483 Lecture Notes - Lecture 9: Wild Type, Genotype, Phylogenetic Tree
5 Jun 2018
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LECTURE 9 Natural selection and evolution
Definitions to know:
•Homologous structures • Analogous structures •Divergent evolution •Convergent evolution
•Common ancestor
•Natural selection •Sexual selection • Adaptation
Gene pool Gene flow Genetic drift Bottleneck effect Founder effect Directional selection
Disruptive selection Stabilizing selection
A bit of history...
• Aristotle believed that species were fixed, Judeo-Christian culture reinforced this with beliefs
that all life forms were created in their present‐day form.
–As archaeology increased in the 1800s and fossils of extinct life forms were found, these
beliefs were
questioned.
Lamarck • Early 1800s
• Life evolved! Individuals adapted to their environment and then passed these adaptations to
their offspring
–E.g. giraffes develop a long neck over their lifetime and give this more extended neck
adaptation to their offspring
The Origins of Species was published in 1859 •The main points :
The theory of evolution (Darwin and Wallace)
1. Descent with modification: modern species have descended from ancestral species
2. Natural selection: the environment acts to select specific traits
• Finch species living on different islands developed different beak shapes over time, based on
the food sources on the island.
• Offspring with traits better suited to their environment are more likely to survive and reproduce
(and passed down theiqualitiests)
Darwin’s observations
Observation 1: • Overpopulation and competition – Populations, can
produce more offspring than the environment can support leading to competition between
individuals for limited resources
Darwin’s observations Observation 2
• Individual variation – Individuals within populations vary in many inherited traits
Darwin’s observations
Conclusion: Unequal reproductive success Individuals best suited to the environment are more
likely to have higher reproductive success
– They will survive better and longer and produce more significant numbers of offspring
find more resources at oneclass.com
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–These offspring, in turn, are likely to be better suited to the environment
Darwin’s Theories
Most controversial theory: All forms of life are related to some extent through branching
evolution from the earliest organisms
People in the 19th century didn’t like the idea very much
Evidence of evolution 1. Fossil record
• Oldest fossils were prokaryotes – indicating
• Transitional fossils
Basilosaurus (ancient whale): anklebone structure similar to pigs, hippos, cows and deer,
strongly suggesting that whales evolved from land mammals
prokaryotes were the first organisms on earth
2. Biogeography
• Regional similarities • Examples: –Wallace line (separate oriental and Australian
– Marsupials in Australia – Lemurs in Madagascar
3. Comparative Anatomy The comparison of body structures in different species
Homologous structures (e.g. the forelimbs of humans, cats, whales and bats have the same
skeletal elements) Evidence of common ancestry Adapted to varying functions over time
4. Comparative Embryology ”Ontogeny recapitulates phylogeny.”
All vertebrate embryos have a developmental stage in which pharyngeal pouches appear on the
throat Develop into different structures later in embryo development, e.g. gills in fish but into
parts of the ear and throat in humans
5. Molecular biology
• The genetic background is documented in DNA!
• The more similar the DNA of two organisms are, the more closely related they are.
• The genetic code is the same for all plants.
Evolutionary tree
Each fork point represents a common ancestor with features shared
by all members of the group after the fork
E.g. Reptile are tetrapods – vestigial structures for the four limbs in snakes
Divergent evolution
•So far, we have talked about divergent evolution –One species (common ancestor) evolved
into different descendants or forms
–Based on homology
–E.g. All lemur species known today shared a common ancestor.
Convergent evolution
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Definitions to know: homologous structures analogous structures divergent evolution convergent evolution, common ancestor, natural selection sexual selection adaptation. Gene pool gene flow genetic drift bottleneck effect founder effect directional selection. A bit of history: aristotle believed that species were fixed, judeo-christian culture reinforced this with beliefs that all life forms were created in their present day form. As archaeology increased in the 1800s and fossils of extinct life forms were found, these beliefs were questioned. Individuals adapted to their environment and then passed these adaptations to their offspring. E. g. giraffes develop a long neck over their lifetime and give this more extended neck adaptation to their offspring. The origins of species was published in 1859 the main points : Observation 1: overpopulation and competition populations, can produce more offspring than the environment can support leading to competition between individuals for limited resources. Darwin"s observations observation 2: individual variation individuals within populations vary in many inherited traits.
