Biology Reference
In-Depth Information
cranial breadth is 136 millimeters or the mean value of maximum length of the radius from
Colombian males is 232 millimeters. Any studies that measure something numerically use
metric variables: studies of stature and of craniometrics are examples (see Moore and Ross
[Chapter 6]; and McKeown and Schmidt [Chapter 12], this volume).
For all the examples listed above, the observation is clear and easy to make. However,
what do we do when we cannot directly see or measure something? One principle we rely
on is the
principle of uniformitarianism
, which states that the natural mechanisms by which
processes occurred in the past are the same mechanisms by which processes occur today (i.e.,
wind erosion, mutation rates of genes, natural selection, and so on). Using this principle we
are able to come to conclusions about things we cannot see or measure directly today. While
initially posited by
Hutton (1788)
and
Lyell (1830)
for geological processes, scientists have
adapted the concept for application to other sciences, such as biology. For example, how
do we know that four and a half million years ago, the geographic locality of Aramis in
East Africa consisted of a woodland environment as opposed to the arid environment it is
today? How do we know how fractures on a bone were caused? How do we know that
a particular prehistoric culture had a specific religious reason for burying bodies with heads
facing a certain direction? Did anyone at the time make observations that they wrote down
for us today? Obviously not
d
but that still begs the question of how we know the answers to
any of these questions or ones similar. The answer lies in inference. An
inference
is an inter-
pretation of an observation. For example, one can infer that bones feel lighter than usual
because some of the mineral that gives them weight has been resorbed due to a disease
the individual developed during life.
3
Based on observations of things we can directly see and measure today, we are able to infer
certain things about the natural world. Aramis contains an abundance of fossils of mammals
that inhabit woodland areas. Based on this and other geological evidence, we can infer it was
not always the arid environment it is now (
White et al., 2009
). We can look at fractures and
infer the biomechanics behind how they were caused based on results from experiments
designed to look at fracture mechanics (see Kroman and Symes [Chapter 8], this volume).
Prehistoric archaeologists and bioarchaeologists can infer information about a culture's reli-
gious beliefs from comparative knowledge of other extant and extinct cultures, and from
a variety of other lines of evidence, including artifacts.
Inference is something we use frequently in skeletal biology. Often we make inferences
based on results from other studies and then test them, such as inferring that if one bone
contains age-related information, then other bones must as well. Another important
example that has resulted in some groundbreaking new research for forensic anthro-
pology involves inferences that change in stature or cranial dimensions over several
decades (known as
secular change
4
) would affect our use of standards created from
skeletal collections of individuals who died 50 or more years ago (
Langley-Shirley and
Jantz, 2010
).
3
The mineral is hydroxyapatite and the disease would be
osteoporosis
.
4
Due to an improvement or deterioration over time in factors such as nutrition, access to medical care,
infectious disease, etc. See discussion in Moore and Ross (Chapter 6) and McKeown and Schmidt (Chapter
12), this volume.
