Quick questions on Evidence for evolution (fossils, biogeography, comparative anatomy, molecular biology): VCE Biology Unit 4

Fossils are preserved remains or impressions of organisms in rock. The fossil record shows that:

Biogeography is the geographic distribution of species. Two patterns emerge:

Anatomical comparison between species reveals patterns that only descent with modification explains.

DNA and protein sequencing have provided overwhelming evidence for evolution:

Each line of evidence can be questioned in isolation, but they converge on the same pattern of relationships. Fossils, anatomy, biogeography and molecules independently produce nearly identical evolutionary trees. The mutual support of independent evidence is the hallmark of a robust scientific theory.

Soft-bodied organisms rarely fossilise; many environments preserve poorly; the record is incomplete. Despite this, every fossil ever found falls into the predicted age order: no rabbits in Cambrian rocks.

Structures with the same underlying anatomical plan but different functions. The pentadactyl limb of mammals, reptiles, birds and amphibians all has the same bone arrangement (humerus, radius, ulna, carpals, metacarpals, phalanges), used for walking, flying, swimming or grasping. Homology supports descent from a common ancestor.

Structures with the same function but different underlying anatomy. The wing of a bird (with arm bones and feathers) and the wing of an insect (with chitin membranes) both produce flight but evolved independently. Analogy is evidence of convergent evolution, not common descent.

Reduced, non-functional remnants of structures that were useful in ancestors. Examples include the human appendix and tailbone, whale pelvis bones, and the eyes of cave fish. Vestigial structures make sense only if the species descended from an ancestor in which the structure was functional.

Vertebrate embryos pass through similar stages (pharyngeal arches, post-anal tail), reflecting shared developmental genes inherited from a common ancestor.

All known organisms use essentially the same DNA codons for the same amino acids. This is strong evidence that all life shares a common origin.

The more recently two species shared a common ancestor, the more similar their DNA and protein sequences. Human and chimpanzee DNA differs by about 1 to 2 per cent. Human and mouse DNA differs by about 15 per cent.

Some sequences accumulate mutations at a roughly constant rate. By counting differences between species and calibrating against the fossil record, scientists can estimate when two lineages diverged. Cytochrome c, mitochondrial DNA and ribosomal RNA are commonly used.

Humans and other great apes share the same broken gene for vitamin C synthesis at the same point in the sequence. The only sensible explanation is inheritance of the defect from a common ancestor.

Viral DNA fragments inserted at the same locations in the genomes of humans and chimpanzees show common ancestry, because the chance of independent insertion at identical sites is negligible.