BIO M02B: Darwinian evolution

before Darwin what did people believe?

nature is fixed and never changes, god made them perfect by divine creationism, new creatures arise when god makes them

Lamarck

first person for theory of evolution, had idea that species change overtime (correct) however though species adapt to environment ( incorrect)

what did Charles Darwin propose?

natural selection as a mechanism of evolution and decent with modification

Charles Lyell

major influence on Darwin, created a way to measure the layers of the earth, discovered earth was older than 10,000 years

Thomas Malthus

major influence on Darwin, discovered once a population goes above the production of food line, we will be in famine and start to die off, only a fraction of the population can reproduce

how did finches help Darwin?

he discovered their beak size was different on every island and was related to their food source, he thought they had a common ancestor leading Darwin to natural selection

natural selection

differential survival and reproduction of individuals based on variation in their traits

cell theory

all cells come from prexisting cells

evolutionary theory

all species came from preexisting species

components of Darwins theory of evolution (4)

1. variation exiss in populations

2. variations have to be heritable

3. some offspring will not survive

4. individuals with favorable traits will survive and reproduce more

what is the base unit for evolution?

populations

what is the source of variation which natural selection acts upon

genes

stabilizing selection

favors average phenotypes over extreme phenotypes

directional selection

favors one extreme phenotype over the other

disruptive selection

extreme phenotypes are favored over average ones, occurs in populations with diverse environments

decent with modification

variation is passed along to the next generation within a population

mutations

sudden change in gene, chromosome, or set of chromosomes

point mutation

a single change in DNA in one nucleotide

deletion

loss of one or more nucleotide

insertion

instert new nucleotide or codon

microevolution

change in gene frequency within a population, can be observed over short periods of time

Artificial selection

intentional breeding ( ex, dogs)

gene flow

migration or immigration

genetic drift

results from random changes/ chance events in gene frequencies, happens in small populations

bottleneck effect

Drastic reduction in population, leads to loss of genetic diversity

founder effect

new population is established by a small number of individuals from a larger population

non-random mating (sexual selection)

individuals choose mates with a particular trait/ phenotype

female choice

male to male competition

fossils

preserved dead animals trapped in sediment (ice, amber, petrified wood, etc)

experimental evolution

can move species to different environments to see how they act and evolve (transplant experiment)

Homology

Similarities in characteristics resulting from common ancestry (human arm vs cat arm), proof of decent with modification

anatomical vestiges

body parts and/or behaviors that no longer serve a function

transitional forms

Transitional animals found in fossil record that are proof of how an animal evolved

embryonic development

can see homologies that are not obvious in adult organisms

ontogeny

how you develop overtime

phylogeny

the evolutionary history of a species or group of related species using phylogenetic trees

molecular homology

links between organisms at the molecular level, can include DNA and protein homologies

convergent evolution

2 different species from different lineages show similar characteristics because they occupy similar environments (traits with similar function that evolved independently, ex bat wings vs bird wings)

analogous structures

different structures adapted to the same ecological niche (ex. evolution of fins and wings)

Homologous structures

same structure adapted to different ecological niches (ex. all mammals have 7 necks bones)

discipline of systematics

classifies organisms and determines their evolutionary relationships

taxonomy

science of naming, describing, and classifying organisms

Carolus Linnaeus

created 2 part naming system (genus species)

created system for classifying organisms based on morphological characteristics

introduced a way to group species in increasingly broad categories (domain, kingdom, phylum, class, order, family, genus, species)

taxon

taxonomic unit used at any level of hierarchy

phylogenetic tree

represents a hypothesis about evolutionary relationships (MUST have a root)

basal taxon

Relatively unchanged, most closely related to the common ancestor

sister taxa

most closely related to each other

polytomy

3 way split in evolutionary tree, shows we dont have enough info to classify yet

cladistics

method of constructing evolutionary relationships based on shared characteristics

cladograms

Evolutionary tree where branch length has no meaning, map is based on descent with shared derived characteristics

node

branching point in cladogram, represent speciation event

clade

group of organisms that consist of a common ancestor and all its descendants (cladogram)

paraphyletic group

consists of an ancestral species and som, but not all, of the descendants ( cladogram)

polyphyletic group

consists of taxa evolved from different recent ancestors (cladogram)

outgroup

a species or group of species that is somewhat closely related to ingroup (the various species being studied), diverged before ingroup

ancestral characters

shared by outgroup and ingroup that predate the divergence of both groups from a common ancestor

symplesiomorphy

shared ancestral characteristic

synapomorphy

indicate more recent ancestor, define a clade