Get
more information about my research:
Research
Topics
As
a paleoanthropologist, I am most interested in the evolution of human
morphological variation, and how different mechanisms (such as
taxonomy, sex,
age, and time) explain what is observed in fossil data.
This question provides a crucial link to the core of
anthropology,
“What makes us human?” Biological
anthropology is in a unique position to integrate biology and culture,
and to
bring together sciences and humanities. This
is reflected in my research so far.
A
significant number of questions in paleoanthropology deal with
variation and
species: Is there too much variation for this fossil sample to belong
to a
single species? Does the new fossil
discovery justify a new species? These
questions are fundamentally about the nature and pattern of
morphological
variation in fossil samples. One
could start from the position that variation calls for taxonomy; hence,
a new
species is proposed when fossils show some difference.
However, I subscribe to an opposite position that
variation within
species should be examined before taxonomic explanation is invoked. My research has shown for several fossil
samples that
there is not too
much variation to invoke an explanation of multiple species: the
habilines (Homo
habilis and Homo rudolfensis)
(Lee
and Wolpoff 2005)
; Homo erectus (or, Homo georgicus) fossils from
Dmanisi, Georgia (Lee
2005)
; and Neandertals and modern humans
(Wolpoff and
Lee 2001; Ahern,
Hawks and Lee
2005)
.
Sexual
dimorphism (morphological differences between two sexes) is one of the
major factors of variation, and its evolutionary changes is the one
topic that I have continued since my doctoral thesis
(Lee 1999)
and developed further. Studies of sexual dimorphism in fossil samples
are hampered by a simple fact that sex is almost always unknown for
fragmentary fossil specimens. I developed
a method (named “ARM” for Assigned Resampling Method) that estimates
the degree of sexual dimorphism in samples of unknown sex, and
demonstrated that the method was reliable
(Lee 2001)
. Using
ARM, I examined the pattern of changes in the sexual dimorphism of the
hominid fossil record and concluded that human sexual dimorphism has
not changed for a long period of time. What
this conclusion implied was that the modern human pattern of sexual
dimorphism has a long history, at least as long as 1 million years.
Modern
humans are unique in having a long life-span and a high proportion of
old people
in a population. However, due to the difficulty of estimating an
accurate
age-at-death in skeletal remains, this question has not been examined
empirically. proposed that longevity be
defined broadly, as the proportion of old
adults relative to young adults (named “OY ratio” for Old/Young ratio),
which can then be analyzed on a large data set of human fossil
materials.
Results showed that longevity increased over time with
statistical
significance, but that the greatest increase occurred with the Upper
Paleolithic, 30,000 years ago
(Caspari
and Lee 2004)
. This time period is associated with a
burst of artistic and
symbolic behaviors that have traditionally been characterized as
uniquely modern
human. The results imply a
selective advantage in having older adults in a society, in forms of
information
transmission from generation to generation. Although
this idea is not new, our research was groundbreaking because we
defined “longevity” in ways that allow an empirical exploration of the
subject
.
Evolutionary
studies inherently deal with changes over time. However,
studying morphological changes over time poses a
statistical
problem: the data points along a temporal sequence are not random, but
directional. Although there are
statistical methods that deal with such relationships, they are of
limited use
in the study of fossils because fossils almost never meet the criteria
for valid
statistical analysis. In addition,
those methods may not provide information about non-linear patterns of
change.
For example, we know without question that brain size increased
over time
in human evolution, and that the increase is statistically significant
. The question remains whether it changed
gradually or
suddenly. Our research showed that
there is no evidence that there was a punctuated change in the pattern
of
increase in hominid brain size since 2 million years ago
(Lee and
Wolpoff
2003)
.
Interpretation
of the biological meaning of differences between samples is a classic
dilemma in
paleontology: are differences between earlier and later fossils due to
evolutionary change within a lineage, due to replacement of an earlier
species
by a later one, or can the differences be attributed to sampling
bias? For
example, Vindija and Krapina are Neandertal sites that differ in time. Differences among the fossil specimens from
the two sites are
undeniable. An early sample might
have a higher proportion of females and juveniles than a later sample
from an
evolving lineage. We showed that it
is quite unlikely that the two samples came from the same population
(Ahern, Lee, and Hawks
2002)
.
What can DNA tell us about our
origins?
Toward
the end of my graduate training, I became interested in population
genetics (Hawks,
Hunley, Lee, and Wolpoff 2000).
Upon completing my doctoral program, I joined the
laboratory of N
Takahata at the Graduate University for Advanced Studies (Sokendai) in
Hayama, Japan, as a
post-doctoral fellow. As
a human paleontologist in a molecular evolution
laboratory, I was a
part of an interdisciplinary effort to understand modern human origins. Our examination of DNA
sequence data showed the range of
conditions under which the multiregional model of
modern human origins would be feasible (Takahata,
Satta, and Lee 2001). The likelihood of realizing those
conditions was
quite small, which some people interpreted to mean that multiregional
evolution
is extremely unlikely to have happened. To the contrary, it is
why we
don't see many other species like humans.
Get
more information about my research:
|