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Topic 5: Ecology and Evolution
5.4: Evolution
Evolution slider
The Big Bang
The Simpsons
Earth’s evolutionary past:• Life from more than 500 million years ago
was greatly different from life today. • Fish fossils have only been found in rocks
500 million years old or younger. (less than 15% of history of life)
• None of todays top predators existed at the time of dinosaurs or before.
• Few organisms today have identical forms in the fossil record. (Exceptions: cockroaches, ferns, certain sharks)
Charles Darwin1809 - 1882
“……can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the lease injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call NATURAL SELECTION.” – On the Origin of Species
Attenborough on Darwin
How Fossils Form
Organism dies and gets buried.
as layers of sediment are added, pressure increases, causing the sediments to compact into rock.
As body decays, minerals seep into the it, filling spaces where gases or fluids used to be — this is known as permineralization.
Alternately, the minerals in it chemically break down and are reformed or replaced.
Eventually, most or all of what is left is a rock-like copy of the body.
Sometimes, organisms are preserved in substances such as amber, ice or tar, as well.
Occasionally, imprints get filled with sediments that harden into rock, creating natural molds or casts. A good example is animal footprints
Evidence for Evolution: fossil record
Life 500 million years ago was very different from life today
Fish fossils only date back to 500 million years ago or younger. (< 15% of history of life)
None of the top predators today existed at the time of the dinosaurs or before
Other than some sharks, cockroaches and ferns, most living organisms have no identical form in fossil record
Whales in the desertWhale evolution: http://www.youtube.com/watch?v=I2C-3PjNGok
Heike’s crabs http://www.youtube.com/watch?v=nVSJNhUhV-4&feature=related
Homologous structures
*Structures which are similar in form and function but are found in dissimilar species.
Example: pentadactyl limbs are five-fingered limbs which differ in shape, number of bones and function.*Evidence for a common ancestor. – different uses, but basic shape and placement are the same
Homologous Structures
Evolutionary Mechanisms
1. Population produces more offspring than the environment can support.Utilize nutrients/energy of parentsForce competition: food, mates, spaceDisease, predation, parasitismLeads to adaptive behaviorsEx. Cuckoo bird Ex. Flowers & insects2. VariationSexual Reproduction
Competition for food• finding• catching• opening• digesting
Predation • catching• fighting• avoiding• escaping Parasitism
• invading• avoiding• removing• tolerating
Disease• invading• avoiding• removing• tolerating
Competition for mates• attracting• fighting• fertilising• providing for
Competition for spaces• living space/shelter• nesting• reproductive space
Variation & survival
ExamplesCamouflage Shapes of body parts such as beaksMating preferences
Causes of variety
1. DNA mutation May produce disease May produce advantage
Each generation only a few mutations.Most are not useful or harmful. Result is a
wide array of variation
as a result of
Random Mutation
Sexual Reproduction
DNA Replicatio
n
Viral infection
Meiosis Random fertilisatio
nRandom
assortment of chromosomes metaphase 1
Crossing over (recombination)
prophase I
Natural Selection
When too many individuals exist for limited resources, survival is determined by surroundings & compatibility of characteristics w/ surroundings.
Natural Selection Steps
1. Over production of offspring w/ variation Useful increase/harmful decrease
survival chance2. Genetic characteristics poorly adapted to
environment - Less successful at accessing resources
3. Genetic characteristics well adapted to environment – more successful at surviving
Steps cont.
4. Organisms that survive to adulthood more likely to reproduce & pass on successful characteristics
5. Over many generations, accumulation of heritable changes results in evolution. Gene pool has changed.
Antibiotic resistance in bacteria
Staphylococcus aureus - bacteriaVariation: MRSA – Methycillin-resistant
MSSA – Methycillin susceptibleEnvironmental change: application of
methycillinResult: MSSA is killed
MRSA survives & reproducesMRSA population increases, dominant strainMethycillin no longer effective against infection
Bacteria can continue to change and become resistant to all antibiotics – superbacteria
Bacteria reproduce asexually. Little variation.
Sources: mutation, plasmid transfer.
Pesticide resistance
Variation: Most individuals are susceptible to pesticide. Some carry a gene for resistance
Environmental change: pesticide sprayedResult: Susceptible population reduced.
Resistant population survives and reproduces
Gene for resistance increases in frequencyResistant population dominatesExamples: resistance of malaria to DDT, Rats
to poison
Not artificial selection:Humans are responsible for environmental
changes- creating environmental changes – pressure organism to adapt or parish.
*adaptations not “chosen” – results of environmental conditions.
*solution at individual level- significant to a specific population
Other examples of evolution in action include resistance to pesticides
