Two major patterns:
there is an enormous diversity of species occupying a wide range of very different habitats
organisms are generally wellsuited 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.
Mutation: the origin of new genetic variation
Genetic drift: changes due to chance, specifically founder effects and population bottlenecks
Gene flow: movement of genes among populations
Natural selection: Nonrandom differences in survival and/or reproduction among individual entities on the basis of differences in
heritable characteristics But only natural selection — nonrandom differences in survival and reproduction among variable individuals —
can result in the evolution of adaptations.
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.
Darwin made extensive reference to selective breeding of domesticated animals and plants, or what he called artificial selection. Unlike
artificial selection, which involves actual “selection” by a human breeder, natural selection does NOT involve choice by any particular agent.
In other words, there is no “Mother Nature” actively examining and selecting the best among the available options. How, then, can natural
Natural selection is simply the necessary logical outcome of these postulates, assuming each one holds true. They are:
1. Individuals within populations are variable.That not every individual is identical in a population is obvious for humans —
simply look around you and you will see plenty of variation. As the mussels have shown us, the same is true of other species as well, even
though we sometimes need to look closely to appreciate it. In light of these and countless other observations, we can conclude that this
postulate holds true.
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. Darwin had no understanding of how this works, but we now understand quite well that it is based on the transmission of genes
encoded in the DNA molecule. Again, we can conclude confidently that this postulate holds.
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”. To take just one example
from our inquiry case, a single female zebra mussel can produce 30,000 eggs at a time, and she may reproduce multiple times. Just imagine
what would happen if half of those grew into adult female mussels which in turn produced 30,000 eggs each, and so on over the generations.
In just a few generations, there would be enough mussels to literally fill the Great Lakes to the brim. Obviously this has not happened,
because the Great Lakes still contain water rather than wall to wall mussels. Not every egg that is laid can grow up to become an egglaying
adult — in fact, only a small minority manage to do so. Once again, we can safely c