4: Social Evolution and Sexual Selection
- Page ID
- 181662
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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 explores the cooperation among unicellular organisms and its significance in the evolution of multicellular life. It examines the emergence of social behaviors, including sexual reproduction, and the dynamics of cooperation and cheating in biological systems. The complexity of defining organisms is highlighted, noting that both individual cells and social groups can be viewed as organisms, especially in eusocial species.
- 4.1: Selecting social (cooperative) traits
- This page explores the evolution of multicellularity through inclusive fitness and kin selection, emphasizing cooperative behaviors such as mutual aid and altruism. It uses the social amoeba Dictyostelium discoideum as a case study, illustrating how individual cells cooperate and sacrifice for the group's survival.
- 4.2: Quorum Sensing
- This page discusses quorum sensing, a process enabling unicellular organisms to gauge population density through signaling molecules. The response is non-linear and dependent on molecule concentration, with a threshold that triggers cellular actions. An example is Vibrio fischeri, which produces light when its population density is adequate, demonstrating how this mechanism optimizes costly biological processes and underscores cooperative behaviors among bacteria in various functions.
- 4.3: Active (altruistic) cell death
- This page explains apoptosis, or programmed cell death, as a crucial evolutionary process that differs from necrosis by being controlled and beneficial for organism development, as well as immune and nervous system formation. It describes how environmental stress can trigger apoptosis in unicellular communities, aiding neighboring cells, and discusses a toxin-antitoxin system that regulates this process, illustrating the importance of altruistic behaviors in defending populations against viruses.
- 4.4: Inclusive fitness, kin and group selection, and social evolution
- This page explores the evolutionary basis of altruism and social behaviors through inclusive fitness, exemplified by worker bees and prey adaptations. It explains W.D. Hamilton's rule (rb > c) showing how altruistic traits enhance reproductive success for individuals and relatives. The "green beard" concept is introduced for kin recognition, while discussing the unintended evolutionary origins of complex human traits such as empathy.
- 4.5: Group selection
- This page explores group selection as an alternative to inclusive fitness, focusing on how the success of a group impacts reproductive outcomes and fosters cooperation and altruism. It uses the bacterium Myxococcus xanthus as an example of such behaviors, where cells aggregate to withstand harsh conditions. The discussion extends to various animal groups that exhibit similar cooperative traits, underscoring the significance of group dynamics in evolutionary advantages.
- 4.6: Defense against social cheaters
- This page explores social cheating in groups, where some individuals exploit cooperation, harming collective outcomes. It draws a parallel to cancer, where mutations lead to loss of social control in cells, causing uncontrolled growth. The text describes mechanisms to regulate social behavior and cancer prevention, including apoptosis and immune surveillance, emphasizing the ongoing evolutionary conflict between cancer cells and biological defenses.
- 4.7: The appearance of multicellular organisms
- This page discusses the evolution of multicellular organisms, emphasizing the role of predation in this process. It details how unicellular algae form multicellular colonies as an adaptation, the importance of cellular specialization, and the independent evolution of multicellularity across lineages. Additionally, it explores the complex behaviors of certain unicellular eukaryotes, as well as questions about evolutionary processes, social interactions, and reproductive strategies.
- 4.8: Origins and implications of sexual reproduction
- This page explores sexual reproduction as a social interaction among distinct organisms, mainly through the example of slime mold Dictyostelium. It describes the fusion of haploid cells to create diploid cells that undergo meiosis, promoting genetic diversity. It addresses the implications of haploid and diploid states for genetic expression and variation, including homozygosity, heterozygosity, recessive alleles, and the influence of lethal alleles on survival and population dynamics.
- 4.9: Sexual dimorphism
- This page explores the definitions of male and female organisms based on gamete size, highlighting evolutionary implications of sexual reproduction and various mating strategies. It examines parental investment, reproductive success, and the influence of behaviors on mating outcomes, including promiscuity and sperm selection.
- 4.10: Sexual Selection
- This page explores sexual dimorphism and reproductive strategies, emphasizing the evolution of distinct traits driven by reproductive pressures. It notes differing partner preferences, with males focusing on physical attractiveness and females on social status or support for long-term bonds.
- 4.11: Curbing runaway selection
- This page addresses sexual selection, using examples like the peacock's tail and Megaloceros giganteus antlers. It discusses the interplay between beneficial traits for mating and the risks posed by predation. The page critiques hyper-competitive evolutionary views, stressing the importance of cooperation for species survival and challenging misconceptions related to Social Darwinism and eugenics.