Ch. 18 Evolution and Origin of Species
All species of living organisms evolved at some point from a different species. It may seem that
living things do not change, that is not the case- evolution is an ongoing process
New era of biology began in 1859 when Charles Darwin published “On the origin of species.”
Descent with Modification:
Darwin never used the word evolution in the first edition of his book
Darwin and Wallace in their trips noted that current species are descendants of ancestral
species
Galapagos finches closely resembled another finch species on the mainland of south Africa
o Thus island species= modified from original mainland species
Natural Selection:
“survival of the fittest”
Favorable traits survive
Whether the favorable is good or not depends on environmental conditions
Variation= differences among individuals in a population
o Must have genetic basis otherwise, the selection won’t be inherited in the next
generation
Note: individuals do not evolve, populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
The traits that are adaptive will vary with different environments
Darwin’s Focus on Adaptation:
Darwin perceived adaptation to the environment and the origin of new species as closely related
processes
The diverse groups of Galapagos finches arose from an ancestral form by the gradual
accumulation of adaptations to different environments
Genetic Diversity in a population comes from two main mechanisms:
o Sexual reproduction
o Mutation
Mutations of DNA are the ultimate source of new alleles, or new genetic variation in any
population
Genetic changes caused by mutation can have 1 of three outcomes on phenotype
o Negative- lower likelihood of survival or fewer offspring- reduced fitness
o Positive- enhance survival; more offspring
o Neutral- no effect on the fitness of the phenotype
Sexual reproduction also leads to genetic diversity
Patterns of Evolution:
Convergent evolution- the evolution of similar, or analogous, features in distantly related groups
o Analogous traits arise when groups independently adapt to similar environments in
similar ways
All species of living organisms evolved at some point from a different species. It may seem that
living things do not change, that is not the case- evolution is an ongoing process
New era of biology began in 1859 when Charles Darwin published “On the origin of species.”
Descent with Modification:
Darwin never used the word evolution in the first edition of his book
Darwin and Wallace in their trips noted that current species are descendants of ancestral
species
Galapagos finches closely resembled another finch species on the mainland of south Africa
o Thus island species= modified from original mainland species
Natural Selection:
“survival of the fittest”
Favorable traits survive
Whether the favorable is good or not depends on environmental conditions
Variation= differences among individuals in a population
o Must have genetic basis otherwise, the selection won’t be inherited in the next
generation
Note: individuals do not evolve, populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
The traits that are adaptive will vary with different environments
Darwin’s Focus on Adaptation:
Darwin perceived adaptation to the environment and the origin of new species as closely related
processes
The diverse groups of Galapagos finches arose from an ancestral form by the gradual
accumulation of adaptations to different environments
Genetic Diversity in a population comes from two main mechanisms:
o Sexual reproduction
o Mutation
Mutations of DNA are the ultimate source of new alleles, or new genetic variation in any
population
Genetic changes caused by mutation can have 1 of three outcomes on phenotype
o Negative- lower likelihood of survival or fewer offspring- reduced fitness
o Positive- enhance survival; more offspring
o Neutral- no effect on the fitness of the phenotype
Sexual reproduction also leads to genetic diversity
Patterns of Evolution:
Convergent evolution- the evolution of similar, or analogous, features in distantly related groups
o Analogous traits arise when groups independently adapt to similar environments in
similar ways
