lecture 1: darwinism, mendelism, and the modern synthesis of evolutionary biology 1)early concepts...

Lecture 1: Darwinism, Mendelism, and the Modern Synthesis of Evolutionary Biology

1) Early concepts of natural selection-Raw material existed long before Darwin-Why did Darwin/Origin have such a large impact?

2) Inheritance-Mendel’s experiments-Mendel’s Laws

3) The Modern Synthesis-Fisher: Polygenic inheritance

Earliest Ideas About Evolution

At the beginning of a dynasty, taxation yields a large revenue from small assessments. At the end of the dynasty, taxation yields a small revenue from large assessments.Government is an institution which prevents injustice other than such as it commits itself.

https://www.youtube.com

Aristotle (384-322 BC)

Scala naturae

Muqaddimah or “Introduction to History” (1377)

It started out from the minerals and progressed, in an ingenious, gradual manner, to plants and animals. The last stage of minerals is connected with the first stage of plants, such as herbs and seedless plants. The last stage of plants, such as palms and vines, is connected with the first stage of animals, such as snails and shellfish which have only the power of touch. The word ‘connection’ with regard to these created things means that the last stage of each group is fully prepared to become the first stage of the next group.

The animal world then widens, its species become numerous, and, in a gradual process of creation, it finally leads to man, who is able to think and reflect. The higher stage of man is reached from the world of the monkeys, in which both sagacity and perception are found, but which has not reached the stage of actual reflection and thinking. At this stage we come to the first stage of man.

https://www.youtube.com/watch?v=2-s1Y5bD66U

Earliest Ideas About Evolution

Ibn KhaldunMuqaddimah or “Introduction to History” (1377)

Mechanics(Newton)

Empiricism(Bacon)

Rationalism(Descartes)

Skepticism(Bayle)

Liberalism(Locke)

The Enlightenment (1620s- 1780s)

Biogeographic PatternsA Huge Natural History Problem: The Story of the Ark

-Columbus (1492)

-Vasco Da Gama (1497)

-Magellan (1522)

15th & 16th Centuries:Age of Exploration

Linnaeus(Carolus Linnaeus) (1707-1778)

Mount Ararat

Buffon 1707-1788 (Georges-Louis Leclerc, Comte de Buffon)

“The ark came to rest upon the mountains of Ararat." (Genesis 8:4)

??

?

?

?

?

?

?

??

platypusriver otter

??

?

?

?

?

?

?

??

Jefferson Buffon

Lewis and Clark Expedition

Other Significant Pre-Darwin Glimpses of NS

-Few had a large impact

James Hutton (1726-1797)

Erasmus Darwin (1731-1802)

William Charles Wells (1757 – 1817)

Patrick Matthew (1790 – 1864)

Jean Baptiste Lamarck (1744-1829)

Edward Blyth (1810 – 1873)

“There is a law universal in nature, tending to render every reproductive being the best possible suited to its condition that its kind…This law sustains the lion in his strength, the hare in her swiftness, and the fox in his wiles…those individuals who possess not the requisite strength, swiftness, hardihood, or cunning, fall prematurely without reproducing…their place being occupied by the more perfect of their own kind, who are pressing on the means of subsistence . . .

CD: “I freely acknowledge that Mr. Matthew has anticipated by many years the explanation which I have offered…under the name of natural selection. I think that no one will feel surprised that neither I, nor apparently any other naturalist, has heard of Mr. Matthew's views, considering…that they appeared in the Appendix to a work on Naval Timber and Arboriculture. I can do no more than offer my apologies to Mr. Matthew for my entire ignorance of his publication.”

Patrick Matthew (1790 – 1864)-Scottish landowner/farmer

-On Naval Timber and Arboriculture (1831)

-Royal Navy: forestry practices

Early Ideas: Evolutionary ProcessesErasmus Darwin (1731-1802)

Physician, poet, naturalist

First formal theories

Organic life beneath the shoreless wavesWas born and nurs'd in ocean's pearly caves;First forms minute, unseen by spheric glass,Move on the mud, or pierce the watery mass;These, as successive generations bloom,New powers acquire and larger limbs assume;Whence countless groups of vegetation spring,And breathing realms of fin and feet and wing.-The Temple of Nature. 1802.

“The final course of this contest among males seems to be, that the strongest and most active animal should propagate the species which should thus be improved.”

Alfred Russel Wallace

British explorer and naturalist

“As animals usually breed much more quickly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species…otherwise the world would long ago have been crowded with those that breed most quickly…it occurred to me to ask the question, why do some die and some live? And the answer was clearly, on the whole the best fitted live …In this way every part of an animals organization could be modified exactly as required, and in the very process of this modification the unmodified would die out, and thus the definite characters and the clear isolation of each new species would be explained.”

Charles Darwin (1809-1882)

Cambridge University

Naturalist on Beagle (1831-1836)

Beagle established him: geologist and biologist

Worked privately on NS for 20+ years

Published On the Origin Of Species by Means of Natural Selection in 1859

7 31 46 51 61

Galapagos mockingbirdNesomimus parvulus

Galapagos finchesGeospiza

John Gould

"I never dreamed that islands, about 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted; but . . . this is the case.—Darwin's journal, 29 Sept.1835

Thomas Malthus (1766-1834)

Political economist: deterioration of Britain

Principles of Population (1798)

“The power of population is indefinitely greater than the power in the earth to produce subsistence for man. Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison with the second.”

"In October 1838, that is fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus' Population, and being well prepared to appreciate the struggle for existence [a phrase used by Malthus] which everywhere goes on from long-continued observation 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 result of this would be a new species. Here then I had at last got hold of a theory by which to work.”

Darwin’s Theory of Natural Selection

Origin: Why so controversial at the time?

Many scientific challenges

St. George Jackson MivartOn the Genesis of Species 1871

Arthur Holmes 1920s

…”we shall require 2,500,000,000 (two thousand five hundred million) years for the complete development of the whole animal kingdom to its present state. Even one quarter of this, however, would far exceed the time which physics and astronomy seem able to allow for the completion of the process.”

Origin: Why so controversial at the time?

A Major Dilemma for Darwin: InheritanceHow was variability carried from one generation to the next?

Late 1800s:

MickJerry

James

Gregor Johann Mendel (1822-1884)

Monastery in Brunn, Austria (now Brno, Czech Republic)

Mechanism of inheritance Conducted experiments on

garden peas

S sS

s

SS

Ss

Ss

ss

Punnett Square

Blending Inheritance?

Mendel Laws

Mendel Results

Early 1900s: Reaction to Mendel

SS ss

Ss

Reaction to Mendel’s Results

The Modern Synthesis of Evolutionary Biology (1936-1947)The Merger of Darwinism and Mendelism

Fisher Mayr-Polygenic traits -Closely related species:

geographically separated

Wright Simpson-Evolution of small populations -FR consistent

with

-Genetic drift and inbreeding gradual divergence and branching

Haldane-Mathematics: selection on polygenic

traits can produce very rapid change

Dobzhansky-Animal populations: lots of genetic variation

-Recessive alleles: reservoir of ‘hidden’ genetic diversity

Ronald Fisher (1890-1962)

Wheat Seed Color

The Genetical Theory of Natural Selection (1930)

Invented statistics

3 loci

7 multilocus genotypes

Nicotiana longiflora East (1916)


Assume incomplete dominance

1/4096


454 F2 plants

Summary: Polygenic Inheritance

Directional selection

Fitness(Selection)

Phenotypes

Response

Most Evolutionary Change:

Major Conclusions of the Modern Synthesis (1930-50s)

Major Conclusions of the Modern Synthesis

Observation 1: Individuals within species are variable.

Observation 2: Some of the variability is passed to offspring.

Observation 3: More offspring are produced than can survive bec resources are limiting.

If 1-3 are true it must be true that:

individuals with favorable variations will live to reproduce and contribute more offspring to the next generation.

Mutation, segregation, independent assortment

As intact alleles

Combinations of alleles across many loci (polygenic traits)

Frequencies of favorable alleles will increase