EXAM 2 BIO173

Evolution

Descent with modification where populations change over time through heritable variation and differential reproduction

Darwin’s argument

Heritable variation leads to differential reproduction which changes populations and can lead to speciation

Natural selection

Process where favorable heritable traits increase in frequency because they improve survival or reproduction

Conditions for natural selection

Variation exists; variation is heritable; variation affects survival or reproduction

Adaptation

Trait that increases fitness and becomes more common in a population over generations

Adaptive evolution

Population becomes better suited to environment as advantageous traits accumulate

Biological fitness

Ability to survive and reproduce relative to others in a population

Adaptive radiation

Formation of multiple species from a common ancestor due to adaptation to different environments

Microevolution

Change in genetic structure of a population across generations

Measurement of microevolution

Changes in allele and genotype frequencies

Hardy-Weinberg equilibrium

Model where no evolution occurs and genotype frequencies remain constant

Purpose of Hardy-Weinberg

Serves as null hypothesis for detecting evolution

Deviation from Hardy-Weinberg

Indicates that evolutionary forces are acting

Allele

Different version of a gene with altered sequence or regulation

Origin of alleles

Mutation or genetic exchange

Mutation

Ultimate source of all genetic variation

Relationship of mutation and selection

Mutation creates variation and selection acts on it

Phenotypic vs molecular measurement

Evolution measured by traits or DNA sequencing

Artificial selection

Human-directed breeding for desired traits

Difference from natural selection

Artificial selection is human-controlled while natural selection is environment-driven

Result of artificial selection

Organisms often differ greatly from wild ancestors

Evidence of microevolution

Direct observation such as antibiotic resistance in bacteria

MRSA example

Resistant bacteria survive antibiotics and reproduce more when antibiotics are present

Trade-off in MRSA

Resistance may be disadvantageous when antibiotic is absent

Speciation

Formation of new species due to reproductive isolation

Species definition

Populations that can interbreed and produce viable offspring

Mechanism of speciation

Subpopulations stop interbreeding and accumulate genetic differences

Role of variation in speciation

Differences in traits can drive reproductive isolation

Host switching

Evolution of pathogens to infect new host species

Examples of host switching

Measles from cattle; influenza from birds; HIV from chimpanzees; COVID-19 likely from bats

Importance of speciation

Explains origin of diseases and biodiversity

Macroevolution

Large-scale patterns of evolution including history of life

Fossil

Preserved remains or traces of organisms from the past

Fossil record

Worldwide distribution of fossils documenting evolutionary history

Key fossil insight

Most fossils differ from living species showing change over time

Strata

Layers of sedimentary rock representing chronological deposition

Law of succession

Fossils appear in predictable order in rock layers globally

Biogeographic fossil pattern

Living organisms resemble fossils from the same region

Transitional forms

Fossils showing intermediate stages between ancestral and derived species

Significance of transitional fossils

Provide direct evidence of evolutionary change

Example of macroevolution

Whale ancestors evolved from land mammals related to even-toed ungulates

Common ancestry

All life forms share a common evolutionary origin

Homology

Similarity due to shared ancestry

Homologous structures

Same ancestor but different function

Convergent evolution

Independent evolution of similar traits in different lineages

Analogous structures

Same function but different evolutionary origin

Vestigial structures

Remnants of ancestral features with little or no current function

Significance of vestigial structures

Evidence of evolutionary history

Molecular homology

Similarities in DNA or genes indicating common ancestry

Universal genetic code

Evidence that all organisms share a common origin

Pseudogenes

Nonfunctional gene copies indicating evolutionary relationships

Evo-devo

Study of how development influences evolutionary change

Differential gene expression

Different genes activated during development to produce structures

Regulatory genes

Control timing

Impact of regulatory changes

Small genetic changes can produce large morphological differences

Cell-cell interactions

Critical for proper development

Regulatory genes controlling body plan and limb development

Limb development example

Hox gene expression patterns determine whether limbs or ribs form

Snake limb loss

Overlapping Hox gene expression prevents forelimb formation

Why evolution is controversial

Microevolution widely accepted but macroevolution challenges beliefs about human origins

Correct phrasing of human evolution

Humans share a common ancestor with monkeys rather than evolved directly from them

Scientific principle

Science does not begin with conclusions but tests evidence

Biodiversity

Variety of life at multiple levels

Genetic diversity

Variation in alleles within populations important for adaptability

Species diversity

Combination of species richness and evenness

Habitat diversity

Variety of environments supporting different species

Biogeography

Study of species distribution across space

Factors affecting species range

Climate

Human impact on biogeography

Introduction of invasive species alters distributions

Assemblage

Group of species living together in a community

Museum collections

Allow analysis of historical biodiversity and environmental change

Species interactions

Relationships between species affecting survival

Competition

Organisms compete for limited resources

Intraspecific competition

Competition within the same species

Interspecific competition

Competition between different species

Exploitative competition

Indirect competition through resource use

Interference competition

Direct interaction blocking access to resources

Mutualism

Both species benefit

Commensalism

One benefits while the other is unaffected

Amensalism

One harmed while the other unaffected

Predation

One organism consumes another

Parasitism

One organism benefits at the expense of another

de Wit replacement series

Experimental method comparing species growth in monoculture vs mixed culture

Monoculture

Growth of a single species alone

Mixed culture

Growth of multiple species together

Destructive sampling

Measuring organisms by removing them from experiment

Independent variable

Factor manipulated in an experiment

Dependent variable

Measured outcome

Positive control

Condition expected to produce a known effect

Negative control

Condition expected to produce no effect

Null hypothesis

Prediction that there is no difference between groups

Mean

Average of data

Variance

Measure of spread of data

Standard deviation

Degree of variation around the mean

Normal curve

Bell-shaped distribution of data

T-score

Statistic comparing difference between means relative to variation

p-value

Probability that observed results are due to chance

Significant result

Low p-value indicating unlikely due to chance

Interpretation of significance

Rejects null hypothesis but does not prove causation