Bio 105 Test 1

George Curvier (1769 -1832)

• French Professor of Natural History of Comparative Anatomist

• Father of Paleontology

• Pioneered the technique of reconstructing entire skeletons of extinct organisms.

  • Giant fossil mammoth found as definitive proof of extinction.

• Work was instrumental in demonstrating a series of mammalian extinction in the paris basin.

• Theory of Catastrophism

• Did not believe in evolution

Theory of Catastrophism

• Series of catastrophes can explain disappearance of extinct species.

Carolus Linnaeus (1707-1778)

• Father of modern taxonomy

• Developed 1st systematic organization of biological organisms.

• Established system of binomial nomenclature for species names

• Published Systema Naturae

• Detailed hierarchal classification of animals and plants

• Linnean Species

System of Binomial Nomenclature

• Very formal rules for naming species

• Every species has its own unique name

  • Described using two names

Linnaean Species

• Species were the lowest level of organization in his hierarchical scheme.

  • Occupied a privileged place since it was the only irreducible entity recognized in taxonomy

  • Represents the essence of biological organization.

• All higher categories are arbitrary constructions which cannot be identified in nature

• Based on phenotype

Charles Lyell (1797-1875)

• Scottish Geologist - contemporary of Darwin

• Earth shaped by geological processes over long periods of time

• Demonstrated a great antiquity for the earth - still active today

• Strongly influenced Darwin

• Theory of Uniformitarianism

Theory of Uniformitarianism

4 claims

• Uniformity of Law

• Uniformity of Process

• Uniformity of Rate

• Uniformity of State

Uniformity of Law

Natural laws remain constant through space and time.

Uniformity of Process

Past phenomena should be explained as the result of processes now in operation.

Uniformity of Rate

Change usually occurs slowly and steadily.

Uniformity of State

Change, although continuous, is non directional and non progessive.

Jean Baptiste Lamarck (1744-1829)

• Early theory of biological evolution

• Animals were recognized as being adapted to their environment - dynamic relationship.

• Environmental change lead to biological change and adaptation.

• Emphasized “inner needs” as driving evolutionary changes.

Lamarckian Evolutionary Interpretation

• Changes in environment can result in changes in the organism during its lifetime.

• Offspring inherit these acquired features.

Thomas Hunt Morgan (1866-1945)

• America geneticist and embryologist

• Noble prize in medicine

• Early 1900s began to study fruit fly genetics

  • discovered that genes were carries on chromosomes, forming mechanical basis of heredity which became basis of modern genetics

• Fruit fly studies revealed presence of numerous small, heritable mutations

• Embraced mendelian genetics and the relevance of mutations for evolution

  • Laid the foundation for natural selection by elucidiating process of heredity.

Gregor Mendel (1822-1884)

• Pea plant experiments

  • Bred pea plants at the abbey and document phenotypic features across generations.

  • Published in 1866 but not widely known until 1890s when rediscovered after his death.

• Theory of Particulate Inheritance

• Principle of Segregation

• Principle of independent Assortment

• Principle of Dominance

Theory of Particulate Inheritance

• Identified genes as units of inheritance

• Established many of the most basic principles which underlie modern genetics.

Principle of Segregation

• Heredity is transmitted by large numbers of independent, heritable units (genes)

  • Occur in pairs in individuals

  • Pairs are, in turn, seperated within the individual during the production the eggs or sperm.

  • Offspring inherit one gene of each pair from each parent.

    • Allows for new combinations of gene pairs to appear in the offspring generations.

Principle of Independent Assortment

• Hereditary units for different traits are generally inherited independently of one another.

• Genes codes for discrete character states

• Different alleles are passed on independently from one another

• Recessive genes reappear in succeeding generations.

Principle of Dominance

• Some alleles are dominant over the other alleles for a given gene.

• Dominant alleles are expressed in a 3:1 ration in second generation.

Dominant Alleles

• If present, always expressed

• Will hide a recessive gene

• Can be a combination of two dominant genes or one dominant and one recessive

Recessive Alleles

Must have two recessive genes for the characteristic to be expressed.

Charles Darwin

• Medical Student at Cambridge

• Sailed around the world from 1831-1836

• Major Contributions;

  • Evolution as such

  • Common descent

  • Multiplication of Species

  • Gradualism

  • Natural Selection

Fixity of Species

• Long held belief that plant and animal species do not change over time and remain identical to how they were originally created

• Great chain of being

• Abandoned in late 19th century.

Great Chain of Being

• Thought of arranged all life in a strict, god - given hierarchal ladder from minerals up to humans and angles

  • Leaving no room for movement or change.

Extinction

• Recognized due to Curvier in 18th century

• Played an important early role in debates on existence of evolution.

Alfred Russel Wallace (1823-1913)

• Independently developed the Theory of Natural Selection

• Founded field of bioogeography

• Began career collecting specimens in the Amazon

  • Looking for evidence of transmutation of species

• Worked in Southeast Asia where he described the geographic distribution of living species and their fossil ancestors

  • Wallaces Line

• Jointly published Theory of Natural Selection with Darwin

Wallace’s Line

• Represents a deep water channel that separates Sundo (North) and Sahul (South) continental south.

• A faunal boundary line separating organisms related to Asian species and those related to Australian species.

• Applies to both land mammals and birds.

Blending Theory

• Genetic material inherited from mother and father blended together

• Seems intuitively correct - offspring look like their parents.

Two Main Issues with Blending Theory

• Implied eventually everything would be fully blended and very similar.

• Seemed to go against the whole theory of Natural Selection producing variation.

Galapagos Islands

• Darwin

• Visit was definitive

• Beaks of Galapagos finches varied according to island inhabited and food consumed

• Darwins Finches

• A kind of natural selection was operating in nature to produce most successful organism.

Darwins Finches

• Size and shape of the beak was related to diet.

  • Through generations, the birds had adapted to different diets.

Theory of Natural Selection

• Origin of Species - 1859 Darwin and Wallace

1.) All species are capable of producing offspring faster than the food supply increases.

2.) All living things show variation and two individuals of a species are unlike.

3.) Because of 1, there are more individuals than can possible survive. Individuals with one or more favorable variations will have a better chance to survive and reproduce.

4.) These favorable variations are inherited and passed on to the next generation.

5.) Over long periods of time, new species would emerge through the gradual accumulation of favorable variations.

Gradualism

• A theory proposing that new species arise from the slow, steady, and continuous accumulation of small genetic and morphological changes over long periods.

• Darwins theory was gradualist in the extreme.

• Relied on the work of Lyell.

• Gradual change (Lyell) + Competition for survival (Malthus)

Salutational Evolution

• Evolution occurs through rapid, large scale changes.

• Rapid reorganization of the organism.

• Major changes can be brought about from one generation to the next.

• Championed by the mutationists.

• Directly opposed gradualism in Darwins theory.

Adaptation

• An inherited physical, behavioral, or physiological trait that helps an organism survive and reproduce in its specific environment.

  • Change over many generations where a population becomes better suited to its habitat.

Modern Synthesis

• 1930’s - 1940s saw an emerging consensus between Mutationists and Selectionists.

• Mutation and Natural Selection not mutually selective but operate together as complementary factors.

  • M = source of new evolutionary material

  • NS = Mechanism that determines which new variations (mutations_ survive and are passed to the next generation.

• Small new changes in the genetic material transmitted from parent to offspring are the fuel for natural selection.

• Macroevolution

• Evolution is a two stage process

Macroevolution

• Evolution above the species level

• An extension of micro-evolution = evolution within a species.

Evolution is a two stage process

1.) The production and distribution of variation

2.) Natural selection acting on this variation. Variation among individuals differently affect their changes for survival and reproduction.

Variation

Inherited differences between individuals.

Mechanisms of Evolution

1.) Natural Selection

2.) Mutation

3.) Gene Flow

• Migration

4.) Genetic Drift

• Founder Effect

Mutation

• Refers to both the process of altering a gene or chromosome as wells as to its product.

  • Only have evolutionary consequences if they are transmitted to succeeding generations

• Occur mainly during DNA replication

• Fixed mutations are referred to as substitutions

• Random process

DNA replications

Cell divisions in humans.

Mutation Substitutions

• When the error becomes the normal state of the allele.

  • Established by genetic drift or natural selection.

Mutation Random Process

1.) Although some mutations are statistically more likely to occur than others, it is not possible to predict precisely which of the large number of gene copies will mutate.

2.) Not directed by Natural Selection

• Not occurring because they are selectively advantageous / selected only once they exist.

Genetic Drift

• Random fluctuations in allele frequencies from one generation to the next due to chance factors.

  • Due to accidents of sampling caused by random variation in the notes of survival or reproduction by different genotype

  • Can have a larger influence on allele frequencies in smaller populations.

  • All populations are potentially subject to random genetic drift but not natural selection - so should be null hypothesis in evolution.

• Founder effect

Founder Effect

• Extreme example of genetic drift

• Genetic makeup of future generations is directly limited by the variation with founding generation.

  • Future generations will show little variation.

• Mutations have greater probability of becoming established.

Gene Flow

• Introduces new genes from outside the population

• Generally accomplished by migration

• Homogenizes different populations of a species

• Important in maintaining reproductive continuity between different populations of a species.

• Characteristics of a species also affect its capacity for gene flow.

Microevolution vs Macroevolution

• Microevolution = evolution below the species level.

• Macroevolution = evolution at the species level and above.

• Microevolutionary Processes

• Macroevolutionary Processes

• Traditionally, macroevolution is believed to be simply the product of microevolution over longer timescales.

• Small, microevolutionary changes over relying on the four microevolutionary mechanisms

  • New species made over microevolutionary processes.

Microevolutionary Processes

• Natural Selection

• Mutation

• Gene Flow

• Genetic Drift

• Operate more quickly and can lead to new species formation

• Observable in nature and in the laboratory.

Macroevolutionary Processes

• Speciation

• Diversification (Evolutionary radiations)

• Longterm evolutionary trends

• Extinction

• Operate more slowly and lead to evolution, diversification , or disappearance of species.

• Only really observable in the fossil records.

Neutral Theory of Microevolutionary Trends

• Lewontin and Hubby (1966) studied the genetic variation in fruit flies

  • Found that one third polymorphic

  • Similar results found in humans

• More genetic variation in natural population than realized that can not be explained by NS

• Motoo Kimura (1986)

• Lead to the Neutralist - Selectionist Debate and emergence of molecular clock techniques.

• Has now become null hypothesis in evolutionary research to be rejected before other processes (NS) can be invoked

Motoo Kimura (1986) Neutral Theory

1.) Most of the variation present within a population is selectively neutral.

2.) Most of the changes in DNA or amino acid sequence are selectively neutral

Selectively Neutral

Don’t influence survival and reproduction.

Punctuated Equilibrium

• observed pattern is the real evolutionary pattern

• How evolution works - hypothesis

1.) New species appear suddenly

2.) No evidence of transitional forms in the fossil records.

3.) Most morphological change (evolution) is associated with speciation.

4.) Between speciation events, the populations remains relatively constant.

• Stasis (equilibrium) is interrupted (punctuated) by speciation events.

- Relies on the biological species concept and the application of a peripatric mode of speciation to the fossil record.

- Transitional forms are not identified in the fossil record because new species form rapidly in a small population and in a location that is geographically separated from region of parent population.

• New species eventually reinvades the geographic range, marking an abrupt appearance of a new species.

Stasis

little change

Punctuated Equilibrium - Corollaries Important

1. Evolution forces acts on a small isolated population

2. More prominent role for genetic drift / founder effect

3. Natural selection also present, but not emphasized

4. Speciation is relatively common

5. Most morphological change occurs during speciation events

6. Cladogenesis (branching pattern) is the only mode of evolution

7. Evolution by phyletic gradualism (lineal pattern) hardly ever occurs if it does at all.

Adaptationism

• An evolutionary theory that view NS as the primary important cause of almost physical and behavioral traits in organisms.

• Adaptation is the objective of NS and by extension, evolution - adaptionist program.

  • Rather than the byproduct

• Focusing on immediate adaptation to local conditions leads to an ignoring of architectural/ structural constraints.

  • Leads to an inversion of explanation

• Current usage is taken to reflect the reasons behind their ancient emergence.

Spandrels of San Marco

• A seminal article from Steven Jay Could and Richard Lewontin

  • Critiques the confusion of cause and effect in evolutionary thinking.

• Focused on purpose in Catholic Cathedral

  • Is there a defined purpose?

  • If it were a feature of animal, is it an adaptation?

  • Is it a byproduct of something else?

• If it were a feature of an animal, it would not necessarily be adaptive.

• If it is a byproduct, then it owes its existence to something else.

• It was secondarily used for a different purpose

  • It is not the reason it exists in the first place.

Selfish Gene

• Highly influential book: Richard Dawkins (1976)

• Offered a Genes Eye look at evolution

• A canon of genetic selectionism

• Normally natural selection is conceived as a competition between individual organisms

  • Real competition is between individual genes to pass on as many copies of themselves as possible to future generations.

• DNA precisely replicates itself

  • Genes that exist today are identical to thier ancestor genes that existed thousands of years ago.

  • Only genes have sufficient permanence ton be considered unit of selection

    • Organisms and their properties are only temporary manifestations - only vehicles for their replicators

• Vehicles

• Replicators

Vehicles

Any relatively discrete entity… which houses replicators and which can be regarded as a machine programmed to preserve and propagate the replicators that ride inside it,

Replicators

= Genes

• Germ Line Replicators

  • Located in reproductive cell

  • Potential ancestor of an indefinitely long line of descendant replicators

• Dead End Replicators

  • Located outside of reproductive cells

• Active Replicators

  • Has some causal influence on its own probability of being propagated.

• Passive Replicators

  • Never transcribed and have no phenotypic expression whatsoever.

Segregation Distortion Genes

• Normally genes within an organism cooperate in the survival and reproduction of the individual

• But in same cases an individual gene can favor its own interests about the whole genoma.

• SD genes violate Mendelian laws and are inherited more than 50 % of the time

  • Disadvantageous for organism since they often have adverse phenotypic effects

  • Selfish genes

    • Have a huge selective advantage

      • If inherited more than 50 % of the time they will increase in frequency and evenly reach fixation in population

Fixaton

• 100 percent frequency.

Why aren’t all genes doing this? Why aren’t they all SD genes?

• Occur at intermediate frequencies

1. Some normal genes were like previously SD genes - many genes that were SD reached fixation and now they follow Mendelian laws.

2. Homozygous (sd/sd) individuals less fertile

• ensures that (sd/+) and (+/+) individuals produce more surviving offspring.

Alturism

• The unselfish concern for or devotion to the welfare of others, often involving personal cost or risk to individual performing the action.

• A behavior pattern is deemed altruistic if it increases the number of offspring reproduced by the recipient and decreases that of the altruist.

  • Often takes place between related individuals - called kin selection.

Kin Selection

• Genetic basis to altruism - gene for altruism

  • Suggest that altruism is really about selfish genes promoting their own survival and reproduction

  • One individual pays the cost and related individual receives the benefit.

Eusociality

• A form of social behavior characterized by the following elements

  • Reproductive division of labor

  • Cooperative raising of the young

  • Overlapping generations

• Often function as a kind of super-organism

Reproductive Division of Labor

Only a portion of the population are engaged in reproductive behaviors. Other individuals are sterile, usually through suppression of reproduction.

Cooperative Raising of The Young

Multiple individuals, in addition to the immediate parents, work together to feed and care the young.

Superorganism

An entity that functions as an organism but is made of parts that can or are properly considered organisms in their own right.

• Darwin supported this notion

• Seems to be the only way to explain the continuous production of sterile individuals

Multilevel Selection

• Natural selection produces adaptations - can operate at different levels of the biological hierarchy.

• Levels / Units of Selection

• What is adaptive at one level might not be adaptive at another level

• Group level adaptations can form when selection is stronger

  • has been developed as one explanatory framework for social behaviors across organisms.

What is adaptive at one level might not be at another level examples

• Segmentation Distorter Genes

  • Adaptive for the individual SD gene (increases propagation) but maladaptive on the individual level (lowered fertility).

• Predator/Prey

  • Selection is weaker on the individual predator than it is on the species.

• Sentries / Guards

  • Selection is stronger on the group level (having a sentry) than it is on the individual level (putting individuals at increased risk of death).

Group Selection

• Goes back to Darwin (1871 Descent of Man)

  • Discussing the evolution of “morality” in humans

• Groups of moral individuals will have an advantage over groups of immoral individuals.

• Cooperative groups are more successful than selfish groups and will contribute more to the gene pool of the species in future generations.

• Group selection was developed specifically to explain cooperative behaviors of individuals in groups.

Sexual Selection

• Similar to natural selection in some ways but reflects the fundamental biological difference between males and females

  • Only one sex reproduces

• Leads to large differences in how sexual selection operates in males and females

• Relies fundamentally on competition within between the sexes

• Embodies many related concepts:

  • Natural Selection vs Sexual Selection

    • Survival vs Reproduction

  • Male vs Female Reproductive Strategies

  • Sexual Dimorphism

  • Sex - Ration of Offspring

  • Honest Signaling

Sexual Selection vs Natural Selection

• Survival vs Reproduction

• Sexual selection can lead to the development of features that seem disadvantageous for survival.

• Reproduction as the “goal” of evolution

• Survival is the short term goal

  • Necessary to reproduce

  • Evolutionarily “invisible”

Reproductive Strategies

• Maximum reproductive success

  • Producing the largest number of offspring possible

  • Goal for both males and females in all organisms

• High Fecundity + High Survival = reptiles

• Low Fecundity + High Survival = mammals

• Low Fecundity + Low Survival = high extinction rate

Fecundity / Fertility

Number of offspring produced

Survival

Number of offspring who survive to reproductive age.

Reproductive Strategy - Males

• Maximum Reproductive Success

• Limitation

  • The number of females he can impregnate

• Strategy

  • Mate with as many females as possible to produce as many offspring as possible.

• Exclude other competitors snd monopolize access

  • lower investment in offspring than females

• Higher maximum number of offspring than in females

  • Males are more r-selected than females

    • More variable in maximum number of offspring,

Reproductive Strategy - Females

• Maximum Reproductive Success

• Limitation

  • The number of offspring she can bear during her lifetime.

• Strategy

  • Be selective in choosing a mate, invest in offspring survival

• Sometimes: Exclude competitors and monopolize access

• Higher investment in offspring than in males.

• Lower maximum number of offspring than in males.

• Females are more k selected than males and there is less variation in maximum number of offspring.

Ronald Fisher

• Early population geneticist

• Emphasized linkage disequilibrium

• Showed how male characters and female choice could theoretically be genetically linked.

• Genes controlling both male features and female mate choice are both heritable.

• Provided an explanation for how sexual could occur and be compatible with natural selection.

Sexual Selection Part 2

• Not widely accepted until 1970s

• Alternatives to sexual selection

• “Good sense” Female choice

• “Good taste” Female choice

Alternatives to sexual selection

• Just Natural Selection is enough

• “Good sense” Female Choice

• “Good taste” Female Choice

“Good Sense” Female Choice

• Not about flashy displays

• More about underlying quality of a mate

• Male criteria are more diverse

  • Increased parental care

  • Higher social rank

• Emphasizes survival of offspring

“Good Taste” Female Choice

• Explains why flashy display develop

  • Accepts a certain “aesthetic” in female choice

• Relies an honest signaling by males

• Phenotypic features favored by females are accurate reflections of mate quality.

Intrasexual Competition

• Male - Male Competition

  • Taken to always be present

  • Favors featured that would presumably also be favored by natural selection

  • Strength, swiftness, natural weaponry, intelligence.

• Female - Female Competition

  • Usually conceptualized as female choice

  • Females have some role in choosing their mates

  • May be based on physical features, behaviors, social rank, etc.

Primate Social Organization

• May reflect intersexual competition

• Male primates attempt to monopolize reproduction and exclude male competitors

• In small groups it is possible for a single male to do this —- Leads to formation of single male and multi female mating system

• As group size increases, becomes less and less possible to monopolize reproduction

• Most primate groups comprised of related females.

Sexual Dimorphism

• Large physical differences between males and females

• Often interpreted as an aspect male-male competition

• More active role for males

  • Higher levels result from males developing more extreme features

• Strongly sexually dimorphic species are characterized by high levels of male - male competiton

  • Frequently associated with single male / multi-female social org

Operational Sex Ratio

• Relative numbers of sexually active males to receptive females at one time

• However;

  • Lower male investment in offspring

• Biased OSRs

Biased Operational Sex Ratio

• Leads to increased intensity of intrasexual competition greater variance in breeding success, and stronger selection for traits affecting competitive ability in males than females.

• Is when sexual selection can operate most strongly - producing most exaggerated male features.

• Female mate choice is weaker or is based on features that enhance male - male competition.

Underlying Assumptions

• Evolution of male features and female preferences / choice are both genetically based.

• Reproduction is the goal of evolution.

Difficulties - Sexual Selection

• Often difficult or impossible to really measure differential reproduction.

• Do these things really lead to increased reproductive success?

• Sometimes difficult to distinguish from Natural Selection.

• Sexual reproduction is perhaps the ultimate example of cooperation, yet sexual selection is all about competition.