Were australopithecines ape--human intermediates or just apes? a test of both hypotheses using the "Lucy" skeleton.
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
Key Words: Human evolution; comparison of human and chimpanzee skeletons; australopithecines.
Human evolution (Study and teaching)
Apes (Study and teaching)
Australopithecines (Study and teaching)
|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|
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.
* 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.
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.
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.
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: firstname.lastname@example.org.
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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