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Module 2Evolutionism and evolutionary theories
What is evolutionism?
"Nothing in biology makes sense if it's not in the light of evolution."
The changes that define the Earth’s history have not been driven by any supernatural entity. They
are the result of natural processes
Creationism vs. Evolutionism
a) Creationist Model: absence of change
b)-d) Evolutionary Models: the existence of change since the origin of
each species
b) Lamarck: Species undergo changes during their evolutionary history,
but no genealogical connection linking the different species is proposed;
each has an independent origin
c) Darwin: species descend from shared ancestors and, of course,
undergo changes since their origin
d) Vision of the evolutionary tree with connections between branches
due to processes of symbiogenesis
Creationism principles:
1) Creationists reject any explanation of the natural world that does not invoke the intervention of a
supernatural entity, such as a god
2) Living beings inhabiting the planet have not undergone any changes, no evolution, since their creation.
The intervention of a divine agent is the cause of creation and the world is conceived as something
immutable and static
Biological evolution / Non-theistic evolution: Life on Earth developed through natural processes without the
need for divine intervention
Theistic evolution / Gradual creation: God guided the process of evolution to create all living things over a
very long time. Combination of evolution with the belief in a divine creator.
Progressive Creation / Old-Earth Creationism: God created different species at different times over millions
of years. God intervened at various points in Earth's history to create new species.
Quick Creation / Young-Earth Creationism: God created everything in a relatively short time, and Earth is
young (around 6,000 to 10,000 years old). All living things were created in a matter of days as described in
the Bible's Genesis account.
, From essentialism to darwinian evolutionism
Darwin invented evolutionism. Everyone used to think, that changes happened from a day to another.
1) Typological thinking (essentialism)
• Any natural system can be classified into natural categories, each defined by an essence that sets it
apart from any other system and is fixed
• The model of the natural ladder (Scala Naturae), which not only proclaims the existence of
fundamentally distinct organisms, each identifiable by the possession of certain type attributes but
also arranges them according to an alleged hierarchy of complexity, with the human species at the
highest rung
2) Pre-darwinian theories of evolution
2.1) Transmutationism (saltationism)
Species change suddenly, rather than gradually and changes happen in leaps/ jumps. It struggled to
explain how entirely new species could originate instantly and simultaneously in many individuals
2.2) Transformationism (uniformitarianism)
Organisms can undergo gradual changes over time. There is a parallel between the process of an
individual transforming as it develops (from a zygote to an adult) and the transformation of one
species into another during evolution.
There are two versions of this concept:
2.2.1) External causes: The environment is capable of modifying and shaping the genetic material
(depending on the use or disuse of an organ), and these gradual changes, acquired during an
individual's lifetime, can be inherited by their descendants (soft inheritance)
2.2.2) ) Internal causes: There is an intrinsic tendency to change, to evolve, towards increasingly
perfect states. It is directed by an internal force.
The three evolutionary explanations (transmutationism, and the two versions of transformationism), were
unable to explain the phenomenon of evolution which lead to darwinian thinking.
,3) Population thinking (darwinian evolutionism)
=> One of the key characteristics of any species is its interindividual variability, rather than being
homogeneous or discrete classes or types. Species evolve because the individuals that comprise them are
"essentially" different from the very moment of conception. Some of them go further than others in their
life journey because they are better adapted in the struggle for survival, and some leave more copies of their
genetic (and phenotypic) traits than others because they are better adapted in the battle for reproduction.
This is the principle of natural selection, i.e., the existence of differential survival and reproduction of
individuals within a species, and this mechanism can lead to evolutionary change, i.e., a change in the
frequency of different genetic and phenotypic traits within a population over generations.
Evidence for evolution
• Fossil record
• Homologous traits
• Analogous traits
• Molecular similarities
• Vestigal / atavistic traits
• Embryo development
• Biogeography
Fossil record
The study of the fossil record, the temporal sequence of different remains, and their age, provides
information about the fact of evolution
Homologous traits
Homologous traits are features or characteristics in different species that share a common ancestry.
These traits are similar in structure or function because they evolved from a common ancestor's trait.
The forelimbs of mammals, such as humans, bats, and whales, While they may have different functions
(e.g., arms, wings, flippers), they share a common skeletal structure, indicating a shared history
Analogous traits
Analogous traits are features or characteristics in different species that have similar functions or
appearances but do not share a common evolutionary origin. These traits have evolved independently in
each species to address similar environmental or functional challenges.
The wings of birds and the wings of insects are considered analogous traits. While both serve the
function of flight, they have different structures (bird wings are modified forelimbs, while insect wings
are exoskeletal extensions) and evolved independently
, Molecular similarities
All cells use DNA as their blueprint
All cells use RNA, ribosomes, and roughly the same genetic code for translation
All cell use the same 20 amino acids to build proteins
All cells use ATP as a use of energy
We share 98% of our genes with other primates. 96% with monkeys. 75% with dogs. 20% with fruit flies
This indicates that our most recent common ancestor with other primates lived more recently than our most
recent common ancestor with monkeys, and so on.
Vestigial vs. Atavistic traits
Traits that currently lack any function, or that have been adapted for a new function. In many cases,
disuse leads to the loss of the organ or its original function
Vestigial —> present in all individuals of the current species
Ex: coccyx, appendix, non-functional wings
Atavistic —> only protested by a few in a exceptional way
Ex: tails in humans, additional toes in horses
Embryonic development
The embryonic development of different species is explained with the theory of evolution of the
organism of the tree of life. All of them have common characteristics in the first periods (ex: in
different groups of vertebrates)
Biogeography / Biostratigraphy
• Examination of how and why different species are distributed across the Earth's surface and in
specific regions
• Study of factors such as geographic barriers (like mountains or oceans), climate, evolution, and
historical events to explain the distribution of species
—Wallace (1823-1913)
• Identification and correlation of fossils found in sedimentary rock layers to create a
chronological framework for geological time
—Wegener (1880-1930)
Darwinian Theory
Darwin: 1809-1882
Wallace: 1823-1913
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