BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 12 - PLANT SYSTEMATICS; DARWINIAN EVOLUTION
Plant systematics: see also
II. Evolution - change over time; Organic Evolution is genetic change
in a population of organisms that over time
A. Must be genetic-inherited, not acquired
B. The concept of evolution
originated long before Charles Darwin (1809-1882)
(384-332 BC.) - saw design and purpose in nature and thought living organisms
moved from an imperfect, simple state to a more perfect, more complex state
Cuvier (1769-1832) - promoted the notion of "Catastrophism" as a result
of his study of fossils. He argued that there were repeat creations and
extinctions, the latter caused by floods or droughts. He published in 1825.
Lamarck (1744-1829) thought organisms were driven by some inner force
toward greater complexity; thought organisms could pass on traits to their
offspring that they acquired during their lives ("Lamarckanism"). Proposed
his theory in 1809. Eramius
Darwin (1731-1802), Charles's grandfather, promoted a version of
Lamarckanism, using mainly animals to
theory although his
style of writing is often more admired than his views on evolution.
Hutton, a geologist, championed "Gradualism", a view supported by
another geologist, and adopted by Darwin. They, like the zoologist
Buffon, were convinced that the earth was hundreds of thousands to million
of years old; not some 6000 years as was maintained by some biblical
Others, contemporaries of Darwin, also worked on the problem of evolution
in the broad sense.
Darwin [REQUIRED READING]
Review [REQUIRED READING]
place in historical time
A. Darwin could not accept the idea that living organisms are "specially
created" or that they are unchanging, appearing today exactly as their ancestors
have always appeared.
B. Proposed that evolution occurs by natural selection
1. 5 year trip as a
geologist/naturalist on the
Beagle - spent time in South America and in
2. He theorized that tortoises,
finches, lizards, "sunflower" trees, and other unique plants and animals
on the Islands were similar to forms on the mainland of South America because
they were descended from those organisms.
3. The differences between each island group resulted from the inhabitants
of each island having been isolated from each other and changing slowly and
separately in response to the conditions on their own island.
C. Timing was right for Darwin's proposal
1. Artificial selection- selecting and breeding only those individuals that
possessed desirable traits
a. Bull dogs, St. Bernards, Chihuahuas, beagles- all same species
b. Cabbage, cauliflower, broccoli, kale, kohlrabi, Brussels sprouts- all
Malthus' work on populations
3. James Hutton (in 1795) and Charles Lyell (in 1831) argued the earth was
far older than had previously been suspected. They argued for a gradual change
over time ("Gradualism") for geological changes.
D. Darwin's mechanism of evolution by natural selection, developed mainly
from 1835-1844 and refined until 1858, was independently developed by
Alfred Wallace (1823-1913),
working in Malaysia and Indonesia in a matter of a few days while ill. He
summarized Darwin's entire theory in a short letter sent to the
Linnean Society of London
in June of 1858.
E. Darwin's work had been seen (as early as 1844) only by the botanist Joseph
Dalton Hooker (1817-1911); Hooker and Lyell showed Wallace's letter to Darwin
and urged a joint publication. This was presented as a joint paper to the
Society on 1 July 1858 with publication of the paper following a few months
F. Darwin abandoned his huge manuscript and decided to publish an "abstract".
This appeared on 24 November 1859 with the title
origin of species by means of natural selection, or the preservation
of favoured races in the struggle for life. The entire printing of 2500 copies
was sold that day.
G. The Origin caused considerable
argument [REQUIRED READING] between scientists and philosophers, with
both noting his theory's
failures [REQUIRED READING].
1. Supporters included
known as Darwin's bulldog; Joseph Dalton Hooker, a botanist at the Royal
Botanic Garden, Kew, England; and Asa Gray, a Harvard University botanist,
his American champion.
2. Opponents included the English zoologist and head of the British Museum
(Natural History) in London,
Sir Richard Owens
and Gray's Harvard fellow professor
IV. Evolution by natural selection
Darwin's [REQUIRED READING] observations about the natural world
1. Variation- individuals vary and this variability is heritable
2. Overproduction- each species produces more offspring than will survive
3. Competition- organisms compete with one another for the limited resources
available to them
4. Natural selection works on the individual phenotype, and thus selects
individuals which, in turn, change the population gene pool
5. Survival to reproduce (survival of the fittest) - individuals that are
selected must be able to produce viable, fertile offspring to pass on the
successful genes within the population
6. Time - long periods of time must be available, since some changes occur
B. As a result of natural selection, there is an increase of "favorable genes"
and a decrease of "unfavorable genes" within a population
C. Over time, enough changes may occur to cause a new species to arise
Rates of Evolution - Two interpretations about the pace of evolution
based on the fossil record
VI. Modern Evolutionary Theory
A. Darwin and Wallace had no concept of modern genetics
B. Early genetics rejected the concept of natural selection
C. Modern views of evolution formulated from 1938 until 1950 by numerous
D. Concept of punctuate equilibrium and related theories proposed from 1972
Other sites of interest:
of Natural Selection
fair summary with animal examples
of the history of systematic botany - More than you need!
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Last revised: August 26, 1998 Straney