topic 11- macroevolution Flashcards
define macroevolution
• Evolution on the grand scale
• Evolutionary events at or above the species level
• Encompasses the grandest trends and transformations in evolution
• History created by the processes (microevolution) with many unique events
• Examples
○ Origin of new higher groups
§ Tetrapods, birds, mammals, whale
two modes of evolution
gradualism. punctuated equil.
describe gradualism
Large differences in phenotype evolves through many slightly different intermediate states
describe punct. eq.
• Punctuated equilibrium ○ Proposed by Niles Eldredge & Stephen Jay Gould in 1972 ○ Provides a pattern of change in fossil record and a hypothesis about evolutionary processes ○ Pattern of rapid evolutionary change in phenotype separated by long periods of little change `
phyletic gradualism ex?
• Molar morphology in the grass-feeding vole • Mimomys during Pliocene & Pleistocene • Enamel, cement, and tooth height • Gradually increased over 1.5 million years
ex of punct. eq.?
• Phylogeny & temporal distribution of a lineage of bryozoans of the genus Metrarabdotos • Long periods of stasis interrupted (= punctuated) by apparent periods of rapid Change
rapid change links that are not to eq?
• Patterns of speciation • Cladogenesis w/o Anagenesis: • e.g., salamanders of genus Plethodon – Diverged 60 mya (molecular) – Little morphological change • Anagenesis w/o Cladogenesis: • e.g., mimetic butterflies – Much geographic variation w/o speciation
difficulties w measuring rates of evolution?
.Difficulties with measuring rates of change in the fossil record
• Calculating change between fossilized end members almost always under-estimates
the maximum rate of evolutionary change
• Average measured rates are usually very low, even though there are episodes of
rapid evolution:
• Measurements are typically made over large amounts of time
measuring change of evolutuon in horse fossils?
• Measuring rates of change in phenotypic characters • Estimated body masses of 40 species in horse family Equidae plotted against geological time • Although smaller species occurred throughout, average body size increased over time
how did darwin understand rates of evo?
- Darwin understood that rates of evolution vary.
* “Species of different genera and classes have not changed at the same rate or in the same degree” - stasis
what did darwin emphasize about rates of evolution?
• However, Darwin (1859) emphasized that rates of evolution were generally low
He wrote
“I do believe that natural selection will always act
very slowly, often only at long intervals of time …..”
• Nevertheless, he argued that
“….. this very slow, intermittent action of natural
selection accords perfectly well with what geology
tells us of the rate and manner at which the
inhabitants of this world have changed.
what did simpson note about rayes of evolution and characters?
Simpson (1953) also noted that rates vary among characters, among organisms, and over time Also proposed terminology Bradytely • Exceedingly slow rate of evolution, manifest by slowly evolving lineages which survive much longer than would normally be expected Tachytely • Evolution at a relatively rapid rate tending to result in speedy differentiation
what are living fossils? ex?
• Living species that appear to have changed little from their ancestors millions of years
ago
• Examples: Horseshoe ‘crab’, tadpole shrimp, coelacanth; cyanobacteria (not much
phenotypic change over last ~3 billion years)
• Would you expect living fossils to differ
from other species in terms of genetic
variation?
• Morphological constancy vs. genetic
constancy
• It is possible to have high level of genetic,
biochemical, and physiological change
“under the surface” while phenotypes
remain constant
• We just cannot see that in the fossil remains!!!
how do whole organisms evolve as coordinated entities
• Diversity within constraint is a general
principle
• Bacteria have huge metabolic diversity,
but much less morphological diversity as
compared with plants and animals
