Transcript Evolution

Evolution
Species – Can you define
what a species is?
Evolution
Species – an interbreeding group of organisms that is
genetically distinct and isolated from other groups of
organisms.
Evolution - (biological definition) - ?
Evolution
Species – an interbreeding group of organisms that is
genetically distinct and isolated from other groups of
organisms.
Evolution - (biological definition) - a change in allele
frequencies over time
Possible Causes of
Evolutionary Change
1) Mutation – new allele created – minor, slow rate, most
deleterious and lost immediately
2) Gene flow in and out of population
 A population is a subgroup of a species within which
members mate randomly
 Emigration and immigration between populations with
slightly different allele frequencies can affect changes
3) Random genetic drift
 Each generation, random events may cause some to die,
survivors will have only a portion of the original set of
alleles in a pop. Therefore, some alleles will be lost by
random chance.
4) Selection (natural, sexual, and artificial selection)
Natural Selection
 Differential reproductive success of
individuals within a species occurring
because of genetic or hereditary
differences among them.
In order for natural selection to work the following
is necessary:
1. Genetic variance in the trait being acted upon
2. Differential survival and reproduction of
offspring due to that genetic variance
1. Genetic Variance in the Trait
• Phenotypic variation in a trait is due to 3
different factors - the influence of
environment, the influence of genes, and
their interaction.
Vp = phenotypic variance
Vp = Ve + Vg + Vi
2. Differential survival and
reproduction of offspring
1. All animals can over reproduce
2. Populations, however, tend to remain stable
3. Limited resources, cause some to die
4. Therefore there is a struggle for existence
Natural Selection Outcome
Thus:
5. Variable traits caused by genetic variability
result in some being better competitors (for
whatever reason)
6. Differential survival and reproduction of
offspring leads to changes in genetic
makeup of succeeding generations
Genetics of Behavior
Evidence for a genetic basis of behavior necessary for evolution of behavior:
1. Difference in behavior among different
strains and mutations
2. Effects of artificial selection on behavior
3. The behavior of interspecies hybrids
4. Instinctive behavior
5. Twin Studies
1. Strain differences
Strain - inbred lineage of some animal such
as of house mice.
By repeatedly mating closely related
individuals, you can get a strain of animal
that lacks genetic variability - homozygous
at most loci on chromosomes.
Southwick (1968) –
• used A/J – non aggressive mice
& CFW – aggressive mice
• Exp) cross-fostered the mice to totally
control for environmental influences
• Outcome: offspring behavior remained true
to the genetic lineage.
Rothenbuhler (1964) – honeybees
2 strains, non-hygienic - was
susceptible to “foul brood”
disease,
While hygienic strain exhibited
the ability to identify sick brood,
rip open the pupal cap and remove
the sick larva
Simple crosses indicated that the
non-hygienic trait was dominant
Two traits involved: uncapping cells and removing
brood
hygienic X non-hygienic = F1 all non-hygienic
F1 back cross with hygienic parent: UuRr X uurr
¼ hygienic, ¼ removed brood if cap removed,
¼ uncapped cell only, ¼ non-hygienic
2 genes: U – doesn’t uncap cells
u – uncaps cells
R - doesn’t remove brood
r – removes brood
2. Artificial selection
1. An animal is chosen for its
behavioral phenotype (observed trait).
2. Those with desired traits are bred;
those with undesired traits are not
allowed to pass on their genes.
3. Humans control selection
Examples: milk production in
cows, friendliness in dogs,
meat production in pigs,
fancy feathers in pigeons, etc.
3. Interspecies hybrids
• a. Dilger (1962) worked with lovebirds
produced sterile hybrids
• b. Agapornis personata (Fischer’s lovebird)–
cuts strips of nesting material and carries them
back to the nest in its beak
• c. Agapornis roseicollis (Peach-faced lovebird) –
cuts strips, tucks them under flank
feathers and carries more than one at
a time to the nest.
Vera Appleyard
Gwen Powell
Fig. 37.2: Addison Wesley Longman, Inc.
Greater and Lesser Prairie
Chickens
• http://www.youtube.com/watch?feature=pla
yer_detailpage&v=pJCy0d94YS0
• http://vimeo.com/39386702
• http://www.youtube.com/watch?v=Lcu7btvi
Ol0&feature=player_detailpage
4. Instinctive behavior
• Some animals perform species- specific behaviors
without an opportunity to learn the behavior.
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Nest and web construction behavior
Courtship displays
Territorial defense and migration
Nursing in mammals
Patterns of development
• Example 2:
Blackcap warblers inherit the direction of
migration and over wintering sites (most fly
from Europe to over wintering sites in
central Africa). A small population spends
the winter in Great Britain. The handreared young of these birds instinctively fly
west when shown the night sky during the
fall migration period.
5. Twin Studies
• Identical twins =
monozygotic twins – single
fertilized egg that splits
• Fraternal twins = dizygotic
twins – two fertilized eggs
(as related a non-twin
siblings)
• Ht, IQ, even criminal
behavior and homosexuality
have a high degree of
genetic influence
Photograph by Martin
Schoeller for National
Geographic Magazine
• Resemblance (correlation) in height of children
of the same parents:
– Siblings (52 pairs)
– Dizygotic twins (52)
– Monozygotic twins (50)
60% variation = genetic
64% (h2 = 0.64)
93% (h2 = 0.93)
• IQ – 384,482, and 687 pairs, respectively:
– h2 = 0.53, 0.63, and 0.87, respectively
• Autism – h2 – 0.7
• Homosexuality – 161 homosexual men and
170 adoptive brothers (reared in same
house) or twins (reared apart)
– 52% of monozygotic twins reared apart = also
homosexual
– 22% of dizygotic twins reared apart = also
homosexual (9.2% non-twin biol brothers)
– 11% of adoptive brothers reared together were
homosexual
Overall it’s estimated that homosexual
behavior has about 50% heritability
Conclusions
• There are different types
of evidence that suggest
genes play a major role
in the development of
behavior
• It follows then that
natural selection can and
does act on behavior and
• Behavior can evolve just
as an animal’s physical
characteristics can
Macroevolution
Phylogeny – the history of descent of a group of
taxa (genera, families, orders, etc.)
a. traits can be homologous – similar due to common
ancestry (= homology)
b. traits can be analogous – no common ancestry, but
similar due to convergent evolution (= analogy)
c. typically referring to morphological and genetic
characteristics, but behavior can also be considered a
trait and used to understand a group’s phylogeny
Construction of a Phylogenetic Tree