Modern Evolutionary Synthesis

• The modern evolutionary synthesis combines Charles Darwin's theory of evolution and Gregor Mendel's ideas on genetics
• It explains how small genetic changes accumulate over time, creating new species

Darwin's Theory of Evolution

• Darwin's idea of natural selection lacked an explanation of how traits were inherited before the Modern Evolutionary Synthesis
• Darwin's theory of natural selection is based on the "survival of the fittest"
  • Organisms with advantageous traits survive longer and pass them to offspring
• Variation, fitness differences, and heredity are required to make it work
• Theodosius Dobzhansky and Ernst Mayr combined Darwin's and Mendel's ideas to create the Modern Evolutionary Synthesis

The Modern Evolutionary Synthesis

• Darwin's ideas and new genetics research led to it.
• It added mutation, gene flow, and genetic drift alongside natural selection

Factors Shaping Life Over Time

• Mutation: random changes in DNA

  • Small DNA changes that happen by accident
  • Mutations create new traits, fueling evolution

• Gene Flow: genes moving between populations

  • Individuals moving to a new group and having offspring bring new genes
  • Gene flow maintains genetic diversity and helps adaptation

• Genetic Drift: random changes in genes

  • Traits become more or less common by chance
  • Genetic drift is especially important in small populations

• Natural Selection: survival of the fittest

  • Individuals with traits suited to their environment survive and have offspring
  • Favorable traits spread and species adapt and evolve

• These four processes work together to shape the change in life over time

Importance of Modern Evolutionary Synthesis

• It helps in understanding how life changes and adapts
• It has uses in medicine
  • How bacteria develop resistance to antibiotics

Applications of Evolution

• Scientists use evolution to breed better crops and animals
• It aids in protecting wildlife by keeping populations healthy
• It helps to understand where we came from and how humans evolved

Modern Evolutionary Synthesis Today

• Main theory of evolution
• Small genetic changes over time lead to big changes in species.

Population Genetics

• It studies how genes change in a group of living organisms over time
• Explains why members of the same species can look or behave differently.
• Scientists study these changes to understand how species evolve
• A population is a group of the same species living together and reproducing
• Its gene pool includes all the gene variations
• Greater genetic diversity improves survival against environmental changes

Factors Affecting Genes

• Mutation changes in DNA that create new traits
• Natural Selection organisms with helpful traits survive and pass those traits to their offspring
• Genetic Drift random changes in gene frequencies, especially in small populations
• Gene Flow movement of genes from one population to another when individuals migrate
• Non-Random Mating when individuals select mates based on specific traits
• Studying these factors helps scientists understand how species adapt and evolve

The Gene Pool

• Refers to all the genes in a population
• It includes different versions of genes(alleles) that determine traits like eye color, or height
• The size and diversity of the gene pool are important for survival
• A large gene pool means more genetic variety
  • Helps populations adapt to changes like climate shifts or new diseases
• A small gene pool can make populations weaker
  • If all individuals are too similar, they may struggle to survive new threats

Microevolution

• Refers to small genetic shifts within a population over time

• Microevolution changes do not create new species

  • Help populations adapt to their environment

• Microevolution happens through five processes:

  • Mutation Changes in DNA that introduce new traits Some mutations are harmful, but others might help an organism survive better A mutation in bacteria that makes them resistant to antibiotics

  • Natural Selection Traits that improve survival and reproduction become more common over generations Giraffes with longer necks surviving better because they can reach more food

Genetic Drift

• Random changes in gene frequency, especially in small populations
• Happens due to chance, not natural selection
• The bottleneck effect is an extreme example that happens when the population size is severely reduced.
• Ex:A flood wiping out most of a small bird population, leaving only a few with a rare feather color

Gene Flow (Migration)

• Movement of genes between populations when individuals migrate andreproduce
• Increases genetic diversity.
• Ex: Wolves from one area joining a new pack, bringing in new genes

Non-Random Mating

• When individuals choose mates based on specific traits, certain genes become more common
• Ex: Peacocks with brighter feathers attract more mates, passing on their genes more often

Why Microevolution Matters

• Microevolution helps populations adjust to their surroundings
• Small changes can add up, eventually leading to macroevolution
• Ex: The peppered moth in England changed color due to pollution Darker moths survived better when trees were covered in soot Insects quickly develop pesticide resistance.

Hardy-Weinberg Theorem

• Mathematical model describing a non-evolving population
• If met, genetic makeup (allele frequencies) of a population remains constant over generations.

Hardy-Weinberg equilibrium

• No Mutations
• No Natural Selection
• Large Population Size prevents random changes
• No Gene Flow
• Random Mating

Causes of Microevolution

• Genetic Drift
  • Bottleneck Effect
  • Founder Effect
• Gene Flow
• Mutation
• Non-random Mating
• Natural Selection
• The forces that cause allele frequencies to change

Genetic Drift

• Change in allele frequencies due to chance events
• Random and not selective
• Two types:
  • Bottleneck effect
  • Founder effect

Bottleneck Effect

• Drastic reduction in population size due to chance event
  • Natural disaster
• Survival is based on chance
• Results in smaller gene pool
• Allele frequencies are different from the original population

Founder Effect

• Few individuals establishing a new population
• Results in a smaller gene pool
• Allele frequencies may differ from the original population

Gene Flow

• Migration
  • Via fertile individuals or gametes
• If high, it can have a significant effect on allele frequencies
• Different from the Founder effect as it does not completely start a new population

Mutation

• Creates new genetic variation in a gene pool
  • It is how all new alleles first arise
• Addition of new allele changes population’s allele frequencies
• Random and not selective
  • But selective