Flashcards that summarize exactly what you need to know about Strand 4: Origin of an idea about origins, Fundamental aspects of evolution and Formation of new species according to the SAGS document. These flashcards will ensure you understand the evolution content well and will help you get through...
Evolution
What is biological
evolution?
How did the scientific
theory of evolution
emerge from different
lines of evidence?
Fossil Records
1. Biological is the change in the gene pool of a population during the course of time by such processes as
Evolution mutation, natural selection, and genetic drift.
*Modification by descent.
2. Fossil A significant source of evidence. Palaeontological evidence that shows micro and macro-evolution.
records or Using radiometric dating that dates rocks, the age of fossils can usually be worked out. The oldest
Modification fossils = oldest layers
by descent Features that show evolution occurred:
- An increase in complexity over time (simplest- oldest, complex – newer)
- An increase in diversity over time
- Descent with modification (fossils of some modern species can be traced back through time
showing changes that occurred)
- Existence of intermediate forms between groups (transitional fossils) (Suggests one group
may have given rise to the other e.g., Archaeopteryx, a vertebrate with both reptilian and
bird features)
Evolutionary changes and evolutionary relationships
are shown in a cladogram (Phylogenetic tree)
, How did the scientific
theory of evolution
emerge from different
lines of evidence?
Biogeography
3. Biogeography Study of where species (both present- day and extinct) occur, and why.
Charles Darwin and Alfred Wallace noticed that:
Different regions with similar climatic conditions contained very different animals and plants.
Living organisms in each region become isolated and were able to evolve/adapt without
competition from (or genetic exchange with) similar species in another region.
*Wallace’s line- first identified by Alfred Russel Wallace during the 1850s – is an imaginary line
that bisects the Malay Archipelago (group of islands) into two parts, north-western (Sumatra
and Java) and south-eastern (New Guinea, Sulawesi and Timor)
- each part has different groups of living organisms despite their similar climate and geology
- deep seaways, which had always existed, prevented the migration of species between the
islands
-two different groups of organisms must have arisen by descent by modification from different
ancestors on each side of the line
- due to plate tectonics, the earth’s crust is constantly changing as continental and oceanic
plates move = mountains rising and falling, oceans forming and disappearing
- changes greatly affected the distribution of organisms (as some became isolated from each
other, they evolved into different species)
- For example, a large land mass breaking up is Gondwanaland which split into South America,
, Africa and Australia. (Continents are still moving – not quick. Continents are constantly
changing.)
How did the scientific
theory of evolution
emerge from different
lines of evidence?
Genetics, Comparative anatomy,
Embryology and Vestigial Organs
4. Genetics Studying and comparing chromosomal DNA and mitochondrial DNA (mtDNA) of different organisms
- All organisms have descended from a common ancestor that modified over time but also
shows how closely organisms are related to each other. (All organisms have dna and rna,
many genes in all living organisms that are encoded to make identical proteins)
5. Comparative By comparing external and internal structures, scientists can find out how related two organisms
anatomy are. Organisms with similar structures or characteristics might have acquired these features from
evidence a common ancestor and therefore are on the same evolutionary lineage = homologies
*Number of shared homologous features between any one species & another indicates how
recently those two species diverged from a shared lineage.
Homologous structures Analogous structures
1. Similar in fundamental structure, position 1. Structures that are similar in different
and development organisms because they evolved in a similar
2. Homologies can be superficially different environment, rather than being inherited
(Can have the same basic structure but do not from a recent common ancestor.
perform the same function) 2. Usually serve the same or similar purposes
3. Lead to divergent/adaptive radiation= 3. Lead to convergent evolution = no common
Common ancestor ancestor.
6. Embryology By studying embryos of various organisms e.g. vertebrates, one can see marked similarities in the
structure during the early stages of development. This supports the idea that these organisms
came from a common ancestor but evolved in different ways.
7. Vestigial Structures or organs that have no function. Often homologous to organs that are useful in other
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