
transverse              of the sacrum           length of sacrum
(side-to-side) width
of sacrum (not
counting 6th sacral
vertebra of chimp)

17. Lateral             prominent               weak
supracondylar ridge
of humerus

18. Lateral             prominent               weak
epicondyle of
humerus

19. Shafts of radius    strongly bowed          straight
and ulna

20. Proximal            present                 absent
extension of
olecranon process of
ulna

21. Medial margin of    concave                 straight
capitate (the carpal
bone at the base of
finger III)

22. Arching of          present; bones          no arching; bones
metacarpals and         concave on palmar       straight
manual phalanges        surface

23. Orientation of      wings stick straight    wings curve around
wings of ilium          out to the sides        toward the belly

24. Dimensions of       much taller than        height and width
ilium beyond            wide                    about equal
acetabulum (hip
socket)

25. Shape of greater    a broad, shallow        a narrow, tight
sciatic notch           curve                   curve

26. Orientation of      acetabulum faces        acetabulum faces
acetabulum              straight out            somewhat laterally
                        laterally               and somewhat
                                                anteriorly

27. Diameter of         approximately equal     greater than
femoral head            to diameter of          diameter of femoral
                        femoral shaft in        shaft in anterior
                        anterior view           view

28. Orientation of
greater trochanter
extends straight
proximally
tip is curved
medially

29. Height of tip of    level with femoral      does not extend as
greater trochanter      head when femoral       far proximally as
                        shaft is vertical       femoral head when
                                                femoral shaft is
                                                vertical

30. Middle part of      slanted                 perpendicular to
distal margin of                                shaft
tibia in posterior
view

31. Transverse width    greater than 1/3        less than 1/4
of medial malleolus     transverse width of     transverse width of
of tibia                entire distal end of    entire distal end of
                        tibia                   tibia

32. Lateral             rectangular             diamond-shaped
malleolus of fibula
in lateral view

33. Distal process      angled medially         extends straight
of talus (tarsal                                distally
bone that supports
the tibia)

34. Medial process      present                 absent
of talus medial and
plantar to tibial
facet

35. Arching of          present; bones          absent; bones
metatarsals and of      concave toward sole     straight
pedal phalanges
other than distal
phalanx

36. Shape of            convex                  concave
proximal margin of
proximal phalanx of
toes I-III in
lateral view

Table 2. Commercially available casts of skeletons of chimpanzee,
human, and "Lucy" (AL 288-1). Listed are the least expensive casts
of which the author is aware.

Cast                        Price (USD)   Vendor

"Lucy": mounted skeleton     $6300.00     Bone Clones

"Lucy": disarticulated       $1900.00     Bone Clones
skeleton

Chimpanzee: mounted          $2900.00     Bone Clones
skeleton

Chimpanzee:                  $1700.00     Bone Clones
disarticulated skeleton

Human: mounted skeleton       $359.00     Anatomical Chart Company

Human: disarticulated         $163.95     Anatomical Chart Company
skeleton

Table 3. Functional hypotheses regarding the chimpanzee, the human,
and "Lucy," and their anatomical predictions.

Hypothesis                          Predictions

The creature habitually walks       1. Thoracic and lumbar centra
quadrupedally, with its back        are of similar size.
horizontal.
                                    2. The head-to-tail length of
                                    the ilium is much greater than
                                    its transverse (side-to-side)
                                    width.

The creature habitually walks       1. Lumbar centra are larger
bipedally, with its back            (especially in cranial and
vertical.                           caudal views, the views from the
                                    head and from the tail
                                    respectively) than thoracic
                                    centra.

                                    2. The head-to-tail length of
                                    the ilium is similar to its
                                    transverse width.

The ability of the creature's       1. The metacarpals, metatarsals,
fingers and toes to grasp           and phalanges are curved
branches is enhanced.               (concave toward the palm/sole).

The ability of the creature's       1. The metacarpals, metatarsals,
fingers and toes to grasp           and phalanges are straight.
branches is reduced.

The creature's capacity for         1. The radius and ulna are
brachiation (locomotion by          strongly curved.
using the hands to grasp
branches while the body hangs       2. The length of the humerus +
beneath, like a human child on      forearm (radius and ulna) is
playground "monkeybars") is         greater than that of the femur +
enhanced.                           tibia.

The creature's capacity for         1. The radius and ulna are
brachiation is reduced.             straight.

                                    2. The length of the humerus +
                                    forearm is similar to or less
                                    than that of the femur + tibia.
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