Macroevolution

Evidence for Evolution

Fossil Record & Biogeography

Fossil record provides an incomplete timeline of evolution from extinct species

Fossils are dated by:

age of rocks around fossils
radiometric dating of isotopes; carbon decay since we know its half life
looking at geographic data/biogeography, we know when Pangea broke up and we can see where organisms lived and where they may have migrated before/after the continents broke up
Also includes extant species that evolved with isolation; eg. islands (like Australia’s marsupials

Anatomy

Homologous structures, are physical features shared due to common ancestry, which show similarities in structure but not necessarily in function. Not to be confused with analogous structures, which are similar in function but not necessarily structure, which provides evidence of convergent evolution, meaning species exhibited similar selective pressures, but not a common ancestry.

Vestigial Structures are non-functional features that no longer serve a purpose in the organism but provide evidence of a common ancestry

Embryology

Study of organism development from egg to adulthood.
Reveals shared developmental pathways among different species.
Haeckel's theory: embryos show stages of evolutionary history (recapitulation).
Developmental changes reflect evolutionary adaptations.
Comparative embryology supports the idea of common ancestry in macroevolution.
ex. Mammal embryos (including humans) develop with tails and, comparatively, look very similar.

Molecular Evidence

Evidence of common ancestry from similarities of:

DNA
mtDNA (mitochondrial)
Amino acids
The more species with a trait (shared character), the earlier this homologous gene evolved (highly conserved)
- Transcription, translation
- Glycolysis

Observed Evolution

Direct observation of evolutionary changes in real time provide evidence for macroevolution.
Observations demonstrate the ability of organisms to adapt and evolve in response to selective pressures as evidence of species change over time.

Examples:

Antibiotic resistance in bacteria
Changes in coloration of the rock pocket mice and peppered moth, etc…

Phylogeny

The evolutionary history of a species (or group of species)

Determined by:

Morphology (structure, fossils, biogeography)
Development
Behavior
Molecular differences (DNA, aa, mtDNA)
Mutation rate

Phylogenetic Trees & Cladograms

Both are diagrams that reflect our understanding of how species evolved
Phylogenetic trees and cladograms are different ways of showing the same thing: which species are most closely related in terms of their evolutionary traits
Nodes are the locations in which organisms evolve from a common ancestor. The species that branch off from a node exhibit free rotation, meaning that the species on them can be swapped and still show the same relation.
Species that are most similarly related are grouped toward the top of a cladogram, while the least similar are toward the bottom, on the longest branches. Species that are less closely related should not exhibit free rotation.
The species/group that is least closely related to the rest of the species (lowest on the cladogram/phylogenetic tree) is the outgroup.

Building Cladograms/Pyhlogenetic Trees

Feature	Antelope	Bald Eagle	Alligator	Sea bass
Lungs	+	+	+	0
Jaws	+	+	+	+
Feathers	0	+	0	0
Gizzard	0	+	+	0
Fur	+	0	0	0

Here, the + means that a trait is present in a certain species, and the 0 means that it’s absent (sometimes the 0 will be a minus sign). Species that have the same traits present/absent are most closely related. Species with the fewest shared traits come first to identify evolutionary changes present in all subsequent species. If an adaptation is unique to one species, a tick mark is added after its node on the cladogram, on the branch, like this:

Since the lamprey shares none of these traits, it is the least closely related and should not have any tick marks. Then, since every subsequent animal has jaws, a tick mark is placed before (continuing for other shared traits). For species that have similar traits to subsequent ones and their own unique trait, you should add a tick mark for it only, as shown above.

Speciation

Key idea: biological species concept

a group of individuals that interbreed with one another and produce viable, fertile offspring
Interbreed means sharing a gene pool

Speciation:The process by which new species arise

One ancestral species splits into descendants that are genetically different enough that they can no longer interbreed. This is the process by which speciation occurs.