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Evolution and evolutionary thinking
What is evolution?
Evolution can be defined as decent with modification - species on earth are descendants of ancestral species
that were different to present-day species
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Evolution can be looked at as a pattern and a process
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They are factual
observations of the natural world
Process - the mechanisms that produce these patterns
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Early Ideas about Natural History
Aristotle - 4th Century - “The Great Chain of Being”, or scala natura; biased hierarchal arrangement of
species, humans were placed above all animals but below angels and god
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He developed
classification using binomial nomenclature (genus and species)
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However he still believed int he
fixity of species
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1707 - 1788 - Count George-Louis Leclerc de Buffon
Published Natural History in 1749, where he stressed upon the importance of a changing universe
(environment) and specifically the changing nature of species
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Although he suggested species could change to adapt to their
environment, he did not believe that species could evolve into new species
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However he was a still a believer of the fixity of species
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He also proposed the theory of catastrophism, whereby the
fossil record appeared as a succession of catastrophic events in the past that occurred suddenly and were
caused by mechanisms different to those operating in the present
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Each boundary between the strata is a representation of a catastrophe
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Catastrophism, however, is NOT change through evolutionary time
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These regions were

wiped clean of ALL living things and new and more advanced forms colonised the regions
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**this was the reasoning for increased complexity in species**
1744 - 1829 - Jean-Baptiste Lamarck
He was the first to suggest a mechanism for evolution
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He stated that evolutionary change explains the patterns in fossils and the
match between organisms and their environment
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As the
environment changes, an animal’s activity patterns also change to accommodate this new environment
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This led to the idea of ‘use and disuse’ which
states that the parts of bodies that are used become larger and stronger while those that aren’t deteriorate
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He also suggested that evolution
happens because organisms have an innate drive to become more complex
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(Example of an antelope like animal
developing a longer neck to form a giraffe for the purpose of eating leaves on a tree)
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1766 - 1834 - Thomas Malthus
He wrote the Essay not the Principle of Population
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So, while populations can increase exponentially while food
resources remain relatively stable, in reality this reproductive potential is greater than the available food
supplies
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**Essay on the principle of population**
In this essay he states two postulates:
1
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The passion between sexes is necessary and will remain nearly in its present states
And given that these are true, he states that ‘the power of population is indefinitely greater than the power in
earth to produce subsistence for man’
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1797 - 1875 - Charles Lyell
He published the “Principles of Geology” in the 1830s
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This means that the mechanisms of change are constant over time, geologic
process are operating today as in the past and at the same rate
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This opposed Cuvier’s theory of
Catastrophism and the idea of “multiple creations”
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1809 - 1882 - Charles Darwin
Was on the HMS Beagle, this was where his idea on the fixity of species was challenged as he observed the
ever-changing world and the evidence for a deep time-scale of the earth
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Uniformitarianism was a more suitable proposal
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He also
notices that there were gradual changes in animals as you moved across different regions, and recognised
that there must have been a common ancestor
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1823 - 1913 - Alfred Russel Wallace
Indecently came up with the idea of species descending from other species and this was influenced by the
environment
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The origins of Natural Selection
Malthus’ essay in 1938 - populations can increase faster than resources constant struggle for existence
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Variation within species
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Natural selection is an underlying
mechanism of decent with modification
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Natural selection occurs
through interactions between individual organisms and their environment but individuals themselves do NOT
evolve; populations evolve over time
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Adaptations are the inherited characteristics of species that enhance their survival and reproduction in
specific environments
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There was a
lot of conflict particularly pertaining to religion
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Selective breeding showed Darwin that
by selecting certain features, you could eventually transform a species
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Small changes in each generation could produce major changes over long periods of time
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Biogeography - Related organisms were often separated by geographic barriers, however their presence in
the same region suggested that they had a common ancestor in the past, and this ancestral population was
divided by a barrier
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Palaeontology - Mining and Canal building led to increasing number of fossil discoveries and these provided
best evidence for evolution during Darwin’s time
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Comparative Anatomy - There’s evidence for vestigial parts, which are non-functional structures inherited
from an ancestor that needed them for another purpose
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Embryology - The study of development also showed vestigial structures during development, thus providing
evidence for evolution as well
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There is the idea that ontogeny (development of organism from earliest state to maturity)
recapitulates phylogeny (goes through the same steps as evolution while developing), however it is now
shown to be more complicated than that
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While the scientific community
became more accepting for evolution as a theory, they were skeptical of natural selection
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Darwin proposed some false theories such as a
‘blending theory of inheritance’ whereby offspring blend their parents attributes but it was criticised that
advantageous traits would be lost in the process of blending
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The gaps the existed betweens forms in nature were another target of criticism as

these gaps made no sense given that organisms evolved gradually, and if natural selection had occurred
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There were three main issues with his way of thinking in the 19th century
**The Descent of Man and Selection in Relationship to Sex - Introduction**
- blending selection (explained above)
- he did not fully comprehend the difference between gene inheritance and the inheritance of habits,
customs and behaviours due to his lack of understanding for genetics; he believed in the ‘fixture’ of
behaviour if it had been repeated for generations by a certain animal
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Darwin’s discrimination
In The Descent of Man, Darwin states that gender equality is impossible to achieve because of the lesser
female brain power presented as an inescapable consequence of nature
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