BIO 212
Environmental Biology
LECTURE 6
Natural Selection and Evolution
Reading: Chapter 5, pp 117-129, + pp 140-141 (The Science Behind the Story Box)
I. WHAT IS EVOLUTION?
A. Evolution is change, and biological evolution can be defined as changes in any attribute of a
population over time.
B. Natural selection is the process of adaptive evolution and is most commonly associated with
evolutionary change.
C. The Origin of Species
1. Charles Darwin’s original view of the diversity of species on earth was based on a literal
interpretation of the bible. The fixity of species.
2. He then went on a five-year voyage to South America and the Galapagos islands.
3. Returns believing that organisms are the product of their environment, and can change
over time.
II. MODES OF EVOLUTION
A. Charles Darwin wasn’t the first to come up with the idea of evolution.
1. However, his contribution was the METHOD by which it occurred. Evolution by
NATURAL SELECTION.
a. Concept of selection by natural means an extension of what humans had been doing for
1,000s of years 2. Artificial Selection – selection for particular traits by humans.
B. Process of natural selection.
Darwin developed the theory of natural selection based upon 4 observations that he made.
1. All plants and animals produce more offspring than are needed to simply replace the
parents.
a. Are humans an exception? Maybe not.
2. All the young are different from one another, and some are better suited for survival
than others. Life is difficult, and not all individuals survive.
3. Many of these behavioral or physiological differences, which we term traits, are
inherited from the parents. Much of the variation we observe is heritable.
4. Some individual lineages are more successful than others. This is not an issue of dying
versus surviving (#2 above), but rather, how many descendants a lineage produces
compared to other lineages.
5. Put these 4 observations together, we can come up with a compact definition of Natural
Selection:
Natural selection is the differential success in reproduction, and its product is
adaptation of organisms to their environment.
a. Put another way:Lineages with the most appropriate biological programming for
prevailing conditions will leave the most descendants.
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BIO 212
Environmental Biology
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6. Natural selection thus occurs from the interaction between the environment and the
inherent variability in a population.
a. Variations in a population arise by chance, but natural selection is not a chance
phenomenon since environmental factors set definite criteria for reproductive success.
C. Natural selection is not synonymous with evolution.
1. Evolution refers to temporal changes of any kind, whereas
2. Natural selection specifies one particular way in which these changes are
brought about.
3. An example of natural selection – The classic study Biston betularia –Peppered moth
a. Caveat – Science is not immutable.
III. SOME OTHER CONSIDERATIONS ON NATURAL SELECTION
A. There are a number of ways to describe the reproductive efforts of individuals.
1. Fecundity – Usually measured as the number of eggs produced by a female.
2. Fertility – the number of eggs that are fertilized.
3. Ecological fitness. The number of offspring that reach reproductive age.
4. Fitness is a relative term, not an absolute term.
5. Natural Selection does not predict perfection