Evolution Year 10 Life Science

Evolution Natural Selection Evolution is the gradual development of different species from a common ancestor over time A species gradually becomes better Adapted to its environment Natural Selection

similar structure and provide evidence of an evolutionary relationship Homologous Structure similar structure and provide evidence of an evolutionary relationship

Homologous Structure Homologous structures are features of organisms that have a similar structure and provide evidence of an evolutionary relationship Similar structure, closely related, different function E.g. wing of bird, wing of bat, leg of lizard, flipper of whale, arm of human all have same basic structure Pentadactyl limb (having 5 digits) However, in each organism is has been modified to suit a different way of life.

Analogous Structures These structures may have come about, due to the environment in which they live in.

Analogous Structures Analogous characteristics are those that look similar but are genetically very different. (no evolutionary relationship) Similar Structure. Not Related. Same environment These structures may have come about, due to the environment in which they live in. Eg. sharks and dolphins seem similar in appearance however genetically these animals are completely different. Both need flippers, to be able to swim in the water. A butterfly and a Bird are completely different species, but both have the similar structure of ‘wings’ to enable them to fly

Divergent evolution Divergent evolution: formation of new species due to change in environment When two or more species evolve from a common ancestor Example: Finches on the Galapagos Islands Evolved into different species to eat different foods

Convergent evolution Where two organisms have similar analogous structures but different ancestors (not related) When two or more unrelated species adopt similar adaptations in response to common environmental conditions Example:  Sharks and dolphins are similar in appearance but are not related

Lamarck's Theory According to Lamarck’s theory, organisms will evolve over time based on the repeated use of body structures. Evolution by inheritance of acquired characteristics

In this example, the Ancestral form consumed plant material and needed extra height to reach the higher branches. Over time, the animal evolved because of constant use of neck muscles and leg muscles to reach higher branches. Lamarck's Theory Giraffe's inherited long necks from short necked ancestors who continually stretched their necks to reach food

Darwin’s Theory Long necked and short necked giraffes once existed together but the long-necked giraffe had an adaptive advantage Darwin proposed that variation was critical in understanding how species change over long periods of time. His argument was that selection can not occur without differences in a population (variation)

Explain how the evolution shown in the diagram below would have occurred according to Lamarck’s theory.

answer The ancestral organism stretched its legs to reach the higher branches. This ‘stretched leg’ characteristic (an acquired characteristic) was inherited by the offspring. These offspring in turn stretched further and then passed on their ‘stretched leg’ characteristic to their offspring. The long-legged form shown eventuated from this stretching and inheritance.

Speciation The theory of evolution by natural selection proposes that all species are related. Some species more closely related than others, but ultimately all life should be able to be traced back to one original species. A change in species is usually due to some form of isolation from an original population

speciation Speciation is the process by which one species splits into two or more separate species. The process of speciation occurs in three steps: Variation: There must be variation in the population Isolation: This means that different groups must be prevented from interbreeding, this stops any differences from one population reaching the other population Selection: Natural selection affects the genotype and causes changes (mutations) that prevent the groups breeding even if they got back together.

speciation

example

questions 1. Describe two ways in which a population may become geographically isolated to form two populations? Ocean, river, mountains, earthquake, sand blocking an estuary, desert/dry conditions, gorge 2. Suggest two reasons why the two separated populations may evolve differently Different mutations occur in each population. Differences in conditions would mean that different characteristics are ‘selected for’ in each population

questions 3. The group of flightless birds, known as ratites, occur in Australia (emu), New Zealand (kiwi), South America (rhea), Pupua New Guinea (cassowary) and Africa (ostrich). How can the distribution of these related species be explained? The ancestral ratite lived on Gondwana (one land mass). When this split to form the continents, the ratites on each continent evolved in isolation, giving rise to the different forms/new species.

Artificial Selection vs Natural selection Artificial selection is the process by which humans deliberately choose to breed particular organisms with desirable features. Eg. domesticated dogs, different breeds of dogs are all one species and different breeds produced by Artificial selection. Natural Selection is the process by which the environment acts on the population

Human Evolution The name of our species “homo sapiens” means the “wise man.” According to fossils we have been around for about 200,000 years. Fossils indicate other human-like species have existed too.

Primates, Hominids and HominiNs Primates include lemurs, monkeys, apes, gibbons and humans. To be classified in this species the organism must have “grasping hands, nails rather than claws and forward facing eyes” Hominids include apes, chimps and humans. (no tail) Hominins are humans and their common ancestors. There are key differences which show how different Humans now are from their original primate ancestors.

How structures have changed…. Humans are now a ‘sub-tribe’ as they have the ability to walk on 2 legs (known as bipedalism) Differences between primates and humans include: Skull Size Jaw shortens location of foramen magnum Vertebral Column (S Shaped) Pelvis (wider) Femur (angled inwards) Feet (flat)

Summary/keywords Pentadactyl limb  having 5 digits Homologous structure  Features of organisms that have a similar structure and provide evidence of an evolutionary relationship (common ancestor). Do not have to have the same function in all species. Analogous structure  Similar Structure. Not Related. These structures may have come about, due to the environment in which they live in. Divergent Evolution  When two or more species evolve from a common ancestor Convergent Evolution  When two or more unrelated species adopt similar adaptations in response to common environmental conditions

Summary/keywords Artificial selection humans deliberately choose which individuals will mate Natural selection the environment acts on the population Darwin’s theory selection cannot occur without differences in a population Lamarck’s theory Evolution by inheritance of acquired traits Genetic isolation keeping potentially interbreeding groups apart by some barrier Evolution  the gradual development of different species from a common ancestor