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

• Male body traits used for display are often strongly developed

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

11.9(3) Effects of experimental alterations of tail length on males’ mating success

• Male body traits used for display are often strongly developed

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

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

11.11(2) Effects of individual selection and group selection on population size in the flour beetle

• Study on effects of selection for different population sizes

11.11(3) Effects of individual selection and group selection on population size in the flour beetle

• 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

11.13(2) 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

11.13(2) Conflict between group and individual selection

• 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)

11.9(3) Effects of experimental alterations of tail length on males’ mating success

• 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 ?