Human Evolutionary Biology

Faculty of the Department of Human Evolutionary Biology

Daniel E. Lieberman, Professor of Anthropology (Chair)
Coren Lee Apicella, College Fellow in the Department of Anthropology
John C. Barry, Lecturer on Human Evolutionary Biology
Judith F. Chapman, Lecturer on Human Evolutionary Biology (fall term only)
Nancy Lou Conklin-Brittain, Lecturer on Human Evolutionary Biology (fall term only)
Peter T. Ellison, John Cowles Professor of Anthropology (on leave 2009-10)
Ian Christopher Gilby, Lecturer on Human Evolutionary Biology (fall term only)
Russell Dean Greaves, Lecturer on Human Evolutionary Biology (fall term only)
Carole K. Hooven, Lecturer on Anthropology, Lecturer on Human Evolutionary Biology (spring term only)
Karen L. Kramer, Associate Professor of Anthropology (on leave spring term)
Susan F. Lipson, Lecturer on Human Evolutionary Biology
Amanda S. Lobell, College Fellow in Human Evolutionary Biology
Luke J. Matthews, Lecturer on Human Evolutionary Biology (fall term only)
Charles Lindsay Nunn, Associate Professor of Human Evolutionary Biology
David Pilbeam, Henry Ford II Professor of Human Evolution (Head Tutor)
Maryellen Ruvolo, Professor of Anthropology (on leave fall term)
Tanya M. Smith, Assistant Professor of Human Evolutionary Biology
Noreen Tuross, Landon T. Clay Professor of Scientific Archaeology (on leave spring term)
Richard W. Wrangham, Harvard College Professor, Ruth Moore Professor of Biological Anthropology (Director of Graduate Studies)

Human Evolutionary Biology provides a general foundation in human and organismic biology as part of the Life Sciences cluster of concentrations. It addresses why humans and primates are the way they are from an evolutionary perspective. Understanding the biological bases for the behavioral and physical traits that distinguish humans from other primates is one of the great challenges of modern biology, and is the focus of Human Evolutionary Biology. Students interested in addressing questions about human and non-human primate cognition from the perspective of human evolutionary biology also may pursue a special program of study affiliated with the University-wide Mind, Brain, and Behavior Initiative. For concentration requirements, see the Department of Human Evolutionary Biology website.

Primarily for Undergraduates

*Human Evolutionary Biology 91r. Supervised Reading and Research
Catalog Number: 3631
David Pilbeam
Half course (fall term; repeated spring term). Hours to be arranged.
Special study of selected topics in human evolutionary biology, given on an individual basis and directly supervised by a member of the Human Evolutionary Biology Faculty. May be taken for a letter grade or Pass/Fail. Signature of faculty supervisor required.

*Human Evolutionary Biology 97y. Sophomore Tutorial in Human Evolutionary Biology
Catalog Number: 2205
David Pilbeam
Half course (spring term). Hours to be arranged.
An introduction to the issues and methods of biological anthropology, including evolutionary theory and its application to humans. Focuses on the comparison of primate and human biology, life history and social behavior as ecological adaptations and their application to understanding human evolution. Weekly readings, discussions, and short writing assignments, with a final research paper and presentation.
Note: Required of and limited to Human Evolutionary Biology and Biological Anthropology concentrators.

*Human Evolutionary Biology 99. Tutorial—Senior Year
Catalog Number: 2840
David Pilbeam
Full course (indivisible). Hours to be arranged.
Research and writing of the Senior Thesis. Limited to honors candidates. Signature of the faculty adviser required.

Cross-listed Courses

*Freshman Seminar 21e. What Can The Fossil Record Tell Us About The Likely Biological Effects Of Climate Change?
*Freshman Seminar 44q. Evolution and Human Behavior
*Freshman Seminar 44s. Neanderthals and Human Evolutionary Theory
*Freshman Seminar 46o. The Evolutionary Significance of Cooking

For Undergraduates and Graduates

Human Evolutionary Biology 1310 (formerly Anthropology 1310). Hormones and Behavior
Catalog Number: 2265
Carole K. Hooven
Half course (spring term). M., W., F., at 11. EXAM GROUP: 4
An introduction to the interaction between hormones and behavior, emphasizing research in humans. General principles of endocrine physiology are presented. The course then focuses on how hormones affect the brain and body in early development and later in adulthood, and the relationship of hormones to sex and gender. We will explore human reproduction, energy metabolism, mating and sexuality, parental behavior, learning and memory, stress, and dominance interactions.
Note: This course is a prerequisite for Human Evolutionary Biology 1418.
Prerequisite: Life Sciences 2 or strong biology background recommended.

Human Evolutionary Biology 1312. Human Sexuality: Research and Presentation Seminar
Catalog Number: 5008 Enrollment: Limited to 15.
Judith F. Chapman
Half course (spring term). F., 1–3. EXAM GROUP: 6, 7
An examination of human sexuality from a scientific perspective. Students will read and present primary scientific literature that highlights current research on a variety of topics including: sexual development, gender identity, sexual orientation, cross cultural variations in mating systems, promiscuity, the evolution of monogamy, sexual attraction, sexual communication, including an exploration of the existence of human pheromones, libido and sexual dysfunction.

Human Evolutionary Biology 1315. Ecology of Modern Hunter Gatherers
Catalog Number: 2051
Karen L. Kramer
Half course (fall term). Tu., Th., 1–2:30. EXAM GROUP: 15, 16
This course focuses on the variable ways that hunter-gatherers interface with their environment and make their living, and the implications of this subsistence strategy for their biology and behavior. During the first part of the course, key theoretical issues and debates that surround the study of modern hunter/gatherers will be discussed. Once this foundation is laid, the course will survey modern and historic hunter/gatherers from all the major geographic regions of the world.

Human Evolutionary Biology 1325. Evolution of Technology
Catalog Number: 2357
Russell Dean Greaves
Half course (fall term). M., W., 1–2:30. EXAM GROUP: 6, 7
An important aspect of what makes us human is our unique reliance on diverse technologies. This class develops inferences about the evolution of technology from modern human traditional cultures, the archaeological record, hominin functional morphology, and comparisons with tool use in other primates. Readings, lectures, and discussions emphasize how technology is used for subsistence, shelter, physical protection, and other behaviors that helped ancestral hominins and contemporary humans occupy a range of variable environments.

Human Evolutionary Biology 1330 (formerly Anthropology 1330). Primate Social Behavior
Catalog Number: 4332
Ian Christopher Gilby and Richard W. Wrangham
Half course (fall term). M., W., F., at 10. EXAM GROUP: 3
A review of the behavioral interactions in natural primate populations, drawing on experimental, observational, and theoretical studies. Discussion of ecological, physiological, and developmental bases of primate social behavior, with special attention to the evolution of patterns of behavioral interactions among individuals of different age, sex, relatedness, and status. Topics include sexual conflict, sexual selection, and mating systems; care of offspring and other aid-giving; manipulative and cooperative aspects of communication; competition, dominance, and territoriality; and the evolution of social relationships.
Prerequisite: Introductory biology or Science B-29 or with permission of instructor.

[Human Evolutionary Biology 1331. Comparison and Adaptation in Primate Evolutionary Biology]
Catalog Number: 8252 Enrollment: Limited to 15.
Charles Lindsay Nunn
Half course (spring term). Tu., Th., 1–2:30. EXAM GROUP: 15, 16
Understanding human evolution requires us to reconstruct the past and identify the adaptive basis of primate traits. How can this be achieved for behavior, language, culture and other traits that lack a clear fossil record? This course will take a hands-on approach to teach new methods for reconstructing evolutionary history. Through readings, computer labs and an independent project, students will investigate cognitive evolution in hominids, primate sociality, and ecological adaptations in humans and nonhuman primates.
Note: Expected to be given in 2011–12.

[Human Evolutionary Biology 1333. Primate Disease Ecology]
Catalog Number: 8036 Enrollment: Limited to 15.
Charles Lindsay Nunn
Half course (fall term). Tu., Th., 10–11:30. EXAM GROUP: 12, 13
Infectious disease plays a major role in the lives of humans, and the same is true of nonhuman primates. This course will explore infectious diseases in humans and nonhuman primates. We will consider similarities and differences in disease ecology in humans and nonhuman primates, and we will investigate the role of infectious disease in primate - including human - evolution.
Note: Expected to be given in 2010–11.

[Human Evolutionary Biology 1351. Reproductive Ecology]
Catalog Number: 3408
Peter T. Ellison
Half course (fall term). M., W., (F.), at 12, and a weekly section to be arranged. EXAM GROUP: 5
A course on the physiological ecology and evolutionary biology of human and primate reproduction. Topics covered include gamete production, gestation, birth, lactation, reproductive maturation, mature reproductive function, aging and senescence.
Note: Expected to be given in 2010–11.
Prerequisite: Life Sciences 2 or Human Evolutionary Biology 1310 strongly suggested.

[Human Evolutionary Biology 1355. Darwin Seminar: Evolution and Emotion]
Catalog Number: 8314 Enrollment: Limited to 20.
Peter T. Ellison
Half course (spring term). M., 1–3. EXAM GROUP: 6, 7
A course on the intellectual history of evolution with rotating topics. This year the focus will be on evolution and emotion, starting with Darwin’s Expression of Emotion in Man and Other Animals and including current research on the philosophy, physiology, neurobiology, and evolutionary significance of emotion.
Note: Expected to be given in 2011–12.

[Human Evolutionary Biology 1371. Paternity, Fidelity and Parenting]
Catalog Number: 0712
Karen L. Kramer
Half course (fall term). Tu., Th., 1–2:30. EXAM GROUP: 15, 16
This course introduces human life history through the topic of male/female relationships, parenting, and family formation. Key issues covered include life history tradeoffs, reproductive strategies, division of labor, pair-bonding and cooperative breeding. Emphasis is placed on examining life history characteristics shared across primates, those particular to humans, and their variation cross-culturally. The course is designed for students studying anthropology, evolutionary biology, evolutionary psychology and other disciplines interested in the relationship between human biology and behavior.
Note: Expected to be given in 2010–11. Junior research seminar. Taught every other year, alternating with Human Evolutionary Biology 1315.

[*Human Evolutionary Biology 1375 (formerly *Anthropology 1375). Testosterone and Human Behavior]
Catalog Number: 6933 Enrollment: Limited to 15.
Judith F. Chapman
Half course (spring term). Th., 3–5. EXAM GROUP: 17, 18
An exploration of current research in human behavior and testosterone, including the relationships between normal variation in testosterone and variation in traits such as cognition, aggression, personality traits, and sexual behavior within both males and females. Medical uses of testosterone, such as anabolic steroids, hormone replacement therapy, and reassignment, are explored.
Note: Expected to be given in 2010–11. Preference given to Human Evolutionary Biology and Biological Anthropology concentrators.

Human Evolutionary Biology 1380 (formerly Anthropology 1380). The Behavioral Biology of Women
Catalog Number: 8721 Enrollment: Limited to 20.
Coren Lee Apicella
Half course (fall term). Tu., Th., 10–11:30. EXAM GROUP: 12, 13
A lecture/seminar course that explores female behavior focusing on evolutionary, physiological, and biosocial aspects of women’s lives from puberty, through reproductive processes such as pregnancy, birth, lactation, to menopause and aging. Also explores female life history strategies in different cultural settings. Topics include cognitive and behavioral differences between men and women and male and female reproductive strategies. Examples are drawn from traditional and modern human societies and data from nonhuman primates are considered.

Human Evolutionary Biology 1383. Why Be Nice? The Biological Basis of Cooperation - (New Course)
Catalog Number: 45731
Ian Christopher Gilby
Half course (fall term). Tu., 1–4. EXAM GROUP: 15, 16, 17
The theory of evolution by natural selection hinges upon the fact that individuals are in constant competition over food, mates and other valuable resources. Yet, many animals frequently behave in ways that benefit others, often at an apparent cost to themselves. Such behavior seems puzzling. Through lecture, discussion and literature-based research, we will investigate the evolution of cooperation in animals as a basis for understanding cooperation in human societies.
Prerequisite: Introductory biology or Science B-29 or Human Evolutionary Biology 1330 or with permission of instructor.

Human Evolutionary Biology 1405. The Biology of Aging - (New Course)
Catalog Number: 30624
Noreen Tuross
Half course (fall term). Th., 2:30–4:30. EXAM GROUP: 16, 17, 18
The seminar will focus on human aging by examining experimental models of aging, mechanisms involved in aging, the role of diet and infection in the aging process and the evolution of the human life span.

Human Evolutionary Biology 1414. Evolution of Human Diet: Research Seminar
Catalog Number: 9881
Nancy Lou Conklin-Brittain
Half course (fall term). W., 1–3. EXAM GROUP: 6, 7
An exploration of modern controversies in human nutrition from an evolutionary perspective, using primate and human dietary adaptations, digestive physiologies, feeding behavior and ecology. We will explore topics including: nutritional requirements, optimal foraging, maternal and infant nutrition, the nature of early hominid diets, the role of hunting and carnivory in human evolution, and finally, the nutritional impact of agriculture and technology on dietary composition and modern human diets.

*Human Evolutionary Biology 1418 (formerly *Anthropology 1418). Endocrinology and Behavior: Research Seminar
Catalog Number: 1437 Enrollment: Limited to 8.
Susan F. Lipson
Half course (fall term). M., W., at 11, and a weekly laboratory either M. or W., 2-5. EXAM GROUP: 4
An introduction to laboratory techniques and research design in behavioral endocrinology. Students conduct pilot research projects.
Note: Preference given to Human Evolutionary Biology and Biological Anthropology concentrators and graduate students.
Prerequisite: Human Evolutionary Biology 1310 or with permission of instructor.

Human Evolutionary Biology 1420 (formerly Anthropology 1420). Human Evolutionary Anatomy
Catalog Number: 6233
Tanya M. Smith
Half course (spring term). M., W., F., at 10. EXAM GROUP: 3
How did the human body evolve, and how does it develop, grow and function? An integrative overview of human anatomy and evolution, with a focus on the musculo-skeletal system, including aspects of developmental biology, functional morphology, physiology, and the fossil record. Topics include: muscle and skeletal development, anatomy, and histology; the biomechanics of muscles and bones; craniofacial growth and development; the functional morphology of chewing, respiration, vocalization, locomotion, and other activities.
Prerequisite: Life Sciences 2 or with permission of instructor.

Human Evolutionary Biology 1421. Teeth
Catalog Number: 8758 Enrollment: Limited to 6.
Tanya M. Smith
Half course (fall term). W., 3–5:30. EXAM GROUP: 8, 9
Teeth are one of the best preserved and most commonly-recovered elements in fossil assemblages. This seminar will focus on ways in which dental remains may inform studies of fossil primate growth and development, ecology, and social structure. Students will read and discuss current scientific literature, and will conduct pilot research projects.
Note: Preference given to Human Evolutionary Biology and Biological Anthropology concentrators and graduate students.

*Human Evolutionary Biology 1450. Human Evolutionary Genetics
Catalog Number: 1769 Enrollment: Limited to 15.
Amanda S. Lobell
Half course (fall term). M., 2–5. EXAM GROUP: 7, 8, 9
This course investigates the human genome in an evolutionary context. Topics to be covered include human and primate comparative genetics, the genetic evidence for modern human origins, human genetic diversity and its functional implications (including disease), and natural selection on the human genome.
Prerequisite: Life Sciences 1b

Human Evolutionary Biology 1455. Primate Genetics - (New Course)
Catalog Number: 97253
Luke J. Matthews and Amanda S. Lobell
Half course (fall term). Tu., Th., 10–11:30. EXAM GROUP: 12, 13
The last few years have witnessed a revolution in the study of primate biology thanks to newly available genetic data. This seminar integrates genetics with behavior and ecology to consider key topics in primate evolution. Major questions posed by this class include how DNA-based evolutionary relationships provide information about primate anatomy, physiology and behavior; the role of dispersal, paternity, and kinship in structuring primate societies; and how gene by environment interactions influence primate behavior.
Prerequisite: Life Sciences 1b.

[*Human Evolutionary Biology 1463 (formerly *Anthropology 1463). Molecular Evolution of the Primates]
Catalog Number: 3359
Maryellen Ruvolo
Half course (fall term). W., 1–4. EXAM GROUP: 6, 7, 8
Introduction to the primates, emphasizing their molecular evolutionary history and the forces that mold their genomes. Topics include the neutral theory of molecular evolution, molecular clock concept and its applications, evolution of multigene families, relationships between primate morphological and molecular evolution, molecular convergences, evidence for horizontal gene transfer in primate genomes, and evolution of simian and human immunodeficiency viruses, color vision genes.
Note: Expected to be given in 2010–11.
Prerequisite: Life Sciences 1b.

Human Evolutionary Biology 1490. Primate Evolution
Catalog Number: 7376
David Pilbeam and John C. Barry
Half course (spring term). Tu., Th., 1:30–3:30. EXAM GROUP: 15, 16, 17
A lecture/discussion course on primate evolution from a paleontological perspective. Following a survey of major primate groups as adaptive radiations, the hominoid fossil record will be reviewed within the context of the mammalian record, a particular focus being the relationship between adaptive, faunal, and climate change. Systems that can be inferred from the fossil record (for example, positional and foraging behaviors) wil be discussed comparatively. Section meetings will focus primarily on the fossil record.
Note: No final exam; research paper required. Can be taken by Human Evolutionary Biology concentrators as a Junior Research Seminar. Introductory courses in paleoanthropology, evolution, genetics, or anatomy helpful.

[Human Evolutionary Biology 1565. Theories of Sexual Coercion]
Catalog Number: 1953 Enrollment: Limited to 20.
Richard W. Wrangham and Diane L. Rosenfeld (Harvard Law School)
Half course (spring term). Hours to be arranged.
Where does interpersonal violence come from? Is it learned? Is it innate? Is it malleable? What are we to make of the gendered difference in the use of violence? What does the study of sexual violence in primates offer to our understanding of its prevalence among humans? In this course, we will examine evolutionary perspectives on male sexual coercion in primates and in humans to search for insights into sexual violence among humans. The review of this body of literature offers different analytical methods for questioning the use of sexual violence in our society, helping us identify new ways of preventing its occurrence.
Note: Expected to be given in 2011–12. Offered jointly with Harvard Law School as LAW-99015A.

[*Human Evolutionary Biology 1580 (formerly *Anthropology 1580). Paleoecology and Human Evolution]
Catalog Number: 3509
John C. Barry
Half course (spring term). Tu., 1:30–3:30. EXAM GROUP: 15, 16, 17
A lecture-seminar course on the principles of paleoecology, including methods used to reconstruct past climate and ecosystems. There will be an emphasis on the ancient environments and paleoecology of early hominids. May be taken as a Research Seminar in Biological Anthropology or Human Evolutionary Biology.
Note: Expected to be given in 2010–11.
Prerequisite: With permission of instructor.

Cross-listed Courses

Life Sciences 1b. An Integrated Introduction to the Life Sciences: Genetics, Genomics, and Evolution
Life Sciences 2. Evolutionary Human Physiology and Anatomy
OEB 10. Foundations of Biological Diversity
OEB 53 (formerly Biological Sciences 53). Evolutionary Biology
*OEB 121a. Research in Comparative Biomechanics
[*Psychology 1151. Cognitive Evolution: Theory and Practice]
*Psychology 1152r. Cognitive Evolution Lab
Science B-29. Evolution of Human Nature
Science of Living Systems 16. Human Evolution and the Human Body

Primarily for Graduates

[Human Evolutionary Biology 2305. Advanced Topics in Human Evolutionary Biology]
Catalog Number: 1009
Daniel E. Lieberman
Half course (spring term). Hours to be arranged.
Reading and discussion of topics in human evolutionary biology and paleoanthropology.
Note: Expected to be given in 2011–12.

Human Evolutionary Biology 2311. Evolutionary Medicine Seminar (Graduate Seminar in General Education) - (New Course)
Catalog Number: 20263
Charles Lindsay Nunn
Half course (fall term). Hours to be arranged.
Evolution is the guiding principle in biology, yet evolution has played only a minor role in medicine and human health. This course will explore the emerging field of evolutionary medicine and its recent applications. The seminar will design and develop a General Education course on these themes for undergraduates.

*Human Evolutionary Biology 2312. Current Topics in Human Evolutionary Genetics
Catalog Number: 1175
Maryellen Ruvolo
Half course (spring term). Hours to be arranged.
Critical reading of current literature on the genetics of living humans and discussion of evolutionary implications.
Note: Open to first and second year graduate students in Human Evolutionary Biology.

*Human Evolutionary Biology 2337r (formerly *Anthropology 237br). Advanced Laboratory Methods in Human Endocrinology
Catalog Number: 5345
Susan F. Lipson 1969
Half course (spring term). Hours to be arranged.
Note: Intended for students engaged in laboratory research on human endocrinology.

*Human Evolutionary Biology 2350a. Laboratory Methods in Primate and Human Nutrition I - (New Course)
Catalog Number: 62293
Nancy Lou Conklin-Brittain 6142 (fall term only)
Half course (fall term). Hours to be arranged.
Independent laboratory study in the biochemical analysis of plant and animal foods, and of human and animal digestive physiology and feeding behavior.

*Human Evolutionary Biology 2350b. Laboratory Methods in Primate and Human Nutrition II - (New Course)
Catalog Number: 99831
Nancy Lou Conklin-Brittain 6142 (fall term only)
Half course (spring term). Hours to be arranged.
Independent laboratory study in the biochemical analysis of plant and animal foods, and of humans and animal digestive physiology and feeding behavior.

[Human Evolutionary Biology 2430 (formerly Anthropology 229). Behavioral Biology Seminar]
Catalog Number: 3777
Karen L. Kramer
Half course (spring term). Hours to be arranged.
Reading and discussion of current research in the behavioral ecology of humans and nonhuman primates. Emphasis placed on comparative and interdisciplinary approaches.
Note: Expected to be given in 2011–12. Required of entering graduate students in Human Evolutionary Biology. Open to other graduate students. Limited to graduate students.

Human Evolutionary Biology 2460. Issues in Human Evolution
Catalog Number: 1073
David Pilbeam
Half course (spring term). Hours to be arranged.
A discussion course for first and second year graduate students in Human Evolutionary Biology. Topics will include origins of hominids, radiation of hominins, origins of the genus Homo, and origins of Homo sapiens.
Note: To be taken while auditing Science B-27.

[*Human Evolutionary Biology 2595ar (formerly *Anthropology 295ar). Laboratory Methods in Evolutionary Genetics]
Catalog Number: 7934
Maryellen Ruvolo 2512 (on leave fall term)
Half course (fall term). Hours to be arranged.
Note: Expected to be given in 2010–11. Limited to graduate students and undergraduates conducting senior thesis research.

*Human Evolutionary Biology 2595br (formerly *Anthropology 295br). Laboratory Methods in Evolutionary Genetics
Catalog Number: 6468
Maryellen Ruvolo 2512 (on leave fall term)
Half course (spring term). Hours to be arranged.
Note: Limited to graduate students and undergraduates conducting senior thesis research.

Cross-listed Course

*Psychology 2381. Hot Topics in Cognitive Science and Neuroscience - (New Course)

Graduate Courses of Reading and Research

*Human Evolutionary Biology 3000. Reading and Research - (New Course)
Catalog Number: 99167
John C. Barry 1892, Peter T. Ellison 7413 (on leave 2009-10), Karen L. Kramer 5769 (on leave spring term), Daniel E. Lieberman 3980, Susan F. Lipson 1969, Amanda S. Lobell 6242, Charles Lindsay Nunn 6146, David Pilbeam 7224, Maryellen Ruvolo 2512 (on leave fall term), Tanya M. Smith 6147, Noreen Tuross 4845 (on leave spring term), and Richard W. Wrangham 2349
Special reading in selected topics under the direction of members of the department.
Note: Consult the appropriate member of the department.

*Human Evolutionary Biology 3001. Reading for General Examination - (New Course)
Catalog Number: 47645
Members of the Department
Individual reading in preparation for the general examination for the doctoral degree.
Note: Restricted to candidates for the doctoral degree and ordinarily to those who have completed at least one year in residence.

*Human Evolutionary Biology 3310 (formerly *Anthropology 3310). Experimental Methods
Catalog Number: 9602
Members of the Department

*Human Evolutionary Biology 3320. Advanced Laboratory and Dissertations - (New Course)
Catalog Number: 62752
Members of the Department

*Human Evolutionary Biology 3400. Advanced Reading and Research - (New Course)
Catalog Number: 77859
Members of the Department
Note: Consult the appropriate member of the department.

*Human Evolutionary Biology 3500. Direction of the Doctoral Dissertations - (New Course)
Catalog Number: 26337
Members of the Department
Note: Concult the appropriate member of the department.

*Human Evolutionary Biology 3600. Current Issues in Human Evolutionary Biology
Catalog Number: 9373
Members of the Department
Half course (fall term; repeated spring term). Fall: Tu., at 12.
Weekly seminars in human evolutionary biology.