Sang-Hee LEE, Ph.D.

Department of Anthropology

University of California at Riverside

Riverside, CA 92521-0418


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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.

Taxonomy: One Species Or Two?

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).

Sex: How Different Are Men and Women, and Since When?

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.  

Age: When and How Did Humans Get Old?

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 . 

Time: When and How Did Our Brains Get So Big?

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).

Sampling Bias: Are the Differences Real or Due to Error?

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:

[ Curriculum Vitae - PDF ] Publications ] Conferences ] Links ]