TOPIC: Evolution
Origin of Life
• Abiotic earth LACKED Oxygen
• Early organism were anaerobic prokaryotes (bacteria)
• All organisms share the same genetic code
Evolution
• Charles Darwin – proposed that organisms (species or populations) change over time
•
Occurs by Natural Selection – “survival of the fittest”
•
Lines of evidence
1) fossils (geologic time)
2) Homologous Structures
3) Analogous Structures
4) Vestigial Structures
5) Embryology
6) Biochemistry
EndoSymbiotic Theory
• Eukaryotic cells evolved from prokaryotes
• Early prokaryotes engulfed other prokaryotes and developed symbiotic relationships
• Evidence includes mitochondria and chloroplast have prokaryotic type DNA
Natural Selection
• Theory of Evolution
• Fit organisms survive, reproduce, and pass on traits
Requirements:
• Variation – immigration, emigration, mutations, sexual reproduction (increase genetic
variation)
• Competition
Evidence of Evolution
1. Fossil Record- Geological time scale
2. Homologous Structures –same basic structure formed from same embryonic tissue
3. Analogous Structures – same basic functions due to same environmental pressures
4. Vestigial Structures – structures that have lost function ex) appendix
5. Embryology – embryos of various species appear identical
6. Biochemistry (also called molecular)– DNA and protein amino acid sequence comparisons –
we all share the same genetic code
Review Questions
• What is a vestigial structure? Name a few in humans.
A structure that was one used in an ancestor but is no longer needed. Appendix, Wisdom Teeth, Ear
Muscles
• What does it mean to be “fit” to an environment?
Adapted to the environment
• What is Darwin’s theory of Natural Selection? What is Artificial Selection
Natural Selection is where organisms that are the best adapted to the environment are able to survive
and reproduce more often that individuals that are not. “nature decides which organisms survive and
reproduce”. Artificial Selection is where humans decide which organisms reproduce such as
breeding cats, dogs, horses, cows, plants.
CoEvolution
• Two organisms evolve in response to each other
• Ex. Flowering plants and their pollinators
• Hummingbird and beak size
• Moth and proboscis size
• There is less competition for food due to evolving together
Adaptive Radiation an ancestral species radiates or diverges into many species.
 Ex) Galapagos Finches
Convergent Evolution
• Unrelated organisms in similar environments evolve to look remarkably similar to each other
• Similarities between Australian marsupials and placental mammals
• Similarity in form between dolphins and sharks
Adaptation
• Trait that increases survival
• For Example,
– Beaks that make it easier to eat insects
– Bright flowers to attract pollinators
– Vascular tissue in plants to adapt to life on land
Speciation
• Evolution of a new species
• must be isolation between populations
Reproductive Isolation
• Cause of speciation
• Geographic isolation – mountains, rivers, canyons
• Temporal isolation – active or reproducing at different times of day or times of year
• Behavioral isolation – differences in mating rituals that prevent reproduction between groups
Gene Flow
• A change in allele frequency that can occur when mating with members from another
population occurs.
– The movement of genes from one population to another.
– Migration – the movement of individuals from one population into the territory of
another.
– Plants migrate, too via wind pollination, streams humans etc.
Genetic Drift
DNA frequency in a population changes simply by CHANCE not fitness
 Survivors are lucky, not more fit
 Deceased are unlucky, not less fit
 Genetic Drift decreases diversity in a population
Causes of genetic drift
Random events:
1. natural disasters – hurricane, volcano, tsunami, earthquake, fire, etc
2. stepped on, ran over, picked up, put on a boat, stuck in a car, stuck to fur or clothing
3. at the wrong place at the wrong time
Antibiotic and Pesticide Resistance
• Populations will eventually become resistant to pesticides and antibiotics with overuse
• Biomagnification
Practice Questions
In the following chart, describe the role of each of the following in developing the current theory of evolution.
Discussion of importance to evolutionary theory
93. What is a vestigial structure? Name a few in humans. See above
94. What are some of the ideas on the origins of life? (a.k.a. where and when did it form?)
Endosymbiotic Theory
95. Discuss the steps in Darwin’s theory of evolution by natural selection. (Chapter 15)
1) Populations of organisms have many genetic variations. Where do these come from? Mutations, sexual
reproduction, meiosis and crossing over
2) Organisms could reproduce exponentially but they don’t. Why not? What are they restricted by?
Limited resources/ limiting factors (space, food, water, mates, habitat)
3) Genetic variations lead to different adaptations. What are adaptations?
A change in a trait of a population that is better suited for surviving
4) Some adaptations have better survival value in certain environments. What does this mean?
Ex: camouflaged to the desert vs. camouflaged to the rain forest
5) Those organisms with adaptations that better fit them to an environment will survive, reproduce and pass
on their genes. What does it mean to be “fit” to an environment?
Better able to survive, reproduce and pass on their genes. Most adapted to the environment
6) The next population will have a high frequency of the genes that have been selected for. Why will the
frequency of selected genes increase? Because those with the selected genes are more likely to reproduce
7) What is Darwin’s theory of Natural Selection? What is Artificial Selection?
See above
8) When this process continues over millions of years, it can lead to speciation. What is speciation?
The formation of a new species from an original parent species
96. Compare and contrast convergent and divergent evolution.
Two organisms look similar, have similar adaptations due to similar environments only- not really
closely related
Divergent evolution is where a population splits into different populations (speciation)
98. What is adaptive radiation? How did the finches of the Galapagos adapt to their environment?
A group of individuals from a population split off and form a new species over a long period of time.
Galapagos finches split off from the mainland to the different islands of the Galapagos
99. Describe how a population of bacteria can become resistant to an antibiotic (or an insect to a pesticide)
using the steps listed above. How is this a direct way to observe evolution?
Some of the organisms have an allele that allows them to be resistant. They survive, reproduce and pass on
that gene.
100. What happens when pesticides and antibiotics are used and how does it relate to evolution?
The organisms that are resistant survive and pass on the resistance gene which causes the population
to evolve (a change in the allele frequency over time)
What is meant by coevolution?
Two organisms evolve together. Flower and its pollinator
24. Give an example of a flowering plant and a pollinator and then describe how coevolution works. (How
does it ensure the survival of a species?)
Butterfly with a long proboscis and a flower with deep nector.