Topic 9: Darwinian Theories ✅ Flashcards
When did Darwin publish his theory on The Origin of Species by Natural Selection?
1859
Evolution
The change in the inherited characteristics of biological populations over successive generations
The Origin of Species Theory
Evolution is defined as descent with modification
The mechanism of evolution is natural selection
The Origin of Species: the 2 main points
- Descent with modification (evolution)
- Natural selection is the mechanism of evolution (descent with modification)
Descent with modification
Evolution
-current species descended from ancestral species
-modification happened along the way
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
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
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
Artificial selection
Process of modification of other species by humans by selecting and breeding individuals with desired traits
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
Adaptation
Evolutionary processes
Enhance the fitness and survival of individuals in their environment
Natural Selection and Adaptation: what conclusions did Darwin draw?
Observation 1: Variation in a population
Observation 2: Overproduction of offspring
Observation 1
Variation in a population
-Members of a population often vary in their inherited traits
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
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
What does Natural Selection NOT create?
New traits
It edits or selects for traits already present in the population
What does Adaptation depend on?
The local environment
It determines which traits will be selected for or against in any specific population
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
