EvolutionChapter 15

Darwin’s Theory of Natural Selection

Evolution

• http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Evolution

• Is it correct to say that Evolution is just a theory? Is gravity just a theory? Defend your answer.

Biological Evolution

• All the changes that have transformed life on Earth from the earliest beginnings to the diversity of organisms in the world today.

• Unifying theme of biology.

Biological Evolution

• Microevolution: evolution on a small scale, affecting a single population.

• Macroevolution: evolution on a large scale affecting changes in species across populations.

Charles Darwin• 1809-1882

• Darwin boarded the HMS Beagle in 1831.

• Darwin’s role on the ship was as a naturalist and companion to the captain.

• Darwin collected biological and geological specimens during the ship’s travels.

http://en.wikipedia.org/wiki/Charles_Darwin

Charles Darwin

http://en.wikipedia.org/wiki/Charles_Darwin

Charles Darwin

• Over the 5 year-voyage, Darwin collected rocks, fossils, plants, and animals.

• Darwin also read Charles Lyell’s Principles of Geology which influenced his thinking about the age of the Earth.

Charles Darwin

• In 1835, the Beagle arrived in the Galapagos Islands.

• This is where Darwin collected many new specimens and began to observe the differences in the varieties of animals among the different islands.

• Darwin was intrigued with species diversity and conceived his theory of natural selection in 1838.

Galapagos

http://dxing.at-communication.com/en/hc8a_galapagos_islands_cq_ww_dx_ssb_contest_2009_dx_news/

Natural Selection• Darwin’s theory had 4 basic principles that

explained how traits of a population can change over time.

• 1) Individuals in a population show differences or variations

• 2) Variations are inherited

• 3) Organisms have more offspring than can survive on available resources.

• 4) Variations that increase reproductive success will have a greater chance of being passed on.

Natural Selection• Results in changes in the inherited traits of a

population over time.

• These changes increase a species’ fitness in the environment.

• 4 Main Principles

• 1) Overproduction of offspring

• 2) Variation

• 3) Adaptation

• 4) Descent with Modification

Natural Selection

• Variation exists within the inherited traits of the individuals.

• An organisms phenotype may influence its ability to find, obtain, and utilize its resources and might affect the organisms ability to reproduce.

• Phenotypic variation is controlled by the organisms genotype and environment.

Variation

Variation

Natural Selection

• Adaptation leads to the increase in frequency of a particular structure, physiological process, or behavior in a population or organisms that makes the organism better able to survive and reproduce.

• Fitness: used to measure how a particular trait contributes to reproductive success.

Adaptation

http://www.medpedia.com/news_analysis/188-CMU-Medical-and-Technology-Review/entries/79874-Guidelines-for-Community-Associated-MRSA

Natural Selection

• Overproduction of offspring: The ability of a population to have many offspring raises the chance that some will survive but also increases the competition for resources.

Overproduction

• Average cardinal lays 9 eggs each summer, if each baby cardinal survived and reproduced, it would take only seven years for the first pair to have produced one million birds.

http://www.fcps.edu/islandcreekes/ecology/northern_cardinal.htm

Natural Selection

• Descent with modification: as the environment of a population changes, the entire process of natural selection can yield populations with new phenotypes adapted to new conditions.

• Each successive living species will have descended, with adaptations or other modifications, from previous generations.

Descent with Modification

http://readingevolution.com/evolution.html

Descent with Modification

http://readingevolution.com/evolution.html

Natural Selection

• http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Natural Selection

• What are the 4 components of Natural Selection? How does Natural Selection affect Hummingbird populations?

Shaping Evolutionary Theory

Why Does Evolution Matter?

• http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

• Why is the theory of evolution important to doctors and the field of medicine? How does it affect the way illnesses and treatments are approached?

Continuity of Life

• Recall:

• All life that has existed on Earth share at least the same 2 structures, Nucleic Acids (DNA and RNA) and Protein.

Continuity of Life

• Recall:

• All ecologically successful organisms have reliable means of passing genetic information to offspring through reproduction.

• Sexual Reproduction: 2 parents, meiosis, gametes.

• Asexual Reproduction: 1 parent, genetically identical offspring.

Continuity of Life

http://csls-text.c.u-tokyo.ac.jp/active/12_01.html

Continuity of Life

• The genetic view of evolution includes the transfer of genetic material through reproduction.

• The continuity of a population/species depends on the process of reproduction.

Mechanisms of Evolution

• Population Genetics

• Natural Selection

• Molecular Biology

Population Genetics• Genetic Drift is the random change in

the frequency of alleles of a population over time.

• In large populations enough alleles “drift” to ensure the allelic frequency of the entire population remains constant from generation to generation.

• In smaller populations the effects of genetic drift become more pronounced and the chance of losing an allele becomes greater.

Population Genetics

http://legacy.hopkinsville.kctcs.edu/sitecore/instructors/Jason-Arnold/VLI/Module%203/Module3Evolution/Module3Evolution7.html

Population Genetics

• Founder Effect

• Extreme example of genetic drift.

• Occurs when a small sample of a population settles in a location separated from the rest of the population.

• Alleles that were uncommon in the original population might become common in the new population.

Population Genetics

• Founder Effect

• Amish Communities

• 6-Finger Dwarfism

http://www.teachersdomain.org/resource/tdc02.sci.life.gen.foundereffect/

Population Genetics• Bottleneck

• Occurs when a population declines to a very low number and then rebounds.

• The gene pool of the rebound population is often genetically similar to that of the population at its lowest level, reduced diversity.

Population Genetics

• Bottleneck

• Cheetahs

• European Bison

http://www.bio.miami.edu/ecosummer/lectures/lec_causesofevolution.html

Population Genetics

• Gene Flow

• The movement of genes into or out of a population.

• Occurs during the movement of individuals between populations which increases genetic variability.

• Gene Flow

• Migration

http://evolution.berkeley.edu/evosite/evo101/IIIC4Geneflow.shtml

Population Genetics• Nonrandom Mating

• Limits the frequency of the expression of certain alleles while increasing the frequency of expression of other alleles.

• Organisms usually mate with individuals in close proximity which promotes inbreeding and leads to changes in allelic proportions that favor homozygous individuals.

• Nonrandom Mating

• Mating preferences

http://biology.unm.edu/ccouncil/Biology_203/Summaries/PopGen.htm

Population Genetics

• Mutations

• Increase the frequency and types of allele changes within populations (genetic variability).

• Provide raw material for which natural selection works.

Population Genetics

• Mutation

• Resistant Lice

http://evolution.berkeley.edu/evosite/evo101/IIIC1aRandom.shtml

Population Genetics

• Hardy-Weinberg Principle

• When there is no change in the allele frequencies within a species, a population is said to be in genetic equilibrium.

• p + q = 1

Population Genetics• Hardy-Weinberg Principle: there are 5

conditions required to maintain genetic equilibrium

• 1) Population must be large with no genetic drift occurring

• 2) No movement in or out of a population

• 3) Must be random mating

• 4) No mutations within the gene pool

• 5) Must be no natural selection.

http://schoolworkhelper.net/2010/07/the-hardy-weinberg-principle/

Natural Selection• Acts to select individuals that are

best adapted for survival and reproduction.

• Three main ways natural selection alters phenotypes:

• 1) Stabilizing selection

• 2) Directional selection

• 3) Stabilizing selection

Stabilizing Selection• Eliminates extreme expressions of a trait

when the average leads to higher fitness.

http://www.mun.ca/biology/scarr/Stabilizing_Selection_in_Humans.html

Directional Selection

• Occurs when an extreme version of a trait makes an organism more fit.

http://avonapbio.pbworks.com/w/page/9429288/Ch-23

Disruptive Selection

• Process that splits a population into 2 groups, tends to remove individuals with average traits.

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_Disruptive.html

Speciation

• The process of forming a new species by biological evolution.

• How does this occur?

• Reproductive Isolation: when organisms in the population are isolated or separated and cannot reproduce with the original population.

Reproductive Isolation

http://evolution.berkeley.edu/evolibrary/article/evo_44

Speciation• Once reproductive isolation occurs,

natural selection and genetic variation increase the differences among the two populations.

• Over time and as new traits are favored in the 2 populations, the populations become so different that they can no longer reproduce with each other.

• This is the point at which the 2 populations are considered different species.

Speciation

• Allopatric speciation: a physical barrier divides one population into two or more populations.

• Sympatric speciation: a species evolves into a new species without a physical barrier.

Speciation

http://en.wikipedia.org/wiki/File:Speciation_modes.png

How Does Speciation Occur?

• Gradualism

• Gradual changes of a species in a particular way over long periods of time.

• Ex) a gradual trend toward larger body size.

How Does Speciation Occur?

• Punctuated Equilibrium

• Periods of abrupt change after long periods of little change.

• Ex) Sudden changes in species size or shape due to environmental factors.

How Does Speciation Occur?

http://lifeofplant.blogspot.com/2011/04/evolution-gradualism-vs-punctuated.html

How Does Speciation Occur?

• Adaptive Radiation/Divergent Evolution

• One population gives rise to two or more species.

• Can occur in a relatively short period of time when one species gives rise to many species due to a new habitat or other ecological opportunity.

Divergent Evolution

http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u4aos2p4.html

How Does Speciation Occur?

• Convergent Evolution

• Evolution among different groups of organisms living in similar environments produces species that are similar in appearance or behavior.

• Produces analogous structures (structures similar in appearance or function that have different evolutionary origins).

Convergent Evolution

http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u4aos2p4.html

How Does Speciation Occur?

• Coevolution

• Two or more species living in close proximity change in response to each other.

• Mutualistic and parasitic relationships are examples of coevolution.

Coevolution

http://biostuds.wikispaces.com/COEVOLUTION

Extinction

• The elimination of a species.

• Often occurs when a species cannot adapt to a change in its environment.

• Can be gradual or rapid.

Gradual Extinction

• Occurs at a slow rate.

• May be due to other organisms, changes in climate, or natural disasters.

Mass Extinction

• Usually occurs when a catastrophic event changes the environment very suddenly (such as a volcanic eruption, or a meteor hitting the earth).

• It is often impossible for species to rapid and extreme environmental changes.

Extinction

• http://www.5min.com/Video/Black-Rhino-Extinct-in-West-Africa-517199585

How Do Species Increase Their Chance

for Survival?

Genetic Variability• Species that interbreed share a common

gene pool (all genes including different alleles of all the individuals in a population).

• Because of the shared gene pool, a genetic change that occurs in one individual can spread through the population through the process of reproduction.

• If this genetic change increases fitness, it will be found in many individuals in the population.

Genetic Variability

• There is a variability of phenotypes within species that increases diversity among the organisms of the species.

• The greater the diversity, the greater the likelihood is for the species could survive during environment changes.

Genetic Variability

• Organisms with phenotypes that are well suited for environmental changes will be more likely to survive and reproduce.

• The alleles associated with these favorable phenotypes should increase in frequency and therefore become more common.

Scientific Evidence Underlying Evolutionary

Theory

Anatomy

• Anatomy: the study of the structures of organisms.

• Scientists study the anatomical traits of organisms to help understand evolutionary theory.

Anatomy

• Species living in similar ecological conditions but different geographical locations may share similar structures and behaviors.

• Anatomical traits that are more favorable for particular environments will become established and be passed on to future generations.

Anatomy• Homologous Structures: anatomically

similar structures inherited from a common ancestor.

• Evolutionary theory predicts that an organism’s body parts are more likely to be modifications of ancestral body parts rather than entirely new features.

• The greater the number of homologous structures the more closely related the 2 organisms.

Anatomy

http://www.newworldencyclopedia.org/entry/Homology_(biology)

Anatomy

• Vestigial Structures: structures that have little or no function to the organism and may be remnants of functional structures in ancestral organisms.

http://www.mvla.net/teachers/TeriF/Biology/Documents/5%20Vestigial%20Organs.BMP

Embryology

• Embryo: early, pre-birth stage of an organism’s development.

• Embryology: the study of embryonic development of organisms.

• Embryology compares the anatomies of embryos of different species.

Embryology

• Similarities in patterns of development or structures that may not be evident in adult organisms become evident when embryonic development is observed.

• The embryos of vertebrates are very similar in appearance early in development.

• This may suggest that these species evolved from common ancestors.

Embryology

http://scrollandquill.wordpress.com/2011/10/29/does-ontogeny-recapitulate-phylogeny-refuting-embryological-“evidence”-for-evolution/

Biochemistry• Biochemistry: the study of the

chemical processes of organisms.

• Scientists study genes and proteins to provide support for evolutionary theory.

• Biochemistry provides evidence of evolutionary relationships when anatomical structures are difficult to use.

Biochemistry

• The more similar the DNA and amino acid sequences in proteins of 2 species, the more likely they are to have diverged from a common ancestor.

Biochemistry

Paleontology

• Paleontology: the study of prehistoric life.

• The fossil record provides evidence of life forms and environments along a timeline.

• This can be used to support evolutionary relationships by showing the similarities between current species and ancient species.

Paleontology

• Examining the fossil record reveals a history of the organisms that lived on Earth and their relative ages.

• The fossil record is considered incomplete because not all organisms form fossils.

Paleontology

• Transitional Fossils: fossils that show links in traits between groups of organisms.

Paleontology

nany41.com

How Do Scientists Use Evidence to Support

Evolution?

Theory vs Law• Theory is a well-substantiated

explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypothesis.

• Laws are quantitative relationships between observable phenomena about how some aspect of the natural world behaves under certain circumstances.

Evidence vs. Proof

• All theories, including cells, atoms, and evolution, can be well-supported by evidence from a variety of sources but cannot be proven.

• The validity of a theory rests in its ability to explain some phenomena.

Evidence

• How is Evolutionary Evidence Used?

• Phylogeny: evolutionary history.

• Scientists study data to trace the phylogeny of a species or group of species.

• Based on this data, the evolutionary theory has been formed.

Evidence

• Scientists must use multiple sources of evidence to draw conclusions concerning the evolutionary relationship among organisms.

• Comparative Anatomy, Embryology, Comparative Biochemistry, and Paleontology

Evidence

• What exactly does the Evolutionary Theory state?

• All forms of life on Earth are related because the ancestry of organisms can be traced back to a common origin.

• Evidence of this shared history can be found in a variety of aspects of living and fossil organisms (physical features, structures of proteins, and sequences found in DNA and RNA).

The Theory of Evolution

• The theory of evolution is a well-tested explanation that accounts for a wide range of observations made in many fields of science.

• No scientists suggest that all evolutionary processes are understand; there are many questions that remain unanswered.

Field of Anatomy• Phylogenies are constructed using

anatomical differences.

• Scientists use the assumption that anatomical differences increase with time.

• The greater the anatomical similarity, the more recently a pair of species shared a common ancestor.

Field of Anatomy• The accumulation of evolutionary

differences overtime is called divergence.

• Sometimes individual structures may suggest evolutionary relationships that imply a process other than divergence.

• This may result from convergence (structures becoming more similar with time).

Field of Embryology

• Information gathered from embryonic development is used to reconstruct phylogenies of highly divergent taxa, such as phyla and classes.

• These taxa have evolved so many anatomical differences they are difficult to compare otherwise.

Field of Paleontology • The fossil record provides

information regarding the relative dates and order of divergence for phylogenies.

• The fossil record is incomplete because not all organisms form fossils.

• Several environmental conditions have to be met for fossils to form.

Field of Biochemistry

• Phylogenies can be constructed by assuming that differences in DNA, proteins, and other molecules increase over time.

• The time since a pair of species has “diverged” can be estimated under the assumptions of a “molecular clock.”

Modern Classification

Phylogenetic Species Concept

• This concept defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent.

• Scientists use different characters to classify organisms.

• These include: morphological characters (anatomical) and biochemical characters (DNA and protein).

Phylogenetic Trees

• A phylogeny or evolutionary tree, represents the evolutionary relationships among a set of organisms or group of organisms.

• The tips of the trees represent groups of descendent taxa and the nodes of the tree represent ancestors of those descendants.

Phylogenetic Trees

http://evolution.berkeley.edu/evolibrary/article/phylogenetics_02

Phylogenetic Trees

• Some phylogenetic trees express only the order of divergence of a species, not time frames.

http://evolution.berkeley.edu/evolibrary/article/phylogenetics_02

Phylogenetic Trees

• Some phylogenetic trees indicate an estimated time of divergence.

What You Need To Know!• When interpreting a phylogenetic

tree, you need to be able to answer the following questions:

• 1) Which groups are most closely related?

• 2) Which groups are least closely related?

• 3) Which group diverged first (longest ago)?

Example

http://www.biologie.uni-hamburg.de/b-online/e28_2/phylogeny.htm

Phylogenetic Trees• Because species are becoming extinct at

an increasing rate, biologists face many challenges when classifying organisms.

• The most recent classification scheme includes:

• Three domains: Bacteria, Eukarya, and Archaea.

• Six Kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.