Transcript Species are “fixed in form”!

EVOLUTION!!!!
CHAPTER 19 and then 21 and then 20!
Pre-Darwin European Views
Species are “fixed in form”!
Plato + Aristotle
Unchanging essences
Ideal or unique forms
“Great Chain of Being”
1579 drawing of the great chain of being from Didacus Valades,
Rhetorica Christiana
Sean Nee (Nature 2005 435:429):
For centuries the "great chain of being" held a
central place in Western thought. This view
saw the Universe as ordered in a linear
sequence starting from the inanimate world of
rocks. Plants came next, then animals, men,
angels and, finally, God. It was very detailed
with, for example, a ranking of human races;
humans themselves ranked above apes above
reptiles above amphibians above fish.
Another contributor to the idea that species are fixed
in form was the idea of …..
Species created for special purposes by God
And finally Linnaeus ….
•Studied natural world to
reveal the Divine Order of
God's Creation
•Naturalist's task to construct
a "natural classification" that
would reveal this order
Portrait of Carl Linnaeus at 32 by J. H. Scheffel. Oil
Painting, 1739.Reproduction courtesy Uppsala University
Art Collections
Smithsonian Museum of Natural History web site
Who chipped away at this idea?
Lamarck..
More known for “inheritance of acquired
characteristics”
•BUT also introduced idea of..
”transmutation of species”
•First to think about one species
changing into another
Life was continuously being generated
Microbes were simply recently generated
organisms
Species could move from one rung of ladder to
another (due to internal urges), turning from one
species into another.
“It was an innate quality of nature that organisms
constantly 'improved' by successive generation, too
slowly to be perceived but observable in the fossil
record.
Mankind sat at the top of this chain of progression,
having passed through all the previous stages in
prehistory.
However, this necessitated the principle of
spontaneous generation, for as a species transformed
into a more advanced one, it left a gap: when the
simple, single-celled organisms advanced to the next
stage of life, new protozoans would be created (by the
Creator) to fill their place.“ http://www.victorianweb.org/science/lamarck1.html
More Pre-DarwinViews
Earth is young and earth events are dramatic and
often catastrophic
Where did this idea come from?
Literal interpretation of Bible
Hutton and Lyell introduced the idea that
the earth was old and that geological
events may occur gradually
Hutton is considered to be
the founder of modern
Geology.
More Hutton and Lyell….
very small changes over long periods add up to
create dramatic large changes=gradualism
They promoted the idea of
Uniformitarianism=geological forces that have
shaped the earth are the same forces that we see
around us today.
We do not need to invoke
supernatural forces..
Pre-DarwinViews
1. Species are fixed in form
2. Earth is young and earth events are
catastrophic
3. Species perfect so cannot go extinct
Extinction implies imperfection
“If God had created all of nature according to a
divine plan at the beginning of the world, it would
seem irrational for Him to let some parts of that
creation die off.
If life consisted of a Great Chain of Being,
extending from ocean slime to humans to angels,
extinctions would remove some of its links.”
UCMP Berkley
Cuvier (founder of paleontology) introduced the idea
of extinction!
• studied elephant fossils found near Paris
• proclaimed that they were a separate species that
had vanished from the earth!
Indian Elephant
vs
Mammoth jaws
Later studied many other big mammal fossils and
demonstrated that they too did not belong to any
species
alive today.
“By the end of the 1700s, paleontologists had
swelled the fossil collections of Europe, offering a
picture of the past at odds with an unchanging
natural world”.
UCMP Berkeley
Pre-Darwin Views
1. Species are fixed in form (Lamarck)
2. Earth is young earth and earth events are
catastrophic (Geologists-Lyell and Hutton)
3. Species perfect so cannot go extinct (Cuvier)
Why are each of these “problems” for Darwin???
Darwin
Life
Voyage of Beagle (left 1831-5yr
trip)
Took Lyell’s book
Did not believe in Lamarck’s
idea that species could change
Reads Malthus and waits 20 years.
Who was Malthus?
•social reformers thought “ills of man”
(suffering, poverty, starvation) could be
eradicated.
•Malthus said these “ills” are inevitable
because poverty and famine are natural
outcomes of population growth and
food supply
•Said there is a “struggle for
existence”.
Early to mid 1800’s was a time of great poverty in
many of the new urban areas
Great potato famine in Ireland occurred around the
middle of the century.
Illustrated London News
mbbnet.umn.edu/doric/icons/potato2.jpeg&imgrefurl
"In October 1838, that is, fifteen months after I had
begun my systematic inquiry, I happened to read
for amusement Malthus “On Population”, and
being well prepared to appreciate the struggle for
existence which everywhere goes on from longcontinued observation of the habits of animals and
plants, it at once struck me that under these
circumstances favourable variations would tend to
be preserved, and unfavourable ones to be
destroyed. The results of this would be the
formation of a new species. Here, then I had at last
got a theory by which to work".
Charles Darwin, from his autobiography (1876)
Darwin applied this to organisms in general
1. Species are capable of over-reproducing
(for ex. a single pair of elephants could
theoretically produce 19 million elephants in
750 years)
2. But populations always tend to eventually run
out of something.. whether it is food or nesting
spots
together this means that there must be a
“STRUGGLE FOR EXISTENCE”
a term Malthus used for humans
Darwin concluded
some live some die... and therefore some
“favorable variations would tend to be preserved
and unfavorable ones destroyed”...
A note from Wallace
Who was Wallace?
•Not well off
•Left school at 14 to work
•Became a commercial
collector, dragging his
brother with him to South
America
By early 1852 Wallace was in ill health and in no condition
to proceed any further. He decided to quit South America,
and began the long trip back down the Rio Negro and
Amazon to Pará. When he finally reached the town on the
2nd of July, he found that his younger brother Herbert had
died of yellow fever.
Within a few days he set out for England. Unfortunately, on
the 6th of August the brig on which he was sailing caught
fire and sank, taking almost all of his possessions--including
some live animals--along with it. For ten days Wallace and
his comrades struggled to survive in a pair of badly leaking
lifeboats, then were sighted and picked up by a passing
cargo ship also making its way back to England. As luck
would have it this vessel was also old and slow, and itself
nearly foundered when hit by a series of storms. In all,
Wallace's ocean crossing took eighty days
www.wku.edu
Several years later on another collecting trip
Indonesia/South Pacific
Malarial fever-”flash of insight”
Both papers were presented at the Linnaean
Society of London
Within a year
Darwin publishes 1859
Thoughts on …….Why do we know Darwin’s
name better than Wallace’s????
What is the difference between evolution and
natural selection?
Evolution is ………
•A change in gene frequencies in a population
over time
•A change in form/trait/behavior/protein
production in a population over time (need to
know that that trait has a genetic basis).
•Darwin called it “descent with modification” and
“transmutation of species”
Note issue of Scale
Natural selection is……….
•The mechanism or engine of evolution
•Differential success in reproduction as a result of
traits that are genetically based
Reception of Darwin’s idea-evolution or
transmutation of species was accepted
So yes, species can change from one thing into another
But there was a persistent misconception….
Any thoughts?
Life is a copiously branching bush,
continually pruned by the grim reaper of
extinction, not a ladder of predictable
progress. Most people may know this as a
phrase to be uttered, but not as a concept
brought into the deep interior of
understanding. Hence we continually make
errors inspired by unconscious allegiance to
the ladder of progress, even when we
explicitly deny such a superannuated view of
life.
Stephen Jay Gould from Wonderful Life
DailyMail UK
www.corante.com/loom/evolve.jpg&imgrefurl
VS
People got hung up on the idea that evolution was
progressive….(*theme*)
Which comment is ladder-ish and which is Bush-ish
“We evolved from a chimp”
“Share a common ancestor”
Reception of Darwin’s ideas
Natural selection part was not accepted.
WHY?....
It was because of this nagging “PROBLEM OF
INHERITANCE”.... (how do traits get passed
down??)
Review Lamarck’s view of inheritance
(Professor of Insects and Worms at Natural History
Museum in Paris)
Body cells would be excited to emit "gemmules" or
"pangenes"
They were discharged into the bloodstream and
circulated around the body then would enter germ
cells
Weismann's “germ–soma” distinction in the 1890s
•chopped off the tails of rats/mice shortly after birth
and then bred the animals
•If acquired characteristics can be passed on then
young should have been born with shorter tails-right?
(1,500 rats over 20 generations OR 68 white mice,
repeatedly over 5 generations, and reporting that no
mice were born in consequence without a tail or even
with a shorter tail)
Many believed in blending inheritance.
What is blending inheritance?? Imagine all these
balls are filled with paint and you mimic
mating by pulling them out of a bucket two by
two….
Fig. 1. Difference between the outcomes from blending and from particulate inheritance. In post-Mendelian terms,
we assume a single diallelic locus, and hence three diploid genotypes (AA, blue; Aa, green; aa, yellow). Under
particulate inheritance, the population's variability is preserved from generation to generation. In contrast, the
conventional wisdom of Darwin's day saw offspring inherit a blend of parents' characteristics, here represented as
the average of the two parental shadings. The result is that the variability diminishes in successive generations
(the variance is halved each generation if mating is at random) SCIENCE MAGAZINE B. MAY
•Variation is lost or
washed out
•Favorable genes are
diluted before selection
can get a chance to
work
•there is nothing for
NATURAL
SELECTION TO “GET
ITS HANDS ON”
•Selection is a weak
process with blending
inheritance
What did Mendel discover and why was he
successful?
1865 Mendel publishes his PARTICULATE
VIEW of Inheritance
(when was on Origin of Species Published?)
•Almost completely ignored
•No one noticed that this particulate view would
make natural selection work
Modern Synthesis
Mid 20’s through early 40’s (Fisher, Haldane, Wright)
•Reconciled natural selection with Mendelian genetics..
•Published substantial works showing that SMALL
amounts of variation within species could over long
periods of time change the appearance of organisms!
Ronald A. Fisher
John B. S. Haldane
Sewall Wright
“Darwin undid the essentialism that Western
philosophy had inherited from Plato and Aristotle and
put variation in its place. He helped to replace a static
conception of the world with the vision of a world of
ceaseless change.”
Futyma 98