SBI3U Evolution

Evolution

Evolution

• The process where significant changes in the inherited traits of a species occur over time

• An ongoing process where species adapt to environmental changes, ensuring species’ survival and reproduction

Species

• A group of organisms that can interbreed to produce offspring that are reproductively isolated from others and evolve independently

Science and Religion

• Science and religion are two different ways of understanding the world and do not need to conflict

• Science is based on evidence whereas religion is based on faith

Scientific Process

• Ongoing process

• Change is expected and accepted

• Has to be testable

• Based on theories and evidence (facts)

• Independently collected

Charles Darwin

• Called the father of evolution

• Proposed natural selection as the mechanism for evolution

• Went on a 5-year trip around the world where he took observations of organisms in South America and the Galapagos Islands

Fossils

• Form from buried organism remains through mineralization due to high pressure

• Complex organism fossils are found at the shallowest depths in younger rocks

• These fossils likely resemble living species

Biogeography

• Focuses on geographical distribution of organisms

• Includes living species and fossils

• Provides evidence for evolution

• Ex: Darwin’s finches

Comparative Anatomy

• Homologous Structures

  • Similar structures

  • Share a common origin

  • Evolved to perform different functions

• Analogous Structures

  • Features are shared by unrelated organisms

  • Evolved to perform the same function

Vestigial Features

• Structures in an organism that no longer function through evolution

• Shows an evolutionary relationship with other living things

• Ex: Human tailbone

Comparative Embryology

• Shared homologous developmental processes

Comparative Biochemistry

• Studies genes and DNA

• Traces the process of evolution

• Homologous genes exist in similar organisms and provide evidence of a common ancestor

Darwin’s Theory of Natural Selection

• Process involves organisms better adapted to environment

• These organisms survive and reproduce more

4 Principles of Natural Selection

• Overproduction

  • Each species produces more offspring than can survive

• Variation

  • Each individual has a unique set of traits

  • Greater variation within species increases survival likelihood

• Competition

  • Individuals compete for limited resources (food, water, space, mates)

  • Fitness: the ability to survive and reproduce

• Selection

  • Individuals with best traits survive and pass traits to offspring

  • Giraffe’s long neck is a product of sexual selection, not natural selection

Sexual Selection

• Selection of traits influences individual’s mating success

• Sexually dimorphous traits tend to be favoured (distinct male and female differences)

• Intersexual Selection

  • Female choice is based on colouration, courtship displays, songs, etc

• Intrasexual Selection

  • Male/male competition, e.g. strength to fight other males or defend territory

Artificial Selection

• Humans modify species through plant and animal domestication

• Domestication has been practiced for thousands of years

  • Modern dog breeds descended from wolves

• Farmers choose best plants for seeds, creating traits beyond natural variability

• Breeders can’t create nonexistent traits

• Undesirable traits may accompany desirable ones

Selective Pressures

• Environmental factors can reduce reproduction

• These factors can cause evolutionary change or extinction due to natural selection

• Examples:

  • Competition

  • Predation

  • Land clearance

  • Pollution

  • Diseases

  • Climate change

  • Parasitism

Microevolution

• Population undergoes small changes over time

• Ex: Bacterial strains gaining antibiotic resistance

Macroevolution

• Large evolutionary changes result in new species

• Ex: Evolution of bat wings

Factors that cause evolution

• Mutations

  • Changes in individual’s DNA can impact population’s gene pool if heritable

  • Ex: Norway rat developing resistance to rat poison

• Gene flow (Migration)

  • Net movement of alleles between populations due to individual migration

  • Ex: A gray wolf from one population mates with a wolf from another population

• Non-random mating

  • Mating based on preferred phenotypes or due to inbreeding

  • Preferred Phenotypes: mate selection based on physical/behavioral traits

  • Inbreeding: clos relatives breed together

• Genetic Drift

  • Allele frequencies change due to chance events

  • Small sample sizes less likely to reflect parent gene pool

Founder Effect

• Small group leaves original population, starts new one

• New population may differ genotypically and phenotypically from parent population

• Ex: Amish populations (limited initial founders and internal marriages)

Bottleneck Effect

• Chance event causes significant population or reproduction reduction

• Leads to decreased genetic diversity due to population reduction

• Ex: Overhunting brought cheetahs near extinction, reducing genetic diversity

Types of Distribution

• Stabilized Distribution

  • Centre phenotypes have highest fitness

• Directional Distribution

  • One phenotypic extreme has highest fitness

• Disruptive Distribution

  • Both phenotypic extremes have highest fitness

Diverging Evolution

Two or more species evolve different traits due to different selective pressures or genetic drift

Converging Evolution

Two unrelated species evolve similar traits due to similar selective pressures

Speciation

Isolated populations no longer exchange alleles and become separate species

Allopatric Speciation

Geographically isolated populations become separate species

Sympatric Speciation

Physically connected populations stop exchanging alleles and become separate species

Reproductive Isolated Mechanisms

• Must be reproductively isolated

• No longer a free exchange of alleles

Prezygotic Mechanisms

Prevent mating or fertilization

Postzygotic Mechanisms

Prevent the development of fertile offspring

Zygote

The cell formed by the union of two gametes in sexual reproduction

Ecological Isolation

• Two populations inhabit different geographical locations

• Alternatively, they inhabit different places within same ecosystem

Temporal Isolation

Two populations can’t exchange alleles due to differing availability times (yearly or daily)

Behavioural Isolation

Two populations don’t respond to each others’ mating rituals

Mechanical Isolation

A physical barrier that prevents mating or fertilization

Gametic Isolation

• Two populations exchange sperm and eggs

• Chemical markers prevent eggs from being fertilized by “wrong” sperm

Zygotic Mortality

Zygote is formed, but fails to develop into maturity

Hybrid Inviability

Hybrid is born, but is either short-lived or unhealthy

Hybrid Infertility

Healthy hybrid is born, but unable to reproduce