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Theory of Evolution  
Chapter Fifteen  
● What is Evolution? 
○ Evolution ​is the change in traits within a population over time 
○ Evolution is the foundation of biology 
○ Studying evolution can help biologists understand why particular genetic traits 
are passed onto offspring and how this can influence future generations 

● Charles Darwin 
○ During the 19th century, many biologists were gathering evidence in support of 
evolution 
○ Charles Darwin’s theory of evolution has become widely accepted by modern 
biology because his assumptions are testable, repeatable, and supported by mass 
amounts of evidence 

● Galapagos Islands 
○ Darwin gathered evidence of evolution during an around the world voyage in 
the 1830s on the HMS Beagle 
○ One of the destinations for this voyage was the Galapagos Islands where Darwin 
conducted research, collected data to support his theory of evolution, and 
published his findings
...
 

● Natural Selection 
○ Natural selection is a mechanism of evolution where individuals that are better 
adapted to their environment survive and reproduce more successfully than 
those individuals that are less adapted  
○ Those individuals that go onto reproduce are “selected for” 
○ Those individuals that do not reproduce are “selected against” 
○ Fitness is the measure of an individual's hereditary contribution to the next 
generation 
○ There are four main principles to natural selection: 
■ Individuals produce more offspring than can survive to maturity  
■ Individuals of a population differ in traits 

■ Individuals compete with each other to survive  
■ Individuals with certain traits are more likely to survive and reproduce, 
which means over time these traits become more frequent  

● Adaptation and Acclimation 
○ Adaptation is a long-term change within a population to accommodate an 
environmental influence 
■ For example, a white rabbit blending into the snow 
○ Acclimation is a short-term change within an individual to accommodate an 
environmental influence 
■ For example, a cat growing a thicker fur coat in response to cold 

● Evolution and Anatomical Structures 
○ Many anatomical structures are evidence of evolution:  
■ Homologous structures occur in different species and originate from a 
common ancestor (for example, forelimbs) 
■ Analogous structures have closely related functions, but do not originate 
from a common ancestor (for example, wings) 
■ Vestigial structures seems to serve no function, but resemble structures 
with functional roles in related organisms (for example, human tailbone) 

● Convergent Evolution 
○ Convergent evolution is a process by which unrelated species evolve similar 
physical traits because they have a similar lifestyles 
■ For example, a sugar glider and a flying squirrel 

● Divergent Evolution  
○ Divergent evolution is a process in which descendants of a single ancestor 
diversity into species that each fit different parts of the environment  
■ For example, Darwin’s Finches have different shaped beaks to eat 
different foods 

● Adaptive Radiation 
○ Adaptive radiation is an evolutionary pattern in which many species evolve 
from a single ancestral species 
○ Therefore, adaptive radiation can lead to divergent evolution 

● Artificial Selection  
○ Artificial selection is a mechanism of evolution in which a human breeder 
chooses individuals that will parent the next generation  
■ For example, there are 654 dog breeds produced by human selection 

● Coevolution 
○ Coevolution is when two or more species have evolved adaptations to each 
other’s influence 

■ For example, birds and flowers 

● Phylogenetic Trees 
○ Phylogeny​ is the study of relationships by ancestry among groups of organisms 
○ A phylogenetic tree can be constructed to demonstrate how organisms evolved 
from a common ancestor  



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