Evolution Flashcards
What theory of classification did Aristotle propose?
Scala Naturae:
-Species are fixed
-arranges species on a scale of increasing complexity
What two principles did Lamarck propose?
- Use and disuse: body parts used extensively become
larger and stronger, unused parts deteriorate - Inheritance of acquired characteristics: modifications
acquired in one’s lifetime can be passed to offspring(not true)
Descent with modification
all of life is connected by common ancestry and
descendants have accumulated adaptations to
changing environments over vast spans of time.
Key features of natural selection
- Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals
- Natural selection increases the frequency of adaptations that are favorable in an environment
- If the environment changes, natural selection may drive adaptation to new conditions, giving rise to new species
4 key points about evolution by natural selection
- individuals do not evolve as it is the population, the
group of organisms, that evolves over time. - natural selection can amplify or diminish only
heritable traits. - evolution is not goal directed; it does not lead to
perfectly adapted organisms. - selection happens by the environment/ ecosystem,
not by the individuals themselves
How have we come across our current understanding of evolution?
Fossils: understanding of similarities, species come and
go
* Homology: similarities in form, behaviour etc.
* Molecular biology: biochemical assays on ancient and
modern samples
* Genomics: sequencing of ancient and modern genomes,
and looking for genetic changes
Homology
Similarity resulting from common ancestry
Vestigial structures
remnants of features that served important
functions in the organism’s ancestors
What similarities are looked for in molecular biology that can link species’ evolutionary relationships?
- Similarities/ differences in
protein structure - Similarities in cell structure
Genome Sequencing
is a laboratory procedure that determines the order of bases in the genome of an organism in one process. Can determine how genetically similar a species is to another.
Phylogeny
The evolutionary history of a species or group of species
Systematics
classifying organisms and determining their evolutionary
relationships
-includes taxonomy
Convergent evolution
occurs when similar
environments and natural selection produce similar
adaptations in organisms from different evolutionary lineages
Analogy
Similarity due to convergent evolution
Difference between homology and analogy
-Similarity resulting
from common
ancestry is known
as homology.
-Analogy: similar environments
and natural selection produce
similar adaptations
Molecular systematics
uses molecular comparisons to build phylogenetic trees.
Steps in the analysis before drawing a phylogenetic tree
1.organize the data: count the number of traits each species has
2.rank the species from lowest to highest number of traits.
3.identify the outgroup, the group with the fewest traits in the table
4.draw a phylogenetic tree, starting with the species with the least traits
5.indicate for each branching point which trait is developed.
Mutation
can occur due to errors in DNA replication (S-phase!)
mixing existing alleles arise every generation from which three random components of sexual reproduction?
- crossing over,
- independent orientation of
homologous chromosomes at
metaphase I of meiosis, and - random fertilization.
Gene pool
consists of all copies of every type of allele, at every locus, in all members of the population.
Microevolution
Changes in the traits of a group of organisms within a species that do not result in a new species.
Macroevolution
Large-scale evolution occurring over geologic time that
results in the formation of new species and broader
taxonomic groups.
– the development of new groups of organisms through
speciation events
– the impact of mass extinctions and recovery on the
diversity of life
Main causes of evolutionary change:
- natural selection,
- genetic drift
- gene flow
Genetic drift
random events that drive genetic change of a population
Fixation
rise to 100% percent frequency of other alleles
Bottleneck effect
sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities
Founders effect
when a few individuals
colonize an island or other new habitat
Gene flow
Organisms and gametes that enter a population may have
new alleles, or may bring in existing alleles but in different
proportions than those already in the population.
Stabilizing selection
favours intermediate phenotypes. For example in number of offspring or birthweight.
Directional selection
individuals at one of the
phenotypic extremes. shifts the overall makeup of the population by acting
against individuals at one
of the phenotypic extremes. Examples: sickle cell anemia in malaria areas, shorter extremities in cold areas.
Disruptive selection
both ends of a phenotypic
range over individuals with intermediate phenotypes. typically occurs when environmental
conditions vary in a way that
favors individuals at both ends of a phenotypic range over
individuals with intermediate
phenotypes. Examples: Peppered moths in polluted vs. non-polluted areas.
Sexual selection
a form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mates
Intrasexual selection
individuals compete directly
with members of the same
sex for mates
Intersexual selection
individuals of one sex (usually
females) are choosy in
selecting their mates.
What constraints are placed on evolution?
- Selection can act only on existing variations. New,
advantageous alleles do not arise on demand. - Evolution is limited by historical constraints. Evolution
co-opts existing structures and adapts them to new
situations. - Adaptations are often compromises. The same
structure often performs many functions. - Chance, natural selection, and the environment
interact. Environments often change unpredictably
Speciation
the process by which one species splits into two or more species
Biological species
– a species is a group of populations whose members
can interbreed in nature and
– produce fertile offspring with each other but not with
members of other species.
– reproductive isolation.
Morphological species concept
based on observable physical traits and can be applied to asexual organisms and fossils
Ecological species concept
defines a species by its
ecological niche and focuses on unique adaptations to
particular roles in a biological community
Phylogenetic species concept
defines a species as
the smallest group of individuals that share a common
ancestor and thus form one branch of the tree of life
Allopatric speciation
Geographically separated from other populations,
a small population may become genetically unique
as its gene pool is changed by
– natural selection,
– mutation, or
– genetic drift.
Habitat differentiation and sexual selection, usually
involving mate choice, can lead to sympatric and allopatric speciation.
Sympatric speciation
occurs when a new species arises within the same geographic area as its parent species. Habitat differentiation and sexual selection, usually
involving mate choice, can lead to sympatric and allopatric speciation.
Polyploidy
duplication of the chromosome number due to errors in
cell division.
What are the mechanisms of macroevolution
- Plate tectonics
- Gene flow, genetic drift, selection, adaptation, isolation à
Speciation - Mass extinctions followed by adaptive radiation
Pangea
About 250 million years ago, plate movements brought all the previously separated landmasses together into the
supercontinent
Ordovician-silurian extinction
440 million years ago.
– Small marine organisms
– Continental drift and subsequent climate change
Devonian extinction
365 million years ago.
– Tropical marine organisms
– Lack of oxygen in the oceans, quick cooling of air temperatures, volcanic
eruptions and/or meteor strikes
Permian-triassic extinction
250 million years ago.
– Range of species, including vertebrates
– Cause unknown—possibly asteroid strikes, volcanic activity, climate change, and microbes
-The Permian extinction is linked to the effects of
extreme volcanic activity.
Triassic-jurassic extinction
210 million years ago.
– other vertebrates; allowed dinosaurs to flourish
– Major volcanic activity with basalt flooding, global climate change, and changing pH and sea levels of the oceans
Cretaceous-tertiary
65 Million Years Ago.
– Mass extinction of large land dinosaurs, allowed development of birds and mammals
– Extreme asteroid or meteor impact
-The Cretaceous extinction, which included most large
dinosaurs, caused by the impact of an asteroid.
Adaptive radiations
periods of evolutionary change in which many new species evolve from a common ancestor.
evolutionary developmental biology “Evo-devo”
combines evolutionary and developmental
biology.
-New forms can evolve by changes in the
number, sequences, or regulation of
developmental genes.
Development of novel traits
complex structures may evolve in stages from simpler versions
with the same basic function
– or from the gradual adaptation of existing structures to new
functions.
