M3.4.1

Question 1

Comparative embryology

Answer 1

• Study of embryonic forms of organisms
• Similar embryonic forms across different species indicates that the species are descended from a common ancestor and share a significant degree of genetic relatedness
• E.g. embryos of the four vertebrate groups (mammals, birds, fish, and reptiles) are structurally similar as embryos and all have gill slits and a tail → modern vertebrates are descended from a common ancestor

Question 2

Comparative anatomy

Answer 2

• Study of common structures in organisms
• Existence of similar structures in many species indicates that they are descended from a common ancestor
• E.g. humans, dolphins, birds and whales all have a pentadactyl limb structure. This is a complex structure, so it is unlikely to be the result of convergent evolution and rather the result of common ancestry
• Also studies vestigial structures

Question 3

Vestigial structures

Answer 3

Structures that functioned in ancestral organisms but are reduced in the descendants.
- E.g. tailbone in humans, wings of flightless birds like ostriches, flightless cormorants, penguins

Question 4

Biochemical similarities

Answer 4

• All living things possess DNA (or RNA) and synthesise proteins from its sequences. These structures are highly complex, and it would be impossible for all living things to develop them independently –> common ancestor.
• Similarities in DNA and amino acid sequences can indicate a genetic relationship between different species, and a common ancestor.
• E.g. humans and chimpanzees share 99% o the same DNA sequences, indicating a high degree of evolutionary relationship.

Vegetation example: DNA from more than 700 eucalypt species and rainforest species e.g. anbinik and Vic Stockwell’s puzzle was sequenced, showing that eucalypts, newcalypts, and mesicalypts were all descended from an unknown proto-eucalypt common ancestor

Question 5

Biogeography

Answer 5

• Study of distribution of plants and animals and how they came to be there
• Environment cannot account for either similarity or dissimilarity, since similar environments can harbour entirely different species groups.
• Affinity or similarity of groups on the same continent (or sea) is closer than between continents (or seas).
• Geographical barriers, such as seas, oceans and mountain chains, usually divide these different groups. The degree of difference between families relates to the rate of migration or ability to disperse across the barriers.
• E.g. Java and New Guinea (Wallace Line) represent a mixing zone of Oriental and Australian fauna, as as the landmasses drifted closer, the geographical barrier became easier to disperse through.