This document summarizes evolutionary theory, covering key figures like Darwin and Wallace, mechanisms such as mutations and speciation, and human evolution from early hominids to modern humans. It provides a concise overview of how life evolves and adapts.
Origin of an idea about origins
According to the IEB SAGS Document candidates should know:
1. that the scientific theory of evolution emerges from different lines of evidence, e.g.
fossil record, modification by descent, and the evidence from biogeography, genetics
as well as other forms of evidence.
2. the role of Erasmus Darwin, Lamarck, Charles Darwin and Alfred Wallace in the
development of the theory of evolution.
Biological evolution is the change in the gene pool of a population during the course of time
by processes such as mutation, natural selection and genetic drift
Evolution is important as it
- Is the foundation of all biological concepts
- Supports and explains concepts of life
Erasmus Darwin
- In the book Zoonomia he put forward the idea that life in earth descended from a
common ancestor
- He also suggested that species must have changed (evolved) over time
Jean-Baptiste Lamarck
- He suggested species were not fixed, he came to this conclusion by various observations
o Living species were different from fossils
o Domestication and selective breeding yielded in changes
o Cross breeding of plant species led to new characteristics forming
Lamarck's idea
- Organisms changed during their lifetime so that they could survive in new environments
and that these acquired characteristics were then passed onto offspring
a. Use and disuse of body parts
When the environment changed, the organism would actively respond by changing so
it could adapt to the new environment. Causing the organ to increase/decrease in
size or even completely disappear
b. Inheritance of acquired characteristic
Phenotypic changes/ characteristics acquired by parents during lifetime are passed
onto their offspring
Example: Giraffe
Long neck and legs of giraffe were the result of generations of short-necked and long-
necked giraffes stretching their necks to feed. He thought that the acquired
characteristics (longer legs/neck) were passed onto the offspring of each generation until
eventually a new species of giraffe with long legs and neck appeared
Why Lamarck was incorrect
- The characteristics acquired during lifetime cannot be passed down to offspring. The
phenotype is altered but the genotype remains the same
Charles Darwin
After his voyage to the Southern Hemisphere, Darwin realized that the earth is extremely
old, there had been great geological change and that isolation led to species changing
His two hypothesis were
1. Modification with descent - diversity of a species is a result of evolution
2. Natural selection - mechanism causing evolution
,Explanation of descent with modification
- All related organisms descended from a common ancestor
- Ancestral species adapted to a variety of new habitats
- Diversification was by branching
- Some species died out
Evidence for the theory of evolution
Fossil evidence (Palaeontological evidence)
- Provides evidence for the theory of descent with modification
- Fossil records indicate evolution has taken place as fossils show an increase
in complexity, increase in diversity, existence of transitional fossils and
overall increase in size
- Common ancestor
- Order of evolution
- Fossils provide a record of past life on Earth and show a chronological sequence
of life forms.
- Transitional fossils, which exhibit characteristics of both ancestral and
descendant groups, support the idea of gradual change over time.
Biogeography
Study of the distribution of extinct and living plants and animals in specific geographic
regions
- Closely related species occur in the same geographic regions, suggests that they may
share a common ancestor
- Regions have been isolated due to barriers, preventing migration/spreading of a species.
This may lead to speciation
- Plants and animals in different geographic regions with similar habitat and climate tend
to differ a lot. Proving that species did not share a common ancestor
- The distribution of species across the globe can be explained by evolutionary processes.
For example, the similarities between the fauna of nearby but isolated islands can be
understood through evolution.
Example: flightless bird
Genetics
Study of inheritance
- Greater similarities in DNA shows a recent common ancestor
- Shows how changes in phenotypes and genotypes are transferred
- Shows how gene pools change and lead to new species
- DNA and molecular genetics provide strong evidence for common ancestry and descent
with modification.
- Homologous structures in the genetic code across different species suggest a shared
evolutionary history.
, Scientists state that organisms are closely related and are likely to have a common
ancestor if they have:
- Identical DNA structure
- Similar sequence of genes
- Similar portions of DNA with no functions
Species that are closely related have a greater similarity to each other than distant species
Modification by decent
- Modifications obtained from the study of the details of the structures of body parts
and systems of organisms that belong to a specific phylum.
- Homologous structure: similar structure in different organisms with the same body plan
that perform the different function (pentadactyl limb)
- Similarities may be traced back to a common ancestor
- Analogous structure: different body structure in different organisms that provide the
same function but don't share a common ancestor (wings)
Embryology
- Similarities in the structure during early stages of development
- Shows a common ancestor
- The similarities in embryonic development among different species support the idea of
common ancestry.
- The presence of vestigial structures in embryos, which are remnants of structures that
were functional in ancestors, is consistent with evolutionary theory.
Vestigial organs
- Some organisms have organs that have decreased in size over time (homologous)
- Proves evidence of a possible common ancestor (whale pelvic bone)
- Homologous structures (structures that have a common evolutionary origin) in different
organisms suggest a common ancestry.
- Analogous structures (structures that have similar functions but different origins) can
be explained by convergent evolution.
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