Essential idea: There is overwhelming evidence for the evolution of life on Earth.
5.1 Evidence for evolution
UNDERSTANDINGS:
U5.1.1 Evolution occurs when heritable characteristics of a species change.
Evolution is the cumulative change in the heritable characteristics of a population, i.e. when heritable characteristics of a species or a biological population change over successive generations. These traits cannot be acquired over a lifetime, they are heritable traits or alleles in an organism’s DNA.
U5.1.2 The fossil record provides evidence for evolution.
The totality of fossils (both discovered and undiscovered) is known as the fossil record
Fossils are the preserved remains of animals, plants, and other organisms from the past. The fossil record shows the gradual change of species over time. The timeline in which fossils appear are what scientists would expect, with bacteria and algae being the oldest in the fossil record, later followed by shelled animals and trilobites, then dinosaurs, early reptiles, birds and mammals.
Many fossil sequences link together present day organisms with their likely ancestors. For example present day horses and zebras are closely related to tapirs and rhinos, which are all linked back to the Hyracotherium, an animal similar to the rhinoceros.
U5.1.3 Selective breeding of domesticated animals shows that artificial selection can cause evolution.
Selective Breeding
U5.1.4 Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
Adaptive radiation: diversification of a species or single ancestral type into several forms that are each adaptively specialised to a specific environmental niche.
UNDERSTANDINGS:
U5.1.1 Evolution occurs when heritable characteristics of a species change.
Evolution is the cumulative change in the heritable characteristics of a population, i.e. when heritable characteristics of a species or a biological population change over successive generations. These traits cannot be acquired over a lifetime, they are heritable traits or alleles in an organism’s DNA.
U5.1.2 The fossil record provides evidence for evolution.
The totality of fossils (both discovered and undiscovered) is known as the fossil record
- The fossil record reveals that, over time, changes have occurred in features of organisms living on the planet (evolution)
- Moreover, different kinds of organisms do not occur randomly but are found in rocks of particular ages in a consistent order (law of fossil succession)
- This suggests that changes to an ancestral species was likely responsible for the appearance of subsequent species (speciation via evolution)
- Furthermore, the occurrence of transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken within a single genus.
Fossils are the preserved remains of animals, plants, and other organisms from the past. The fossil record shows the gradual change of species over time. The timeline in which fossils appear are what scientists would expect, with bacteria and algae being the oldest in the fossil record, later followed by shelled animals and trilobites, then dinosaurs, early reptiles, birds and mammals.
Many fossil sequences link together present day organisms with their likely ancestors. For example present day horses and zebras are closely related to tapirs and rhinos, which are all linked back to the Hyracotherium, an animal similar to the rhinoceros.
U5.1.3 Selective breeding of domesticated animals shows that artificial selection can cause evolution.
Selective Breeding
- Breeding plants and animals for specific genetic traits.
- Shows a good record of recent changes in genetic characteristics over a few dozens of generations that man has selected to breed.
- For example, chickens that produce more eggs or cows that produce more milk are selected to breed, hopefully passing these traits onto next generations.
- Plants can be bred in a similar manner based on useful or beneficial characteristics breeders would like to see in the next generation of plants.
- The evolution of domesticated dogs has produced many different breeds through artificial selection.
U5.1.4 Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
Adaptive radiation: diversification of a species or single ancestral type into several forms that are each adaptively specialised to a specific environmental niche.
- Comparative anatomy of groups of animals or plants shows certain structural features are basically similar, implying a common ancestry
- Homologous structures are those that are similar in shape in different types of organisms despite being used in different ways
- An example is the pentadactyl limb structure in vertebrates, whereby many animals show a common bone composition, despite the limb being used for different forms of locomotion (e.g. whale fin for swimming, bat wing for flying, human hand for manipulating tools, horse hoof for galloping, etc.)
- This illustrates adaptive radiation (divergent evolution) as a similar basic plan has been adapted to suit various environmental niches
- The more similar the homologous structures between two species are, the more closely related they are likely to be
U5.1.5 Populations of a species can gradually diverge into separate species by evolution.
U5.1.6 Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
APPLICATION:
A5.1.1 Development of melanistic insects in polluted areas.
Peppered moth
A5.1.2 Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.
- Crocodiles walk or crawl on land using webbed hind limbs for swimming.
- Penguins use hind limbs to walk and forelimbs for swimming.
- Frogs use all four limbs for walking and hind limbs for jumping.
- Within a population there is genetic variation. If two populations of the same species become separated so that they do not reproduce or interbreed because they become separated by geographical boundaries; for example one group migrates to an island or they became separated by a mountain range, then natural selection will act differently on those two separate populations
- Over time, these populations change so that they are recognizably different and can or do not interbreed if they were to merge together again. This process is called speciation.
U5.1.6 Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
- When populations diverge over time and are separated, one would expect these populations to be in different stages of variation or divergence and not transition into completely 'separate' distinct organisms immediately or, on the other hand, all be the same unchanged species - evolution and divergence takes time, it is not an immediate process
- Darwin gave many of these examples that showed populations that are slightly different, but are not clearly separate species
- Examples of this are the Lava lizards and finches of Galapagos
- Species gradually diverge and there is no defined period where they will be completely separated into two species.
APPLICATION:
A5.1.1 Development of melanistic insects in polluted areas.
Peppered moth
A5.1.2 Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.
- Crocodiles walk or crawl on land using webbed hind limbs for swimming.
- Penguins use hind limbs to walk and forelimbs for swimming.
- Frogs use all four limbs for walking and hind limbs for jumping.
Essential idea: The diversity of life has evolved and continues to evolve by natural selection
5.2 Natural selection
UNDERSTANDINGS:
U5.2.1 Natural selection can only occur if there is variation among members of the same species.
U5.2.2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
INDEPENDENT ASSORTMENT:
UNDERSTANDINGS:
U5.2.1 Natural selection can only occur if there is variation among members of the same species.
- Within a species, different individuals of that species show genetic variation
- Individuals that are best suited for their environment will survive and reproduce
- If there was no variation within a species, then all individuals would be the same and no individual would be favoured over the other and natural selection would not take place.
U5.2.2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
- Sexual reproduction occurs when two different members of a species create offspring that have a combination of genetic material contributed from both parents.
- During meiosis 50% of the females chromosomes will end up in the egg (haploid gamete) and 50% of the male’s chromosomes will end up in the sperm (haploid gamete).
INDEPENDENT ASSORTMENT:
- During metaphase I, when homologous chromosomes line up at the equator, the paired chromosomes can randomly arrange themselves in one of two orientations (paternal left / maternal right OR maternal left / paternal right)
- When the chromosomes separate in anaphase I, the final gametes will differ depending on whether they got the maternal or paternal chromosome
- Independent assortment of chromosomes creates 2n different gamete combinations (n = haploid number of chromosomes)
CROSSING OVER:
- During prophase I, when homologous chromosomes pair up as bivalents, genetic information can be exchanged between non-sister chromatids
- The further apart two genes are on a chromosome, the more likely they are to recombine
- Crossing over greatly increases the number of potential gamete variations by creating new genetic combinations.
RANDOM FERTILISATION:
GENETIC MUTATIONS:
Genetic mutations might occur where new alleles are produced. Genetic mutations are the original source of variation within a species.
U5.2.3 Adaptations are characteristics that make an individual suited to its environment and way of life.
U5.2.4 Species tend to produce more offspring than the environment can support.
- Fertilisation results from the fusion of gametes from a paternal and maternal source, resulting in offspring that have a combination of paternal and maternal traits
- Because fertilisation is random, offspring will receive different combinations of traits every time, resulting in near infinite genetic variability.
GENETIC MUTATIONS:
Genetic mutations might occur where new alleles are produced. Genetic mutations are the original source of variation within a species.
U5.2.3 Adaptations are characteristics that make an individual suited to its environment and way of life.
- Where and how an organism lives is largely due to its specific adaptations that allow it to survive and reproduce in a particular area or habitat. In other words their structure allows them to function in that environment.
- Polar bears are well adapted to life in the Arctic. They have a large layer of blubber to keep them warm. They are strong swimmers, aided by their strong forearms and layer of blubber for buoyancy. They have hollow fur to aid in insulation as well. For plants, cacti have water storage tissue and spines (prevent water loss) because of the infrequent rainfall in the desert.
- Adaptations develop over time through natural selection.
U5.2.4 Species tend to produce more offspring than the environment can support.
- The Malthusian dilemma states that populations tend to multiply geometrically, while food sources multiply arithmetically
- Hence populations tend to produce more offspring than the environment can support
- For example, fish produce thousands of eggs but only few make it to adulthood. Plants also can produce hundreds or thousands of seeds to be released into the environment.
- When parents don’t spend much or any time caring for their young, they produce many offspring. This is a reproductive method used to ensure some offspring survive as the next generation.
- Parents that put a significant amount of time and energy protecting and raising their young tend to have far smaller litters, i.e. most mammals.
- The population density that the environment can support is called the carrying capacity. If there are too many organisms, the demand for resources increases. However, there is a limited supply of resources in an ecosystem. Overpopulation and a limited amount of resources creates competition within a population.
U5.2.5 Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Within a population, there is genetic variation between the individuals in the population. The organisms with the beneficial characteristics will be able to out-compete the other individuals with the less beneficial or harmful genetic traits for limited resources and mates. Therefore, these individuals will survive and reproduce and pass these genetic traits onto the next generation of offspring. Organisms with less desirable traits will die or produce less offspring.
U5.2.6 Individuals that reproduce pass on characteristics to their offspring.
U5.2.7 Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
APPLICATION:
A5.2.1 Changes in beaks of finches on Daphne Major.
A5.2.2 Evolution of antibiotic resistance in bacteria.
Within a population, there is genetic variation between the individuals in the population. The organisms with the beneficial characteristics will be able to out-compete the other individuals with the less beneficial or harmful genetic traits for limited resources and mates. Therefore, these individuals will survive and reproduce and pass these genetic traits onto the next generation of offspring. Organisms with less desirable traits will die or produce less offspring.
U5.2.6 Individuals that reproduce pass on characteristics to their offspring.
- The organisms that survive and reproduce pass beneficial traits on to their offspring
- Over many generations the accumulation of these beneficial genetic traits may result in a change in the population known as evolution
- For another species to develop, these genetically different individuals eventually have to become reproductively isolated (separated from the general population) where they will only reproduce with individuals with similar genetic traits
- Acquired characteristics of an individual such as large muscles are not passed on to an organism’s offspring.
U5.2.7 Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
- Since the better adapted individuals of a species are the ones that survive, reproduce and pass their genes on to the next generation, these alleles will become more frequent within the population
- The same would hold true for individuals that are less suited to an environment. These individuals will reproduce less frequently and die more often, thus decreasing the frequency of their alleles within a population
- These changes happen over many generations.
APPLICATION:
A5.2.1 Changes in beaks of finches on Daphne Major.
A5.2.2 Evolution of antibiotic resistance in bacteria.
- Antibiotics kill bacteria directly or weaken the bacteria so your immune system can fight and destroy the invading pathogen.
- If a patient has a bacterial infection, when antibiotics are given to fight the infection the majority of the original population of bacteria will be destroyed.
- However, some of these bacteria might not die because of changes within their DNA. These changes could be caused by mutations within their genome or the transfer of an antibiotic resistant gene from another bacterium.
- Resistance is more likely to occur if the proper amounts of antibiotics aren’t taken or if a patient doesn’t finish the prescription.
- These resistant bacteria will survive and reproduce, creating more identical resistant bacteria.
- If given the same antibiotic, these bacteria will no longer be destroyed.
- Another antibiotic can be prescribed to kill these new resistant bacteria.
- Resistance can be passed onto other pathogenic bacteria, creating more species of resistant bacteria.
- Some examples of bacteria known to develop resistance are Treponema pallidum which causes syphilis and the bacteria that causes tuberculosis (Mycobacterium tuberculosis).
Essential idea: Species are named and classified using an internationally agreed system.
5.3 Classification of biodiversity
UNDERSTANDINGS:
U5.3.1 The binomial system of names for species is universal among biologists and has been agreed and developed at a series of congresses.
U5.3.2 When species are discovered they are given scientific names using the binomial system.
U5.3.3 Taxonomists classify species using a hierarchy of taxa.
The order goes: You can remember this by:
Kingdom King
Phylum Phillip
Class Comes
Order Over
Family For
Genus Good
Species Spaghetti
U5.3.4 All organisms are classified into three domains.
UNDERSTANDINGS:
U5.3.1 The binomial system of names for species is universal among biologists and has been agreed and developed at a series of congresses.
- Formal two naming system of classifying species
- Originally developed by Swedish naturalist Carolus Linnaeus
- Currently, many scientists and specialists meet in a series of International Congresses of Zoology which meet in different cities every 4 years
- They meet to discuss their findings regarding genetics, animal behaviour and classification
- A main topic is the binomial nomenclature system and decisions regarding the classification of new organisms or the reclassification of old ones because of new evidence regarding ancestry.
- The main objectives with regards to using the binomial nomenclature system developed are to:
- Make sure each organism has a unique name that cannot be confused with another organism
- The name can be universally understood regardless of the nationality or culture that is using the name
- Stability exists within the system by not allowing people to change the name without valid scientific reasons.
U5.3.2 When species are discovered they are given scientific names using the binomial system.
- The first name in the binomial naming system is called the genus and is always capitalized
- The second name starts with a small letter and is called the species
- The binomial system allows for scientists across cultures, regions and languages to communicate effectively with regards to specific organisms.
U5.3.3 Taxonomists classify species using a hierarchy of taxa.
- A taxon means a group of something
- Scientists arrange or organize species in to a hierarchical set of groups in order to organize organisms into specific similar groups based on similar characteristics
- As one goes higher up on a classification chart, the greater the number of species are included into the group
The order goes: You can remember this by:
Kingdom King
Phylum Phillip
Class Comes
Order Over
Family For
Genus Good
Species Spaghetti
U5.3.4 All organisms are classified into three domains.
U5.3.5 The principal taxa for classifying eukaryotes are kingdom, phylum, class,
order, family, genus and species.
U5.3.6 In a natural classification, the genus and accompanying higher taxa consist of
all the species that have evolved from one common ancestral species.
For natural classification, it is assumed that all members of that group shared a common ancestor at some point in their history. This can be seen in their structure. Unnatural or artificial classification for example would be birds and flies. They both can fly; however flight evolved separately and they are classified separately .
U5.3.7 Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Sometimes new evidence is found that shows scientists that members of a particular group do not share a common ancestor as once originally thought. Sometimes other species that were once thought to be a lot different, are found to be more similar; sharing a common ancestor. This switching of classification is an ongoing process as new discoveries or better methods of classification are found. Putting apes together with humans in Hominidae was one of these cases.
U5.3.8 Natural classifications help in identification of species and allow the prediction of characteristics shared by species within a group.
For natural classification, it is assumed that all members of that group shared a common ancestor at some point in their history. This can be seen in their structure. Unnatural or artificial classification for example would be birds and flies. They both can fly; however flight evolved separately and they are classified separately .
U5.3.7 Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Sometimes new evidence is found that shows scientists that members of a particular group do not share a common ancestor as once originally thought. Sometimes other species that were once thought to be a lot different, are found to be more similar; sharing a common ancestor. This switching of classification is an ongoing process as new discoveries or better methods of classification are found. Putting apes together with humans in Hominidae was one of these cases.
U5.3.8 Natural classifications help in identification of species and allow the prediction of characteristics shared by species within a group.