Download Evolution notes Evolution as a Concept fall 2013

Biol 4974/5974 Evolution as a concept
8/22/2013
Evolution as a Concept
Learning goals
Understand how the meaning of “evolution” itself and
how it has changed over the last two centuries.
The factors that led to these changes.
Evolution as a “theory” and what that means.
How evolution can be studied using the scientific
method.
“Universal properties” among organisms
• Same mechanism of inheritance; same genetic
code in DNA.
• Bodies built of cells.
• Living organisms reflect the sum of inherited
changes over “billions of years of existence on
earth.”
1
Biol 4974/5974 Evolution as a concept
8/22/2013
What do we mean by evolution?
Based on Latin term evolutio. Meaning?
• Used to describe the development of an organism.
• Tracked to 18 century view: “preformation.”
e.g, butterfly coming out of a chrysalis
e.g., pea aphid (asexual)—multiple generations of embryos p. 5.
Common definitions of evolution (see text p. 4):
1. “The process by which different living organisms are thought
to have developed or diversified during the history of the
earth.”
2. The gradual development of something , from a simple to a
more complex form. For example, a concept or language.
3. “A pattern of movements or manuevers.”
4. “Chemistry—giving off a gaseous product.”
Merriam Webster online
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
: one of a set of prescribed movements
2
a: a process of change in a certain direction : unfolding
b: the action or an instance of forming and giving something off : emission
c (1): a process of continuous change from a lower, simpler, or worse to a higher, more
complex, or better state : growth (2): a process of gradual and relatively peaceful social,
political, and economic advance
d: something evolved
3
: the process of working out or developing
4
a: the historical development of a biological group (as a race or species) : phylogeny
b: a theory that the various types of animals and plants have their origin in other preexisting
types and that the distinguishable differences are due to modifications in successive
generations; also: the process described by this theory
5
: the extraction of a mathematical root
6
: a process in which the whole universe is a progression of interrelated phenomena
Older views
• Spontaneous generation: small organisms
P. 7 Johann van Helmont
Box 1.1, p. 8—countered experimentally by
Francesco Redi
• Fixation of species (Great Chain of Being) from
Aristotle on. Species constancy.
Challenges:
• Fossil discoveries coming to light, late 18th
century and lots in 19th century.
2
Biol 4974/5974 Evolution as a concept
8/22/2013
Darwin and Wallace
• Together presented a mechanism, Natural Selection, that
could connect all organisms
• “A single tree of life.”
• 1859, On the Origin of Species
Defined the study of evolution as:
• “The origin and transformation of species.
• “The transformation of major groups or lineages of organisms
and the search for their ancestors.
• “The transformation of physical features, such as jaws, limbs,
kidneys, and nervous systems within lineages of organisms.”
Natural selection provided the mechanism for these changes.
Modern synthesis
• Natural selection was a challenge to accept until Mendelian
genetics was understood.
• Side-tracked by the implications of mutation.
• Mutation implied major evolutionary jumps (saltations) rather
than gradual change.
• Countered with Hardy-Weinberg “equilibrium,” which
detected natural selection at work.
• RA Fisher’s models of Mendelian inheritance.
Evolution is hierarchical
• Genotype level
• Organismal level
• Population level
• Need to understand all the levels to
understand how evolution works and the
effects over time.
3
Biol 4974/5974 Evolution as a concept
8/22/2013
Why is evolution a “theory”?
• Is that a criticism?
• What is a theory in science?
Can we use the scientific method
to study evolution?
• How can we study something we cannot see?
(what about gravity, atoms, the theory of relativity? Can we see
these?)
• See P. 13 and Box 1.1
For example, we can test evolutionary ideas by
• Generating hypotheses tested by examining the fossil record.
• Generate hypotheses testing by comparing different
organisms or constructing relationships.
• Test hypotheses by conducting experiments (e.g., Box 1.3)
4