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GCSE level exam revision notes on Evolution:
2.
Other Evolution Theories e.g. Lamarckism
- idea that changes that
occur in an organism during its lifetime can be inherited
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Sub-index of biology notes on all aspects of EVOLUTION
(2) Other Theories of
Evolution e.g. Lamarckism
Other
theories, including that of Jean-Baptiste Lamarck (1744-1829), are based mainly on the
idea that changes that occur in an organism during its lifetime can be
inherited.
Lamarck theorised (~1809) that an organism
(plant/animal) can pass on advantageous characteristics that the organism has acquired in
its lifetime i.e. can pass on these acquired characteristics to its
offspring and successive generations.
Lamarckian inheritance is also known as
the 'heritability of acquired characteristics'.
Lamarck envisaged that if some
characteristic of an animal was particularly essential for its survival,
then that characteristic could become enhanced through successive
generations.
He imagined that if a beneficial
characteristic is used a lot by an organism, then that organism
could become more developed with this trait and the organism's
offspring would inherit this acquired advantageous adaptation.
e.g. if a giraffe kept on
stretching more and more for food, its neck would get longer and so
offspring would be born with the potential to grow longer necks to
reach for food other animals couldn't access.
This is quite contrary to Darwin's theory
of evolution, which is based on the idea that variation occurs all the time
and the plant/animal species whose characteristics are best suited for it to
survive will survive!
In the vast
majority of cases this type of inheritance cannot occur.
There is a small, but growing body of
evidence to show, that environmental conditions may have an effect on the
genes-DNA of subsequent generations i.e. the characteristics of 'gene
expression' may be altered slightly.
The mechanism is not fully understood
yet, but, it does show how science can reject a theory and then, quite
correctly, bring it back into recognition in a very selective way.
Scientists like Charles Darwin
(1809-1882) will always come up with different hypotheses to explain
observed phenomena eg how animals have evolved over time, but ultimately an
accepted theory must be supported by as much available evidence as possible.
To date, most evolution evidence fits in
with Darwin's theory of evolution, a theory which is accepted by most
scientists today.
Apart from naturalist's studies of
the plant and animal characteristics and behaviour, the advent of
molecular genetics is now providing an insight into the biological
mechanism of how natural selection can happen.
Whenever scientists come up with
alternative hypothesis to explain some phenomena, it should not be accepted
without thorough research and observations (experimental evidence) to
support the hypothesis and become accepted theory.
Lamarck's hypothesis was rejected
because experimental observations did not support it.
The science of genetics has provided
plenty of evidence to support Darwin's evolution theory.
Even the discovery of new
fossils
is providing fresh evidence to describe with increasing detail how
organisms have developed over time.
There is also 'modern' examples of
bacteria quite rapidly evolving to become resistant to antibiotics - a
most unfortunate, and potentially fatal for us, case of natural
selection.
Key points
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Key
ideas about Lamarck's theory of evolution - Lamarckism
Lamarckism: The Theory of
Inheritance of Acquired Characteristics
Jean-Baptiste Lamarck (1744–1829)
was a French naturalist who proposed one of the earliest theories of evolution.
His theory, known as Lamarckism, suggested that organisms
change over time due to their use and disuse of traits and that
these changes are passed on to offspring.
Key Principles of
Lamarckism
-
Use and Disuse:
-
If an organism
uses a particular structure or organ frequently, it becomes
larger, stronger, or more developed.
-
If an organism
does not use a structure, it gradually shrinks or
disappears.
-
Inheritance of
Acquired Characteristics:
-
Changes that occur in an
organism during its lifetime are passed on to its offspring.
-
Example: Lamarck believed
that giraffes originally had short necks but stretched
them to reach higher leaves. Over generations, their necks became
longer.
Limitations of Lamarckism
-
Modern genetics has
disproven Lamarck’s theory because acquired traits do not
alter an organism’s DNA.
-
Experiments (e.g., cutting off
mice tails for generations) showed that offspring still had tails,
proving that acquired traits are not inherited.
Other Theories of
Evolution (Excluding Darwin & Wallace)
(Not on UK GCSE syllabus
specifications, but interesting)
Orthogenesis
(Straight-Line Evolution)
-
Proposed that evolution
follows a predetermined path rather than being influenced
by natural selection.
-
Suggests that organisms evolve
in a linear direction due to internal forces
rather than environmental pressures.
-
Example: Some scientists
believed that horses evolved in a straight-line progression
from small ancestors to modern horses.
Mutation Theory (De
Vries)
-
Hugo de Vries (1848–1935)
proposed that mutations (sudden genetic changes) are the
main drivers of evolution.
-
Unlike gradual changes,
mutations create new traits instantly, which may be
beneficial or harmful.
-
Example: Some plants develop
new flower colors due to mutations, leading to variation in
populations.
Saltation Theory (Sudden
Evolution)
-
Suggests that evolution occurs
in large jumps rather than gradual changes.
-
Supports the idea that
major mutations can lead to new species in a short
time.
-
Example: Some amphibians may
have evolved suddenly from fish-like ancestors rather than
through slow transitions.
Conclusion
While Lamarckism was an important
early attempt to explain evolution, modern science has shown that genetic inheritance (not acquired traits) drives evolution.
Other
theories, such as Orthogenesis, Mutation Theory, and Saltation Theory,
have contributed to our understanding of how species change over time.
Summary of learning objectives and key words or phrases
Know that there are other theories of evolution,
particularly that of Lamarckism or Lamarckian inheritance.
Lamarck proposed it is possible for advantageous characteristics
to be acquired by an organism in its lifetime and these can be inherited in its
offspring and enhanced through successive generations.
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