A Natural History of Families

A Natural History of Families

by Scott Forbes

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ISBN-10: 0691130353

ISBN-13: 9780691130354

Pub. Date: 01/02/2007

Publisher: Princeton University Press

Why do baby sharks, hyenas, and pelicans kill their siblings? Why do beetles and mice commit infanticide? Why are twins and birth defects more common in older human mothers? A Natural History of Families concisely examines what behavioral ecologists have discovered about family dynamics and what these insights might tell us about human biology and behavior.


Why do baby sharks, hyenas, and pelicans kill their siblings? Why do beetles and mice commit infanticide? Why are twins and birth defects more common in older human mothers? A Natural History of Families concisely examines what behavioral ecologists have discovered about family dynamics and what these insights might tell us about human biology and behavior. Scott Forbes's engaging account describes an uneasy union among family members in which rivalry for resources often has dramatic and even fatal consequences.

In nature, parents invest resources and control the allocation of resources among their offspring to perpetuate their genetic lineage. Those families sometimes function as cooperative units, the nepotistic and loving havens we choose to identify with. In the natural world, however, dysfunctional familial behavior is disarmingly commonplace.

While explaining why infanticide, fratricide, and other seemingly antisocial behaviors are necessary, Forbes also uncovers several surprising applications to humans. Here the conflict begins in the moments following conception as embryos struggle to wrest control of pregnancy from the mother, and to wring more nourishment from her than she can spare, thus triggering morning sickness, diabetes, and high blood pressure. Mothers, in return, often spontaneously abort embryos with severe genetic defects, allowing for prenatal quality control of offspring.

Using a broad sweep of entertaining examples culled from the world of animals and humans, A Natural History of Families is a lively introduction to the behavioral ecology of the family.

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Princeton University Press
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6.10(w) x 9.20(h) x 0.70(d)

Table of Contents

Preface xi

Chapter 1: Blame Parents 1
Do the Good Die Young? 3
The Family Myth 5

Chapter 2: The Optimistic Parent 9
The Evolution of Family Size 9
The Puzzle of Obligate Brood Reduction 10
How Many Babies? 11
Avian Families 16
Core and Marginal Offspring 16
Asymmetric Sibling Rivalr Creates Disposable Offspring 18
The Evolution of Family Structure 19
What Is Parental Optimism? 21
Why Parental Optimism? 23
Tracking Erratic Resources 23
Replacement 27
Facilitation 28
Multiple Incentives for Parental Optimism 29
Are Humans Optimistic Parents? 31

Chapter 3: Why Parents Play Favorites 32
Mom Always Liked You Best 32
The Fivefold Advantage of Favoritism 33
1. The Benefits and Costs of Unequal Parental Investment 34
2. Divestment of Unneeded Offspring 36
3. Benefits of Diversification 39
4. Correcting Earlier Decisions 41
5. Bet Hedging and Brood Reduction 41

Chapter 4: How Parents Play Favorites 43
What Is a Phenotypic Handicap? 43
How Birds Play Favorites 44
Primar Versus Secondar Handicaps 44
How Blackbirds Play Favorites 45
Reversible Handicaps 46
How Marsupials Play Favorites 47
Brood Reduction in Rabbits 49
How Plants Play Favorites 50
Different Species, Same Idea 51
Humans Play Favorites Too 52
Birth Order and Favoritism 53

Chapter 5: Family Conflict 55
Genetic Conflict between Parents and Offspring 55
Parent-Offspring Conflict 57
Pregnancy and Parent-Offspring Conflict 58
Natural-Born Cancers 60
Imprinted Genes in Humans 62
Genetic Conflict and Beckwith-Wiedemann Syndrome 64
Parent-Offspring Conflict over Embryo Growth 64
Imprinting and Gestational Diabetes 65
Pregnancy Sickness and Genetic Conflict 66
HCG: The Hormone of Pregnancy Sickness? 68
Evolution of Chorionic Gonadotropins in Primates 70
Chorionic Gonadotropins and Miscarriage 70

Chapter 6: Selfishness Unconstrained 78
Brood Parasitic Birds 79
Old World Cuckoos 79
. . . and New World Cowbirds 80
Cowbird Mafia? 80
Cuckoo Catfish 81
The Origins of Brood Parasitism 81
Adopting Runaways? 82
Forced Adoption of Nonkin 83
Voluntar Adoption of Nonkin 85
The Lesson of Brood Parasitism 86

Chapter 7: Screening for Offspring Quality 87
The Logic of Progeny Choice 87
Sequential versus Simultaneous Progeny Choice 88
Progeny Choice in Humans 89
Adaptive Miscarriage 90
Chromosomal Defects in Humans 91
Sex Chromosomes and Birth Defects 94
Turner's Syndrome and Genomic Imprinting 96
Birth Defects and Maternal Age 96
Rejecting Low-Quality Embryos 97
HCG and Adaptive Miscarriage 98
Relaxed Screening in Older Mothers? 100
Why Relaxed Selection? 103
Why More Spontaneous Abortions in Older Mothers? 104
The Origin of Genetic Defects 105
The Shadow of Menopause 105
Screening, Maternal Age, and the Role of Genomic Imprinting 106
Maternal Age and Twinning 108

Chapter 8: Why Twins? 109
The Evolution of Brood and Family Size 109
Fault-Tolerant Design in Humans 111
Twinning as an Insurance Strategy 112
Insurance Offspring in Birds 113
In Vitro Fertilization and Twinning 114
Age, Trisomy 21,and Twinning 117
More Than Just Polyovulation 118
Twinning and Individual Optimization 121
Fit or Fat? 124
A Womb for Two 126
Natural Selection on Twinning Frequency 126
Brood Reduction before Birth? 127

Chapter 9: Fatal Sibling Rivalry 129
Siblicide 129
Desperado Siblings Result from Extreme Favoritism 132
The Good and the Best 133
Facultative Versus Obligate Brood Reduction 135
Ultraselfish Alleles 137
Human Twins 139
''Biological'' Influences 144

Chapter 10: Family Harmony 147
Cooperation in Families 147
The Arthur Dent Effect 148
Why Cooperation? 148
The Road to Cooperation 150
Parental Optimism and the Evolution of Cooperation 151
Polyembryony and New Roles for Marginal Offspring 152
Parasitoid Wasps 153
Adaptive Suicide? 154
The Benefits of Teamwork 156
Social Insects: The Ultimate Team Players 157
Trophic Offspring 160
Sibling Synergies in Birds and Mammals 160
Conflict When Necessary, but Not Necessarily Conflict 162
Cooperative Defense . . . against Parents? 166
Facilitation in Humans? 167
Finding Their Niche: Birth Order and Human Behavior 168

Chapter 11: Cannibalism and Infanticide 171
The Pathways to Cannibalism 171
Honey, I Ate the Kids 171
Offspring Designed to be Eaten 174
The Pathways to Infanticide 175
Sexually Selected Infanticide 175
Killer Rodents 176
Infanticide in Families 178
The Unwilling Parent? 178

Chapter 12: Brave New Worlds 182
Artificial Parental Optimism and Infanticide 184
An Epidemic of Multiple Births 185
Risks of Multiple Gestation 186
The Ghost in the Machine 187
Embryo Reduction 188
Artificial Progeny Choice 189
Refining Artificial Progeny Choice 190
Does Assisted Reproduction Cause Low-Quality Progeny? 191
Send in the Clones 192
Parental Optimism and the Law of Unintended Consequences 194
Blame Parents 195

Chapter 13: Debunking the Family Myth 197

Selected References 201
Index 229

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