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Define evolution.
A4.1.1: Evolution as a change in the heritable characteristics of a population.
Evolution is the process of cumulative change in the heritable characteristics of a population.
Compare Darwinian evolution to Lamarckism evolution.
In Darwinian evolution, the traits that are passed down are decided by nature, while in Lamarckism Evolution the behavior of parents is passed down.
In Darwinian Evolution, the traits that are passed down are heritable and behavior has nothing to do with it. Acquired traits are passed down in Lamarckism.
Darwinian evolution is supported by genetics, but Lamarckism Evolution is not.
Distinguish between heritable and acquired characteristics.
A4.1.1: Evolution as a change in the heritable characteristics of a population.
Heritable characteristics are passed down genetically from one generation to their offspring, while acquired characteristics are not passed on from one generation to the next.
Heritable traits are defined by the DNA from a parent, while acquired traits are influenced by factors.
Genetics encode and influence heritable traits, but acquired traits are influenced by the environment.
Heritable traits take part in evolution, while acquired traits do not take part in evolution.
Outline the relationship between time, evolutionary relationships and biological sequence (nitrogenous base or amino acid) similarities between species.
A4.1.2: Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins.
Time increases the number of mutations, and thus, differences in biological sequence.
The more similar the sequence, the less time has past for the sequence to acquire mutations and diverge from each other, so the more recent the common ancestor, the more closely related the organisms.
Less time has past —> Less time for sequence to acquire mutations & diverge from each other —> More recent common ancestor —> Sequences are more similar —> organisms are more closely related
Sometimes amino acids sequences don't provide enough detail, so DNA or RNA base sequences are used to compere closely related organisms.
Define selective breeding and artificial selection.
A4.1.3: Evidence for evolution from selective breeding of domesticated animals and crop plants
Selective breeding is intentionally choosing parents with the most genetic characteristics and breeding them together to produce offspring with the desired traits (a form of artificial selection).
Artificial selection is the process by which humans choose individual organisms with certain phenotypic trait values for breeding.
Outline how selective breeding can lead to rapid evolutionary change.
A4.1.3: Evidence for evolution from selective breeding of domesticated animals and crop plants
By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations.
Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period.
Explain an example of artificial selection in a crop plant.
A4.1.3: Evidence for evolution from selective breeding of domesticated animals and crop plants
Breeding plant crops has allowed for the generation of new types of foods from the same ancestral plant source.
Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection.
This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves).
Explain an example of artificial selection in a crop plant.
A4.1.3: Evidence for evolution from selective breeding of domesticated animals and crop plants
Example 1: Horse Breeding
Horses have been selectively bred across many generations to produce variation according to a targeted function
Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
Draft horses have been bred for power and endurance and hence are sturdier and stockier
Example 2: Cow Breeding
Cows have been selectively bred across many generations to produce offspring with improved milk production
Farmers have also targeted the breeding a cows with a mutation resulting in increased muscle mass
The resulting stock of cattle (termed Belgian Blue) have excessive bulk and produce more edible lean meat
Example 3: Dog Breeding
Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man
Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast
Toy dogs (e.g. chihuahuas) were selectively bred for their dimunitive size
Define homologous structure.
A4.1.4: Evidence for evolution from homologous structures.
Homologous structures are structures similar in form but found in seemingly dissimilar species.
List examples of different types of homologous structures at different levels of biological organization.
A4.1.4: Evidence for evolution from homologous structures.
Pentadactyl limbs are in a variety of different animals, but they may have different functions:
Human hands are adapted for tool manipulation (power vs precision grip)
Bird and bat wings are adapted for flying
Horse hooves are adapted for galloping
Whale and dolphin fins are adapted for swimming
Define pentadactyl limb.
A4.1.4: Evidence for evolution from homologous structures.
Pentadactyl limbs are five-fingered limbs.
List the bone structures present in the pentadactyl limb (specific names of bones are not required).
A4.1.4: Evidence for evolution from homologous structures.
Pentadactyl forelimbs:
Humerus
radius
ulna
carpals
metacarpals
phalanges
Define divergent evolution.
A4.1.4: Evidence for evolution from homologous structures.
Divergent evolution is the development of dissimilar traits in two species from a common ancestor.
Describe how divergent evolution explains the pattern found in pentadactyl limb structure yet allows for the specialization of different limb functions.
A4.1.4: Evidence for evolution from homologous structures.
Homologous structures indicate that species diverged from a common ancestor. Thus, divergent evolution explains how species that share a common ancestor will keep some traits from the common ancestor. At the same time, because of divergent evolution, species develop differences since splitting from a common ancestor. In the case of pentadactyl limbs, the structure may be the same, but the species have diverged, so the functions of the limbs have changed.
Define analogous structure.
A4.1.5: Convergent evolution as the origin of analogous structures.
Analogous structures are structures that have a common function, but they do not have a common structure.
They are evolved by convergent evolution.
State an example of an analogous structure found in two species.
A4.1.5: Convergent evolution as the origin of analogous structures.
Wings are in bird, bats, and insects. They all evolved by convergent evolution because they are all used for flying, but none of the groups share a common ancestor.
Outline how convergent evolution results in analogous structures.
A4.1.5: Convergent evolution as the origin of analogous structures.
Convergent evolution is the independent evolution of similar structures in unrelated or distantly related species.
If two groups of largely unrelated organisms are exposed to similar environments, they may independently develop similar adaptations to survive, which results in analogous structures.
Define speciation.
A4.1.6: Speciation by splitting of pre-existing species.
Speciation is the process of an evolving population to change significantly enough so that the production of offspring with the original population becomes impossible.
Compare the process of speciation with that of gradual evolutionary change in an existing species.
A4.1.6: Speciation by splitting of pre-existing species.
Gradual evolutionary change within a species is not speciation unless the original species evolves into a population of organisms which are no longer able to reproduce with the original population.
State the impact of speciation and extinction on the total number of species on Earth.
A4.1.6: Speciation by splitting of pre-existing species.
Speciation increases the total number of species on Earth.
Extinction reduces the total number of species on Earth.
List two processes required for speciation to occur.
A4.1.7: Roles of reproduction isolation and differential selection in speciation.
Reproductive isolation
Differential selection
Define reproductive isolation.
A4.1.7: Roles of reproduction isolation and differential selection in speciation.
Reproductive isolation occurs when there is a barrier which prevents individuals from reproducing.
Outline how reproductive isolation and differential selection lead to speciation.
A4.1.7: Roles of reproduction isolation and differential selection in speciation.
Speciation can only occur if populations of a species are reproductively isolated. The two separate populations are no longer to exchange genes, so different mutations occur separately in both populations. Eventually, this produces variations in each group that is not present in the other, and the two groups can no longer interbreed.
Differential selection allows individuals to adapt to different niches, form subpopulations within a species, change the genetic makeup of entire populations, and allow certain organisms to reproduce better than others. Subpopulations might develop their own advantages, and form a trait that becomes so significant that it may eventually lead to speciation.
Outline the speciation between chimpanzees and bonobos.
A4.1.7: Roles of reproduction isolation and differential selection in speciation.
The Congo River split the original population apart into the North and the South.
The population that are now chimpanzees were north of the Congo River. Chimpanzees got their aggression from a lack of food and a gorilla population (competition), so they fought for food and went to get food higher in the trees
The population that are now bonobos were south of the Congo River. Bonobos are calmer, more cooperative, and easygoing because they had more food to eat, so they didn’t need to fight for food to survive. If you fought for food, you became an outcast.
Compare allopatric and sympatric speciation.
A4.1.8: Differences and similarities between sympatric and allopatric speciation
Allopatric speciation occurs due to geographical isolation, but sympatric speciation is not due to geographic isolation. In allopatric speciation, the two populations don’t inhabit in the same area, are exposed to different selective pressures, so they evolve into different species. However, in sympatric speciation, the two populations inhabit in the same area, but something else is keeping them from interbreeding (behavior or timing).
Both allopatric and sympatric speciation result in new species that are not capable of interbreeding to produce fertile offspring
Explain temporal, behavioral and geographic isolation as mechanisms of reproductive isolation.
A4.1.8: Differences and similarities between sympatric and allopatric speciation
In temporal isolation, organisms reproduce at different times. Because they can’t reproduce at the same time, they are reproductively isolated, even if they inhabit the same area.
Behavioral isolation occurs when individuals have different behavior which stops them from reproducing together. For instance, some may have different mating rituals (songs or dances) that keep them reproductively isolated.
In geographic isolation, two species physically cannot interbreed because they are separated by a geographic feature. Thus, they are physically reproductively isolated.
Describe an example of temporal, behavioral and geographic reproductive isolation.
A4.1.8: Differences and similarities between sympatric and allopatric speciation
Different species of cicadas have different life cycle lengths, either 13 or 17 years. Cicadas remain as larvae underground during most of their life cycle. At the end of the life cycle, the adults emerge, live for a short time above ground, reproduce, then die. The adult cicadas with a 13-year life cycle will rarely be present at the same time as the cicadas with a 17-year life cycle. Cicadas can live in the same location but mate at different times (reproductively isolated), so they are an example of temporal isolation.
The geographical ranges of Western & Eastern meadowlarks overlap, and they are capable of reproducing together. However, they do not reproduce with each other because they use different songs to attract mates. Thus, they are an example of behavioral isolation.
Chimpanzees and bonobos were once one species, but the Congo River divided them into the North and the South. The group to the North (chimpanzees) of the river was exposed to different selection pressures than the group to the South, so they developed their own traits until they could no longer interbreed. Because the two groups were physically reproductively isolated by the Congo River, a geographical feature, this is an example of geographic isolation.
Outline the cause and consequence of adaptive radiation.
A4.1.9: Adaptive radiation as a source of biodiversity.
Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line.
Adaptive radiation occurs when members of a single species occupy a variety of distinct niches with different environmental conditions.
Consequently, members evolve different morphological features (adaptations) in response to different selective pressures.
Outline an example of adaptive radiation as a source of biodiversity.
A4.1.9: Adaptive radiation as a source of biodiversity.
Lemurs
Primates found in Madagascar & the Comoro Islands (off the south-east coast of Africa) are an example of adaptive radiation.
Millions of years ago, lemurs could proliferate without competition from monkeys or apes millions of years ago. They had large numbers of offspring, which provided greater chance for diversity.
Some lemurs adapted to living on the ground, living in lush rainforests, living in deserts. Some are nocturnal & others are diurnal (active during the day).
No other living lemurs are anywhere else in the world, but fossils of ancestors were found in Africa, Europe, and Asia
This is likely because lemurs couldn’t compete with apes & monkeys. Lemur-like organisms became more rare as apes & monkeys became more prevalent.
Continents & islands usually have either prosimians (such as lemurs) OR anthropoids (such as monkeys & apes) – NOT BOTH.
Finches of the Galapagos Islands
Darwin’s finches demonstrate adaptive radiation and show marked variation in beak size and shape according to diet
Finches that feed on seeds possess compact, powerful beaks – with larger beaks better equipped to crack larger seed cases
In 1977, an extended drought changed the frequency of larger beak sizes within the population by natural selection
Dry conditions result in plants producing larger seeds with tougher seed casings
Between 1976 and 1978 there was a change in average beak depth within the finch population
Finches with larger beaks were better equipped to feed on the seeds and thus produced more offspring with larger beaks
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