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Summary Fundamental Aspects of Evolution - Life Sciences
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Fundamental Aspects of EvolutionMacroevolution
- The change that occurs at or above the level of species over long periods of time
- Not easy to ‘see’ instead multiple lines of evidence are used: molecular sequencing data, geology, fossils
and living organisms
- Phylogeny: scientific study of evolutionary relationships among species
- Phylogenetics: the study of evolutionary relationships among groups of organisms discovered through
lines of evidence
- Tree of life: A metaphor describing the relationship of all life on earth in an evolutionary context
Patterns repeated on the tree of life
Stasis/Equilibrium
- They don't change much for a long time
- Some lineages have changed so little for such a long time: living fossils
Lineage-splitting (Speciation)
- Patterns can be identified by constructing and examining a phylogeny
- Might show cladogenesis or anagenesis
- Cladogenesis: Parent species splits into two distinct species forming a
clade (a life-form group consisting of a common ancestor and all its
descendants)
- Anagenesis: The ancestral species gradually accumulate changes until
eventually the species is distinct enough and different from its
original starting form and can be labelled as a new species
- Paleontologists see cladogenesis as more important than anagenesis in evolution
- Cladogenesis shows macroevolution while anagenesis shows microevolution
, Adaptive radiation
- The burst of divergence from a single lineage to give rise to many new species
from a single ancestor
- Occurs to fill up new ecological niches: Finches on the galapagos islands
example
- Over time the evolved organisms adapt and change further
Examples:
- Some 315 mya reptiles became truly terrestrial and no longer relied on returning to water for
reproduction (unlike amphibians), the development of the amniotic egg which retains water allows for
them to breed on land where they diversified rapidly into various new niches
- Later a similar more rapid burst of diversification gave rise to birds
- After dinosaurs became extinct there was an explosion of mammalian evolution with many different
species appearing the same time
Extinction
- Can be frequent or rare event or it can occur over many lineages (mass extinction)
- Over 99% over species have gone extinct
Trends in macro-evolution:
- Increased complexity
- Increase body size
- Evolution of habitats
Rates of change in evolution
Gradualism
- Species evolve gradually by small changes over long periods of time
- Eg: humans follow a linear pattern of evolution
Punctuated Equilibrium
- The speed at which evolution takes place
- Fossils were studied where no/little changes occurred over long periods of time
- This alternated with short periods of time where rapid changes occurred through natural selection
- Supported by the absence of transitional fossils indicating the period of rapid change
- Implies phenotypic modifications occur when species first branch off from parent
and then change little after that (provided environment stays stable)
- Events that change the environment speed up evolution because species would need
to quickly adapt
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