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 catastrophicWhere did this idea come from?Literal interpretation of Bible

Hutton is considered to be the founder of modern Geology.

Hutton and Lyell introduced the idea thatthe earth was old and that geological events may occur gradually

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???

DarwinLife

Voyage of Beagle (left 1831-5yr trip)Took Lyell’s bookDid 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 inevitablebecause 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 Newsmbbnet.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 long- continued 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 concludedsome 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