4: Social Evolution and Sexual Selection
- Page ID
- 3884
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 4.0: Introduction
- This page delves into the intricacies of defining organisms, highlighting the fluidity of life and indistinct organismal boundaries. It covers reproduction and interaction in unicellular and multicellular forms, with special attention to eusocial organisms that reproduce collectively. The discussion contrasts colonial organisms with individuals, emphasizing specialized cells and social behaviors in evolution.
- 4.1: Selecting social (cooperative) traits
- This page explores the evolution of multicellularity within the framework of evolutionary theory, focusing on inclusive fitness and kin selection. It underscores the significance of cooperation, empathy, and altruism in evolution, exemplified by Dictyostelium amoebae's self-sacrificial behaviors.
- 4.2: Quorum Sensing
- This page discusses quorum sensing, a mechanism in unicellular communities where organisms detect population density via secreted signals, activating group responses at specific thresholds. It highlights the example of Vibrio fischeri, which forms a beneficial relationship with the squid Euprymna scolopes, aiding in camouflage through bioluminescence.
- 4.3: Active (altruistic) cell death
- This page covers programmed cell death (apoptosis), emphasizing its role in development and contrast with necrosis, which causes inflammation. In unicellular organisms, environmental stresses prompt active cell death through quorum sensing, aiding neighboring cells by releasing nutrients. A stable toxin and unstable anti-toxin regulate this mechanism, with stress potentially favoring cell death.
- 4.4: Inclusive fitness, kin and group selection, and social evolution
- This page explores the evolution of social and altruistic behaviors in organisms, citing examples such as worker bees and distasteful prey. It introduces Hamilton's Rule, which posits that altruistic traits can evolve if they benefit relatives more than they cost the individual. The concept of inclusive fitness is discussed, emphasizing familial bonds in altruism.
- 4.5: Group selection
- This page explores group selection in evolutionary biology, presenting it as an alternative to inclusive fitness. It highlights that small groups can act as single entities, gaining evolutionary advantages through cooperation and altruism. Myxococcus xanthus serves as an example with its formation of fruiting bodies for survival.
- 4.6: Defense against social cheaters
- This page explores how cheaters affect social organisms, including microbes and multicellular entities, disrupting cooperation. It highlights the example of cancer cells, which grow uncontrollably due to failure in social controls. The page examines mechanisms such as apoptosis and immune responses that maintain social structures, while also discussing the evolutionary struggles between cooperation and cheating.
- 4.7: Driving the evolutionary appearance of multicellular organisms
- This page explores the evolution of multicellular organisms, emphasizing the role of cooperative behaviors and survival strategies in prokaryotic and eukaryotic organisms. It discusses predation as a catalyst for multicellularity and the transition from colonies to specialized organisms, exemplified by jellyfish stinging cells.
- 4.8: Origins and implications of sexual reproduction
- This page explores sexual reproduction, emphasizing its cooperative aspects compared to asexual reproduction. It notes that while sexual reproduction is usually identified with two sexes, unicellular eukaryotes can exhibit various mating types. The fusion of gametes from different mating types enhances genetic diversity.
- 4.9: Sexual dimorphism
- This page examines the biological definitions of male and female organisms based on gamete size and reproductive investment, noting that larger eggs (females) and smaller sperm (males) create distinct reproductive strategies. It highlights female control in mating success, using examples like wild fowl, and draws parallels to modern contraceptive methods that allow conscious reproductive choices for both sexes.
- 4.10: Sexual Selection
- This page explores sexual dimorphism and diverse reproductive strategies among males and females, illustrating how morphological and behavioral traits affect mate selection. It emphasizes females' preference for males with strong genetic indicators, discusses parental versus offspring interest conflicts, and examines the evolution of mating signals, including deceit and cooperation between genders.
- 4.11: Curbing runaway selection
- This page explores sexual selection and its role in balancing traits, illustrated by examples like peacock tails and Megaloceros giganteus antlers. It challenges misconceptions of evolution as mere ruthless competition linked to Social Darwinism and eugenics, which inaccurately categorize individuals as "unfit." The authors highlight the importance of cooperation in human societies and emphasize that evolution is a complex interplay of traits and environmental stability.
Contributors and Attributions
Michael W. Klymkowsky (University of Colorado Boulder) and Melanie M. Cooper (Michigan State University) with significant contributions by Emina Begovic & some editorial assistance of Rebecca Klymkowsky.