Evolution
What it is, and what it isn’t.
Introduction
• In this presentation we shall study what evolution is and what it isn’t.
• According to standard biology textbooks, evolution is defined as “the change in allele frequencies in a
population.”
– Allele: a specific version of a gene that codifies for a physical trait.
– Frequency: a fraction or ratio of alleles.
– Population: a group of organisms of the same species that live in the same ecosystem.
• What these textbooks don’t tell you is that this is a definition of what theists/creationists call
‘micro-evolution’.
Introduction
• Mirco-evolution:
– The idea that a group of organisms of the same species changes its accidental traits over time (“the change in allele frequencies in a
population”).
– Has been amply observed to occur in nature.
– E.g., peppered moth, bacteria and antibiotics.
– It is due to many factors (as we shall see),
including adaptation to the environment through natural selection.
– The idea is not a claim regarding the origin of species.
Introduction
• Macro-evolution:
– The idea that a new species originates from an old species.
– It is the basis of the Darwinian theory of the origination of all species from a primitive
life-form.
– Has never been observed to occur in nature.
– Many biologists assume that macro-evolution is the result of micro-evolution occurring over
milliions/billions of years.
– This reasoning implies that species differ only accidentally.
Introduction
• Many scientists and philosophers fail to admit that there is an essential distinction between micro- and macro-evolution, but the
distinction is a logical consequence of the
distinction between accidental and substantial change (and between substance and
accident).
• We shall now see how micro-evolution works, what are its factors, and why it does not
amount to macro-evolution.
The Factors of Evolution
• According to biologists, evolution is caused by four factors:
– Natural selection – Genetic drift
– Gene flow – Mutation
• We shall now study each.
Natural Selection
• Definition: The process through which individuals with certain traits that are better adapted to the environment have greater reproductive success than individuals with other traits.
• It can be broken down into four postulates:
– The individuals of a population vary in their traits, such as shape and size.
– Some of these traits are hereditary. For example, tall parents tend to have tall offspring.
– Only a fraction of all the individuals in the population survive long enough to reproduce.
– Individuals with certain traits have greater reproductive success.
– See video: http://www.youtube.com/watch?v=LyRA807djLc
• The Result:
– Not a new species, but an adaptive change in the allele frequency of the population.
Gene Flow, Genetic Drift, and Mutation
• These Three are Non-Adaptive Factors of Evolution:
– Gene Flow: Change in allele frequencey in the population due to a migration of individuals.
– Genetic Drift: Change in allele frequencey in the population due to a sampling error.
– Mutation: Change in allele frequencey in the population due to a genetic copy error.
• They are non-adaptive factors because they happen randomly and their result tends to be deleterious for the species.
• Result:
– Only a random, merely accidental change within the same species occurs.
– A new species is not produced, not even in the case of mutation. The offspring with mutations can reproduce with individuals of the previous generation, which do not have the mutation (so they belong to the
same species).
– If the mutation occured within the sex chromosome, it is possible that they cannot reproduce, but if they cannot reproduce, then they will not be the beginning of a new species.
Mutation
• Mutación: The introduction of new alleles due to an
imperfection in the process of copying genetic information.
• Mutation in itself is not adaptive, but it can be coupled with natural selection and cause
an adaptive change.
• Together with natural selection, deleterious mutations are
eliminated and adaptive mutations remain.
The result is an adaptive, though accidental, change in allele frequencies.
In-Class Micro-Evolution Lab
A. Allele Frequencies in the Population
• Each student represents 100 finches that live in a region in Ecuador, South America.
• Students are divided into three groups:
– Some represent finches with short and wide beaks.
– Others represent finches with average beaks.
– Others represent finches with long and slim beaks.
• Count the number of finches and calculate frequencies.
In-Class Micro-Evolution Lab
B. Migration to the Galapagos Islands
• A group of finches (randomly-selected students from all three groups) migrate from the continent to the Galapagos Islands.
• Count the number of finches (both in the continent and in the Islands) and calculate frequencies.
• What happened? Natural selection? Mutation? Genetic drift? Gene flow?
Evolution? Macro-evolution? Micro-evlution?
In-Class Micro-Evolution Lab C. Drought
• A drought occurs. Trees with juicy fruits dry up and die.
• Only trees with dry, hard seeds remain.
• Finches with long and slim beaks cannot break the dry, hard seeds and most die (delete most of those students from the list).
• Finches with short, wide beaks can break the hard seeds and have a much higher reproductive success (add students to the list).
• Those with medium beaks have average reproductive success (delete half).
• What happened?
– Natural selection?
– Mutation?
– Genetic drift?
– Gene flow?
– Evolution?
– Macro-evolution?
– Micro-evolution?
In-Class Micro-Evolution Lab
D. Several Generations Afterwards
• The finches reproduce multiple times..
• The frequencies of each generation are multiplied by a random factor (flip a coin).
• Calculate the frequencies of the third generation.
• What happened?
– Natural selection?
– Mutation?
– Genetic Drift?
– Gene Flow?
– Evolution?
– Macro-evolution?
– Micro-evolution?
What Evolution is Not
• Micro-evolution, the only kind of evolution ever observed, is not an adaptive change of a single individual over time.
• It is not a change from one species to another.
• It is not a conscious or intelligent adaptation on the part of any individual from the population.
• It does not rule out (in fact, it requires) that there is an intelligent designer that directs
micro-evolution.
Conclusion
• Hence, when they speak of ‘evolution’ they
equivocate between micro- and macro-evolution,
• They argue in favor of (macro-) ‘evolution’ thus:
P1: Whatever is observed in nature is a fact of science.
P2: But evolution has been observed in nature.
C: Therefore, evolution is a fact of science.
• Refutation:
– I concede P1.
– I distinguish P2: That micro-evolution has been
observed in nature, I concede. That macro-evolution has been observed in nature, I deny.
– I distinguish the conclusion. That micro-evolution is a
‘fact of science’, I concede. That macro-evolution is a
‘fact of science’, I deny.
