Summary IEB Grade 12 Notes on Diversity, Change and Continuity of Life
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Course
Life Sciences
Institution
12th Grade
Book
Life Sciences
In-depth notes created according to the 2021 IEB SAGS document for matric life sciences. Vital components have been covered. These notes are not only summaries of the strand 4 syllabus, but are the required topics to be studied for the IEB finals and can be used as a study source. Topics in this do...
Origin of an Idea About Origins
Diversity, Change and Continuity of Life
SAGS List
Candidates should know:
The scientific theory of evolution emerges from different lines of evidence, e.g., fossil record
(grade 10), modification by descent, and the evidence from biogeography (grade 11),
genetics (grade 12) as well as other forms of evidence.
The role of Erasmus Darwin, Lamarck, Charles Darwin, and Alfred Wallace in the
development of the theory of evolution. Discuss how new scientific evidence is introduced,
presented, and accepted by society and how it impacts on society. Consider
- the acceptance of scientific theory by society in relation to belief systems.
- the historical time at which it is presented.
- the manner in which it is presented
- to whom it is presented.
Alternatives to Darwin's explanation:
- People have diverse ways of understanding the history of life and the place of
humans in life.
Science has limits:
- it can explain physical structures and events, but not spiritual or faith-based
matters. Both are important to humans, but in different ways.
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,Notes Compiled by Giorgia Lobban (2021)
DEVELOPMENT OF THE THEORY OF EVOLUTION
Evolution= The gradual change or development of something.
Biological Evolution
The change in the gene pool of a population during the course of time by such processes
such as mutation, natural selection, and genetic drift.
Descent with modification.
This definition covers microevolution (evolution within a species) and macroevolution
(the descent of different species from a common ancestor).
Foundation for understanding all biology.
Supports and explains many aspects of our everyday lives.
Challenges people to really think for themselves.
Origination of Species Diversity
a. Before 1700
Species were unrelated and remained unchanged.
The earth was young.
b. 1700 to early 1800
Erasmus Darwin, Charles Darwin’s grandfather, and Jean-Baptiste Lamarck began
challenging these concepts.
Through studying fossil collections and being aware of the huge diversity of living organisms,
they became convinced that:
Species has changed gradually overtime.
The earth was millions of years old.
Erasmus Darwin
1731-1802
He put forward the idea that life on earth descended from a common ancestor.
He also suggested that species must have changed overtime.
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,Notes Compiled by Giorgia Lobban (2021)
Jean-Baptiste Lamarck
1774-1829
He put forward his ideas on evolution in his book about a decade later.
He proposed that species were not fixed.
He reached that conclusion through various observations such as:
Living species are different to fossil types, so life forms must have changed overtime.
Domestication and selective breeding resulted in animals and plants changing.
Crossbreeding of plant species often lead to new characteristics appearing.
Lamarck’s Suggestions About Change Within Species
He proposed that change was a natural phenomenon.
He suggested that organisms changed during their lifetime so they could survive new
environments and that the acquired changes were passed on to offspring.
His hypothesis on how change took place was as follows:
Use and disuse of body parts.
o Lamarck believed that when the environment changed, the organism would actively
respond by changing so it could adapt to the new environment.
o E.g., the more the organs were used, the more they would increase in size and
efficiency and the less the organs were used, they would get smaller and soon
disappear.
Inheritance of acquired characteristics.
o Acquired
o These phenotypic changes or characteristics acquired by parents during their
lifetime were then passed on to their offspring.
o Populations changed and new species were formed.
An example of Lamarckism:
o Lamarck considered that the long neck and legs of the modern giraffes were the
result of generations of short-necked and short-legged ancestors stretching their
necks to feed on the leaves at progressively higher levels.
o He believed that acquired characteristics, longer legs and a longer neck were
passed on to the offspring.
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, Notes Compiled by Giorgia Lobban (2021)
Reliability of Lamarck’s Theory
His belief that the environment can produce phenotypic changes in an individual was
correct.
However, he was incorrect in thinking this caused evolutionary change.
At the time, nothing was known about genetics and how characteristics were transferred
from parents to their offspring.
Only in the 1930s, thanks to work done by Mendel, was it known that the transfer of
characteristics by genes became known.
SUMMARY
Erasmus Darwin and Jean-Baptiste Lamarck believed that:
Species have common ancestors
Evolution occurred as species adapted to their environment.
c. Early 1800 to early 1900
Charles Darwin
Alfred Russel Wallace
Charles Darwin
1809-1882
Started formulating his theories in the late 1830s after a five-year expedition.
The data he collected made him aware of:
Immense diversity among living and extinct organisms.
Variation of individuals of the same species, suggesting species weren’t
unchangeable.
Often puzzling distribution of different species.
The earth is extremely old allowing for species to evolve and he was able to see
these changes through fossils in layers of sedimentary rocks.
There has been great geological change overtime with different areas and land
masses becoming isolate.
Isolation leads to species changing.
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