Biology Unit 2

Scientific Theory

• Serves as an explanatory model accounting for lots of evidence

Theory of Biological Evolution

• All living things share a common ancestor
• All organisms are distant cousins
• Evolution includes descent with modifications

Carolus Linnaeus

• Founder of biological nomenclature
• Relatively few species formed many new species via hybridization and inbreeding

Comte de Buffon

• Species are subject to change over time, leading to the rise of new organisms
• Similar organisms share common characteristics

Erasmus Darwin

• Charles Darwin's Grandfather
• All life may have originated from a single source

George Cuvier

• Proposed species extinction and creation occur due to multiple events
• Example: Mammoths and elephants relating to extinction.

Charles Lyell

• Geological change occurs slowly and gradually, as opposed to suddenly and catastrophically
• Natural laws are consistent throughout time

James Hutton

• Rock formations are continually being formed
• Evidence supports the theory of uniformitarianism
• Earth formed entirely by slow processes such as erosion and sedimentation, shaping the landscape over time

Charles Darwin

• Born on February 12, 1809, in Shrewsbury, England
• Attended Oxford to study medicine
• Studied marine invertebrates, developed an interest in natural history
• Realized he disliked medicine in 1827 at age 18 because he couldn't bear the sight of blood
• Left Oxford, went to Cambridge University to become a clergyman
• The HMS Beagle set sail on its voyage in 1831
• The ship conducted surveying work in South America
• Charles Darwin served as the ship's naturalist

The Galapagos Islands

• The Beagle visited four of the Galapagos Islands
• Darwin collected and drew plants and animals in detail
• Darwin wrote descriptions of the geography and geology of each island in his diary alongside observations of the species inhabiting them

Patterns in Diversity

• Species vary globally, as Darwin noticed
• Distantly related species in similar habitats in different areas of the world appeared and acted similarly
• Some regions have unique organisms found nowhere else
• Plants and animals of South America differ from those in Europe or Africa

Local Species Variation

• Related animal species in different local habitats have different features, like tortoises on islands
• Many different finch species existed, each adapted to particular food sources on its island
• The plants and animals of South America differed from those in Europe or Africa

Species Variation Over Time

• Fossil studies revealed patterns
• Species in South America descended from ancestral species on that continent
• Fossilized remains that resembled no living creatures made Darwin wonder about the cause of species extinction

Geological Change

• Darwin read Charles Lyell's book and observed geological processes during his voyage
• Darwin witnessed an earthquake and the upward movement of land

Darwin's Theory Development

• Darwin analyzed his collection and believed species could change or evolve
• Thomas Malthus' essay stated that the production of more individuals than the environment can support leads to a struggle for existence
• Darwin applied Malthus' ideas to all species, which led him to propose a mechanism of evolutionary change

Darwin's "The Origin of Species"

• All species on Earth are descended from ancestral species
• Natural selection drives species to change over time

Descent with Modification

• Descendants of early organisms diversify into various habitats, adapting to different ways of life
• Descent with modification explains life's diversity
• Example: Rabbits (jackrabbit, snowshoe hare)

Natural Selection

• Depends on the struggle for existence
• Relies on natural variations among members of a species
• Takes into account the environment's role in evolution

Struggle for Existence

• Environments cannot support the amount of individuals produced, leading to a struggle for existence among a population's individuals
• Only a small percentage of offspring survive each generation, due to starvation, predators, disease, and failure to reproduce

Variation

• Members of the same species have differences, such as hair and eye color in humans
• A lot of these variations are heritable
• Favorable variations in the local environment lead to higher offspring production

Role of Environment

• A key element in an organism's survival depends on how well it fits its environment
• Lamarck believed the environment made organisms get traits that help them survive
• Darwin proposed that the environment selects individuals that have variations best suited for survival

Evidence for Evolution

• Chronological remains in rock layers reveal life's history
• Ancestral forms link the past and present
• Provides evidence for species extinction
• Fossil record limitations with evidence for evolution
• Species lacking hard tissues, like bones or shells are rarely fossilized

Geographic Distribution: Closely Related, But Different

• Island finches descended from a single species from South America
• Finches adapted to local island environments
• Example: Beak shape adapting to specific foods

Distantly Related, But Similar

• Similar habitats select for similar adaptations
• Selection pressures cause species to develop similar adaptations for survival

Comparative Anatomy

• Structural similarities among species reveal evolutionary history
• Example: Human arms, cat forelegs, whale flippers, and bat wings have a similar combination of bones, but differ in function

Homologous Structures

• Structures are similar but do not share the same function
• More recent ancestor function differs

Vestigial Structures

• Structures that had important functions in an ancestral species that no longer serve clear function in modern descendants
• Structures are usually reduced in size (Ex. Whales' hind legs, the human appendix)

Analogous Structures

• Features that perform the same function but are anatomically different
• Present in distantly related species (Ex. a bat wing, butterfly wing and bird wing)

Comparative Development

• Embryos of closely related organisms share similar stages in development
• Example: All vertebrates have an embryonic phase with pharyngeal pouches (fishes, frogs, snakes, birds, primates)

Molecular Biology

• DNA molecule components' sequences are passed from parent to offspring
• Provides a record of hereditary background of an organism
• Species are more closely related with shared genes and protein sequences

Artificial Selection

• Selective breeding of domestic plants and animals to produce offspring with desirable traits
• Artificial selection can produce great change in species over short time
• Humans choose traits to become more common versus natural selection favors organism survival
• Negatives to artificial selection is species can't hunt or reproduce

Changes in Beak Shape:

• Beak sizes have changed according to the environment over the past 30 years
• Birds with larger beaks successfully cracked large seeds in the dry season, so their population increased
• Birds with smaller beaks got nutrients during the wet season, thus their population grew

Antibiotic Resistance in Bacteria

• Bacteria have many variations where some are destroyed by antibiotics but others are resistant
• Resistant bacteria survive due to natural selection

Microevolution

• Generational changes to gene pool
• Hardy-Weinberg Equilibrium: populations that don't change gene pools are not evolving
• Gene pool equilibrium means allele frequencies are constant over time
• Populations rarely stay in hardy-Weinberg Equilibrium for long

Mechanisms of Microevolution

• Microevolution: change in allele frequencies across generations in a population
• Evolution on a small scale
• Natural Selection: non-random process, where the environment increases beneficial allele frequencies, causing adaptation evolution

Types of Selection

• Directional Selection: selection favors an increase or decrease in a trait from the current population average
• Occurs if phenotype range has a certain side with a higher fitness than the rest
• Stabilizing Selection: selection against individuals exhibiting differences in current population trait average
• Favouring the average size
• Disruptive Selection: selection for two or more varying trait forms differing from current population
• Environment favors individuals with a trait end rather than those of intermediate variation

Sexual Selection

• Sexual selection affects the next generation's gene pool when individuals reproduce
• All organisms are "programmed" to pass genes
• Influences mating success via a specific trait, appearance, or behavior

Sexual Dimorphism

• When males and females look different
• Male usually has a special feature to attract a mate

Animal Examples of Sexual Selection

• Birds of Paradise have bright feathers and dance to attract mates
• Male Peacocks display cumbersome back feathers
• Male Crabs have large claws to defend mating territory
• Penguins look the same (no sexual dimorphism) but rely on courtship and rock presentation

Detrimental Appearances and Behaviors

• Appearances and behaviors can attract predators
• Displays exist to contribute to gene pool

Artificial Selection

• Intentional breeding for traits
• Reduces genetic variability
• Can have negative unintended results

Genetic Drift

• Genetic Drift is a random process that changes the gene pool of a population by chance
• All populations are impacted; more impact on smaller populations

The Bottleneck Effect

• Natural disasters reduce population size, resulting in genetic drift and reduced gene pool
• Chance events may cause certain alleles to be more frequent versus others

The Founder Effect

• Small groups separating to create genetic drift
• Change in allele relates to the genetic make up of the colony founders
• The alleles determine the makeup of the colony

Gene Flow: Random Process

• The exchange of genes with another population
• Selective pressure
• Neighbouring colonies allow for sexual reproduction
• Fertile individuals or sex cells migrate between populations
• Reduces genetic differences
• Populations can mix with a common gene pool

Speciation

• Founder's effect and genetic drift occur when a small number separate from their original population
• Stabilizing selection occurs more in environment that favors the most common phenotypes

Hybrids and Species

• Hybrid is when offspring come from the mating of different species, which is rare
• Species = interbreeding organisms that produce viable offspring in natural conditions
• Microevolution and adaptation explain population evolution, referring to changes in allele frequencies
• Macroevolution encompasses dramatic changes like that of different species, the extinction of species, and the evolution of major new features
• Speciation is the origin of new species

Reproductive Barriers Between Species

• Reproductive barriers lead to isolation

Geographic Isolation

• Populations separated by geographic barriers such as rivers, mountains, or bodies of water
• Geographic barriers depend on organisms ability to move

The "Splinter" Population

• A separated population evolves, changing allele frequencies via selection or drift
• New environments will cause species to either not survive or potentially become new species

Occurrence of Speciation

• Speciation only happens if original population is no longer able to breed with the new

Reproductive Barriers

• Prezygotic mechanisms prevent mating by habitat, where species use different location niches so are less likely to mate.
• Another part of prezygotic mechanisms is temporal isolation where species have different breeding seasons
• Behavioural Isolation: different courtship or mating behaviours
• Prezygotic isolation includes the prevention of fertilization by mechanical and gametic isolation
• Mechanical Isolation includes structural differences in reproductive organs where they are incompatible
• Gametic Isolation is where the egg and sperm of different species can't cross react

Postzygotic Mechanisms

• Hybrid Inviability: reduced fitness hybrid with early death or reduced health
• Hybrid Infertility: infertile hybrids that survive adulthood
• Hybrid is mix of 2 different species

Adaptive Radiation

• Adaptive radiation involves a common ancestor that species evolve from
• Adaptive radiation is the same as divergent evolution

Diversity on Islands

• The diversity of species on an islands is a product of founder effect, natural selection, and reproductive isolating mechanism

Convergent Evolution

• Two species will share similarities in phenotype over time
• Natural selection produces striking similarities among a distant species
• Selective pressure gives rise to to species
• Example: Sharks and dolphins evolved the same body shape, but are different species

Rate of Speciation

• Gradualism: incremental genetic changes over time
• Punctuated Equilibrium: new species bud from parent with some change then little
• Humans affect evolutionary change directly and indirectly
• Examples: commercial fishing, habitat loss, and selective hunting

Coevolution

• Survival requires dependent species and linked pathways
• One species changes based on another (ex. orchid or moth evolution)
• Poison arrow frog warning behavior or coloration

Flowering Plants and Pollinators

• Flowering plants and pollinators have a mutualistic relationship

Mutualism

• Symbiotic relationship that benefits both species
• The flowering plant pollen is shared to the pollinator
• Scent signals pollinators/mutations
• Flower shape matches pollinator species

Plants and Herbivorous Insects

• Defence comes in the form of toxic substances
• Natural selection alters any ineffective variation
• Some Insects alter to cope with the poisons
• Ex. the monarch butterfly and the milkweed plant

Mimicry

• To gain a survival advantage, one species mimics another
• Ex. a hoverfly mimicking a wasp

Evolution of Complex Features

• Complex traits start with simpler features

Eyes of Molluscs

• Molluscs have varied eyes

Cumulative Selection

• Structures are refined over time to become more complex

Adaptation of Existing Structure to New Functions

• Certain materials change over time to allow for different functions
• Ex. Chitin
• Natural selection reworks existing structures
• EX: penguin flippers

Establishing Phylogenetic Relationships

• Phylogeny is evolutionary development determining realtedness
• Fossil, physiology, dna and protein analysis determine relatedness
• Phylogenetic tree show evolutionary relationships

Phylogenetic Trees

• Evolutionary family tree
• Base has oldest ancestor with upper branches having descendants
• Forks mean speciation in the past
• Deeper branch the less related
• Each branch is known as a clade

Cladistics

• Sequences branches of phylogenetic tree
• Related groups will have a common ancestor
• Organisms will share a homologous structure outside of the clade

Cladograms

• Derived branches on diagram
• Traits cause the divergence between ancestors

Constructing a Cladogram

• Fewest traits outgroup left while the most traits placed furthest right
• Common ancestor at the bottom

Systematics

• Systematics studies biological diversity
• Combining fossil, comparative sequencing and cladistics