BIO120H1 Chapter Notes - Chapter 5: Hornet, Adaptation, Genetic Variation

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28 Sep 2018
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BIO120: Why Evolution is True, Jerry A. Coyne (Ch.5 The Engine of
Evolution)
In association with Lecture 4 & 5
The Engine of Evolution
- Hornet is adapted to kill; as if it was designed for mass slaughter where many of their traits work
together to make the wasp a killing machine
o Large size
o Stinger
o Deadly jaws
o Big wings
o Marking pheromones and deadly venom in sting
o Rapid flight
o Coordinated attacks on bee nests
o And savage hungry behavior that prompts hornet attacks
- Native honeybees have a defensive system designed to protect themselves against hornets, where
they swarm and roast their enemy evolved response to repeated attacks by hornets
o European honeybees that are only just recently introduced into an environment with
hornets lack a defense mechanism because they evolved in an area lacking predatory
hornets and natural selection didnt require them to adapt to such attacks
o It can be predicted that either honeybees will die out or will find their own evolutionary
adaptation to the hornets that may or may not be the same as that of the native bees
- Adaptations that help organisms build a defense system allows an even playing field
- In nature, animals can appear to be designed perfectly for their physical environment and the
organisms around them easy to understand why creationism was so widely believed
- In The Origin, Darwin proposed that natural selection could produce the same results that
celestial design would; but it posed a number of problems because there was little direct evidence
for selection in natural populations since selection is an extremely slow process that only alters
populations over many years its hard to observe
- Mice Example darker soils harbor darker mice so that they can camouflage better and hide
from their predators; natural selection acts on the coat colour of mice by changing the genetic
composition of a population through a chance mutations that increases in proportion when a
specific coat colour survives longer and produces more offspring than the other variant
- Natural selection is not a mechanism imposed on a population from outside; it’s a process of how
genes that produce better adaptations become more frequent over time
- Species dont try to adapt to their environment, theres no will involved, adaptation to the
environment is an inevitable phenomena if a species has the right kind of genetic variation
- Three things are involved in creating an adaptation by natural selection:
1. Starting population has to have variants in traits, otherwise the trait can not evolve
2. Some proportion of the variation has to come from changes in the forms of genes,
where variation has to be heritable
3. Genetic variation must affect individuals probability of leaving offspring
- Genetic variation is generated by mutations responsible for varying human eye colour, blood
type, height, weight, biochemistry etc.
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- Mutations occur regardless of whether they are useful or harmful to the individual; most are
harmful or neutral, but some do end up being useful
- Theres no known biological method that increases the chances of a mutation being helpful to an
organism; chance of a mutation arising is indifferent to whether it would be helpful or hurtful to
the individual
- Evolution by natural selection is a combination of randomness and lawfulness; there is first a
random or indifferent process of the generation of mutations both good and bad, and then a
lawful process of natural selection that orders the variation by keeping the good and winnowing
the bad
- Misunderstanding about Darwinism is the idea that, in evolution, everything happens for a
reason; if evolution is forced to depend on random mutations alone, species would quickly
degenerate and go extinctchance alone cant explain the marvelous fit between individuals and
their environment
- Natural selection is the filtering of that variation in individuals and is manifestly not random, but
rather a molding force that accumulates genes that have a greater chance of being passed on than
others, and by doing so, makes individuals of a species more adaptable to their environment
- The theory of natural selection is to explain how every adaptation evolved, step by step, from
traits that preceded it; it has to explain both cooperative and antagonistic behaviours
- Selection has to mold traits in a particular way:
1. Has to gradually create them, step by step from precursors
2. Adaptations must evolve by increasing the reproductive output of its possessor
- An adaptive trait evolved by natural selection would have had to plausibly evolve in a step-by-
step scenario for the evolution of that trait, with each step raising the fitness of its possessor
- Passing on a gene requires that you first survive to age at which you can have offspring, but if a
gene knocks you off after reproductive age, then it has no evolutionary disadvantage
accumulation of these genes can explain why we deteriorate as we reach old age
- We do not expect to see adaptations in one species that benefit only members of another species;
adaptations always increase the fitness of the individual, not necessarily the group or the species
natural selections acts for the good of the species but evolution can produce features that help
an individual, while harming the species as a whole, but we never expect to see adaptations that
benefit the species at the expense of the individual
- Evolution Without Selection
o Every individual has two copies of each gene which can either be identical or different
(homozygous or heterozygous); sexual reproduction results in one copy of each gene
from one parent combining with one copy of each gene of the other parent that will create
the offspring
o Proportion of different alleles changes over time by chance, where new mutations may
enter the fray and themselves rise or fall in frequency due to random sampling
o Random change in frequency of genes over time is genetic drift; it’s a legitimate type of
evolution involving changes in frequencies of alleles over time, but it doesnt arise from
natural selection
o Accidents of sampling can happen when a population is founded by a few immigrants,
which occurs when individuals colonize an island or new area
o Both drift and natural selection produce genetic change that we recognize as evolution;
drift is a random process, while selection is the antithesis of randomness
o While genetic drift changes frequencies of alleles regardless of usefulness, selection
always gets rid of harmful alleles and raises frequencies of beneficial ones
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