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Chapter 9: Theory of evolution by natural selection (9.2 Speciation and…
Chapter 9: Theory of evolution by natural selection
9.1: Evolution and biodiversity
Evolution
The change in the genetic composition of populations over time
can be observed as changes in
allele
frequencies (gene variants) and
Phenotype
(physical traits) in a population
Species can evolve in response to changes in
environmental conditions
or
after populations become isolated and accumulate genetic differences
Biodiversity
(the diversity of life) increases as genetic changes and results in
genetic variation
and the divergence of populations species
However
Biodiversity can also lead to loss of biodiversity through
Extinction of alleles, populations and species
Theory of evolution by
natural selection
accounts for different evolutionary processes and the diversity of life on Earth
Mechanism for evolution:
Natural Selection
Charles Darwin and Alfred Russel Wallace independently arrived at the same theory of how the mechanism for evolution is based on natural selection
Theory of evolution by natural selection: Species were not created in their present forms but had evolved from ancestral species
Two key observation of Evolution from natural selection
Members of a population often vary in their inherited traits
All species produce more offspring than their environment can support, and most of these offspring fail to survive and reproduce
Based from these observations, Darwin and Wallace drew 2 conclusions
Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
The unequal ability of individuals to survive and reproduce will lead to the accumulation of favourable traits in the population over generations
Theory of evolution based on natural selection: also called
Darwinism
Darwin and Wallace were unaware of the genetic basis of heritable traits and the mechanism of
heredity
Phenotype of an organism is an expression of its underlying genetic information or
genotype
"Survival of the fittest"
Some phenotype will have a high
adaptive value
and give individual an advantage over individuals with phenotype of lower adaptive value
Fittest: An organism's ability suitability to its environment
Having advantageous phenotype means the individual is more likely to survive to reproduce and pass their alleles on to the next generation
Natural Selection in Action
Insecticide Resistance
Ex: Insecticides are used to protect crops. Most of the insects dies to the insecticide but because some are naturally, some are resistant to insecticide causing it to survive. These individuals are more likely to reproduce and therefore will pass on their inheritance to the next generation. The resistant trait increases and eventually approaching 100% of the insects being resistant to insecticide.
Lactose tolerance
Most humans were originally lactose intolerant, unable to digest that component of of the nutritious food. Yet the people who are able to lactose tolerant prospered better and reproduced more successfully than the lactose intolerant proportion.
The frequencies of the alleles for lactose tolerance increased in the population
Today, lactose intolerance is rare in populations
Lamarckism vs Darwin
Lamarckism:
behaviours during an organism's lifetime result in physical changes that are passed on to offspring.
Darwin:
Theory of evolution by natural selection
Species usually change according to the ecological factors.
Potential for physical and other change in species due to natural selection is immense
He noted the similarity of natural selection to
artificial selection
Summary of natural selection
Natural selection does not involve intent.
organism never plan their eventual outcome, not even the most sophisticated camouflage or mimicry
. It rewards whatever has already survived with ongoing survival: it does not estimate the likely chance of survival in the future
Selection does not work for the survival of the species. The mechanism favours individual survival and reproduction
Natural selection does not always lead to greater complexity or sophistication, rather sometimes it can lead to simplification
Fitness in Darwinian fitness means suitability for a particular environment
Genetic variation not affecting the phenotype is selectively invisible and may accumulate over time
Not all traits serve a survival function. Some are simply effects of developmental processes or other characteristics
Natural selection does not produce perfection. Selection favours " good enough selection" that may be inelegant or inefficient
The evolution of complex structures such as eyes always proceeds in stages, each providing some advantage
Punctuated Equilibrium
Modification to Darwinism is called punctuated equilibrium, explains rapid evolutionary change
Charles Darwin predicted evolution occurs gradually but 70% of the fossil reflected that fossil sequences show relatively rapid change rather than gradual change
Rapid evolutionary change us caused by the sudden changes in the environment
Ex: Hare and the Tortoise analogy
Punctuated Equilibrium shows sudden jumps; sudden changes punctuated in the equilibrium
Types of evolution
Coevolution
species that interact closely will exert selection pressures on each other. Both species also experience similar environmental conditions
Coevolution happens with 2 species evolving together in a reciprocal response to selection pressures
Ex1: New variations of flowers appear through mutation and these may be more likely to survive and produce seeds. As a result, some pollinators will be more suited to these flowers and will therefore evolve alongside the flowers.
Ex2: Prey and predator relationship: Predators pick off the weaker prey, stronger individuals are left to survive. The next generation of predators will need to be stronger and faster to keep up with the stronger prey
Parallel Evolution
the evolution of similar feaures in related species that have experienced similar environments and selection pressures
ex: similarities in the coloration of different bird species that live in similar environments
Convergent evolution
Evolution through natural selection of similar features in unrelated groups of organisms. unrelated species that have adapted to a particular environment in similar ways are said to have converged or become more alike
Ex: marsupial sugar glider and placental flying squirrel both have developed large membranes between their fore and hind limbs that enable them to glide successfully.
Similar selection pressures tend to produce a strong resemblance among unrelated species
ex: eyes of vertebrate and cephalopod
Divergent evolution
Happens by random factors such as
genetic drift
or by natural selection, separated populations gradually become different.
After enough difference accumulated, populations lose the ability to interbreed and therefore give rise to new species in a process called
speciation
Ex: Finches of the Galapagos Island
9.2 Speciation and microevolutionary change
The ability to
interbreed
defines species
Migration of individuals result in gene flow. It is when new and different individuals join the population from a different gene pool or when some individuals leave a population
Different selection pressures and different mutations in the separated populations cause them to become genetically different
Genetic isolation of one species from another can be a result of one or more mechanism. This includes
Prezygotic mechanism (mechanism that act before reproduction.)
Postzygotic mechanism (after reproduction)
Species
In order to become considered members of the same species, individuals must be genetically similar enough to produce fertile
viable offspring
viable offspring: Members of the next generation who survive to maturity and are able to reproduce successfully
Species can also be thought of as a
gene pool
that is isolated from the gene pools of other species
Gene pool: all the alleles possessed by members of a population, which may potentially be passed to the next generation
Prezygotic Isolating Mechanism
these are those that prevent individuals from different species from interbreeding
It prevents
Coming into contact
prevents mating when they do come into contact
or prevent fertilisation when mating occurs
Geographical isolation
Separated by physical and geographical barriers
Ecological Isolation
Populations occupy differnet
ecological niches
within the same ecosystem
ecological niche: The role of an organism or group of organisms in an ecosystem, including its position in the food web, how it obtains its food and how it reproduce
Sometimes flowering can overlap and produce
hybrids
(offspring of two different species)
Temporal isolation
Breeding cycles or active times of populations do not overlap
Ex: nocturnal animals are unlikely to breed with dirunal one
Behavioural Isolation
Occurs when behaviours such as mating calls and courtship rituals are different. This mechanism only possible to
animals
It is often the result of sexual selection
Ex: birds have different vocal signals such as bird songs
Gamete mortality
This occurs after mating has taken place
Egg and sperm (gametes) fail to fuse in
fertilisation
and
zygote
does not form
zygote: A stage of animal development after fertilisation and before cell differentiation
fertilisation: penetration of an egg by sperm and fusion of the egg and sperm nuclei
Ex: sperm of one species may not be able to recognise the egg of another without the appropriate signalling molecules, or the conditions of the female reproductive tract of one species may not sustain the sperm of another species.
Postzygotic isolating mechanisms
they are those that typically prevent a zygote of two different species from developing into fertile adult
Offspring resulting from interbreeding between individs from different species are called hybrids
Hybrid inviability is a mechanism of reproductive isolation in which the sperm from one species successfully fertilises the egg of another species to form a hybrid zygote , but hybrid zygote has unmatched chromosomes.
This results to normal embryonic development not being able to proceed because of the lack of homologous chromosome pairs in the zygote. The zygote doesn't usually survive long
Sometimes zygote survive and undergoes cell division, but the offspring does not develop fully and will not reach adult hood. This is known as reduced hybrid viability
Most hybrid that develop are sterile, meaning they cannot produce offspring themselves
This relates to the homologous pairs in chromosomes. Without homologous pairs, meiosis cannot proceed normally and the gametes if formed at all cannot interact correctly in order for fertilisation to occur
Ex: Mule (hybrid of horse and donkey)
Usually the first generation of hybrids is semi fertile and can occasionally produce offspring when reproducing with another hybrid or with one of parental species. however, second generation is typically sterile
Sexual selection
selection pressure that also functions as a prezygotic isolating mechanism
Chosen traits in mating are often indicators of good health, strength and fitness or high adaptive value
Ex: birds
Barn swallows select mates based on the length of tail streamers (elongated tops of tail feathers), which indicate health and fitness
Speciation
evolution from an ancestral species
Allopatric speciation
Happens when population becomes divided by a geographical barrier. Spatial isolation prevents individuals of separated subpopulations from interbreeding
Overtime, different environmental selection pressures and genetic drift drive sub populations may diverge genetically and physically to the point where they can no longer interbreed, therefore being considereed distinct species
Ex: Western Australia has a very high number of
endemic
species both plant and animal. This is due to the parition of Australia causing them to have eastern and western zone
Tasmania also have many unique species as a result to separation
Adaptive Radiation
the rapid divergent evolution of a large number of related species from a single common ancestor
This occurs as organism adapts to new conditions and opportunities. This can occur following changes to the environment where vacant ecological niches are available. Adaptive radiation can result in a wide diversity of species, each with unique adaptations to their environment
Ex: Finches of the Galapagos island
Ex 2: The family Macropodidae
Microevolutionary changes
Microevolution
involves changes in alleles, populations or species over short periods of evolutionary time. Mutation, migration, genetic drift and natural selection are the main processes that drive micro-evolutionary change. An accumulation of these things can lead to speciation
Evolution of the Platypus
(pg. 404- 405)
They are the remains of egg-laying mammals called
monotremes
They produce milk from pores in the skin, like sweat in contrast to the
lactation
(milk production)
Evolution of the Horse
(Pg. 405-408)
Has one of the most complete
transitional series
in palaeotology
Modern horses are examples of postzygotic isolation
In recent past, incompatibility between species results from chromosomal differences and may have appeared through instant speciation
Sometimes chromosomes fail to separate properly during meiosis (knwon as
nondisjunction
, resulting in offspring with an extra set of chromosome
mos destined to not produce but if an affected mate is founded, their offspring may be viable. They will constitute a new species, phenotypically similar to the original but no longer reproductively compatible
9.3 Macroevolution and Biodiversity over time
It means change above the species level
It is essentially the cumulative results of microevolution over very long periods
Geological Time Scale of the Earth
The history of Earth and evolving life can traced using the
geological time scale
which covers events that occurred on Earth from its formation to now
Cliff often show layered sequences of different- looking ricks, each with specific collections of fossiled remains of ancient organism within the rock strata (singular
stratum
)
The arrival of
radiometric dating
allows the exact ages of the rocks to be measured
Geological time scale can be divided into many subdivisions. From largest to smallest:
Eon, eras, periods, epochs
Precambrain Time
The Hadean
plate tectonics
Archaean Eon
stromatolites
It is not a true geological eon, era, period or epoch
Divided into
The Hadean
The Archaean eon
The Proterozoic eon
Theories on how life came about
The primordial soup theory
amino acids
The RNA theory
Hydrothermal vents theory
Evolution of cellular organism
bacteria and archea (prokaryotes)
endosymbotic theory
, a bacteria now clear that bacteria entered archaen cells, but were not consumed and continue to live
combo of types of porkaryotes was effectively birth of eukaryote
Proterozoic eon
The cryogenian period: Snowball Earth
The Ediacaran period: Multicellular life diversifies
cyanobacteria
The Palaeozoic Era
Cambrian period: The
cambrian explosion
Ordovician period: the first vertebrates
second largest
mass extinction
Silurian period: the first life on land
Devonian period: the first land vertebrates
tetrapods
(four footed)
Examples: amphibians
Carboniferous period: abundant forests
Permian period: the greatest mass extinction
Pangaea
single supercontinent
The Mesozoic Era: The age of the dinosaurs
Triassic Period: The first mammals
Jurassic period: The age of the dinosaurs
Cretaceous period: The flowering plants
Angiosperms
(flowering plants)
Laurasia
and
Gondwana
The Cenozoic Era: The rise of birds and mammals
Palaeogene period: mammals diversify
Neogene period: the first
hominins
Quaternary period: the expansion of modern humans