Topic 9: Darwinian Theories ✅ Flashcards by C F

When did Darwin publish his theory on The Origin of Species by Natural Selection?

1859

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Evolution

The change in the inherited characteristics of biological populations over successive generations

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The Origin of Species Theory

Evolution is defined as descent with modification

The mechanism of evolution is natural selection

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The Origin of Species: the 2 main points

Descent with modification (evolution)
Natural selection is the mechanism of evolution (descent with modification)

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Descent with modification

Evolution

-current species descended from ancestral species

-modification happened along the way

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Natural selection is the mechanism of evolution

Individuals with favorables inherited traits are more likely to survive and reproduce
-survival of the fittest

Accumulation of these favorable heritable traits in a population over time=> higher proportion of individuals with better traits

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Natural selection

Evolutionary process

Occurs when a population’s heritable variations are exposed to environmental factors that favor the reproductive success of some individuals over others

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Natural selection: step by step

Populations with varied inherited traits
Elimination of individuals with certain traits
Reproduction of survivors
Increasing frequency of traits that enhance survival and reproductive success

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Artificial selection

Process of modification of other species by humans by selecting and breeding individuals with desired traits

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Natural selection and adaptation

Darwin proposed that natural selection is the mechanism for evolutionary adaptation of populations to their environments

Natural selection: process in which individuals with favorable inherited traits are more likely to survive and reproduce

Adaptation: evolutionary processes that enhance the fitness and survival of individuals in their environment

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Adaptation

Evolutionary processes

Enhance the fitness and survival of individuals in their environment

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Natural Selection and Adaptation: what conclusions did Darwin draw?

Observation 1: Variation in a population

Observation 2: Overproduction of offspring

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Observation 1

Variation in a population

-Members of a population often vary in their inherited traits

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Observation 2

Overproduction of offspring

-All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce

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Darwin’s Theory:Natural Selection and Adaptation

Observations:
1. Variations in the heritable characteristics of individuals in a population

Overproduction of offspring: organisms produce more offspring than the environment can support

Conclusions:
1. Survival of the fittest- individuals that are well suited to their environment tend to leave more offspring than other individuals

Adaptations in the population- over time, favorable traits accumulate in the population

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What does Natural Selection NOT create?

New traits

It edits or selects for traits already present in the population

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What does Adaptation depend on?

The local environment

It determines which traits will be selected for or against in any specific population

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What do Adaptations vary with?

Adaptations vary with different environments

Example of Natural Selection and Adaptation

Thalassaemia

Survival of thalassaemia allele heterozygous carriers in countries where malaria was endemic

Explanation:
Plasmodium malariae (the protist that causes malaria) replicates in mosquitoes which live in (sub-)tropical regions

-this microorganism infects RBC and digest haemoglobin

-heterozygous carriers of the thalassaemia allele have lower haemoglobin levels=> more resistant to Plasmodium infection

Natural selection favoured selective survival of carriers of the thalassaemia allele

What is the cause of thalassaemia

Evolution

Scientific evidence for evolution

New discoveries are filling gaps identified by Darwin in The Origin of Species

-direct observations

-homology

-the fossil record

-biogeography

Direct observations of Evolutionary Change

-Natural selection in response to introduced plant species

-the evolution of drug-resistant bacteria

-the evolution of insecticide-resistant mosquitoes

-enhanced survival of thalassaemia carriers upon exposure to malaria

The evolution of drug resistant bacteria

Bacteria have short generation times (can divide every 1-3 hours)

Allows rapid adaptive evolution (adaptation) of bacteria

Eg: development of antibiotic resistance

Staphylococcus aureus

Bacterium

Responsible for wide range of human infections

-became resistant to penicillin in 1945, 2 years after it was first widely used

-became resistant to methicillin in 1961, 2 years after first widely used

MRSA

Methicillin-resistant S. Aureus Dangerous pathogenic strain

Methicillin

A beta-Lactam antibiotic -binds to and inhibits the enzyme transpeptidase MecA gene Natural selection: when exposed to methicillin, MRSA strains are more likely to survive and reproduce than non-resistant S. Aureus strains -MRSA strains are now resistant to many antibiotics

Transpeptidase

Responsible for the formation of peptidoglycan in the bacterial cell wall

MecA gene

Encodes a protein that binds beta-Lactam antibiotics =>transpeptidase remains active in the presence of beta-Lactam =>prevents them from inhibiting cell wall synthesis =>Antibiotic resistance development

Evolution of insecticide -resistant mosquitoes

Development of resistance to insecticide DDT Month 0- resistance 4% Month 8- resistance 45% Month 12- resistance 77%

Homology

Similarity between different species that results from common ancestry

Homology types

Anatomical homologies: similarities in anatomical features (homologous structures) Molecular homology: similarities in genetic material

Homologous structures

Anatomical similarities that represent variations on a structure present in a common ancestor

Comparative embryology

Reveals anatomical homologies not visible in adult organisms

Eg of molecular homologies

Genes shared among organisms were inherited from a common ancestor

Eg of anatomical homologies

Vestigial structures -organism structures that have lost all or most of their original function during the course of evolution -remnants of features that served important functions in the organism’s ancestors

Eg of vestigial structure

Human appendix -from fully functional cecum to current human appendix Human ancestors ate more easily digested foods => became less reliant on cellulose-rich plants => cecum became less necessary Mutations for small cecum size accumulated in human population => cecum continuously shrinking Once necessary cecum degraded to current appendix

Appendix

Dead-end pouch forming part of large intestine Darwin suggested that the appendix was used for digesting leaves by herbivores Herbivorous animals have a very long cecum that hosts bacteria to digest cellulose

Evolution is the change in __1 of __2 over __3

Change in the 1(inherited characteristics) of 2(populations) over 3(successive generations)

Regarding evolution; individuals do not evolve..

Populations evolve over time

Darwins evolution theory

Descent with modification by natural selection

Natural selection summary

Process in which individuals with favorable inherited traits are more likely to survive and reproduce It is the mechanism for adaptation => increases the adaptation of organisms to their environment over time

Adaptation summary

If the environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

What effect can Natural Selection have on heritable traits that vary in a population?

Can only increase or decrease

Overview of Natural Selection and Adaptation

Population of Organisms →Hereditary variations →Overproduction and struggle for existence →Differences in reproductive success →Evolution of adaptions in the population