Evolution lecture 5 Flashcards
What is evolution?
the process by which the inherited characteristics of populations change over generations, leading to the eventual formation of new species
- is ongoing
- is the principle that all life shares a common ancestor
What are the names of the two scientists who discovered and described the mechanism for evolution?
Charles Darwin and Alfred Russel Wallace
What did Darwin do?
- Was a naturalist
- Visited South America, Australia, Africa
What did Wallace do?
- was a naturalist who studied insects
- collected insects in 1848-1852
-1854 -1862 collected insects in Malay archipelago
What were Darwin’s finches
- Darwin observed that each island had its own finch species
- the finches were very similar to one another and also a finch species on the mainland in South America
- species had unique beak shapes
- very small differences in beak size/ shape between the most similar
- Darwin thought that the island species might all be modified from one original mainland species
- Beaks adapted differently on each island in order to better allow the finches to acquire different food sources
What are the 3 Natural Selection?
is the inevitable result of three principles that operate in nature
1) characteristics of organisms are inherited ( i.e from parents to offspring)
2) more offspring are produced than are able to survive ( i.e. not all can survive and reproduce due to limited resources)
3)offspring have different characteristics are inherited
What is adaptation?
A heritable trait that aids the survival and reproduction of an organism in its present environment
What is divergent evolution? Provide example
-The process by which different organisms having common ancestors develop different traits or characteristics to adapt to the changing environmental conditions and needs
- accumulation of differences between groups that can lead to new species formation
Example: vertebrate limb
- structure shows common origins
- blind cave fish
What is convergent evolution? Provide example.
-the process whereby distantly related organisms independently evolve similar traits to adapt to similar necessities.
when similar structures arise through evolution independently in different species
- even though features in a species may look the same as those in another species, they do not share any recent common ancestry
- any similarity due to adaptations in response to similar environmental pressures
Examples: wings used in flight
- evolved independently in insects, birds and bats
- wings look similar and are used for similar purpose
- but not a close relationship between insects, birds, and bats
- vision in human and octopus
- very similar eyes, but evolved independently not a close evolutionary relationship
- white color of artic fox and ptarmigan bird
- animals living in the arctic have temporary white coverings during winter to blend with the snow and ice
- both adapted white color to avoid predation
- no common ancestor who was white
What is analogous structure? Provide example.
Structures that are similar in function and appearance BUT do not share a common ancestor
Example: wings of bats and insects
What is Homologous structure? Provide example.
Structures that share similarities, despite differences resulting from evolutionary divergence
- did not evolve independently, but have common ancestor who shares that structure
- similarities in anatomy between species often shows their descent from a common ancestor which had a similar physical form
Example:
Bones in the appendages of a human, dog, bird, and whale share same overall construction and common ancestor
- wings of hummingbird and ostrich
both are birds and descended from a common ancestor with wings
- wings did not evolve independently in each bird lineage
What is vestigial structure? Provide example
A structure in an organism that has no apparent function at all, and appear to be a residual part from a past ancestor
Example: wings on flightless birds, traces of pelvic bones in whales and snakes
- appendix in humans
What is changing allele frequencies in a population? Provide example.
- Allele frequencies change due to natural selection
- If an allele confers an advantageous phenotype (i.e. individual survives longer and reproduces more), that allele will be inherited by those offspring and in greater frequency in the next generation
- Since allele frequencies always add up to 100%, when frequency of one allele increases, others decrease
- Highly beneficial alleles may become fixed
- this means every individual of the population may carry the allele after a few generations
Example:
- E.g. wing colour of peppered moths
- gene for wing color shows mendelian autosomal inheritance
* Before industrial revolution in UK, most moths
were light (dd)
* Blended better against the bark of trees and
could better avoid predation
After industrial evolution, soot from coal turned
tree trunks black
* Moths with dark wings (DD or Dd genotype) were
now better at blending with trunks and avoiding
predation
* Colour of moth population shifted from light to
dark
* Now the air is cleaner, and moth population is
mostly white again
What is mutation?
random changes to genetic material
What is migration into or out of population? Provide example
new individuals/loss of individuals causes changes in ratio of organisms with specific alleles in a population
-gene flow is the flow of alleles in and out of a population resulting from the migration of individuals or gametes
Example: allele for brown color in beetles is introduced into green beetle population
What is genetic drift?
- the change in frequency of an existing gene variant in the population due to random chance.
- shows the most effect in small populations
- occurs because the alleles in an offspring generation are a random sample of the alleles in the P generation
- alleles may or may not make it into the next generation due to chance events
- allele frequencies in a population will change with each generation
What is genetic drift disaster?
must be one that kills for reasons unrelated to the organisms traits ( hurricane or lava flow)
- wipes out many due to chance
- some survive due to chance
- those that survive don’t have superior genes for facing that disaster
What is the founder effect? Provide example
when some small portion of a population leaves to start a new population in a new area, or is divided from population by a barrier
- individuals not likely to be representative of entire population’s genome
- genetic diversity possible in new population depends on range of alleles in founder
Example:
-Afrikaner population of Dutch settlers in
South Africa
-Huntington’s disease, one type of anemia
Sexual selection
A type of natural selection
* Some individuals have more offspring than
others due to increased ability to attract mates
* can lead to the evolution of dramatic traits that
often appear maladaptive in terms of survival
* traits persist because they give their owners
greater reproductive success
traits selected for become enhanced in the
males (e.g. fighting ability, feather colour)
* But, balance maintained between forces of
natural and sexual selection
* Natural selection will select against a
character’s further enhancement (e.g. antler
size) if it negatively affects survival of the male
More advantageous for female fitness to avoid
predation than to attract more matings
what are the two ways sexual section occurs
1) male–male competition for mates
* Takes the form of fights between males
* Can be ritualized, or pose threat to survival
* 2) female selection of mates
* Females may preferentially choose males with
specific traits (e.g. brighter feathers, larger
antlers, better mating dance, better territory)
Examples of sexual selection
E.g. colourful feathers makes a male more
obvious to predators
* E.g. long-lasting displays like birdsong by
males in mating season may be too
energetically expensive
What are fossils
Show that organisms are not the same today
as they were millions of years ago
* Fossil record tells the story of the past and
shows the development of form over time
What is species?
Species: a group of individuals that are able to
interbreed and produce fertile offspring
What is speciation?
the formation of two species from
one original species
* When one ancestral species splits into two or
more descendant species
* Thought to occur in two different ways
What is allopatric speciation? Provide example
geographic speciation
* When populations of the same species become
geographically separated from one another for
long enough that genetic differences accumulate
and they are no longer able to interbreed
* Could occur due to separation by a mountain or
if populations become trapped on different
islands
Example:
E.g. spotted owl speciation on
west coast of US
* northern spotted owl has
genetic and phenotypic
differences from its close
relative, the Mexican spotted
owl (southern)
* glaciers of the ice age divided an
initial population into two
What is Dispersal?
if a few members of a species move
to a new geographic area
What is vicariance? provide example.
if a natural situation arises to
physically divide organisms
Example: volcanic eruption separates a population
What is adaptive radiation? Provide example.
when multiple speciation
events originate from a single species
Example: lemurs in Madagascar
What is sympatric speciation? Provide example.
new species evolve from
an ancestral species while sharing the same
geographic location
How can this occur when a population is not
geographically separated?
* could begin with a chromosomal error during
meiosis or the formation of a hybrid individual
with too many chromosomes
How can this occur when a population is not
geographically separated?
* Could occur through a mutation which allows some
member of a species to eat a new food source
* May move to a different area of the habitat where
that food is found and be more likely to breed with
each other
Examples: apple maggot fly , Lake Victoria has adaptive radiation of
cichlid fish through sympatric speciation, around half of plants relate back to a species
formed in this way
