11 Bio - Mod 3 (4)

Evidence to Support the Theory of Natural Selection

Evidence

• To prove the theory of Natural Selection:

  • Biochemical evidence

  • Comparative anatomy

  • Comparative embryology

  • Biogeography

  • Fossil evidence

Biochemical evidence

• All living things share the same macromolecules such as protein and DNA as well as the process of cellular respiration

• The biochemistry of organisms shows the relatedness of organisms through their proteins and DNA

• Amino acid sequencing is when the amino acids align themselves in a particular order creating a specific protein

• e.g haemoglobin is a protein sequence only found in animals

• Similarities in amino acid sequence suggest common ancestors, differences show that the evolution of that organism

• Phylogenetic trees use branching diagrams to represent the evolutionary relationships between organisms

• DNA hybridisation is when a single strand from two organisms are combined to determine whether they form strong bonds (more similar) or weak bonds (dissimilar)

• DNA sequencing is the most accurate biochemical technique, as it relies on advanced technology, determining the sequences of the four bases in a strand of DNA and comparing it with another specie.

Comparative anatomy

• Study of the differences and similarities between the structure/anatomy of organisms

• The more similarities imply that they have a common ancestor (divergent evolution)

• Organs that have the same structure but have different functions are known as homologous (same evolutionary origins)

• e.g pentadactyl (5 digit) limbs are in all vertebrates therefore are homologous

• Analogous structures prove convergent evolution

• These organs vary in their structure but are used for the same purpose

• They started off different and evolved independently to become similar as they face similar selection pressures

• e.g Australian echidna and European hedgehog both have protective spines to scare predators but have other dissimilar features

• Vestigial structures are evolutionary remnants of body parts that no longer provide a useful function, providing evidence for common ancestors

• e.g the pelvic bones in whale and snakes serve no purpose

Comparative embryology

• Comparison between the developmental stages of species

• Related species are similar in their embryonic development

• e.g amphibians and fish show the presence of gills in the early stages of life as they are descendants from a common ancestor

Biogeography

• Study of the geographical distribution of organisms both living and extinct

• For speciation to occur the population must be physically isolated from the other group

• The new species will be more similar to species that live close by rather than far away, even if the species living far away are within similar environmental conditions

• The new species are also more similar to species that lived in a common area before splitting off

• On Galapagos, Darwin noted that animals near the mainland were a little different from those on islands however still maintain some resemblance

• e.g the distribution of emus in Australia and ostriches in South Africa as they have similarities that suggest common ancestry

• This supports the theory of adaptive radiation (migration of organisms to an area which is advantageous with its traits) or diversification of species evolved from a common ancestor due to the migration to a new environment

Fossil evidence

• Fossils provide direct evidence into the existence of an organism

• Formed by an organism dying and being buried with a lack of oxygen. Minerals fill the cast of what used to be organism, pressure solidifies the organism and the fossil is eventually unearthed.

• Relative dating:

  • Used to determine the chronological order or sequence of a fossil by comparing it to age of another substance

  • Stratigraphy relies on the formation of sedimentary rock layers

  • The oldest fossils are found at the bottom and the youngest at the top, known as the law of superposition

• Absolute dating:

  • Also known as radiometric dating

  • Quantitive age of the specimen is determined by the decay of radioactive isotopes into stable new elements at a constant rate known as half-life

  • Carbon-14 dating is a technique used to date any once-living fossils up to 50,000 years old

• Transitional/intermediate form fossils represent the change in organisms over a long period of time

Megafauna - fossil evidence

• Megafauna are giant animals of a region

• Megafauna in Australia are proven by Indigenous artworks

• With the absence of these fossils, the paintings can reveal the anatomy, variations and distribution of a species