Bio 11: Unit 3 Test

Evolution

All the changes that have transformed life on earth from its earliest beginnings to the seemingly infinite diversity that characterizes it today

What is Evolution

Process in which significant changes in the inheritable traits of a species occur over time

Macro evolution

Origin of taxonomic groups higher than the species level. Mainly studies using fossil records

Formation of Fossils (Sedimentary rock)

Richest source of fossils:

• Specimens rich in minerals may remain as fossils (Ie. teeth, bones, and shells)

How Fossils Form

1. Water carries small rock particles to lakes and seas

2. Dead organisms are buried by layers of sediment, which forms new rock

3. The preserved remains may later be discovered and studied ‘

Formation of Fossils (Petrification)

Some organic material can be preserved in between rocks and remain preserved through petrification (mineralization)

• The process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals

Formation of Fossils (Preserved Specimens)

• Found in acid bogs, tar pits, permanently frozen ground, amber, or hardened tree sap

• When conditions prevent most decomposition, organisms may be preserved nearly intact

Origins of Diversity

The diversity of species → Resulted due to the formation of different species

• Charles Darwin proposed the idea of Natural Selection in 1859

Natural Selection

• Environment selects individuals with the characteristics that allow them to survive over other individuals with characteristics that are not suited for the environmental conditions

• Selected within the variation of the population → selected organisms produce more offspring

Genetic Diversity

Basis of Natural Selection

• Changes in the characteristics of a species are produced by combination of

1. Random genetic mutations

2. Selection for a particular characteristic which increase survival and breeding success → survival of the fittest

Charles Darwin

• Worked as a naturalist

• Collected specimens, made observations

• Left England believing that species could not change

Alfred Russell Wallace

• Came up with a theory very similar to Darwin’s

• Not knowing about Darwin’s ideas, he sent a copy of his paper

• Darwin quickly wrote: “The Origin of Species”

Galapagos Islands

Key to the development of Darwin’s theory

2 Points made by Darwin

1. Species were not specifically created in their present forms but have evolved from ancestral species

2. Described the mechanism of evolution as natural selection

Aristotle’s Views on Evolution

Aristotle believed that Organisms range from simple to complex in a hierarchy → species are fixed and do not change

• Ladder of life

Natural Theology

• God created each individual species for a particular purpose in nature

• Classification revealed the “order” of God’s plan (fixed species)

Jean Baptiste Lamark

• Spontaneous generation of species

• Species change over time into new species

• Inheritance of acquired characteristics

Lamark’s Proposed Mechanism

1. Use and Disuse: Organs used extensively become larger/stronger, the ones that aren’t use deteriorate

2. Inheritance of acquired characteristics: Body builder wills on strong/large muscles to offspring

Lamark vs Darwin

• Lamark believed that a species could alter it’s characteristics solely based on use and disuse, then pass this on to offspring

• Darwin found out that natural selection was the reason for change in characteristics during evolution. Those with favourable characteristics that helped increase survival, were able to live longer and create offspring.

Evidence for Evolution and Natural Selection

1. Biogeography

2. Comparative Anatomy

3. Fossil Evidence

4. Comparative Embryology

5. Biochemistry

Biogeography

• Geographic distribution of species

• Islands have many species of plants and animals found nowhere else BUT are closely related to species of the nearest mainland

• Example: Darwin’s Finches on Galapagos Islands

Micro evolution

A change in gene (allele) frequency within a population over time

• Evolution on the small scale

Mechanisms of Microevolution

1. Genetic drift (Bottleneck Effect, Founder Effect)

2. Gene Flow

3. Mutations

4. Non-Random Mating

6. Natural Selection

Genetic Drift

• Changes in frequencies of alleles in a breeding population → occurs due to chance events

• Two situations that lead to populations small enough for genetic drift to occur are Founder Effect and Bottleneck Effect

Bottleneck Effect

Natural disasters, disease may reduce size of pop. drastically → small surviving populations unlikely representative of the original population.

Founder Effect

A few individuals from a population start a new population with a different allele frequency than the original population

Gene Flow

Movement of alleles IN or OUT of the population due to the migration of individuals → can introduce new alleles into a population and increase genetic diversity

Mutations

Change in the DNA sequence introduces NEW alleles into a population

Non - Random Mating

Individuals of a certain phenotype choose similar mates OR one with preferred phenotypes

Natural Selection

Alleles being passed on to the next generation in different proportion than the original population

→ due to differential success in survival and reproduction

Types of Natural Selection

1. Stabilizing Selection

2. Directional Selection

3. Disruptive Selection

4. Sexual Selection

Reminder: Natural selection can affect the frequency of an inheritable trait in different ways depending on which phenotypes in a varying population are favoured

Stabilizing Selection

• Acts against extreme phenotypes and favours the more intermediate variants

• “Average” = Best Adapted

Directional Selection

Favours an increase OR decrease in the value of a trait from the current population average

• Favours relatively rare individuals with more extreme variations of a trait from the average

• Occurs during periods of environmental change or colonization of a new habitat

Disruptive (Diversifying) Selection

Environmental conditions vary favours extreme phenotypes over intermediate phenotypes.

• Two or more variations or forms of a trait that differ from the current population average

Sexual Selection

Favours the selection of any trait that influences the mating success of the individual

Sexual Dimorphism

Marked differences between the sexes (the result of sexual selection)

• Not always adaptive (ie. bright plumage = increased predation)

• Therefore, in many cases there is a compromise between the two selection forces

Four reasons why Evolution does NOT Fashion Perfect Organisms

1. Existing structures are modified rather than scrap ancestral structures and re-design new models

2. Adaptations are often compromises (Eg. Agile humans → given up structural reinforcement, therefore more prone to sprains, torn ligaments

3. Not all evolution is adaptive (Chance events can happen)

4. Natural selection can only edit variations that exist → new genes do not exist on demand