Biology U2: Evolution (L2.0-2.7)

Proximate Explanation

Explains or describes how a system works (what/how)

Ultimate Explanation

Explains why living systems are the way they are (why)

3 Broad Observations of Life

Life is suited for it's environment, there is unity in life (similarities between species), diversity of life

Evolution

The idea that all species are descended from ancient species which gradually became different over time

Creationism

God created an infinite and continuous series of life forms, all organisms were created in their present form, have remained unchanged, and will remain unchanged

Catastrophism

appearance of new species and the disappearance of others: past catastrophic events led to mass extinctions in specific regions, which were later repopulated

Uniformitarianism

mechanisms of change are constant over time; geological processes operated at the same rate in the past as they do today

Lamarck

Body parts that are used would become larger and stronger, and unused ones would disappear, inheritance of acquired characteristics: organisms can pass on their own modifications to their offspring

3 Patterns of Diversity

Global: similar organisms around the world/rare organisms in a specific region, Local: organisms living in a similar region but with different environments have different features, Time: species vary over time and share similar geographical distributions

Darwin and Wallace

In 1858, Wallace and Darwin published the hypothesis of evolution by natural selection

This pushed Darwin to publish "On the Origin of Species" in 1859

Adaptation

gradual changes to structures, physiology, or behaviours that helps an organism survive and reproduce in a particular environment

Variation

structural, functional, or physiological differences between individuals within a species, determined by the environment to see which variations are neutral/beneficial/deleterious

Theory of Evolution by Natural Selection

descent with modification explains life's unity/diversity, natural selection matches the organism to it's environment (environment increases allele frequency to lead to evolution of adaptations)

Descent with Modification

all species are descendants of ancient species, differences accumulate over time

Mechanism of Natural Selection

process by which individuals with inherited characteristics well suited to their environment leave more offspring: the survivors' offspring also have those useful traits. causes a population to change over tim as natural selection can increase the match between organisms and their environment (advantageous traits are more common)

Selective Pressure

environmental condition that selects for/against certain characteristics (phenotypes)

MNS Observation 1

members of a population often vary greatly in their traits

MNS Observation 2

traits are inherited from parents to offspring (heritable variation): offspring do NOT come out with same variation

MNS Observation 3

all species are capable of making more offspring than the environment can support

MNS Observation 4

because of lack of resources, or other selective pressures, many offspring do not survive: those that do have adaptations, survive

Note about Natural Selection

natural selection can amplify or diminish only heritable traits.

natural selection can only act on existing variation! It does not create new traits.

adaptations don't create perfect animals, but help organisms "outperform" other individuals in their population

favoured traits depend on environmental context

Homology (comparitive anatomy)

traits with different function, but similar origin or anatomical structure (due to common ancestry)

Divergent Evolution (comparitive anatomy)

occurs when 2 or more species evolve increasingly different traits resulting from differing selective pressures

Vestigial Features (comparitive anatomy)

remnants of features that served a function in the ancestor but do not currently serve a purpose

Convergent Evolution (comparitive anatomy)

occurs when 2 or more species become increasingly similar in response to similar selective pressures

Analogous Features (comparitive anatomy)

traits with same function, but no similar origin or anatomical structure

Homology in Comparitive Development

similar early embryological development due to common descent

DNA Similarities (molecular biology)

the genetic code is universal therefore we all must have a common ancestor

Protein Similarities (molecular biology)

closely related organisms have proteins in common (cytochrome C is very common)

Molecular Biology

more closely related organisms have more similar DNA sequences and protein structure

Artifical Selection

selective breeding to produce offspring with genetic traits valued by humans (selective pressure is due to humans, not environment)

Antiobiotic Resistance

selective pressure trying to kill bacteria; if treatment is incomplete, bacteria survive and reproduce (natural selection did not create drug resistance; simply favours drug resistance trait)

Fossils (fossils)

remains of organisms buried in sediments

Fossil Records (fossils)

chronological collection of life's remains in the rock layers

Extinctions (fossils)

modern and extinct animals that resemble each other share similar distribution

Transitional Fossils (fossils)

show links between groups of organisms

Biogeography (geographic distribution)

geographical distribution of species

Continental Drift (geographic distribution)

slow movement of continents over time (all continents were connected together as Pangea, broke apart and drifted approx. 200mya)

Hardy-Weinberg Equilibrium (HWE)

a theory that states that allele/genotype frequencies will remain constant in populations if there are no other evolutionary influences

5 Criteria for HWE

no natural selection, no gene flow, no mutations, random mating, large population

Stabilizing Selection (natural selection in HWE)

individuals near the center of the phenotype range have a higher fitness than individuals at either end of the range

Directional Selection

individuals at one end of the phenotype range have a higher fitness than individuals in the middle or other end of the range

Disruptive Selection (natural selection in HWE)

individuals at either end of the phenotype range have a higher fitness than individuals near the middle of the range

Random Mating (random mating in HWE)

all individuals have an equal probability of getting a mate

Non-Random Mating: Sexual Selection (random mating in HWE)

type of natural selection that involves some individuals with certain inherited traits getting more mates than others (decision of individuals, NOT the environment)

Sexual Dimorphism (random mating in HWE)

when males and females of a species have drastically different phenotypes

Genetic Drift

change in the allele frequency (gene pool) of a population due to chance (more likely in smaller populations as larger populations are less likely to undergo change by chance)

Bottleneck Effect

natural disasters drastically reduce the size of a population, reducing the size of its gene pool (increases genetic drift, reduces genetic diversity, certain alleles are represented more and others are eliminated)

Founder Effect

small number of individuals from a large population leave and start a smaller population in an isolated environment (inreases genetic drift, reduces genetic diversity, allele frequency changes due to small population, new pop. is different than founder and source population)

Gene Flow

exchange of genes with another population: both populations exchanging genes will become similar (introduces new allele into a population, variation is reduced between both populations)

Deleterious Mutations (mutations in HWE)

mutations that are disadvantageous to individuals; they reduce fitness/reproductive success

Beneficial Mutations (mutations in HWE)

mutations that are advantageous to individuals; they increase fitness/reproductive success

Neutral Mutations (mutations in HWE)

neither an advantage or disadvantage

Mutations

alter gene frequencies, introduce new alleles to a population, unlikely to cause evolution (rare to pass on to generations), +natural selection = large effect if new alleles produce increase/decrease fitness

3 Mechanisms that Alter Allele Frequencies

natural selection (only evolutionary mechanism to consistently lead to adaptive evolution), genetic drift, genetic flow

Antiobiotic Resistance

when germs, such as bacteria, evolve to overcome the effects of the medicines that were once used to kill them

Adaptive Evolution

increasing the match between populations and their environment

Speciation

The process by which one species splits into 2 or more (formation of new species)

Macroevolution

More dramatic biological changes; origin of different species, formation of major groups of organisms (plants vs animals), extinction of species, and evolution of major new features (wings)

Microevolution

--> Speciation --> Macroevolution

Morphological Species Concept

Structural features: can be applied to species with unknown behaviours (fossils), BUT it is subjective and misleading

Ecological Species Concept

Looks at ecological niche and how members of the species interact with the non-living and living part of their environment: applied to both asexual/sexual organisms, BUT defining different niches can be subjective

Biological Species Concept (BSC)

a population or group of populations whose members have the ability to breed with one another in nature and produce fertile offspring

Fertile Offspring

capable of mating and producing offspring (members of one species cannot successfully interbreed with members of other species)

Speciation Steps

population seperates and gene flow stops, individuals genetically diverge + different environmental pressures, individuals are reproductively isolated and now different species

Reproductive Isolation

inability of 2 organisms to successfully reproduce due to physical/behavioural barrier (can become different species)

Reproductive Barriers

stop gene flow between populations, leads to populations becoming so genetically different that they no longer reproduce

Prezygotic Reproductive Barriers

blocks fertilization from occuring

Postzygotic Reproductive Barriers

acts after a zygote has been created

Habitat Isolation (prezygotic)

2 different species occupy either different habitats, or different niches in the same habitat, the differences in their ecological needs isolates them from one another so they rarely meet

Temporal Isolation (prezygotic)

different species breed at different times of the day, different seasons, or different years, therefore preventing breeding

Mechanical Isolation (prezygotic)

differences in morphological features may make two species incompatible

Behavioural Isolation (prezygotic)

different species use different courtship and mating clues to find and attract a mate

Gametic Isolation (prezygotic)

male gametes may not be able to recognize and fertilize an egg of different species

Zygote Mortality (postzygotic)

mating and fertilization are possible, but the zygote is unable to properly develop due to genetic differences

Hybrid Infertility (postzygotic)

hybrid offspring are healthy and viable, but sterile

Hydrid Breakdown (postzygotic)

first generation hybrids are viable and fertile, but when they mate, their offspring are feeble or sterile

Allopatric Speciation

populations are geographically isolated from each other, and over time, genetically diverge (more common)

Sympatric Speciation

populations are not geographically seperated, but diverge anyways (less common)

Adaptive Radiation

single species rapidly evolves into a number of distinct but closely related species (small scale divergent evolution), filling an ecological niche and increasing biodversity

Cumulative Selection

evolution of a simple structure into a more complex one through a series of small adaptations

Coevolution

process where one species evolves in response to the evolution of another species

Theory of Gradualism

gradual changes in morphology over years, occurs in environments that change slowly

Theory of Punctuated Equilibrium

long periods of equilibrium interrupted by episodes of rapid speciation, occurs in environments that change rapidly

Characters

quantifiable, heritable traits

Phylogeny

grouping species based on evolutionary [history] relationships, done by looking at characters

Cladogram

represents hypothetical relationships between groups of organisms (eg. family tree)

Roots (cladogram)

represent ancestral lineage

Tips and Branches (cladogram)

represents descendants of the ancestor

Speciation Event + Node (cladogram)

split of a lineage is represented as branching, the point is called a node and the event is called the speciation event

Sister Groups (cladograms)

new emerged lineages after a lineage splits or branches

Phylogenies

trace patterns of shared ancestry between lineages, where each lineage has a unique history