Recall,
Gradual Evolution vs. Punctuated Equilibrium
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What do these two diagrams represent?
Gradual Evolution
New species arise through the gradual
transformation of ancestral species
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Punctuated Equilibrium
Species evolve very rapidly
Speciation usually occurs in small
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When two specimens first evolve, they
appear very similar to their ancestors.
Gradually they become more distinct.
A lot of fossils species can be found.
These fossils represent the transitional
form.
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isolated populations
No fossils of transitional form can be
found
The new species do not change very
much over long periods of time
Ex. Volcanic Eruptions, meteor impacts
affect the evolution on Earth.
Patterns of Evolution
Adaptive Radiation
 When many related species evolved from a single ancestral species.
 Most commonly occurs when species of organisms successfully invades an isolated region
where few competitive species exist.
 If new habitats are availablenew species will evolved.
Divergent Evolution
 Is the process of two or more related species becoming more and more dissimilar
 E.g. adaptive variation
o Red fox-lives in mixed farmlands and forests. The red colour helps it blend in with
the surrounding trees.
o Kit fox-lives on plains and in deserts. Its sandy colour helps conceal it from prey and
predators.
o Fiches of the Galapagos.
Convergent Evolution
 Unrelated species become more and more similar in appearance as they adapt to the same
kind of environment. (selective pressures)
 E.g.
o cactus –America desert (fleshy stems arms with spines)
o euphorbia- African desert
o shark and dolphin-similar body shape
Coevolution
 is the joint change of two or more species in close interaction.
 E.g.
o predators and prey
o parasites and their hosts
o plants and animals that pollinate them
o flowers that have coevolved with bats and light in colour so bats can easily locate
them.
Balanced vs. Transient Polymorphism
Recall,
Polymorphism – one or two forms of a phenotype seen in a population
Balanced Polymorphism – When frequency of the phenotypes remain constant over periods of time
Ex. Sickle Cell anemia
- Recessive allele – Fatal when homozygous genotype occurs
- However, the allele is prevalent in countries where malaria is present
- Individuals with heterozygous combination of alleles are protected from malaria
- Therefore, a balance exists
Transient polymorphism – when frequency of a particular allele changes over a period of time
Ex. Sickle cell anemia
- If a population with a high frequency of the sickle cell allele moves into an area where malaria is
not present
-selective pressures will cause the frequency to decrease over time. (There is no benefit to having
that allele)
-Eventually, the allele will be pushed out of the population.
Ex. Industrial Melanism
-Due to industrial pollutions (anthropogenic causes), species have become adapted to acquire dark
colours
-This increases survival rate – camouflaged against predators.
Examples of Evolution in response to environmental change;
1. Darwin Observation
 Many species today believed to be descendent
from a few ancenstral types which adapted
to different environments
 E.g. 13 species of finches found nowhere else
but the Galapagos Is. and all showing definite
similarities.
Difference was in beak structure
2. Antibiotic resistance in bacteria
 Initial development of antibiotics such as penicillin caused death of many bacteria exposed to
the drugs.  Very Effective
 Repeated applicationsrise in bacteria resistant to antibiotics
 Antibiotic resistance trait selected