Summary:
Professor
Henry McHenry and Katherine Coffing of the University of California—Davis’ hypothesis
is that the 1.9-million-year-old Homo rudolfensis, discovered on Lake Turkana,
Kenya in 1972, represents a transition between the Genus Australopithecus and
the Genus Homo. As such, their article focuses on the time period between 2.5
and 1.8 million years ago. Among the authors’ stated reasons for focusing on
this particular period of time is the fact that it is during this period that
stone tools first appear, and the latter end of this time period is represented
by Homo habilis, discovered by Louis and Mary Leakey in Olduvai Gorge, Tanzania
in 1955. In keeping with their thesis, however, the authors’ analysis raises
disagreements as to in which genera habilis, like rudolfensis, belongs: Homo or
Australopithecus.
They
begin the article in the introduction with a discussion of Nariokotome Boy, a
1.6-million-year old Homo ergaster also discovered at Lake Turkana in 1984. The
upper limit of the authors’ target time period, 2.5 million years ago, is
represented by Australopithecus aethiopicus, discovered in Southern Ethiopia in
1967, which the paper’s analysis places, along with its fellow “robust”
Australopithecines, or “Paranthropus” in a sister clade of the Genus Homo. 2.5
million years ago is also represented in the fossil record by the first
Australopithecine ever discovered: Australopithecus africanus, first discovered
by Raymond Dart in 1924, which the paper’s analysis places as being more
distantly related to the Genus Homo than the robust Paranthropus. One reason
why the authors focus on Nariokotome Boy is that he most clearly demonstrates
the morphological changes that took place in the transition from Australopithecines
to the Genus Homo. At age eighteen, Nariokotome Boy was 160 centimeters [63
inches] tall. [4] The paper’s analysis puts his height at adulthood at over six
feet tall, and contrasts this against Australopithecines, averaging only 120
centimeters [less than four feet] in height.
The
article also points out the decrease in sexual dimorphism between
Australopithecines and Homo, with male Australopithecines averaging a full
fifty percent larger than females. In the case of the most famous Australopithecine
specimen, the 2.9-million-year-old Australopithecus afarensis, discovered in
Ethiopia by Donald Johansson in 1973, this translated to a dimorphism of a full
fifty centimeters [1.6 feet] between males and females of the species. [2] By
contrast, anatomically modern Homo sapiens have a sexual dimorphism of, at
most, only fifteen percent between males and females of the species, which
translates to a difference of only fourteen centimeters [5.5 inches].
In
spite of Leakey, upon discovering Homo habilis with stone tools, naming his
species the Latin name for “Handy Man”,
the article notes the fact that the earliest evidence of stone tools is with Australopithecus
garhi, discovered in Afar, Ethiopia in 1996, and which predates the
two-million-year-old Homo habilis by more than half a million years. [Page 129]
The paper raises another possible toolmaker in Paranthropus robustus, one
member of the “robust” Australopithecines, which coexisted with Homo habilis
two million years ago. [Page 130]
According
to the authors, one of the most “frustrating” factors in the
difficulty of determining whether Homo rudolfensis belongs in the Genus
Australopithecus or Homo is the fact that, like with Homo ergaster, few or no
full fossil skeletons of Homo rudolfensis exist complete with the bones of the
forelimb, especially the hand and fingers.
This is significant, as the authors explain, because Australopithecus afarensis
had forelimb and finger fossils showing distinct tendencies toward an arboreal
ancestry, in spite of predating the first evidence of stone tool making with
Australopithecus garhi by only half a million years. [Page 129]
Moving
on, the authors point out that the thorax of Australopithecus afarensis is
funnel shaped, resembling that of members the family Pongidae, as contrasted
against the barrel-shaped thorax of humans today. The authors interpret the
funnel shape of the Pongid thorax as an arboreal adaptation in
Australopithecines. [Page 131] The authors attribute the difference in thorax
shape between Australopithecines and Homo, in part at least, to differences in
the size and shape of the hip. In addition to being an adaptation for bipedal
locomotion from arboreal ancestry, they raise the possibility that the
difference in size and shape of hips between Australopithecines and modern
humans is due to adaptations to childbirth as well. They suggest that pelvic
size was less of a factor in childbirth in Australopithecines than in modern
humans due to their relatively smaller cranial sizes. [Page 133]
Statement of Thesis:
In
their abstract, in their introduction and in their conclusion, McHenry and
Coffing state the same facts and ask the same question. The statement of facts:
“Significant
changes occurred in human evolution between 2.5 and 1.8 million years ago.
Stone tools first appeared, brains expanded, bodies enlarged, sexual dimorphism
in body size decreased, limb proportions changed, and cheek teeth reduced in
size and crania began to share more unique features with later Homo” [Page
125] The question: “This paper reviews what can be said, and with what level of certainty,
about these transformations.” [Page 126] The combination of these same
facts and this same question, as the only readily recognizable repeated theme
between the abstract, introduction and summary of the paper, form the closest
thing that can be found to a thesis statement by McHenry and Coffing.
Methodology:
McHenry
and Coffing’s 23-page-long article, published in the peer-reviewed scientific
journal Annual Review of Anthropology
can and should be considered a scientific literature review, considering that the
last 6 pages [pages 140-146] of the article consist very nearly entirely of a
bibliography of cited works. Outside of the body of the text, data is only ever
presented in the form of three graphics. The first of these three, on page 127,
alone is drawn from a half a dozen sources.
Organization of Paper:
In
spite of its 23-page length, McHenry and Coffing go out of their way to
organize their paper in a way that makes it easy to locate particular
information and data. They separate the paper into sections and subsections.
Quality of Discussion and Interpretation:
Due
to having no fewer than half a dozen different theses regarding several
different scientific subject disciplines, in spite of their best efforts,
McHenry and Coffing’s 23-page-long article can be and is quite dense
Even
though the in-text references get dense, all 64 cited works in the
half-dozen-page-long bibliography are either articles from peer-reviewed
scientific journals or books from academics, scholars and scientists. It should
be noted, in all fairness, than nearly a third of those citations, eighteen of
them on page 144 are references to articles from one of the paper’s authors,
Henry McHenry himself. It is, however, gratifying that, in addition to half a
dozen citations on page 142, Doctor Donald Johansson also receives a mention by
McHenry and Coffing in the “Acknowledgments” section on page
140, as does Leakey, who is also cited half a dozen times on page 143.
Primary
External Works Referenced:
1. Berger,
Lee and Churchill, Steven, et al. “Australopithecus
Sediba At 1.977 Ma And Implications For The Origins Of The Genus Homo”.
Science, Volume 33, Issue 6048
(September 9, 2011). Pages 1421-1423.
2. Blumberg,
Bennett and Todd, Neil. “On The
Association Between Homo and Australopithecus”. Current Anthropology, Volume 15, Number 4 (December 1974). Pages
386-388.
3. Bryn,
Brandon. “Australopithecus Sediba May
Have Paved the Way For Homo”. American Association For the Advancement
of Science. September 8, 2011
4. “The
Nariokotome Homo Erectus Skeleton (A.K.A. The Turkana Boy; KNM-WT 15000).”
Nature. 2014
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