BIO EXAM 3

Hypothesis

• A testable, tentative explanation of a natural phenomenon

• ex: hypotheses about origin of life offer explanations for how biological life emerged from non-living matter

Scientific Theory

• A well-supported explanation backed by extensive evidence, testing and debate

Scientific Theory Example

• The theory of evolution explains what happened after life appeared specifically how life has changed and diversified over billions of years. It is supported by multiple lines of evidence such as fossils, comparative anatomy, and DNA sequence similarities across species, all which suggest common ancestry

Evolution

• occurs through natural selection, where individuals with advantageous adaptation- traits that increase survival and reproductive success (fitness) in a particular environment are more likely to pass those traits to the next generation This process is also called descent with modification.

Abiogenesis

• Life arising from non-living matter or the formation of organic molecules from inorganic molecules, under early Earth conditions

• three hypotheses of the origin of life: early earth conditions, hydrothermal vents, meteorites

• four requirements

3 Hypotheses of Origin of Life : Early Earth Conditions

• Atmosphere with methane, ammonia, hydrogen, and water; energy for chemical reactions from lighting, UV radiation, volcanoes, and/ or hydrothermal vents

• Miller-Urey Experiment: A recreation experiment of possible early earth conditions to create organic molecules

3 Hypotheses of Origin of Life : Hydrothermal Vents

• or alkaline vents

• Early oceans were acidic, while these vents were alkaline, resulting in a pH gradient that could be harnessed for reaction energy for synthesizing organic molecules

3 Hypotheses of Origin of Life : Meteorites

• May have deposited amino acids into oceans

Abiogenesis: Four Requirements

• Biomolecular building block like amino acids and nucleotides must be made in the environment

• These building blocks must be able to self assemble into biomolecules (amino acids into proteins)

• Biomolecules must assemble into protocells (primitive cells)

• Cells must be able to replicate and pass on genetic information

Major Events in the history of life

• The appearance of prokaryotic organisms

• The appearance of eukaryotic organism

• The colonization of land

• Mass extinctions affecting the present life forms

First Life

• Prokaryotic, anaerobic (no oxygen needed) microbes ~ 3.5 billion years ago

Photosynthesis

• Cyanobacteria (photosynthetic prokaryotes) oxygenated the atmosphere (~2.5 billion years ago)

Eukaryotic Cells

• Developed via endosymbiosis; mitochondria and chloroplasts originated from bacteria

Endosymbiosis Hypothesis

• An ancestral prokaryotic cell engulfed an aerobic bacterium which evolved into a mitochondrion giving rise to the first eukaryotes.

• In some cases, it also engulfed a photosynthetic bacterium, which became a chloroplast, leading to photosynthetic eukaryotes.

Endosymbiosis Hypothesis Evidence

• Mitochondria and chloroplasts are bacterial-sized with double membranes.

• Their inner membranes have bacterial-like enzymes and transport systems.

• They replicate like bacteria and contain circular DNA.

• They have the machinery to transcribe and translate their DNA.

• Ribosomes, RNA sequences, and antibiotic sensitivity resemble bacteria more than eukaryotic cytoplasm

Multicellular Eukaryotes

• 1.2 billion years ago; enabled specialization and complex organisms

Precambrian

• Origin of life, first cells

Paleozoic

• Cambrian explosion (rapid diversification)

Mesozoic

• Age of dinosaurs

Cenozoic

• Rise of mammals

Extincion

• loss of a species; can drive adaptive radiation

Adaptive Radiation

• Rapid diversification to fill ecological niches

Big Five Mass Extinction (Old to recent)

1. Ordovician (~444 mya)

2. Devonian (~375–359 mya)

3. Permian (~252 mya)

4. Triassic (~201 mya)

5. Cretaceous (~66 mya)

Fossil Record

• The preserved remains or traces of past organisms found in sedimentary rock layers called strata

What can fossil records tell us?

▪ Emergence of major life forms (like terrestrial vertebrates)

▪ Appearance of key adaptations (such as flight)

▪ Impact of mass extinctions on biodiversity

How are fossils dated?

• Radiometric Dating: Age is determined by the decay of radioactive isotopes.

• Half-Life: The rate of decay. Specifically, the amount of time required for half of the amount to decay.

Natural Selection

• a process in which individuals with inherited traits that increase survival or reproduction leave more offspring, changing the frequency of favorable adaptations in a population.

• Over time, this can lead to the formation of new species.

Who proposed the modern theory of evolution in 1859?

• Charles Darwin

• Biological evolution refers to cumulative changes in populations over time

  (not individuals) or descent with modification through natural selection.

Requirements for Evolution by Natural Selection

• Individuals in a population vary in their traits.

• Some of these trait differences are heritable.

• Individuals differ in reproductive success.

• Certain traits influence reproductive success; these advantageous traits are said to be naturally selected.

Grants’ Finches Study

• Studied finch beak depth in Galapagos over three years.

Findings

1. Evolution can occur rapidly.

2. Evolution can occur on very small scales.

Key Points on Natural Selection and Evolution

• Individuals do not evolve. Populations evolve.

• Natural selection can only act upon traits that differ within a population.

• Favored traits depend on the existing environment.

• Natural selection occurs within a population and cannot produce new traits in response to a need.

• Evolution can be gradual, occurring over millions or billions of years, but it can

also happen rapidly and be observed in just a few years.

• Evolution does not always move in one direction.

T/F: Evolution always moves in one direction

• FALSE

T/F: Individuals do NOT evolve

• TRUE

• population evolve

Favored traits depend on?

• Existing environment

Natural selection can only act upon traits that?

• differ within a population

Natural selection occurs within a population and cannot?

• produce new traits in response to a need

Macroevolution

• large-scale changes over many generations, resulting in the descent of different species from a common ancestor

Endemic Species

• Found only in one location

Gene flow

• Movement of alleles between populations

Population

A group of individuals of the same species that live in the same area and interbreed

Allele

Versions of genes

Gene Pool

Sum of all alleles in a population

Allele Frequency

The frequency (percentage) at which an allele occurs in a population’s gene pool

Mutation

a random change in the nucleotide sequence of an organism’s DNA that results in new alleles.

Why are mutations important in evolution?

• It is the ultimate source of genetic variation because it creates new alleles

• Mutations happen randomly- there is no intention behind their occurrence

• Mutation alone isn’t enough to change the allele frequency within a population; it often needs to be an advantageous, heritable mutation that can be selected for or against.

Microevolution

small-scale changes in gene frequency from one generation to the next

Mechanisms of microevolution: Mutation

• Creates new alleles; random but essential for variation.

Mechanisms of microevolution: Natural Selection

• Increases frequency of beneficial alleles; reduces harmful alleles.

Mechanisms of microevolution: Genetic Drift

• Random changes in allele frequencies; significant in small populations.

  • Bottleneck Effect: Population reduced drastically; allele frequencies change randomly.

  • Founder Effect: Small group colonizes a new area; allele frequencies may differ from parent population.

Bottleneck Effect

• Population reduced drastically; allele frequencies change randomly.

Founder Effect

• Small group colonizes a new area; allele frequencies may differ from parent population.

Gene Flow

Migration of alleles between populations; can increase or decrease fitness.

Measuring Evolution

• Count allele and genotype frequencies across generations.

Hardy-Weinberg Equilibrium (HWE):

• No evolution occurs if there are no changes in allele frequency

• p + q = 1

p= freq. of dominant allele (A)

q= freq. of recessive allele (a)

• p² + 2pq + q² = 1

• p²= freq. of homozygous dominant genotype (AA)

• 2pq= freq. of heterozygous genotype (Aa)

• q²= freq. of homozygous recessive genotype (aa)

Conditions for HWE: large population, no mutation, no migration, random mating, no selection.

Condition for Hardy-Weinberg Equilibrium (HWE):

• large population

• NO mutation

• NO migration

• random mating

• NO selection

Directional Selection

Favors one extreme (peppered moths → dark coloration)

Stabilizing Selection

Favors intermediate traits (human birth weight)

Disruptive Selection

Favors extremes (seed-eating birds with small or large beaks)

Sexual Selection

A process in which individuals with certain inherited traits are more likely than others of the same sex to obtain mates.

Intersexual Selection: Mate choice

Traits that attract members of the opposite sex (e.g., bright feathers, courtship displays)

Intrasexual Selection: Competition

Traits that help compete with members of the same sex (e.g., antlers, fighting ability)

Macroevolution

• large-scale changes over many generations, resulting in the descent of different species from a common ancestor

Speciation

• the process by which one population splits and evolves independently, potentially resulting in a new, distinct species that is still related to the original population.

Allopatric Speciation

Geographic isolation → genetic divergence (e.g.,snapping shrimp).

Sympatric Speciation

New species arise without geographic separation via habitat differentiation, sexual selection, or polyploidy (e.g., apple vs hawthorn fly).

How do scientists define a species?

• Morphological: Based on physical traits.

• Biological: Based on reproductive potential and fertile offspring.

• Phylogenetic: Based on ancestry using DNA, morphology, and biochemistry.

• Ecological: Based on niche differentiation.

Reproductive Isolation

• the prevention of gene flow between populations, resulting in the inability to produce biologically fertile offspring.

Prezygotic Barriers (Before Fertilization)

• Habitat Isolation

• Temporal Isolation

• Behavioral Isolation

• Mechanical Isolation

• Gametic Isolation

Postzygotic Barriers (After Fertilization)

• Reduced viability

• Reduced fertility

• Hybrid breakdown

Phylogeny

evolutionary history of a species or group of related species

Cladistics

Method for constructing phylogenetic trees by grouping organisms into clades

Clades

groups of organisms with shared ancestry

Node

Branching point

Sister taxa

closest relatives

Phylogenetic tree

• represents hypotheses about how organisms are evolutionarily related to one another

Homology

• Shared traits from a common ancestor

Analogy

• Similar traits due to convergent evolution

Convergent evolution

• The process in which unrelated species independently evolve similar traits because they adapt to similar environments or ecological niches.

Shared Ancestral Character

• A trait that is present in a common ancestor and is found in all or most of its descendants.

Shared Derived Character

• A trait that evolved in a particular lineage and is shared by its descendants but not present in distant ancestors

Taxonomy

Classification system of organisms

Taxon

any level in the hierarchy of taxonomic groups

• Taxonomic groups (from broad to narrow):

Domain → Kingdom → Phylum → Class → Order → Family → Genus →Species

Taxonomic Groups

Domain → Kingdom → Phylum → Class → Order → Family → Genus →Species

Binomial Nomenclature

• Genus + Species

Hominins

• Humans and extinct relatives after splitting from the chimpanzee lineage

• Ardipithecus → Australopithecus → Homo

Key Adaptations: Skeletal Differences

1. Foramen Magnum

2. Spine

3. Chest/Rib Cage

4. Knee/Valgus Angle

5. Feet

6. Hands

Key Adaptations: Bipedalism

• ability to walk on two feet

Key Adaptations: Thermoregulation

• loss of hair, sweating

Key Adaptations: Brain Enlargement

• Hominin skulls show increasingly flatter faces, reduced jaws, and larger cranial cavities, indicating increased brain size.

• This expansion is associated with cognitive evolution, including language, cooperative behavior, and advanced tool use.

• These changes may be linked to shifts in diet, gene deletions affecting heavy-duty myosin (related to jaw muscles), and differences in expression of the FOXP2 protein

How did H. sapiens populate the world, and where did modern humans originate?

• Out of Africa" hypothesis: Scientists propose that modern humans (Homo sapiens) originated in Africa approximately 300,000–150,000 years ago and later spread globally through migration and reproduction.

• This hypothesis is supported by fossil evidence, patterns of genetic variation, DNA mutation rates, and evidence of interbreeding with other ancient human populations

  • (e.g., Neanderthals and Denisovans)

How did Homo sapiens outcompete other Homo species?

• Homo sapiens outcompeted others mainly due to adaptability and social/cognitive advantages, not just physical differences.

  • Greater adaptability (flexible behavior, better response to environmental change)

  • More advanced social structures, communication, and tool use

  • Possible advantage in cognitive abilities (brain development differences)

  • Mount Toba super volcano eruption → population bottleneck, favoring adaptable groups

  • Competition for limited resources

• Other contributing factors:

  • Climate change

  • Disease

  • Interbreeding (genetic blending with other species)

Do humans continue to evolve?

• Yes, humans continue to evolve physiologically, genetically, and culturally, influenced by environment, diet, disease, and technology.

Evidence of Recent Human evolution

1. Lack of wisdom teeth

2. Lactose intolerance

3. Appearance traits (ex: blue eyes and straight black hair)

4. Disease resistance (ex: malaria resistance)

Who is Dragon Man?

• A denisovan