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Lecture

BIOL 103 Lecture Notes - Goose Bumps, Brussels Sprout, Common Dolphin


Department
Biology
Course Code
BIOL 103
Professor
Peter T Boag

Page:
of 4
Evolution and Diversity Lecture 2
- Fossil intermediates
o E.g. evolution of whales
o Whales and hippos evolved in parallel from ancient Artiodactyls
(cloven-hoofed mammals)
- Deep Time
o Difficult for us, impossible for Darwin to grasp vast time spans
available for evolutionary change
- Darwin familiar with results of plants and animal breeding, done empirically,
without knowledge of genetics
- Geographic distribution and Evolutionary history
o Darwin saw other species distributed around the Earth now that we
know about plate tectonics we know more about this idea
o Darwin did not understand plate tectonics
o Knew about beaches being raised over night, and even more over time
made him realize that the Earth was very dynamic (plated could
move, lands could change) so natural selection made sense
- Artificial Selection on Wild Brassica: Process
o Parental generation: select individuals with the largest and most
compact flowering stalks, and breed them
o Generation 2: of the offspring, select the individuals with the largest
and most compact flowering stalks, and breed them
o Generation 3: do as what was done in generation 2
o Generation 4: after many generations, average flowering stalks are
much larger and more compact
- Artificial Selection in Brassica: Results
o Flowers: broccoli and cauliflower
o Stems: kohirabi
o Terminal bud: cabbage
o Leaves: kale
o Axilliary buds: Brussels sprouts
o They all look like a different species, but all the same different
phenotypes exaggerated by artificial selection
- Evidence of Evolution: comparative anatomy
o Homologous features
Derive from same structure in common ancestor
o Homoplastic (analogous) features
Similar functions in distantly related organisms result of
convergent evolution
o Vestigial Structures
Remnants of structures indicate adaptations wax and wane as
environments change
o Many results are from parallel selection, not necessarily common
ancestry
- Homology in Animal Genes
o Homologous traits: similarities are inherited from a common ancestor
o There is a change in how they are regulated which is how
development changes
- Homoplastic (analogous) phenotypes can be misinterpreted as homology
o Analogous Traits: similarities result from convergent evolution
o Common dolphin and Ichthyosaur look similar and have a similar
function, but they have a different ancestor
- Convergent Evolution: unrelated mammals eat ants and termites in similar
ways and display many other structural and functional similarities
- Goose bumps are vestigial trait
o Human goose bumps are note useful to humans
o For other animals, goose bumps are useful
o Erect hair on chimp (insulation, emotional display)
- Appendix is a vestigial trait in humans
o They are involved in digesting cellulose material
o Smaller in humans because of our diet it can cause problems
(appendicitis)
o In stone age time, we could get cholera, would loose bolily fluids,
appendix used for something after intestinal disease
- Evidence for evolution from developmental and molecular biology
o Development reveals ancestral structures no longer obvious in adults
o Protein and DNA sequences contain records of evolutionary change
o Phylogency
Evolutionary history of group of related species, displayed as
Phylogenetic trees
Diagrams showing lines of descent based on molecular data
(more later)
- Developmental Homology
o Species that differ as adults often bear similarities as embryos
o Gill ridges in human embryos indicate humans evolved from aquatic
animals with gill slits
o Human embryos have long bony tails; features distinguishing species
often appear later in development
o Today, know that conserved homeotic genes responsible in part for
embryo similarity
o “Ontogeny recapitulates phylogeny” means “development repeats
evolution”
o Advanced organisms forced to go through stages of less advanced
organisms during development are temporarily less advanced species,
this is not true, it is a flawed theory
o Sequences are interesting because going back to homeotic genes they
make sense, unraveling of genetic code, same set of instructions,
tweaking in genetic code in later stage of developmental processes
that leads to the differences in phenotype
- Phylogenetic tree of whales and closest living relatives based on how similar
their homologous DNA sequences are signature still there in DNA and bones,
not obvious in phenotypes
- Closing Notes
o Individuals do not evolve; populations evolve the relative frequency of
individuals with heritable differences changes, some evolution is
‘neutral’ e.g. mutations in nonfunctional ‘junk DNA’
o Adaptations are
Evolved characteristics enhancing an organism’s survival or
reproduction in a particular environment (their Darwinian
fitness)
May be structural, physiological, behavioural, or a combination
- Proximate vs. Ultimate Explanations
o Be careful:
Adaptation is also used in non-evolutionary contexts to
describe the decline in response of a sensory receptor after
repeated or prolonged stimulation, e.g. deafness after a rock
concert
The same observation can have both an immediate,
mechanistic = proximate explanation not requiring
evolutionary thinking, and a more fundamental, historical =
ultimate explanation involving an evolutionary perspective
o A physician might say: “You can’t hear because heavily amplified
music damages hair cells in the organ of Corti” (see text chapter 45)
(proximate)
o An evolutionary biologist might say “You can’t hear because natural
selection favoured ancient humans with ears sensitive to low intensity
sound in the 1000 4000 Hz range, to detect approaching predators
in an environment devoid of sounds like those at a modern rock
concert” (ultimate)
Variation and Natural Selection in Populations
- Review Key Terms
o Phenotype
o Genotype
o Locus
o Allele
o Dominant Allele
o Recessive Allele
o Homozygous
o Heterozygous
- Population’s gene pool:
- Includes all the alleles for all the loci present in the population
o Each diploid individual has a maximum of two different alleles at each
locus, but additional alleles may exist at the same locus in other
individuals
o Summed across thousands of loci, one individual has only a small
fraction of the alleles present in an entire population
- Evolution of populations is best understood in terms of frequencies
measured at various levels: