Evolution

What is evolution?:

What is evolution?:

Biological evolution is change in the genetic traits of populations over generations. That is the change in the frequency of alleles in a population 

Understand that organisms on the planet today have evolved from previous lifeforms over the past 3.6 billion years

• Over billions of years, genetic variations and adaptations have led to the diversity of species we see now

• each organism is connected through a shared evolutionary history

• Define populations

A population is a group of individuals of a single species that live in a particular area and interact with one another 

Evolution occurs within populations and does not occur within individuals 

• Know that evolution happens at the scale of populations, not within individuals

This means that evolution affects groups of organisms (populations) over generations through changes in genetic traits, rather than happening within a single individual’s lifetime. Individual organisms don’t evolve; instead, the traits in a population change over time as certain traits become more common or less common.

• Define variation within a population

• Variations are differences in traits between individuals of the same species. Variations are necessary for a population to evolve 

• Variations + genes

Individuals within the same species have the same number and types of genes but different alleles (variations of the genes)

• Know the 4 main mechanisms of evolution and how they contribute to changing a population:

  • Mutation (the source of variation in populations)

Individual variation in traits within a population must be present for evolution to occur. For example, a population of beetles might begin with very little variation in colour. In each generation, random genetic mutations occur, producing new variation in colour. Over many generations, red beetles might become more common. This is a change in the genetic  traits in a population over many generations. So its a case of evolution 

Gene flow

-The migration of individuals from one population to another (of the same species). 

- Introduces new phenotypes into populations 

• Genetic drift

• Changes in populations due to random/chance events (such as a natural disaster) 

• More significant in small populations 

• Natural selection (expanded in points below)

• Individuals with the phenotypes that are best suited to their environment survive and reproduce

Know that the concept of geological time is used to represent the history of the Earth

• Geological time is a system used to organise Earth’s history into specific time intervals.

• These intervals, like eons, eras, periods, and epochs

• By dividing history this way, scientists can study the processes that have shaped land, oceans, and life forms over millions and billions of years.

Eras of Earth's history

•  Precambrian - 4560-570 mya 

• Palaeozoic - 570- 245 mya 

• Mesozoic - 245 - 65 mya 

• Cenozoic - 65 mya present 

• Know that Earth has changed considerably over its life, both in terms of lifeforms and major events (such as asteroid impacts, continental drift)

• Earth has gone through major physical and biological transformations.

• Asteroid impacts, for instance, have triggered mass extinctions

• this changes Earth’s surface by forming, breaking, and shifting continents.

• changes have impacted climate

• sea level

• and the distribution of plants and animals, resulting in the biodiversity on todays earth

Know that evolution happens slowly and gradually over a very long period of time

• Life on Earth evolves slowly over a long time.

• Small genetic changes build up over many generations, which takes especially long for species with long lifespans.

• Over millions of years, these changes can lead to new adaptations or even new species.

• Define biodiversity

Biodiversity is the variety of life on Earth 

Species diversity-

- the number of different species within an ecosystem 

Genetic diversity

the range of genetic variation within a species 

Importance of biodiversity - 

• Severe storms, droughts and fires can reduce the populations of different types of living things. 

• In an ecosystem, each living thing has a relationship to other living things and non living things 

• If biodiversity is low then the loss of one species might place the entire ecosystem at risk of collapse 

• Understand the role of evolution in generating biodiversity

Evolutionary processes have created the biodiversity on Earth today, and which has previously existed on Earth. 

• Define extinction and some of the factors which cause extinction

Extinction is the process in which a species completely dies out, leaving no living members. Extinctions can occur naturally but are often accelerated by human activities. Several factors contribute to extinction:

• Habitat Loss: Destruction of habitats due to deforestation, urban development, and agriculture reduces the living space and resources available for species.

• Climate Change: Altered temperatures, sea levels, and weather patterns make it difficult for species to survive in their traditional environments.

• Pollution: Contaminants like plastic, chemicals, and waste harm ecosystems and can poison wildlife.

• Overhunting and Overfishing: Excessive hunting and fishing reduce populations faster than they can reproduce.

• Invasive Species: Non-native species introduced to new environments can outcompete, prey on, or bring diseases to native species.

• Mass extinctions: Events like volcanic eruptions, earthquakes, asteroid impacts, glacial cycles etc

• Know what is meant by mass extinction, and some of the factors which have caused mass extinctions

Mass extinction refers to a rapid and widespread loss of biodiversity, characterised by the extinction of a large number of species across various groups in a relatively short geological time. It typically involves the loss of about 75% or more of species.

Some factors that caused it…

• Rapid global cooling 

• Falling sea levels

• Asteroid impacts 

• Volcanic activity 

• Increase in methane and CO2 gases 

• Understand the importance of maintaining genetic diversity in a population

Genetic diversity is important for a population because it helps species adapt to environmental changes, resist disease and pests, and avoid inbreeding: 

• Adaptability

• - Genetic diversity helps species adapt to new diseases, warmer climates, and other environmental changes. 

• Inbreeding avoidance

• - Inbreeding can reduce a species' ability to survive and reproduce. It can occur when populations are small and isolated. 

• Ecosystem stability

• - Genetic diversity helps maintain ecosystem stability and services. These services include coastal protection, water management, and pest and disease management. 

• Species diversity

• - Genetic diversity within species can increase species diversity by affecting niche space and competition. 

• Conservation

• -Genetic diversity is a fundamental tool used by conservationists to save species

Define adaptation

A genetic trait of an organism which increases its likelihood of survival in its environment 

An adaptation may not necessarily be advantageous in other environments 

Structural/physical adaptations

Anatomical or morphological features of an organism.

Include features such as:

• Body coverings (fur, bright feathers, spines…)

• Limb specialisations (webbed feet, opposable thumbs, wings, flippers…)

• Sensory organs (eyes, ears….)

Behavioural adaptations

The things that an organism does which help them survive and thrive.

Often relate to:

• Communication

• Social/territorial interactions (including conflict and cooperation)

• Mating behaviours

• Obtaining food

• Maintaining homeostasis

Physiological adaptations

The way an organism responds on a cellular and molecular level.

Often relate to:

• Regulating body temperature

• Water balance

• Nutrient balance

• Reproductive strategies

• Senses and processing of sensory information

Define natural selection

Natural selection is the process by which individuals with advantageous traits are more likely to survive and reproduce, leading to the gradual evolution of a species.

• Describe the 4 steps of evolution by natural selection

Variation -  a lot of random mutations in genes

Selective pressures - struggle for survival. (competition for resources between individuals)  Not all individuals in the population can survive 

Traits selected for and against -  Some variations help organisms survive (they are selected for/have a selective advantage). Organisms with less favourable characteristics die out (selected against). ‘Survival of the fittest”. 

Changes overtime- The organisms that survive pass on their traits to the following generations and overtime the population changes to become better adapted to its environment.  

Know how natural selection relates to adaptations

A population contains variations in genetic traits. These come from random mutations 

Selection pressures act on the populations. Some traits make it less likely for an individual to survive and reproduce.

New random variations are produced in each generation. A trait that helps an individual survive and reproduce is an adaptation. 

Natural selection gradually changes the frequency of traits in the population

Over many generations, the population as a whole becomes better adapted to the environment 

• Definition of a species (reproduce viable/fertile offspring)

Members of the same species are able to interbreed to produce viable and fertile offspring.

If the offspring of two organisms are not fertile (able to reproduce), then they are considered to be different species

eg. lion + tiger = liger

• Describe the 4 stages of speciation, including the role of geographic isolation, natural selection and time

• Stage 1: Populations of the original ancestral species form

• Stage 2: Populations become geographically isolated, cutting off migration between populations

                   Physical barriers:

• River

• Mountains

• Continental drift

• Rising sea levels

• Climate change

• Stage 3: Different selection pressures act on the populations and favour those individuals with traits suited to each environment.

• Stage 4: Over a long period of time reproductive isolation occurs - even if the barriers are removed, individuals from different groups are unable to interbreed to produce viable/fertile offspring. 

They have become different species.

Define reproductive isolation

• the inability of a species to breed successfully with related species due to geographical, behavioural, physiological, or genetic barriers or differences.

Speciation- The process by which new species are formed from an original ancestral species. The formation of new species increases species biodiversity. 

Subspecies- Some species exhibit considerable variation across their range, and therefore groups in different regions are further classified as subspecies. (in time they may become separate species)

• Define artificial selection/selective breeding

Also known as selective breeding.

Artificial selection involves humans selecting individuals (plants or animals) that have the most desirable phenotypes, and exclusively breeding these individuals.

Over several generations, this process will change the population to become more suited to human needs/desires.

• Identify the difference between natural selection and artificial selection

• Artificial selection - human select individuals with the most desirable phenotypes.

• Natural selection - nature selects individuals with the fittest phenotypes.

• Know some common examples of artificial selection

• Humans have controlled the breeding of domesticated animals and plants for centuries - significantly shaping many of the plants and animals we know today.

• Know some of the issues related to artificial selection

Reduced genetic diversity: Repeatedly breeding for specific traits can decrease variation, making populations more vulnerable to diseases and environmental changes.

Inbreeding risks: Limited gene pools increase the risk of genetic disorders and health problems.

Unintended traits: Focusing on certain traits may lead to unwanted characteristics, like aggression in dogs or poor fertility in crops.

Ethical concerns: Selecting for extreme traits can raise animal welfare concerns, such as breathing issues in certain dog breeds.

• Explain how the study of fossils provides evidence for evolution

Fossils are the remains (bones, teeth and shells) or traces (footprints, imprints or fossilised faeces) of organisms from a past geological age embedded in rocks. Provide evidence of the pre-existing life forms that lived on Earth. However the fossil record is largely incomplete.

Transitional fossils

Fossils which are an intermediate between an ancestral species and a descendant species and show characteristics of two different species. 

Help to establish an evolutionary relationship between species which appear very different to each other. 

Describe the circumstances that must be met for fossilisation to occur

Most commonly occurs when:

The organism is rapidly covered by sediment, meaning it is hidden from scavengers and decomposition is slowed.

Bones and other hard structures are better able to resist weathering processes and are more likely to form fossils.

Over a long period of time the sediment surrounding the fossil forms into sedimentary rock.

• Describe how fossils can be dated using stratigraphy (relative dating)

Relative dating- Determining the order of age of fossils (without finding their precise age)

stratigraphy- Studying rock layers, allows us to determine the relative age of fossils. Deeper layers= older fossils 

Define absolute dating

Absolute dating- Provides a precise estimate of a fossil's age 

Radioisotopes, such as carbon 14 are present in all living things. When an organism dies, the amount of these radioisotopes decreases. 

The time it takes for half the radioisotopes to decrease is called the halflife. 

If scientists know the length of a radioisotope half life they can determine how many half lives have passed by measuring the amount of radioisotopes and therefore determine the age of the fossil. 

• Calculate the number of half-lives that have passed based on the remaining percentage of a radioactive isotope

EXAMPLE- A fossilised piece of coral was found at a beach in Beaumaris, Melbourne. Scientists at the Melbourne museum determine that the fossil has ⅛ of radioactive carbon-14 remaining. 

1. Calculate the number of half lives that have passed in the fossil

2. If 1 half life= 5000 years, calculate the age of the fossil 

SOLUTION- a) After 1 half life, ½ of the radioactive material will remain 

After 2 half lives ¼ radioactive material will remain (½ x ½ ) 

After 3 half lives, ⅛ of the radioactive material will remain (½ x ¼ ) 

Therefore 3 half lives have passed. 

b) if 1 half life = 5000 years, 3 half lives= 15000 years. The fossil is 15000 years old. 

• Know how comparing anatomy can provide evidence for evolution

Comparative anatomy-

 Similarity in the structural features of organisms provides evidence of their evolutionary relationship. 

• Define analogous and homologous structures

Analogous- Structures that serve the same function in different organisms due to similar environmental selection pressures, but are structurally different as there is no recent common ancestor. 

• Wings in birds, insects, bats, pterosaurs 

• Fins in fish and flipper in whales/dolphins 

Homologous structures- Structures in different species which are similar due to being inherited from a recent common ancestor. 

• Although different mammalian species have highly modified forelimbs there are similarities in the bone structure. 

• These similarities suggest a common evolutionary ancestor for all mammals 

• Over the course of evolution, mutations and different selection pressures modified these structures and they are now used for different purposes 

• Know how comparative embryology can provide evidence for evolution

Comparative embryology-

Similarities in the developing embryos of different species. 

• Suggests a common evolutionary ancestor and common genes 

• E.g human embryos develop gill-like structures and tails during their early development because they have the genes for these structures as they evolved from ancestors that had genes for gills. These genes get ‘switched off’ during later stages of development. 

Define biogeography

• The study of geographical distribution of organisms 

• As a result of a continental drift through plate tectonics, over time land masses drifted apart from the continents that we know today. 

• As the land masses drifted, populations of organisms were separated, forming new species. 

• Groups of similar species such as the ratites (flightless birds) on several continents can be explained by biogeography.

• Know how comparing DNA (sequences of DNA bases) and proteins (sequences of amino acids) can be used as evidence for evolution

Molecular biology- Comparing the similarities in molecules that make up organisms e.g 

• Genes (sequence of DNA bases)

• Proteins (sequence of amino acids) 

• Haemoglobin 

• Cytochrome C

• The more similar the molecules of two different species, the more closely related they are. 

Be able to interpret evolutionary trees to determine relatedness between species

• A visualisation of the relatedness of different species

• Each branch point represents a shared ancestor between groups of species

mutations

New alleles arise because of small changes in the DNA sequence, known as mutations 

Some mutations are not obvious in the appearance of an organism however others cause variations in the physical appearance (phenotype) of the individual 

Mutations which lead to variations which aid the organisms survival are known as adaptations