BIOLOGICAL EVOLUTION
Definitions
● Biological evolution is defined as descent with modification through the mechanism of
natural selection and refers to the cumulative changes that occur in a population from
generation to generation over time
● Microevolution refers to changes in allele or genotype frequencies in a gene pool of a
population over time (small-scale evolutionary change within species level)
● Macroevolution refers to large-scale phenotypic changes in populations that generally
warrant their placement in taxonomic groups at the species level or higher; descent of
different species from shared ancestors over many generations
Lamarck’s theory of evolution
(1) Use and disuse of organs
(2) Inheritance of acquired characters
Darwin-Wallace’s theory of evolution (Darwinism)
(1) Observation #1: Organisms have great potential to reproduce
● Tendency to produce more than can survive
(2) Observation #2: Constancy in numbers due to environmental restrictions
● Limited resources, most populations maintain relatively constant numbers as majority of
offspring die before reaching sexual maturity
(3) Inference #1: Struggle for existence
● Competition among individuals is inevitable in order to survive
(4) Observation #3: Variation within a population
(5) Inference #2: Survival of the fittest by Natural Selection
● Natural selection is the process by which the environment selects for well-adapted
individuals with inherited traits that are best suited to the local environment
● Better-adapted (fitter) individuals with the selective advantage will be more likely to
survive to reproductive age and produce more offspring
(6) Observation #4: Differential reproduction leading to reproductive success (like produces like)
● Those that survive to breed are likely to produce offspring similar to themselves
● The advantageous traits that give them the edge in the struggle for existence are likely to
be passed on to the next generation, making the offspring better-adapted to the
environment
(7) Formation of new species
● Over many generations, the proportion of individuals possessing the advantageous traits
increases whereas the proportion of those lacking the traits decreases, leading to
evolution of the population
● A new species is formed after the accumulation of several characteristics and adaptive
mechanisms in a particular population over many generations
Copyright © 2019 tonyndr
,Modern theory of evolution (Neo-Darwinism)
● Incorporates principles of Mendelian genetics and knowledge of molecular biology
(1) Observation #1: Organisms have great potential to reproduce
● Tendency to produce more than can survive
(2) Observation #2: Constancy in numbers due to environmental restrictions
● Limited resources, most populations maintain relatively constant numbers as majority of
offspring die before reaching sexual maturity
(3) Inference #1: Struggle for existence
● Competition among individuals is inevitable in order to survive
(4) Observation #3: Variation within a population
● Arises as a result of spontaneous mutations of genes
(5) Inference #2: Survival of the fittest by Natural Selection
● Individuals with genetic variations best adapted to the new environment are at a
selective advantage and will be more likely to survive to reproductive age and produce
more offspring
(6) Observation #4: Differential reproduction leading to reproductive success (like produces like)
● Over generations, proportion of individuals who possess the favourable genes/alleles
and are at a selective advantage increases while the proportion of those at a selective
disadvantage decreases
● Leads to changes in allele and genotype frequencies
(7) Formation of new species
● Can only happen if populations are separated so that they do not interbreed
● The separated populations adapt to their own particular environments and may diverge,
eventually forming new species over a long period of time through reproductive/genetic
isolation
Comparing Lamarck’s and Darwin’s theory of evolution
Similarities
Evolution occurs via descent of species from common ancestors
Differences
Beneficial characteristics are formed as a Beneficial characteristics exists due to
result of the new environment (inner wants) to variations within the population which occur
make individuals more adapted (use and spontaneously before a change in the
disuse of organs) environment
No mechanism proposed (or incorrect Evolution occurs through the mechanism of
mechanism) natural selection
Beneficial characteristics acquired during the Those that survive to breed are more likely to
lifetime of the individual are inherited by produce offspring similar to themselves
offspring (differential reproduction) and pass on the
advantageous traits
Copyright © 2019 tonyndr
, Comparing Darwinism and Neo-Darwinism
Similarities
Organisms have great potential to reproduce
Constancy in numbers due to environmental restrictions (limited resources)
Struggle for existence
Differences
Variation among offspring Variation among offspring controlled by genes
and is a result of spontaneous mutations
Survival of the fittest by Natural Selection: Survival of the fittest by Natural Selection:
Better-adapted (fitter) individuals with the Individuals with genetic variations best
selective advantage will be more likely to adapted to the new environment are at a
survive selective advantage and will be more likely to
survive
Differential reproduction: proportion of Differential reproduction: proportion of
individuals possessing the advantageous individuals who possess the favourable
traits increases over generations genes/alleles and are at a selective advantage
increases over generations (changes in allele
and genotype frequencies)
New species form through accumulation of New species form only through
modifications and adaptations genetic/reproductive isolation and thereafter
accumulation of modifications and
adaptations
Evidence for Darwin’s theory of evolution
[#1: Homologies and divergent evolution]
Homology: similarity in characteristics resulting from shared ancestry
Structural/anatomical similarities in homologous structures (anatomical homologies) suggest
that species descended from a common ancestor with that feature
● Divergent evolution: species diversified and diverged from a common ancestor to
colonise different environments
● E.g. homology of the forelimb and hindlimb bones of vertebrates (pentadactyl limb has
been modified to allow vertebrates to perform different functions in different
environments)
● E.g. anatomical similarities during early embryonic development of vertebrates
○ Paired pharyngeal pouches and a post anal tail
● E.g. vestigial structures: structures with no apparent function but resemble structures
present in ancestors
○ In humans: coccyx (fused tailbones), third molars (wisdom teeth) and muscles that
move the ears
○ In modern whales: vestigial pelvic girdle and hindlimb bones suggest they
evolved from land ancestors
Copyright © 2019 tonyndr
Definitions
● Biological evolution is defined as descent with modification through the mechanism of
natural selection and refers to the cumulative changes that occur in a population from
generation to generation over time
● Microevolution refers to changes in allele or genotype frequencies in a gene pool of a
population over time (small-scale evolutionary change within species level)
● Macroevolution refers to large-scale phenotypic changes in populations that generally
warrant their placement in taxonomic groups at the species level or higher; descent of
different species from shared ancestors over many generations
Lamarck’s theory of evolution
(1) Use and disuse of organs
(2) Inheritance of acquired characters
Darwin-Wallace’s theory of evolution (Darwinism)
(1) Observation #1: Organisms have great potential to reproduce
● Tendency to produce more than can survive
(2) Observation #2: Constancy in numbers due to environmental restrictions
● Limited resources, most populations maintain relatively constant numbers as majority of
offspring die before reaching sexual maturity
(3) Inference #1: Struggle for existence
● Competition among individuals is inevitable in order to survive
(4) Observation #3: Variation within a population
(5) Inference #2: Survival of the fittest by Natural Selection
● Natural selection is the process by which the environment selects for well-adapted
individuals with inherited traits that are best suited to the local environment
● Better-adapted (fitter) individuals with the selective advantage will be more likely to
survive to reproductive age and produce more offspring
(6) Observation #4: Differential reproduction leading to reproductive success (like produces like)
● Those that survive to breed are likely to produce offspring similar to themselves
● The advantageous traits that give them the edge in the struggle for existence are likely to
be passed on to the next generation, making the offspring better-adapted to the
environment
(7) Formation of new species
● Over many generations, the proportion of individuals possessing the advantageous traits
increases whereas the proportion of those lacking the traits decreases, leading to
evolution of the population
● A new species is formed after the accumulation of several characteristics and adaptive
mechanisms in a particular population over many generations
Copyright © 2019 tonyndr
,Modern theory of evolution (Neo-Darwinism)
● Incorporates principles of Mendelian genetics and knowledge of molecular biology
(1) Observation #1: Organisms have great potential to reproduce
● Tendency to produce more than can survive
(2) Observation #2: Constancy in numbers due to environmental restrictions
● Limited resources, most populations maintain relatively constant numbers as majority of
offspring die before reaching sexual maturity
(3) Inference #1: Struggle for existence
● Competition among individuals is inevitable in order to survive
(4) Observation #3: Variation within a population
● Arises as a result of spontaneous mutations of genes
(5) Inference #2: Survival of the fittest by Natural Selection
● Individuals with genetic variations best adapted to the new environment are at a
selective advantage and will be more likely to survive to reproductive age and produce
more offspring
(6) Observation #4: Differential reproduction leading to reproductive success (like produces like)
● Over generations, proportion of individuals who possess the favourable genes/alleles
and are at a selective advantage increases while the proportion of those at a selective
disadvantage decreases
● Leads to changes in allele and genotype frequencies
(7) Formation of new species
● Can only happen if populations are separated so that they do not interbreed
● The separated populations adapt to their own particular environments and may diverge,
eventually forming new species over a long period of time through reproductive/genetic
isolation
Comparing Lamarck’s and Darwin’s theory of evolution
Similarities
Evolution occurs via descent of species from common ancestors
Differences
Beneficial characteristics are formed as a Beneficial characteristics exists due to
result of the new environment (inner wants) to variations within the population which occur
make individuals more adapted (use and spontaneously before a change in the
disuse of organs) environment
No mechanism proposed (or incorrect Evolution occurs through the mechanism of
mechanism) natural selection
Beneficial characteristics acquired during the Those that survive to breed are more likely to
lifetime of the individual are inherited by produce offspring similar to themselves
offspring (differential reproduction) and pass on the
advantageous traits
Copyright © 2019 tonyndr
, Comparing Darwinism and Neo-Darwinism
Similarities
Organisms have great potential to reproduce
Constancy in numbers due to environmental restrictions (limited resources)
Struggle for existence
Differences
Variation among offspring Variation among offspring controlled by genes
and is a result of spontaneous mutations
Survival of the fittest by Natural Selection: Survival of the fittest by Natural Selection:
Better-adapted (fitter) individuals with the Individuals with genetic variations best
selective advantage will be more likely to adapted to the new environment are at a
survive selective advantage and will be more likely to
survive
Differential reproduction: proportion of Differential reproduction: proportion of
individuals possessing the advantageous individuals who possess the favourable
traits increases over generations genes/alleles and are at a selective advantage
increases over generations (changes in allele
and genotype frequencies)
New species form through accumulation of New species form only through
modifications and adaptations genetic/reproductive isolation and thereafter
accumulation of modifications and
adaptations
Evidence for Darwin’s theory of evolution
[#1: Homologies and divergent evolution]
Homology: similarity in characteristics resulting from shared ancestry
Structural/anatomical similarities in homologous structures (anatomical homologies) suggest
that species descended from a common ancestor with that feature
● Divergent evolution: species diversified and diverged from a common ancestor to
colonise different environments
● E.g. homology of the forelimb and hindlimb bones of vertebrates (pentadactyl limb has
been modified to allow vertebrates to perform different functions in different
environments)
● E.g. anatomical similarities during early embryonic development of vertebrates
○ Paired pharyngeal pouches and a post anal tail
● E.g. vestigial structures: structures with no apparent function but resemble structures
present in ancestors
○ In humans: coccyx (fused tailbones), third molars (wisdom teeth) and muscles that
move the ears
○ In modern whales: vestigial pelvic girdle and hindlimb bones suggest they
evolved from land ancestors
Copyright © 2019 tonyndr
