Download C. The Origin of Species

BIO 212
Environmental Biology
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LECTURE 6
Natural Selection and Evolution
Reading in Environment, Raven et al. Chapter 4, pp 64 -67
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 5 observations that he made.
1. All plants and animals produce more offspring than are needed to simply replace the
parents. (#1 Overproduction in Environment, p 65)
a. Are humans an exception? Maybe not.
2. All the young are different from one another, and some are better suited for survival
& reproduction than others. (#2 Variation in Environment, p 65)
Individuals vary in their ability to survive, and living long enough to reproduce.
Moreover, individuals differ in the number of offspring they are capable of producing.
This is all about genetic potential. Nos. # 4 & 5 (below) reflect what happens when
genetic potential meets the limits of reality (e.g. resource availability, predation)..
3. Many of these behavioral or physiological differences, which we term traits, are
inherited from the parents. (part of #2 Variation) Much of the variation we observe is
heritable. If a trait is not heritable, cannot be passed to the next generation, and
evolution cannot occur.
4. Differential survival. Some individual lineages are more successful than others.
(#3 Struggle for existence in Environment, p 65)
There are more organisms (due to #1) then there are resources to support them. Some
lineages are better competitors for those resources, and hence, they are more likely to
survive and leave offspring behind.
BIO 212
Environmental Biology
5. Differential reproduction. (#4 Differential reproductive success in Evolution, p 65)
Given their genetic lineage and the limits of the environment, some individuals will
produce more offspring than others. Those that leave more offspring will come to
dominate the gene pool in future generations. This is the key to natural selection.
Populations evolve, not individuals.
)Put these 5 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.
Put another way: Lineages with the most appropriate biological programming for prevailing
conditions will leave the most descendants.
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
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