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Lecture 1

BIOL 1070 Lecture Notes - Lecture 1: Bivalvia, Holocene Extinction, Local Extinction


Department
Biology
Course Code
BIOL 1070
Professor
Shoshanah Jacobs
Lecture
1

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Unit 3 bio 1070
Adaptation and Specialization
When we look at the natural world as biologists, we see two major patterns: 1) there is an enormous
diversity of species occupying a wide range of very different habitats, and 2) organisms are generally
well-suited to life in their particular habitat. Both of these are the result of evolution, the first relating to
processes that generate new biological diversity (and those that eliminate existing diversity), and the
second being the result of long periods of evolution by natural selection.
As we saw in class, natural selection is not the only mechanism of evolution. Mutation (the origin of new
genetic variation), genetic drift (changes due to chance, specifically founder effects and population
bottlenecks), and gene flow (movement of genes among populations) also contribute to changes in the
proportion of genes and heritable phenotypes in populations over time. But only natural selection — non-
random differences in survival and reproduction among variable individuals — can result in the evolution
of adaptations.
Natural selection: Non-random differences in survival and/or reproduction among individual entities on the
basis of differences in heritable characteristics.
Adaptation: 1) a characteristic that enhances the survival and/or reproduction of organisms that bear it,
relative to alternative (especially ancestral) character states; 2) a physical, physiological, behavioural, or
other characteristic evolved through natural selection. Adaptation is NOT the change undergone by an
individual organism during its lifetime in response to external conditions.
Population: for sexual species, a group of interbreeding individuals and their offspring.
Alleles: alternate (i.e., different and mutually exclusive) forms of a gene. e.g., “B” (brown eyes) versus “b”
(blue eyes).
Genotype: the set of genes possessed by an organism.
Phenotype: the physical expression of the genotype (in combination with the environment).
Frequency: the proportional representation of a phenotype, genotype, gamete, or allele in a population.
e.g., 6 out of 10 have blue eyes = 60% = a frequency of 0.6.
he Basis of Natural Selection
In the Origin of Species, Darwin had two major objectives: the first was to provide convincing evidence
that species are related through common ancestry, and the second was to argue that his mechanism of
natural selection could account for changes through time and the resulting differences among species.
These are two different issues. In principle, it is possible that species are related by common descent but
that natural selection is not the dominant mechanism that explains this fact. However, when it comes
specifically to adaptive changes among species and the traits of organisms that allow them to survive
successfully in their environments, natural selection is indeed the only known mechanism that can provide
a scientific explanation.
natural selection does NOT involve choice by any particular agent. Natural selection is simply the
necessary logical outcome of these postulates, assuming each one holds true. They are:
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1. Individuals within populations are variable.
That not every individual is identical in a population is obvious for humans..
2. This variability among individuals is at least partly heritable.
Offspring tend to look more like their parents than like unrelated members of the population, and this is
due to the existence of a mechanism of inheritance by which traits are passed on from parent to offspring.
3. Not everyone survives and reproduces, and some individuals are more successful than others.
Many more offspring are produced in each generation than could possibly survive, a phenomenon known
as “overproduction”. a single female zebra mussel can produce 30,000 eggs at a time, and she may
reproduce multiple times.
4. The differential survival and reproduction of individuals is associated with the heritable
variation among individuals (i.e., it is non-random).
This is the key to natural selection, that the individuals who do manage to reach adulthood and have
offspring of their own are, on average, better suited to surviving and reproducing in their particular
environment because of traits that they inherited from their parents.
Assuming that all four of these postulates are true, then natural selection will inevitably result. That is,
heritable traits that contribute to greater survival and reproductive success will be passed on more often
than traits that do not, and from one generation to the next they will represent a larger proportion of the
population.
How Natural Selection Works
Adaptation in an evolutionary sense does NOT involve changes by individual organisms in response to
pressures imposed by the environment.
This is how the evolution of antibiotic resistance works in bacteria. Individual bacteria vary in how
sensitive they are to antibiotic treatment, such that the most susceptible are killed early in the treatment
whereas more resistant individuals survive and reproduce.
In the case of the Blue-B-Gone animation, the resistant red dots were already present in the population in
low numbers. Before the population was treated with Blue-B-Gone, the difference between blue and red
dots may have been irrelevant, but once the environment changed to include a substance toxic only to
blue dots, the red phenotype became advantageous..
It is also possible for resistance genes to move from one population of bacteria to another through gene
flow. This is why it is a significant concern that resistant bacteria from one place might be introduced into
a new area where the bacteria are not currently resistant.
the Accurate Language Challenge:
Bacteria that cause disease exist in large populations, and not all individuals are alike. If some individuals
happen to possess genetic features that make them resistant to antibiotics, these individuals will survive
the treatment while the rest gradually are killed off. As a result of their greater survival, the resistant
individuals will leave more offspring than susceptible individuals,
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