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Race, Genomics,
and Human Evolution
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by Joelle Presson and Jan Jenner
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ISBN: 978-1-60927-256-2
Contents
Introductionix
About the Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Chapter 1
The Framework of Biology
1
Threads … Four Corners Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Biology Touches Every Aspect of Your Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
1.2Life is Defined by a Set of Features That All Living Things Share . . . . . . . . . . . . . 4
1.3 Levels of Organization Are Characteristic of Life . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Evolution and Natural Selection Have Produced Life’s Diverse Forms . . . . . . . . 12
1.5 Biology Applies the Methods of Science to the Study of Life . . . . . . . . . . . . . . . .14
1.6 Weaving Life’s Tapestry: What Causes Four Corners Disease? . . . . . . . . . . . . . . 23
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Chapter 2
Life Evolves: Darwin and the Science of Evolution31
Threads … Dinosaurs and Birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.1Evolution Is the Central Idea of Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2The Intellectual Climate of the 1800s Set the Stage for
Charles Darwin’s Ideas About Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3Darwin Discovered the Fundamental Principles of Evolution . . . . . . . . . . . . . . . 35
2.4Scientific Studies Document Natural Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.5Scientific Evidence Supports and Expands Darwin’s Conclusions . . . . . . . . . . . . 48
2.6Arguments Against Evolution Are Not Supported by Scientific Evidence . . . . . . 55
iii
2.7 Weaving Life’s Tapestry: Are Birds Dinosaurs? . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Chapter 3
Biological Classification
63
Threads … So Close and Yet So Far . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.1 Classification is Sorting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2Biological Classification Has a Long History . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3Cells Are Classified into Three Phylogenetic Groups . . . . . . . . . . . . . . . . . . . . . . 69
3.4A Phylogenetic Classification of Eukaryotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.5Weaving Life’s Tapestry: So Close and Yet So Far . . . . . . . . . . . . . . . . . . . . . . . 75
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Chapter 4
The Evolution of Homo sapiens81
Threads … Who Were the Little Humans of Flores Island? . . . . . . . . . . . . . . . . 82
4.1An Asteroid Crash Allowed Mammals to Diversify . . . . . . . . . . . . . . . . . . . . . . 82
4.2Geologic and Climate Changes Influenced Primate Diversification . . . . . . . . . . 85
4.3Human Traits Reflect Our Evolution from Earlier Primates . . . . . . . . . . . . . . . . 87
4.4Human-like Species Emerged Gradually Over
the Past Five Million Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.5Evolutionary History Reveals Many Kinds of Humans . . . . . . . . . . . . . . . . . . . . 95
4.6Weaving Life’s Tapestry: Who Were the Little Humans of Flores Island? . . . . . 102
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Chapter 5
Life Emerges from Chemistry: Atoms and Molecules109
Threads … Cryopreservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
iv 5.1New Properties Emerge When Substances Interact . . . . . . . . . . . . . . . . . . . . . . 110
5.2Matter Is Made of Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.3Bonds Hold Atoms Together in More Complex Structures . . . . . . . . . . . . . . . . 117
5.4The Chemicals of Life Interact in Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.5 Weaving Life’s Tapestry: The Science of Cryopreservation . . . . . . . . . . . . . . . . 128
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Chapter 6
Biological Molecules
135
Threads … Mad Cow Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
6.1Life Depends on Complex Biological Molecules . . . . . . . . . . . . . . . . . . . . . . . . 136
6.2Biological Molecules Are Built Around Carbon Atoms . . . . . . . . . . . . . . . . . . . 138
6.3Lipids Are Biological Molecules That Do Not Mix Well with Water . . . . . . . . 141
6.4Carbohydrates Are Made of Carbon, Oxygen, and Hydrogen . . . . . . . . . . . . . . 144
6.5Nucleic Acids Are Strings of Nucleotides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.6Proteins Are Folded Chains of Amino Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
6.7Hemoglobin Is an Example of the Emergent Properties of Proteins . . . . . . . . . 154
6.8 Weaving Life’s Tapestry: What Causes Mad Cow Disease? . . . . . . . . . . . . . . . . 155
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Chapter 7
Life Is Cellular: Cell Structure and Function
163
Threads … Superman and Spinal Cord Injury . . . . . . . . . . . . . . . . . . . . . . . . . 164
7.1Living Things Are Made of Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
7.2The Cell Membrane Protects Internal Processes and
Allows the Cell to Interact with the Environment . . . . . . . . . . . . . . . . . . . . . . . 168
7.3Cells Interact with the Environment via Membrane Proteins . . . . . . . . . . . . . . 174
7.4The Inside of a Cell Is Highly Organized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
v
7.5Weaving Life’s Tapestry: Christopher Reeve and
the Search for Treatments for Spinal Cord Injuries . . . . . . . . . . . . . . . . . . . . . . 187
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Chapter 8
The Master Molecule of Life: DNA—Structure and Function
195
Threads … Tuberculosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
8.1DNA Is the Master Molecule of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
8.2Scientific Sleuthing: The Discovery of the Structure of DNA . . . . . . . . . . . . . . 201
8.3The Structure of DNA Is a Double Helix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
8.4The Structure of DNA Contains Genetic Information . . . . . . . . . . . . . . . . . . . 206
8.5DNA Directs the Synthesis of Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
8.6DNA Helps to Explain the Unity and Diversity of Life . . . . . . . . . . . . . . . . . . 216
8.7 Weaving Life’s Tapestry: Conquering Tuberculosis . . . . . . . . . . . . . . . . . . . . . 218
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Chapter 9
Life Renews Itself: Reproduction of Cells
225
Threads … Progerias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
9.1Life Continues Because Organisms Reproduce . . . . . . . . . . . . . . . . . . . . . . . . . 226
9.2Eukaryotic Chromosomes Have Characteristics
That Allow Sexual Reproduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
9.3Cell Division Is the Cellular Basis for Reproduction . . . . . . . . . . . . . . . . . . . . . 231
9.4The Cell Cycle Is the Orderly Progression of
Cellular Activities of Eukaryotic Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
9.5Sexual Reproduction Involves the Fusion of Haploid Gametes . . . . . . . . . . . . . 241
9.6Meiotic Cell Division Produces Gametes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
9.7Weaving Life’s Tapestry: Are Cell Proliferation and Aging Related? . . . . . . . . . 250
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
vi What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Chapter 10
Constructing Life: The Control of Eukaryotic Gene Expression257
Threads … The Death of Times Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
10.1The Development of Multicellular Organisms
Involves Cell Division and Cell Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . 258
10.2During Development Cells with the Same DNA Gradually
Come to Express Different Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
10.3The Structure of Eukaryotic DNA Allows Control of Gene Expression . . . . . . . 262
10.4Transcription Is Controlled by Transcription Factors . . . . . . . . . . . . . . . . . . . . 266
10.5Gene Expression Controls Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
10.6Normal Development Is the Result of the Progressive
Differentiation of Embryonic Stem Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
10.7Weaving Life’s Tapestry: Times Beach and the Effects of Dioxin . . . . . . . . . . . 274
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Chapter 11
Rules of Inheritance: Classical Genetics281
Threads … Eugenics and Fitter Families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
11.1The Science of Genetics Brings Together DNA,
Cell Division, and Gene Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
11.2Gregor Mendel Was the First Systematic
Researcher in the Field of Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
11.3Mendel Discovered Three Rules of Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . 287
11.4More Complex Patterns of Inheritance Are an
Extension of Mendel’s Basic Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
11.5Knowledge About DNA Illuminates Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . 301
11.6Weaving Life’s Tapestry: The Genetics of Eugenics . . . . . . . . . . . . . . . . . . . . . . 305
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
What Do You Think . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
vii
Chapter 12
Human Maternal DNA Lineages: Mom’s Story313
Threads … Lilly’s Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
12.1Human Maternal Lineages: A Starting Point for
Understanding Modern Human Ancestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
12.2DNA Mutations Reveal Lineages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
12.3DNA Mutations Track Lineages of Living Populations . . . . . . . . . . . . . . . . . . . 317
12.4Mitochondrial DNA Reveals Maternal Lineages . . . . . . . . . . . . . . . . . . . . . . . . 320
12.5mtDNA Haplogroups Reveal Human Maternal Lineages . . . . . . . . . . . . . . . . . 322
12.6Weaving Life’s Tapestry: Who Were Tanisha’s African
Maternal Ancestors? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Chapter 13
Human Paternal DNA Lineages: Dad’s Story331
Threads … The Legacy of the Mongol King . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
13.1Paternal Lineages Can Be Constructed Using the Y Chromosome . . . . . . . . . . 332
13.2Distribution of Y Chromosome Haplogroups Reveals
the Migrations of Human Paternal Ancestors . . . . . . . . . . . . . . . . . . . . . . . . . . 335
13.3Do Maternal and Paternal Ancestors Share the Same History? . . . . . . . . . . . . . 337
13.4DNA Can Answer Questions About
Mating Patterns in the Americas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
13.5Weaving life’s Tapestry: The Legacy of the Mongol Khan . . . . . . . . . . . . . . . . . 342
Now You Can Understand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
What Do You Think? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
Chapter Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
Appendix A: Periodic Table of Elements347
Appendix B: Answers to Quick Check and Review Questions349
viii Introduction
Dear Students,
T
he book in your hands is a work in progress. It is our first effort to bring you a new kind of
biology text—one that is expressly tailored for the fall 2011 University of Maryland course, Race,
Genomics, and Human Evolutionary History. Writing such a text is an ambitious undertaking. It
usually takes a decade to produce a college biology textbook, but we have been given a boost by
our previous text, Biology: Dimensions of Life, and by the nimble work of the publishing team
at University Readers. At the time of this writing, the text is not complete. Some topics covered
in the course will not be covered in this text. And, because genomics and paleoanthropology are
such rapidly developing fields, we plan to update and expand this work each semester that the
course is offered, adding chapters, illustrations, and new features as time permits.
Before you begin your exploration of these topics, we would like you to understand the
perspective of this text and of the course. First, consider your own ideas about the concept of race.
When you hear the word, you probably think of groups such as Asians, Hispanics, blacks, and
whites. Or you might think of African Americans, European Americans, Hispanic Americans,
and Asian Americans. Take some time to think about what these terms mean. How are they
defined? Are they useful categories for describing human diversity?
Race is not a new idea, and the idea of race is deeply ingrained. Most humans identify with
their own population and see other populations as “different,” even when those populations
live nearby and share a common history. “Us” versus “them” is a commonly expressed view. Yet
popular thinking about race—and even the conventional societal definitions of race—tend to
be somewhat muddled. Many people believe races are valid distinctions that separate human
populations into discrete groups. Others think human races are akin to various breeds of dogs,
cats, or other animals—different but not really as distinct as separate species are. To mix up
thinking even more, many people see cultural heritage as an important part of the definition of
race. Recent biological research offers a different view of human diversity than what is reflected
in conventional concepts of human races.
You may be wondering how this new “biological view” is different from previous and scientifically unproven definitions of race put forth by biologists. Here is the difference: In the past, some
scientists and the general public have tried to extrapolate the results of limited scientific studies
and apply them to the idea of race. Many of these ideas have not been supported by scientific
research. Today there is a body of scientific research that is directly focused on human genomic
diversity. These studies do not stretch previous research into an uncharted domain. The conclusions—although limited—are founded in and supported by research evidence. Modern studies of
genomics show that all humans are closely genetically related and that our human family can be
organized into various branches of a family tree. You will explore the evidence for this approach
ix
to understanding human biological diversity in this text. Our goal is for you to develop a deep
comprehension of this modern approach to human diversity and to understand how it differs from
the conventional categories of race.
To understand this modern biological view of human diversity, you must first master an
understanding of some basic chemical and biological processes. For instance, without a basic
understanding of biological chemistry, cell biology, protein structure and function, DNA
structure and function, genetics, and evolution, you will find it difficult to understand human
lineages, the biological basis for certain traits, and topics such as the appropriateness of race-based
medicine. In this book you first will gather the biological knowledge that is fundamental to an
understanding of biological diversity and its relationship to ideas of race. Then you will explore
the information that biology has to offer about race. In the end, we trust that your view of the
issue of race will have been informed and transformed.
Despite their ubiquitous use, racial labels are loaded with controversy. This controversy comes
in part from the underlying assumption that there are deep biological differences between races.
In other words, even though culture, history, and language play large roles in how races are
defined, many people assume that races differ on biological traits and that these differences cannot readily be changed by any environmental influence. Furthermore, when people adopt this
assumed justification for racial categories, they often conclude that the traits of some races are
better than the traits of other races. As you know, this is one of the insidious foundations for
racism in the thoughts and beliefs of many people. In this course you will address some of these
issues from the perspective of the results of scientific research.
You probably expect that the science of biology, the underlying foundation of this text, would
have answered the question of the biology of race long ago. You might have heard there is
“evidence” supporting the idea that races differ along certain biological traits. Indeed, many welltrained biologists have argued in the past that races are biologically different and that some races
are better than others with respect to certain traits. The premise of this text is that these conclusions were at best premature and at worst an inappropriate application of the known science.
This text will make every effort to stick to what is well supported by a body of scientific evidence.
To the extent possible, we will present that evidence and let you reach your own conclusions, but
it is inevitable that our own conclusions will be expressed. As you will see, we conclude that thus
far those studies do not support the idea of races as they are conventionally defined. And we do
not see any evidence for deep biological differences between the conventionally defined racial
groups or between different branches of the human tree.
One of the most important conclusions from the modern study of human biological diversity
is that all humans are genetically very closely related, as well as genetically very similar. Within
this close relationship, different branches of the human family tree can be sorted out. This is no
different from the understanding that you are genetically similar to your entire extended family,
but you are more closely related to your siblings than to your cousins. These conclusions come
from the modern field of genomics. Genomics is similar to, but not quite the same as genetics.
Genetics is the study of how traits are inherited and how DNA sequences control or contribute
to those traits. You may be expecting that a text and course on race and genomics will spend a
lot of time on genetics—on the genes that control or contribute to traits and how these genes
differ between races. This is not what you will find. One reason is that there is limited evidence to
support racial genetic differences, in part because modern definitions of race have little biological
meaning. More importantly, modern science has focused on genomics because the technology
and concepts available today lend themselves more to genomic than genetic studies. Genomics
is the study of DNA sequences without any necessary focus on what those genes do. Genomic
research reveals the broad patterns of DNA sequences and how they vary or are the same across
x Race, Genomics, and Human Evolution
individuals, groups, and species. This kind of research may seem odd, but as you will see, a great
deal can be learned about how individuals and groups are genetically related without knowing
anything about how those DNA sequences contribute to the traits of those individuals or groups.
This course and text will focus more on genomics and only somewhat on genetics.
Our goal in this text is not to give you definitive answers. Our expectation is that you will
study this material, supplement it with your own study of the original research literature, and
come to your own understanding of human biological diversity. We look forward to your feedback on our book and our course.
Sincerely,
Jan Jenner & Joelle Presson
About the cover
People may seem to be different from each other. They may seem to look different, act differently, and think differently. You may group these physical differences as typical of various human
races; yet, from a biological perspective, people are much more similar than they are different.
Biologists understand human biological similarities and differences by looking at the human
family tree. The cover figure shows the human family tree, starting with our hominid ancestors
who lived over four million years ago. The tree extends from this common ancestor to the related
human groups who live in various regions of the world today. The figure emphasizes that all living
humans share a common ancestor and so are closely related. Notice the DNA molecule in the
background. It underscores the genetic basis of this common ancestry and relationship. DNA
links humans to our ancestors and to one another. In this text you will explore this evolutionary
history and you will study how modern groups of humans are related. As a result you will better
understand your own biological heritage, and you will understand your relationship to all other
modern humans and to our relatives who lived in the distant past.
In this simplified tree the past starts at the bottom right. Here you see the oldest human-like
species known. This is the famous Ardi—Ardipithecus ramidus, who lived in Africa 4–5 million
years ago. She was short and small-brained, probably lived in forests next to savannas, but was able
to walk upright when she needed. The various Australopithecus species are represented by the next
image up the tree; they lived in Africa about three million years ago. They were short like Ardi,
but had even more upright posture and slightly larger brains. The history of human evolution
has many varieties of extinct species that are not shown in this tree, but one major group is called
Homo erectus, shown next up the tree. Homo erectus was very much like modern humans in size
and habits, but they lived from 2 million to 30,000 years ago. Homo erectus migrated out of Africa
extensively, eventually taking up residence all through the Old World. Homo neanderthalensis, the
next figure upward in the tree, lived fairly recently in Europe and the Middle East, from 100,000
to 25,000 years ago. Although they are distinctly different from modern humans, Neanderthals
are our closest extinct relatives. All modern humans, Homo sapiens, are descendants of an ancestor
who emerged in northern Africa about 200,000 years ago, and spread outward from its African
home about 50,000 years ago. Stemming from this common ancestor, all modern humans belong
to a single family tree.
Introduction xi
The Framework of Biology
1
Mount Vernon Man Dies from Hantavirus
November 9, 2003
Threads …
Four Corners Disease
1.1
Biology Touches Every
Aspect of Your Life
1.2
Life Is Defined by a Set
of Features That All
Living Things Share
1.3
Levels of Organization
Are Characteristic of Life
1.4
Evolution and Natural
Selection Have Produced
Life’s Diverse Forms
1.5
Biology Applies the
Methods of Science to
the Study of Life
1.6Weaving Life’s Tapestry:
What Causes Four
Corners Disease?
Panic and Concern: Four Corners Disease.
In May 1993 a fatal epidemic erupted in the Four Corners area,
triggering an intensive effort to identify the cause of the disease
and find a cure. (© iStockphoto LP)
Local woman dies of Hantavirus
May 10, 2003
1
Threads …
Four Corners Disease
On May 14, 1993, a young Navajo man was brought to
the medical center in Gallup, New Mexico (see chapteropening photo). He was feverish and gasping for air and his
condition rapidly worsened. As a medical team struggled to
save him, his blood pressure dropped, his breathing became
more strangled, and quite suddenly he died.
Because the young man died of unknown causes, an
autopsy was ordered. The pathologist who performed it
noted something odd. Just five days earlier he had seen
another case just like this one: a young woman who had
died from similar, flulike symptoms. Odder still, the pair
turned out to be an engaged couple, and the young man had
been brought to the emergency room while traveling to his
fiancée’s funeral.
Because the young couple’s deaths were mysterious,
swift, and similar, the hospital notified the New Mexico
Department of Health. They warned doctors throughout
the state that a fatal epidemic might be developing in the
Four Corners region—an area where Arizona, Colorado,
New Mexico, and Utah join. Doctors were asked to be alert
for reports of other, similar deaths. Within days what the
media were calling Four Corners disease had claimed more
victims. All were young and otherwise healthy; all had had
flulike symptoms; all the deaths were swift and agonized.
News of Four Corners disease spread panic and concern
among the general population, and authorities at the Centers
for Disease Control and Prevention (CDC) in Atlanta,
Georgia, responded swiftly. Within just one month workers
identified the cause of the disease and tracked it to its source.
By ­mid-­June the outbreak was understood in a larger context,
and people in the region were given practical advice on how
to prevent, detect, and get early treatment for the disease.
This success story is an outstanding example of how science
solved a problem and provided fast answers that saved lives.
If you were a member of a team assigned to solve a new
disease, how would you proceed? What assumptions about
nature and life would guide your work? What rules of logic
would help you to draw conclusions? How would you decide
which of the many possible explanations to believe and act
on? In this chapter you will be introduced to the scientific
approach to solving problems that has been so successful in
revealing life’s secrets.
1.1 B iology Touches Every
Aspect of Your Life
biology the study of life
Science is an intellectual pursuit that has
a profound influence on your life. If you
compare how you live with life in the 1800s,
changes wrought by technology are obvious.
Sanitation, convenience foods, cars, computers, cell phones, and ­
e-­
mail are just a few
examples of everyday applications of scientific discoveries that make your life so different
from your g­reat-­
great-grandparents’. Many
other ­
far-­
reaching applications of scientific
discoveries that affect how you live come from
biology, the study of life. Medical advances
are an example. When you go to the doctor for
antibiotics to treat an infection, you probably
don’t think about the biologists who made
your treatment possible. From scientists of the
1700s who first peered into microscopes and
saw tiny ­life-­forms to p
­ resent-­day researchers
who reveal how those ­
life-­
forms can cause
2 Race, Genomics, and Human Evolution
diseases, the treatment of infectious diseases is
based on biological science.
Discoveries in biology have made headlines
in recent years. These include new antibiotics;
contraceptives; drugs for high cholesterol and
high blood pressure; treatments for clogged
arteries, cancer, diabetes, and AIDS; genetic
tests for a variety of diseases; and techniques
that can ensure that your child does not
inherit a serious genetic disease. All of these
recent medical advances are rooted in biology.
Table 1.1 shows other less ­
well-­
publicized
areas where biology affects modern life. For
example, microbes routinely are used to help
clean up toxic waste sites and oil spills. Insights
from studies of how living things depend on
their environments can help us to predict
what Earth’s future will be like if humans
continue to overpopulate, deplete, and pollute
environments. Other applications of biology
allow scientists to construct machines that can
sense the environment, make decisions, mimic
Table 1.1 Biology in the News.
Headline
From a Few Genes, Life’s Myriad Shapes.
New York Times, June 2007.
Description of story
Researchers in the field of “evo-devo”—evolution and development—have found
that only a handful of genes controls the diversity of body shapes found in animals.
Studies in evo-devo are allowing scientists to understand how genetics, evolution,
and development combine to produce animal diversity and human diversity.
Over-the-Counter DNA Testing: Wave of the
The kits allow genetic testing for risks of a variety of disorders, including cystic
Future or Waste of Money? Walgreens Rolls Out a
fibrosis, Alzheimer’s, and breast cancer. It remains to be seen how effectively people
Genetic ‘Spit Kit’ Test With Pathway Genomics.
can use this kind of genetic information.
ABC News Medical Unit, May 11, 2010.
The Ethics of Genetic Tests for Would-Be Parents.
NPR, January 13, 2011.
New genetic tests allow parents to find out their own risks of passing on a genetic
disorder, and to test their own embryos and choose to birth children who do not
carry a particular genetic mutation. Parents will have to be well informed about
genetic testing and about the genetic disorders in order to make ethical decisions in
this complex arena.
Athletes Beware, Scientists Hot on Gene Doping
Trail. Wired Magazine, February 4, 2010.
Some companies are trying to sell genetic engineering kits to athletes, promising
that athletic performance can be increased by taking a “pill” that will alter their
genes. It is not at all clear whether such “kits” would actually work. Scientists are
already trying to find ways to detect evidence of gene doping.
Children who form no racial stereotypes found.
Nature News, April 2011.
Scientists have long suspected that racial stereotyping is an expression of the fear of
strangers and of those who are “not like us.” New research has found a genetic
mutation that supports this view.
Genetic Ancestral Testing Cannot Deliver On Its
Promise, Study Warns. Science News, October
2007.
Many companies promise the ability to find out a person’s ancestral heritage through
genetic testing. But, these tests come with assumptions, scientific underpinnings,
and caveats, which prospective buyers must understand in order to interpret their
results.
movements of people and other animals, and
even surpass human mental abilities. In these
and many other ways, biological science has
daily impacts on your life.
Biology is a sprawling science. It encompasses a wide range of topics from electrons to
ecosystems. This range is reflected in the work
of people who “do” biology. For instance,
many biologists focus their studies on cells.
Such investigations include the chemicals
that make up cells, how cells use energy, build
complex structures, or reproduce. Studies of
organisms, defined as entire living things,
reveal how cells work together in plants, fungi,
or animals. Other biologists concentrate on
the ways different organisms interact with one
another and with their environments, such as
the interactions within families of elephants,
the effects of pollutants on various species
of algae, how birds migrate to their winter
homes, or how new species evolve. All of these
studies and many more are part of the science
of biology.
Four Major Themes Run Through
Your Study of Biology
Although biology is a large and complex field,
it has several recurrent themes. In the chapters
ahead you will encounter four of these biological themes. One theme is that complex things
happen when simpler things interact. This
idea is known as emergent properties, and you
will discover it repeatedly during your study
of biology. A second theme can be expressed
as unity and diversity. This means that living
things share fundamental structures and functions and are similar in many ways, yet each
individual organism is unique and slightly
different from all others. A related biological
theme is evolution by means of natural selection,
a process that explains the unity and diversity
of life. This principle describes how some traits
remain the same, while others change over
generations. It also explains how these changes
over the course of Earth’s history have led to
the evolution of totally new kinds of organisms. As a final theme, wherever feasible this
organism the entire
body of a living thing
The Framework of Biology 3
Quick Check
1.1
1. What are the four
major biological themes
that you will encounter
in this book?
book will explain the scientific processes that
generate biological knowledge. Watch for
these four themes throughout the chapters
ahead. They will help you to make better sense
of the new information you will learn.
In this introductory chapter you will explore some of the most important findings and
conclusions in biology and consider how scientists use scientific approaches to reach their
conclusions. This chapter is not a summary of
the text. Rather, it provides the framework for
your study of biology and gives you the basic
vocabulary and concepts needed before you
begin your journey into the study of life.
1.2 L ife is Defined by a Set
of Features That All
Living Things Share
cell the smallest
structural unit of life
cell membrane the boundary that
separates a cell from
other cells and from
the environment while
it allows a cell to
communicate with the
environment
Biology is the study of life, but what exactly
is life and how are living things different from
nonliving things? For instance, what is there
about you, the bacteria in yogurt, or a potted
plant that is different from a watch, a yogurt
container, or a flowerpot? Although living things
are remarkably diverse, all have common features that collectively make each of them alive.
Non­
­
living things might have some of these
features, and only a living thing will have all of
them. Here are some of the most obvious ones.
• Life happens only within cells. All organisms are made up of one or more cells;
each cell is limited by a physical boundary.
• Living things are highly complex and
organized.
• Living things strictly control their internal
environments and keep internal conditions within certain limits.
• Living things respond to and interact with
the external environment.
• Living things use energy to power their
internal processes, build internal structures, and grow.
• Living things carry instructions for
conducting their internal processes and
use these instructions to reproduce.
4 Race, Genomics, and Human Evolution
Let’s briefly consider each of these characteristics that collectively differentiate something
that is alive from something that is not alive.
Life Happens Inside Cells That Are
Complex, Highly Organized, and
Homeostatic
One universal aspect of life on Earth is that it
happens inside cells. A cell is the basic structural unit of life. Cells come in many sizes and
shapes, and organisms consist of one or more
cells. Figure 1.1 shows how varied cells can be;
their variety reflects the amazing diversity of life.
How do you know if something is a cell?
One characteristic feature of a cell is the
boundary that separates the life within the cell
from the nonlife outside of the cell. You are
familiar with the boundaries of living things
such as your own skin, the bark of a tree, or
the shell of a crab, but you may be less familiar
with the boundary around each cell, called the
cell membrane (Figure 1.2). It protects the
delicate processes of life from the environment
surrounding the cell and allows a cell to communicate with the environment.
It is the processes that go on inside of a cell
that make it alive. These processes are complex
and highly organized. What does this mean?
Complex means that cells have many different
structures and a multitude of chemical processes; organized means that these structures
and processes are not in disarray. It might
help to think of a room before and after you
straighten it. Of course your room is complex.
Not only does it contain your “stuff”—clothes,
books, and furniture—but also it houses the
complex activities that happen in your room,
what biologists would call your “processes.”
For instance, you might study, listen to music,
watch TV, and pet your cat—all in this same
room. Before you tidy up, things are scattered
everywhere. Once you have straightened the
room, the things in it still are complex, but
they are more organized because you have
shelved the books, put away your clothes, and
gathered up your dirty laundry. This may even
inspire you to focus time just on your cat, then
read awhile, and then listen to music. You
(a)
(b)
One cell
Bacterium
(c)
(d)
Red blood cell
White blood cell
Figure 1.1 All Living Things Are Made of Cells. (a) Bacterial cells, (b) Cells of an onion, (c)
Human blood cells, (d) Tissues in the stem of a plant are made of many individual cells.
(a: Erik Erbe & Christopher Pooley; b: kaibara87; c: Bruce Wetzel & Harry Schaefer; d: Rolf Dieter Mueller)
can see that both situations—before and after
straightening—are complex, but the room is
organized only after you have cleaned it up.
In a similar way, life is both complex and organized. Every living cell has an ordered, complex, internal structure. Of course, you cannot
see subcellular structures with unaided vision,
but you can observe the complexity and organization characteristic of life at other levels. An oak
tree provides a good example. Its roots, trunk,
branches, twigs, buds, leaves, flowers, and acorns
give the tree a complex structure (Figure 1.3),
but there is order in this complexity. Roots are
underground, the trunk supports the branches,
and the branches repeatedly fork and diverge to
form the canopy that reaches upward. Leaves
have characteristic structures and are arranged in
a pattern on the tree. Flowers are reproductive
structures that appear only at a specific season of
the year. Pollinated flowers may mature into
seed-­
­
bearing acorns, and in organized ways
staining yeast cells with a special dye allows the
proteins in their cell membranes to become visible as they glow shades of red,
orange, yellow, and green.
Seeds within acorns grow
into new mature oak trees. If
you take a few moments to
look at the natural world, you
will find other examples of
the complexity and organization of life.
Life accomplishes this
order and organization because the activities that go on
inside an organism are strictly
controlled. Again, think of
your room. If you want to Figure 1.2 A Membrane Surrounds a Cell.
keep your room and your ac- When yeast cells are stained in a particular
tivities organized, you must way, the proteins in their cell membranes
absorb the dye and fluoresce red, orange,
control where you put each
yellow, or green. (Masur)
item and what you do at
The Framework of Biology 5
Figure 1.3 An Oak Tree Has a Complex and
Organized Structure.
homeostasis the
stable internal
conditions of an
organism that support
life’s cellular and
chemical processes
each moment. For instance, a book could go
either on the desk or on the shelf and still be
organized, but it can’t go into the pile of laundry. Cells and organisms also have ways to control structures and activities to ensure that the
ordered life of a cell does not fall into chaos.
Even 40 minutes after exposure to 0°C air, human body
temperature remains relatively constant and has fallen
only about 0.5°C. Internal body mechanisms, including
shivering, help maintain a steady body temperature.
Human body temperature (°C)
39
Air temperature
is 0°C (32°F)
Exposure to 0°C air
38
Air temperature
is 36°C (72°F)
37
36
0
10
20
30
40
50
60
Time (minutes)
70
80
Figure 1.4 Maintenance of a Steady Body
Temperature Is a Homeostatic Mechanism.
• Why has the person’s body temperature fallen
only 0.5°C when the outside air temperature is
about 38°C colder than indoor air?
6 Race, Genomics, and Human Evolution
To manage life’s chemical processes, living
things also must regulate the quantities and
characteristics of the chemicals they contain.
The inside of a cell is mostly water, but many
chemicals are dissolved in that water—and
these are critically involved in the structures,
processes, and activities that collectively are
called life. While external environmental
conditions may fluctuate wildly, the internal
environment of a cell cannot. Factors such as
the amount of water, amount of salt and other
chemicals, and acidity are carefully regulated.
Some organisms also regulate more complex
traits such as body temperature or food intake.
The delicate balance of internal aspects
that all living organisms maintain is called
homeostasis. If this internal chemical balance
is upset—that is, if homeostasis is disrupted—
an organism easily can die. Homeostasis is
reflected in the way many systems of the human body work. Control of body temperature
is a good example (Figure 1.4). If a mammal,
such as a human, is suddenly put in a very
cold environment, body temperature will not
fall dramatically. Body systems respond to the
cold and maintain body temperature close to
normal. Only after a long time in the cold will
body temperature begin to fall.
Living Things Respond to and Interact
with Their Environments, Use Energy,
and Reproduce
To survive, every organism must interact with
its environment. Plants must locate and grow
toward a source of light or water. Other organisms must locate and take in food (Figure 1.5).
An individual might move toward a potential
mate, or its offspring, or need to know how
wet, or hot, or salty the environment is. You
might need to know if the person walking
behind you is an innocent stranger, an old
classmate, or someone to run from. All cells
must sense and respond to their environments.
Another important point about living organisms is that they are active. Structures inside
of cells move, cells move, and organisms that
are made of many cells move. To carry out all of
these activities, living organisms must have a
Figure 1.5 Predator Eats Predator. This
robber fly has wrestled a dragonfly to the
ground and is sucking out its body fluids.
(Thomas Shahan)
source of energy. For now energy will be defined as something objects have that gives them
the ability to do work. In its need for a source of
power, life is no different from a lawnmower, an
electric toothbrush, or a cell phone. The Sun is
the ultimate source of energy for nearly all organisms. While plants, some bacteria, and algae
can harvest the Sun’s energy directly, the rest of
us obtain energy by eating plants or other living
things (Figure 1.6). Living organisms spend
much time getting energy and
DNA
converting it to a form their cells
readily can use.
When people work together to
complete a complex set of tasks, it
helps if they have instructions. In a
similar way cells need instructions
to carry out the processes of life.
The instructions for the activities
that go on in a cell are contained
in large molecules called DNA, an
acronym for deoxyribonucleic
acid (Figure 1.7). Although the
details of the DNA molecule differ, the instructions it carries are
made of the same chemicals and
work in the same way in all organisms. The structure of DNA and
the consistent way it works to direct living processes are the basis
for the unity of life. As you will
read in later chapters, though,
DNA molecules differ slightly be- Figure 1.7 DNA Molecules Carry the
tween individuals, and these subtle Instructions for All the Processes of
variations are responsible for the Life for All Organisms.
incredible diversity of life.
In addition to providing in­structions for
a cell’s activities, DNA gives organisms the
special ability to reproduce. The DNA molecule can be copied exactly, and the copy can
Quick Check
1.2
be given to new cells, which can outlive the
parent cell. Without this special ability, life
1. What is the function
of the cell membrane?
would not continue over time. When DNA is
2.Describe homeostasuccessfully copied and a new cell is made, the
sis, using adjustments in
process ensures that the new cell has the same
body temperature as an
instructions and operates by the same rules as
example.
did its parent cell.
1.3 Levels of Organization
Are Characteristic of
Life
Figure 1.6 Predator and Prey. The cat’s body
will convert the mouse’s tissues to energy and
useful chemicals. (Lxowle)
The complex interactions within and between
living organisms can seem baffling, but you
can begin to comprehend them by considering
something that biologists call levels of organization. This idea is that living things can be
energy the ability to
do work
DNA (deoxyribonucleic acid) the
molecule that carries
the instructions for life
The Framework of Biology 7
chemical element a
basic kind of matter
atom the smallest unit
of an element that has
all of the properties of
that element
organelle subcellular
groups of molecules
that have specific
functions within cells
grouped into increasingly complex units. An
analogy might be helpful here. Imagine that
you work for a large drug company trying to
develop a drug to treat heart disease. Your job
is to run chemical analyses on compounds
that field agents find in the forests and jungles
of the world. But of course you do not work
alone. You are part of a research unit where every person’s job is related to heart disease; each
week all the people in your unit meet to trade
ideas and discuss their work. The heart disease
research unit is part of a larger group that includes biologists and medical doctors who will
test the potential treatments in animals and in
people. The entire heart disease workforce also
would include people who might market and
sell any treatments developed. And this large
heart disease workforce is just one of many
groups in the large drug company. Each level
has its own complexity, which builds as you
go from one level of organization to the next.
Life is organized in a similar way. The
simplest level of organization involves the
interactions of the chemicals that make up
life. The groupings continue through different
types of cells, to the cells that interact within
larger organisms, to organisms that interact
with one another. The most complex level
of organization includes every organism and
the nonliving environmental components
that support them. There are many levels of
organization in between these endpoints.
Individual Organisms Are Made of
Chemicals, Cells, Tissues, and Organs
The first level of life is not actually alive but is the
foundation on which life is built.
NOT ALIVE
ALIVE
Life is made of chemical building
Atoms and molecules are found
The properties of life emerge from
blocks called chemical elements
in living organisms, but they are
interactions of biological molecules
not alive.
when they combine to form a cell.
(Figure 1.8). Each element is a
basic kind of matter. The smallest
Different combinations of
unit of an element that has all the
A cell is made of molecules
biomolecules form organelles.
formed into organelles.
properties of that element is an
Organelles
Sugar
atom, and life is composed of just
Viruses are
Nucleus with DNA
not alive.
a handful of elements. Hydrogen
(H), carbon (C), oxygen (O), and
Viruses
Protein
DNA
nitrogen (N) are a few examples of
molecule molecule
elements that are important
chemical building blocks of life.
Of course, life is more intricate
Nucleotide
than the atoms of hydrogen or
Amino acid
oxygen. Atoms combine to form
Cell membrane
Lipid
more complex structures such as
molecules.
Biomolecules are
The next level of organizamade from atoms.
Water
tion brings us closer to the
realm of life (Figure 1.8).
Molecules and atoms are not
by themselves alive, but in the
right combinations and under
the right chemical and physical
Hydrogen
Phosphate
conditions they combine to form
Oxygen
Carbon
Figure 1.8 From Atoms to a Cell, Life Has
Nitrogen
organelles, subcellular groups
Levels of Organization.
of molecules that have specific
Atoms are the
Start
smallest units
functions within cells. Cells are
•
Why
isn’t
a
DNA
molecule
alive?
here
of elements.
the basic units of life. Anything
8 Race, Genomics, and Human Evolution
less than a cell is not alive. A virus is a small
structure made of biological molecules, but it
is not a cell. A virus cannot independently use
chemical energy to build its own structures or
carry out life’s processes. So a virus is not alive.
You will learn more about viruses in upcoming
chapters. The point here is that as far as we
know, only cells are alive.
Organisms that have just one cell are unicellular organisms. Despite their small size,
(a) A unicellular organism like Euglena has just a
single cell with many complex organelles.
Eyespot
Nucleus
Cell membrane
(b) Trichoplax is a simple multicellular organism that
has many cells arranged around a fluid-filled cavity.
Each cell has complex organelles.
Upper
layer
of cells
unicellular organisms can have incredible
complexity (Figure 1.9a). Organisms made of
two or more cells are called multicellular organisms. Just as people in an organization
specialize in certain jobs, different cells of
multicellular organisms can specialize in certain jobs. Because of this, multicellular organisms can do interesting and complex things
that unicellular organisms cannot do. Figure
1.9b shows Trichoplax, one of the simplest
known multicellular organisms. Trichoplax has
just five types of cells, but they aren’t organized
into tissues. A tissue is a group of similar cells
gathered together into a unit that performs a
specific function. For instance, blood is a tissue that transports nutrients and water. Muscle
is a tissue that contracts and moves body parts.
In more complex multicellular organisms,
different kinds of tissues are grouped into organs to perform even more complex tasks
(Figure 1.10). For example, individual bones
are organs that are part of the skeletal system.
Bones are composite structures that, like all
organs, are formed of several kinds of tissues
such as connective tissues, blood, blood
NOT ALIVE
virus a small, nonliving
structure that incorporates biological molecules
unicellular organism an organism made of
just one cell
multicellular organism an organism made of
two or more cells
tissue a group of similar
cells gathered together
into a unit that performs
a specific function
organ a grouping of
different types of
tissues that work
together to perform a
specific task ALIVE
Organelles form cells.
Organelles
Cell
Lower layer
of cells
Fluid-filled
cavity
Cells form
tissues and
several tissues
form an organ.
Tissue
(bone)
Biomolecules form
cellular organelles.
(c) At its largest, Trichoplax is about ten times
the size of Euglena.
Blood vessel
Bone cells
.
Organs
Biomolecules
Skeletal
system
Atoms form molecules.
Euglena is
Trichoplax is 700 micrometers
6.8 to 8
at its widest dimension.
micrometers long.
Figure 1.9 A Complex Unicellular
Organism and a Simple Multicellular
Organism. Euglena spirogyra has just
one cell with complex organelles.
Trichoplax adhaerens is one of the
simplest multicellular organisms.
Start
here
Hydrogen
Oxygen
Nitrogen
Phosphate
Carbon
Organ
systems
Organism
Leg
bone
Organs with the
same general
function form
organ systems.
Organ systems
form an organism.
Figure 1.10 Levels of Organization: From Atoms to an Organism.
The Framework of Biology 9
organ system a group
of organs that work
together to perform a
specific body function
population a group of
individuals of one kind
of organism living in
one geographic locality
vessels, and nerves. Connective tissue binds
the bone to the rest of the body, while blood
and blood vessels supply nutrients to bone
cells and remove wastes. Bone cells secrete deposits of calcium around themselves, forming
patterns of concentric rings. Just as atoms are
not alive by themselves, tissues and organs are
not by themselves whole organisms. Organs
that perform related functions are grouped
into an organ system that accomplishes a
major body function. For instance, all of the
bones in the body are all part of the skeletal
system, which has the job of supporting and
protecting the body’s soft tissues. Table 1.2
lists the major organ systems of the human
body. Finally, an organism consists of the
whole body of a living thing, so you are an
organism and a rooster, a Euglena, a Trichoplax,
an oak tree, a bacterium, and a mosquito are
organisms too.
Individual Organisms Interact as Part of
One or Several Groups
If you took a careful census of the organisms
that live in your backyard, you would probably
discover thousands of different kinds, most of
them small, and many of them insects. Not
only are there lots of different organisms, but
they can be viewed as components of larger
interacting biological systems. Let’s consider
some of the interactions in the lives of one such
insect, a leaf cutter ant that lives in rain forests
in Central and South America (Figure 1.11).
Ants interact with each other, with other kinds
of organisms like the plants whose leaves they
gather, and with the nonliving parts of their
environment like soil, water, and air. A group
of individuals of one kind of organism living
in one geographic locality is called a population. All of the populations of a single kind
of organism form a species. All individuals of
a species have similar characteristics that help
define them as one species.
One of the important lessons from modern
biology is that individual organisms do not
exist in isolation. Instead, every individual
depends on others for its survival. Leaf cutter ants are part of a colony whose members
accomplish different tasks and support each
other. Worker ants use their ­sharp-­edged jaws
to snip off bits of plants and carry these back
to the colony. There the raw plant matter is
chewed and the mulch is added to the colony’s
underground garden of fungus that provides
food for the colony. The tiniest workers tend
the fungus garden. As a whole the colony
enriches the soil it lives in, and so it has an
impact on other organisms that live there. As
Table 1.2 Major Human Organ Systems and Their Functions.
Organ System
Integumentary
Major Components
Skin, hair, nails
Function
Protection from water loss, mechanical injury, and infection
Muscular
Skeletal muscles
Movements of body parts and of whole body
Skeletal
Bones, ligaments, tendons
Support of body and protection of internal organs
Digestive
Mouth, pharynx, esophagus, stomach, intestines,
liver, pancreas, gallbladder, anus
Digestion and absorption of food, and elimination of
food wastes
Circulatory
Heart, blood vessels, blood
Movement of substances to and from individual cells
Respiratory
Trachea, breathing tubes, lungs
Gas exchange: obtaining oxygen and releasing carbon dioxide
Lymphatic and
Immune
Lymphatic vessels, lymph nodes, lymph, immune
Defense against infection and cleanup of dead cells
cells, bone marrow, thymus, spleen, white blood cells
Excretory
Kidneys, ureters, bladder, urethra
Endocrine
Pituitary, thyroid, pancreas, ovaries, testes, and other
Coordination of body functions by hormones
glands that secrete hormones
Nervous
Brain, spinal cord, nerves, sense organs
Sensing internal and external stimuli and coordination of
entire body’s functions
Reproductive
Ovaries, testes, and related organs
Reproduction
10 Race, Genomics, and Human Evolution
Elimination of metabolic wastes and regulation of
chemistry of blood