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Natural selection

Natural selection

• Concept of natural selection is simple, but mechanism is subtile

• Deals with survival and reproduction

• Comprises the only known process that offers an explanation for the origin of adaptations

11.1 Different forms of leaves on the aroid vine Monstera tenuis in tropical American forests

• Different forms of leaves on the vine Monstera tenuis in tropical American forests

• Example of adaptive development in relation to environmental parameters

11.2 Pseudocopulatory pollination

• Adaptive shapes of flowers for pseudocopulatory pollination in the Australian orchid Chiloglottis formicifera

• Shape is combined with other traits such as odour

11.3(2) The kinetic skull of snakes

• Adaptive skeletal structure of poisonous snakes

11.3(1) The kinetic skull of snakes

• Adaptive skeletal structure of poisonous snakes

• Form complex mechanisms “redesigned” through modification of existing skeletal structures in other reptiles

11.4 Weaver ants (Oecophylla) constructing a nest

• Level of complexity of cooperative behaviour reaches climax in social insects

• Genetically inherited behaviour increases the reproductive success of the queen

Process of natural selection

• Design and function

• Consistent difference in fitness among phenotypically different classes of biological entities

• Fitness as a product of survival and reproductive success

• Individual versus genic selection

• Natural selection versus chance effects

11.5 A child’s toy that selects small balls

• Selection for small size results in selection of red balls

• By chance, natural selection can lead to selection for correlated traits

• Selection always acts for a particular phenotypic trait, but results in selection of the genes that code for this trait

11.7 Allele frequency fluctuates due to hitchhiking in a laboratory population of Escherichia coli

• Example of hitchhiking through fluctuations in frequency of his- and his+ alleles in E. Coli

• Illustrates selection for new advantagous mutations and selection of neutral alleles at the linked his locus

11.9(1) A male long-tailed widowbird in flight

• Male body traits used for display are often strongly developed

• Relationships with fitness can be examined through correlative or experimental studies

11.9(2) Effects of experimental alterations of tail length on males’ mating success



11.11(1) Effects of individual selection and group selection on population size in the flour beetle

• Study on effects of selection for different population sizes


• Study on effects of selection for different population sizes


• Study of effects of selection for different population sizes

• Treatment C shows characteristics of individual selection

• Treatments A and B show characteristics of group selection

• Selection can act both within and between populations

• Selfish genetic elements

11.12 The mythical self-sacrificial behavior of lemmings

• Mytical self-sacrificial behaviour of lemmings

• Altruists versus cheaters

• Lower average turn-over of populations than of individuals reduces likelihood of strong group selection

11.13(1) Conflict between group and individual selection

• Conflict between group selection and individual selection

• Altruistic traits may evolve through group selection if the rate of extinction of populations with selfish genotypes is very high


• Conflict between group selection and individual selection

• Altruistic traits may evolve through group selection if the rate of extinction of populations with selfish genotypes is very high


• Because individual selection works faster than group selection, selfish individuals rapidly increase within populations

• May spread towards neighbouring populations though gene flow

• Leads to fixation of selfish genotypes (even if causing population extinction)

11.14(1) The evolution of altruism and selfishness by kin selection

• Evolution of altruisim and selfishness by kin selection

• Kin selection operates at the level of individual genes

• Both behavioural strategies potentially increase the inclusive fitness of the actor

11.14(2) The evolution of altruism and selfishness by kin selection

• Evolution of altruisim and selfishness by kin selection

• Kin selection operates at the level of individual genes

• Both behavioural strategies potentially increase the inclusive fitness of the actor

11.17 Exaptation and adaptation

• ‘Preadaptation’ versus ‘exaptation’

• Wings in alcids can be regarded as exaptations

• Wings in penguins can be regarded as adaptations

11.18 Cross section of a bird’s eye, showing the pecten

• Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancestral character state

• Indications for adaptation: complexity

11.19 Small surfaces shed the hot boundary layer of air more readily than large surfaces

• Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancetsral character state

• Indications for adaptation: design (functional, morphological, fysiological)


• Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancetsral character state

• Indications for adaptation: experimental evidence

11.20 Testes versus body weight among polygamous and monogamous primate taxa

• Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancestral character state

• Indications for adaptation: comparative studies

• Convergent evolution as natural evolutionary experiments

• Hypothetico-deductive methods

11.21 The problem of phylogenetic correlation in employing the comparative method

• Hypothesis testing assumes statistically independent data

• Study of convergent evolution for hypothesis testing on adaptations assumes independent convergent evolutionary events

Conclusive remarks

• Necessity of adaptation ?

• Perfection ?

• Progression ?

• Harmony and balance ?

• Morality and ethics ?