Descent With Modification:

a Darwinian View of Life

Chapter 22BCOR 012 A

January 21, 2011

In 1645, Bishop Ussher of Ireland stated that the Earth must have been created on October 26th, 4004 BC.

Jean Baptiste Lamarck1744-1829

Curator at the Natural HistoryMuseum in Paris

“… Nature has in favorable times, places, and climates multiplied her first germs of animality, given place to developments of their organizations, . . . and increased and diversified their organs. Then. . . aided by much time and by a slow but constant diversity of circumstances, she has gradually brought about in this respect the state of things which we now observe.

Text of a lecture given by Lamarck at the Musée National d'Histoire Naturelle, Paris, May 1803

SEA CLIFF WITH STRATA AT JOGGINS, NOVA SCOTIA

SCALE TREE TRUNK FOSSILIN PLACE IN THE STRATA AT JOGGINS, NOVA SCOTIA

DIAMETER OF TRUNK: 60 cm

COAL MEASURE SEQUENCE AT POINT ACONI,CAPE BRETON ISLAND.

COAL

SHALE (MUD STONE) with scattered leaf fossils

SHALE with rootbearing Fossils in place

Leaf, Stem, and Cone Fossils of the Scaletrees

One inch

Rootbearing Fossil of the Scaletrees

One inch

WILLIAM SMITH (1769-1839)and his map.

William Smith’s map - inferring a vertical sequence upward from older to younger rocks.

Jurassic beds near Lyme Regis on the south coast of Dorset, England, and ammonites from one of the beds. While studying these beds and others about 1800, William Smith developed the concept of "guide fossils."

Georges Cuvier (1769-1832) and Alexandre Brongniart (1770-1847) early recognized the phenomena of restriction of distinctive fossils to particular zones, formations or series — guide fossils — and applied this tool in their stratigraphical studies. Moreover, they observed a pattern or trend in the change from level to level. Of the shells found in the upper, more recent levels, he states that the "eye of the most expert naturalist cannot distinguish from those which at present inhabit the ocean." Forms of life recovered from successively more ancient strata were observed to become progressively more strange and "peculiar" (Cuvier 1817:13, 108-109).

Charles Darwin, 1809-1882

Reverend John Henslow,1796 - 1861

clergyman and naturalist

Henslow’s sparrow

Robert FitzRoy,Captain of the H.M.S. Beagle

The Voyage of the H.M.S. Beagle

1831-1836

Blue-black Grassquit, Volatinia jacarina

Genetic Analysis and Phylogeny of the Galapagos Finches

Darwin’s Beagle Voyage Observations:

• Geographic regions have distinctive floras and faunas

• Islands are centers of endemism• Organisms are adapted to the conditions under which they live

• Geographically neighboring regions have related species.

Charles Lyell,

1797-1875

UNIFORMITARIANISM

Hutton and Lyell’sinfluence on Darwin:The idea that slow processes operating over vast periods of time could produce great changes.

Darwin’s 1837 phylogeny

Alfred Russell Wallace1823-1913

Charles Lyell, a geologist, presented the work of both men at a meeting of the Linnaean Society in 1858.

Darwin in 18591st printing sold out in a single day!

Five premises underlying Darwin’s theory:

• Variability: Populations of organisms are variable• Heritability: Some of the variable traits are passed

from generation to generation• Overproduction: More individuals are produced in

a population than will survive to reproduce• Competition: Individuals compete for limited

resources• Differential Survival: Those individuals better

suited to their environment will leave more descendents than less well suited individuals.

Evidence Supporting Darwin’s Views ...

The equivalency of structures serving quite different functionsprovides evidence of common ancestry.

HomologyHomology

Variation under domestication: an entire array of dogs have been bred from a

wolf-like common ancestor.

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowersand stems

Broccoli

Cauliflower

Flowerclusters

Cabbage

Terminalbud

Lateralbuds

Darwin reasoned that if, under artificial selection, so much change could be produced in a relatively short time, than what a great amount of change should be possible over hundreds of thousands of generations!

Two main features of the Darwinian view of life:

• The diverse forms of life have arisen by descent with modification from ancestral species

• The mechanism of modification has been natural selection operating over immense spans of time

Evolution Explains Three Key Observations About

Life:

• The good “fit” of organisms to their environment (adaptation)

• The unity ( shared characteristics ) of life

• The diversity of life

Charles Darwin, 1809-1882

On the Shoulders of Giants -Scientists Who Influenced Darwin

JAMES HUTTON 1726-1797

Geologist, chemist, naturalist, father of

modern geology

GRADUALISM

Hadrian’s wall

Hadrian wished to consolidate his boundaries. He visited Britain in 122 AD, and ordered a wall to be built from west to east "to separate Romans from Barbarians".

Charles Lyell,

1797-1875

UNIFORMITARIANISM

Hutton and Lyell’sinfluence on Darwin:The idea that slow processes operating over vast periods of time could produce great changes.

Georges Cuvier (1769-1832) recognized the restriction of distinctive fossils to particular geological series.

• Moreover, he observed a pattern in the change from level to level. Of the shells in the upper, more recent levels, he states, " the eye of the most expert naturalist cannot distinguish from those which at present inhabit the ocean." Forms of life recovered from successively more ancient strata were observed to become progressively more strange and "peculiar" (Cuvier 1817:13, 108-109).