A concise, bullet-pointed summary on Evolution Studies. Covers strictly what you need to know for all tests and assessments (as dictated by the SAGS guidelines). Includes annotated diagrams and images to illustrate points mentioned, as well as additional research, helpful when understanding the work
simple but detailed, comprehensive notes that have been way more helpful than any other resources. I really appreciate the effort that went into everything and how concise you were able to make them!
Chloë van Beukering Evolution Studies Life Sciences Notes 2020
Evolution
- Species: defined as a group of similar individuals in a population that have the ability to breed
with each other and produce viable/fertile offspring
What is Biological Evolution?
- Any process by which new species are formed or by which existing species grow and change
Divided into two types:
1. Micro-evolution
- Occurs within a species
- Small changes (due to mutations) in populations occur over a fairly short period of time to
produce new species
2. Macro-evolution
- Occurs between species
- Large-scale evolution occurring over geological time, resulting in the formation of new groups
of organisms, such as the origin of mammals and the wide range of flowering plants
Modes of Evolution
1. Gradualism
- A theory which holds that profound change is the cumulative product of slow but continuous
processes
- Gradual change over long period of time
- For e.g. horse (Equus) evolution would be a gradual macro-evolution
2. Punctuated equilibrium
- Periods of rapid change followed by long period of no change
- Most species will exhibit little evolutionary change for most of their history, remaining in a
stable (morphological) state
- When significant evolutionary change occurs it is generally restricted to rare and geologically
rapid events of branching speciation
- Resulting in a species splitting into two distinct species, rather than one species gradually
transforming into another
- Consists of morphological stability and rare bursts of evolutionary change
Cladograms
- Digram that depicts evolutionary relationships among groups
- Based on phylogeny, which is the study of evolutionary relationships
- Sometimes a cladogram is called a phylogenetic tree
- Biologists can look at individuals to discover their pattern of evolution, and group them
accordingly
- Called Evolutionary Classification
- Cladistics is a form of analysis that looks at features of organisms that are considered
“innovations”, or newer features that serve some kind of purpose
- These characteristics appear in later organisms but not early ones and are called Derived
Characteristics
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, Chloë van Beukering Evolution Studies Life Sciences Notes 2020
- Cladistics is a type of classification in which all organisms that have descended from a common
ancestor are grouped together and called a clade
- A group of organisms classified cladistically can be represented visually by means of a
cladogram
Construction of a cladogram:
1. Lay out all organisms being studied. List all the characteristics you see for each object and
tabulate these traits
2. Draw a table of the data. In the first column list all the characteristics found in the group. In the
rows list the organisms in the group. Place a tick in a cell if the organism shows the
characteristics listed
3. Identify the characteristic all of the organisms have in common. This is the primitive or original
characteristic
4. Look at the common characteristics that only a portion have in common. These are the
derived or advanced characteristics. The largest group of these derived characteristics will be
the first to branch from the main trunk of the cladogram
5. Look for further characteristics that are common to only a portion of the group and add these
to the cladogram until the groups can be sorted no further
Jean Baptiste de Lamarck
- A French naturalist
- Believed that evolution occurred through a mechanism called ‘the inheritance of acquired
characteristics’
- Means that organisms, by striving to meet the demands of their environments, acquire
adaptations and pass them by heredity to their offspring
- The discovery of genetics by Mendel disproved this theory
- The use and disuse inheritance is: supposedly the more a part of the body is used, the bigger
it becomes and can then be passed on to offspring
- In other words, new structures and organs are produced to meet the organisms’ changing
needs. These acquired structures are inherited by following generations
- NB example: giraffe’s neck
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