BIO110 Darwinian Evolution

Darwinian Evolution

Chapter 7

History of Evolution

• Lamarck was one of the first to suggest that species change over time (evolution)

• Another scientist, Lyell suggested that an old Earth had gradually changed through slow, accumulating processes.

• In 1859, British naturalist Charles Darwin published On the Origin of Species by Means of Natural Selection

• In the Origin of Species Darwin introduced the concepts of evolution and natural selection

What did Darwin discover?

• First, modern species have descended from common ancestors (evolution)

• Second, natural selection is the mechanism of evolution

What needs to be occurring for natural selection to happen?

• •Overproduction

  –More individuals are born than can be supported by the environment.

• •Limited resources

  The amount of resources (such as food, water, shelter, sunlight) stays relatively constant

What needs to be occurring for natural selection to happen?

• •Competition

  More offspring are born than can be supported by limited resources; not all individuals survive and reproduce

• •Variation

  Darwin also observed that no two individuals are alike

Multiple Choice

Which observation from Darwin suggested that more individuals were born than could be supported?

• Variation

• Competition

• Overproduction

• Limited Resources

Multiple Select

The conclusion Darwin came to about competition was due to which other observations?

• Overproduction

• Limited Resources

• Variation

Multiple Choice

The 4 factors (Overproduction, Limited Resources, Competition, and Variation) all led to the conclusion that what could be occurring?

• Sexual reproduction

• Bottleneck event

• Natural selection

• Gene flow

What is Natural Selection?

• It's a little more than just "survival of the fittest"

• Those individuals with variations that make them best suited to their environment will, on average, be more likely to survive and reproduce

Important Points about Evolution

• Individuals don’t evolve.

  Natural selection acts on individuals, but only populations evolve

• Natural selection works with heritable traits. Only genetically coded traits are subject to natural selection.

• Evolution does not have a goal.

  Evolution occurs in response to local environmental conditions, not future ones

Evolution is witnessed as an adaptation?

• Individual with traits that enhance survival and reproduction will have, on average, more offspring

• Adaptation is the accumulation of these favorable traits in a population over time

Multiple Choice

Can individuals evolve?

• Yes

• No

Multiple Choice

Can individuals experience natural selection?

• Yes

• No

Multiple Choice

What is the goal of evolution?

• Make better, fitter organisms

• More more offspring

• More genetic variation

• There is no goal

Evidences for Evolution

Chp 7

Fossil Records

• The fossil record provides important evidence for evolution

• Fossils form when organisms die, fall into accumulating sediment, and are compressed into rock

• Fossils can be dated using their geological position or through radiometric dating

Vestigial Structures

• Structures that are still seen in anatomy, but no longer used.

• Transitional forms (vestigial structures) provide evidence of change within lineages from structures no longer used

Biogeography

• Biogeography is the study of the geographic distribution of species

• Tracing where species are and where they came from allows scientists to visualize their lineages

Comparative Embryology

• Comparisons of the body structures of modern organisms is called comparative anatomy

Homologous Structures

• Examination of animal forelimbs shows they are all constructed from similar bones

DNA and Bioinformatics

• All life uses DNA for genetic code

• Closely related species will have similar DNA and protein sequences.

  –Such as in primates

• Bioinformatics employs computational tools to process genetic data

Multiple Choice

Which type of evidence for evolution can be found in anatomical structures seen in organisms that are no longer used?

• Homologous structures

• Biogeography

• Vestigial structures

• Comparative embryology

Multiple Choice

Antelope species can be found on several continents that are far apart with no access to one another. What type of evolutionary evidence is this?

• Homologous structures

• Bioinformatics

• Fossil records

• Biogeography

Multiple Select

Which type of evidence for evolution suggests a common ancestor?

• fossil records

• homologous structures

• comparative embryology

• Bioinformatics

Populations are the units of Evolution

Chp 7

Evolution and Natural Selection on Populations

• Natural selection acts on individuals

• However, evolution is defined only in terms of changes in a population over time

• Review: A population is a group of individuals of the same species living in the same place at the same time

Population Gene Pool

• The gene pool consists of all versions of all the genes carried by all the individuals in a population

• Genetic variation in a gene pool can arise through mutation

• Sexual reproduction ensures that genes are randomly mixed

Natural Selection on the Gene Pool

• Traits that enhance survival and reproduction will be represented with increasing frequency in the gene pool

• A generation-to-generation change in the gene pool is called microevolution, which is evolution occurring on its smallest scale

• Taken over many generations, microevolution can result in the gradual adaptation of species to the local environment

Evolutionary Mechanisms

(Hint: We already covered Natural Selection) Chp 7

Fitness

• Darwinian fitness is the contribution that an individual makes to the gene pool of the next generation in comparison to the contributions from other individuals

• The strongest individual not always the fittest

• There are many sorts of adaptations that can improve fitness (ex: camouflage)

Genetic Variation

• 1.Mutations: Random changes to DNA can create new genes.

• 2.Sexual recombination: During the formation of sperm and eggs, chromosomes can exchange pieces of DNA, shuffling genes.

Genetic Drift

• Genetic drift is a change in a gene pool when survival and reproduction is due to chance alone

• –For example, genes may be lost if a few individuals die or migrate at random.

• –Genetic drift can be important in small, or isolated, populations.

Examples of Genetic Drift

• If a population is drastically reduced in numbers, that is a bottleneck

• If a few individuals migrate to a new isolated habitat, that is a founder effect

• In either case, by chance, some genes will be lost from the gene pool

Multiple Select

Which of the following can cause genetic drift?

• Bottleneck event

• Founders effect

• Chance

Gene Flow

• Most populations are not isolated.

  Gene flow is the genetic exchange among populations due to migration

• Gene flow tends to reduce differences among gene pools

Sexual Selection

• Sexual selection is a form of natural selection that depends on an individual’s ability to obtain a mate

• Females may choose males for their traits

• Males may compete with each other for access to mates

Multiple Choice

Does gene flow increase or decrease the difference between 2 different populations' gene pools?

• Increase

• Decrease

Multiple Select

In which ways can sexual reproduction cause increased variation that powers evolution?

• Crossing over

• Independent Assortment

• Random Fertilization

• Mutations

Macroevolution and Speciation

Chp 7

Macroevolution & Speciation

• Macroevolution is genetic change on a large scale

• Speciation is the evolutionary formation of new species

Speciation Pathways

• In nonbranching evolution, an ancestral population changes gradually.

• In branching evolution, an ancestral population splits into two or more populations.

What is a Species?

• The most commonly used definition of species is a population that is capable of interbreeding to produce healthy, fertile offspring

• Why can't similar species mate together?

Reproductive Barriers

• Behavioral isolation: Members of a species often identify each other through specific rituals

• Mating time differences: Many species are able to reproduce only at specific times

• Habitat isolation: If species live in slightly different habitats, they may never meet

Reproductive Barriers (cont')

• Mechanical incompatibility: Members of different species often cannot mate because their anatomies are incompatible

• Gametic incompatibility: The gametes (sperm and egg) of different species usually cannot fertilize each other

• Hybrid weakness: Offspring of two species may be unfit, or they may be sterile

Multiple Select

Check the following requirements for an offspring of 2 organisms of the same species. Must be:

• Sterile

• Fertile

• Healthy

• Have many offspring

Multiple Select

Which reproductive barrier(s) could be the reason why two similar species that live in the same area cannot mate?

• Geographic isolation

• Behavioral isolation

• Mating time differences

• Habitat isolation

So, How do new species arise?

• Some event separates a population:

  –Time, space, or genetics

• Populations then diverge along their own evolutionary path

Allopatric vs Sympatric

• Allopatric speciation may occur when a physical barrier isolates populations (Ex: Grand Canyon separating single population into two)

• Sympatric speciation occurs with no geographic isolation (Ex: Speciation in plants can occur suddenly due to large-scale genetic changes such as wheat)

Taxonomy and Classification

Chp 7

Taxonomy

• Taxonomy is the identification, naming, and classification of species

• Every organism can be placed into the taxonomic hierarchy, which starts with the domain and ends with the species name

• Life is classified into one of three large groups called domains based on cell type

Tiger Classification Example

•Domain

•Kingdom

•Phylum

•Class

•Order

•Family

•Genus

•Species

Phylogenetic Trees

• Phylogenetic trees are evolutionary maps that present a hypothesis about the evolutionary history of related species

• A clade is any group of species that consists of an ancestral species and all its descendants

• The tips of the tree represent groups of the most recently evolved species

• To determine how closely related two species are, find their most recent common ancestor

Summary/Study Topics

Darwin and his observations, Natural selection, microevolution (gene pool), Genetic drift causes, Macroevolution, speciation types, reproductive barriers, taxonomy and classification