5.1.1 Evolution and Totality of fossils
Evolution: Change in the heritable characteristics of a species |
Direct Fossil: Bones, teeth, shells, leaves etc |
Indirect Fossil: footprints, tooth marks, tracks, burrows etc. |
The fossil record reveals that changes occur over time in the features of organisms on the planet. |
The law of fossil succession - organisms are not found randomly but in rocks of particular ages in a particular order, suggesting that modern organisms evolved from ancestral species (speciation). |
Transitional fossils - intermediary forms over the evolutionary pathway from a single genus, provides evidence for evolution - eg. birds from prehistoric reptiles |
The fossil record demonstrates that prokaryotes precede eukaryotes, and that invertebrates precede vertebrates. |
The fossil record is incomplete - fossilization requires specific circumstances to occur, and only the hard parts of an organism is preserved. |
Radioisotope dating & carbon dating can help determine the age of fossils |
Gradualism: Gradual change from common ancestors over time, eg. Galapagos finches |
Punctuated Equilibrium / Catastrophism: (Cambrian explosion): a long period of no change, and a catastrophic event that causes a short and sudden period of big change , eg. volcanic eruptions |
5.1.1 Selective Breeding
Artificial selection by man to produce desirable traits in an animal's offspring |
As a result, domesticated breeds of animals can vary compared to the wild counterpart. |
Examples: Racing horses (speed), draft horses (endurance), sheepdogs (herding), cattle (increased milk or meat), greyhounds (racing) |
5.1.2 Homologous / Analogous Structures
Homologous Structures |
Analogous Structures |
inherited from a common ancestral origin, does not necessarily have the same function |
inherited from different ancestral origins, may have similar function but different bone structure and origin |
appearance and function diverge over time to make use of environmental niches (Adaptive radiation / divergent evolution). The more similar the structures, the more likely they are closely related |
selective pressure / similar habitats and diets causes the structures to become similar in function or appearance (Convergent evolution) |
the feature is adapted to suit various environmental needs |
different species evolve the trait independently |
example: pentadactyl limb (humans, horse, cats, whales bats) |
example: human eyes and octopus eyes, wings of insects and birds, tail fin of orca and shark |
the pentadactyl limb evolved to suit environmental niches for locomotion, eg., galloping, flying, swimming, using tools in humans |
the eyes of the human and the octopus evolved independently out of a need to see. wings in insects and birds evolved independently out of a need to fly |
homologous genes, DNA, embryo structure and other biological molecules are used to determine homologous structures and evolutionary relationships |
Pentadactyl Limb
Limb Structures |
Single proximal bone (front / top bone) - humerus, femur |
Two distal bones (back / bottom bone) - radius & ulna, tibia & fibula |
Group of wrist / ankle bones - carpals, tarsals |
Series of bones, 5 digits - metacarpals & phalanges, metatarsals & phalanges |
Evolutionary differences can be seen in the varying length and thickness of the bone. Some metacarpals and phalanges ( finger bones) were lost in the penguin's forelimb. |
5.1.2 Speciation
Where populations of a species gradually diverge into separate species (ie, they cannot interbreed to produce fertile offspring) |
Biological separation: species cannot interbreed due to biological obstacles such as size or number of chromosomes |
Geographical separation: species cannot interbreed due to geographic obstacles - often occurs after a species extends its range by migrating to an island & is why Australia has many endemic species (only found in a certain geographical area) |
Continuous variation across a geographical range of related populations match the concept of gradual divergence - as speciation occurs gradually, it can be difficult to group for species and variation |
Continuous variation between populations provide evidence for evolution of species and the origin of new species by evolution |
5.1.2 Industrial Melanism
An example of how changes to an environment can cause an evolutionary adaptation |
Biston betularia - roosts during the day and active at night, are prey to birds |
In the countryside / unpolluted areas, peppered moths are dominant as they can camouflage on the lichen to hide from predators |
In industrial areas where sulphur dioxide kills lichen and soot darkens trees, melanic moths are dominant as their darker colour can help camouflage against the darker trees and protect against predators. |
The dark allele is dominant over the light allele & codes for the moth to make more melanin |
In industrial areas, melanic moths were more likely to survive and thus pass on the melanic allele to their offspring |
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