The Fossil record…

Life has changed & changed the Earth
Succession of types

LaMarck
•	Organisms adapted to 
their environments
•	through acquired traits
•	change in their life time
•	Use & Disuse
organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm
•	Perfection with Use & Need
the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat
•	transmit acquired characteristics to next generation 
In historical context
Charles Darwin
•	1809-1882
•	British naturalist
•	Proposed the idea of evolution by natural selection
•	Collected clear evidence to support his ideas
Voyage of the HMS Beagle
•	Travels around the world
•	1831-1836
•	makes many observations 
of natural world
•	main mission of the Beagle was to chart 
South American 
coastline
Voyage of the HMS Beagle
•	Stopped in Galapagos Islands
Galapagos
The Birds…
•	Galápagos birds
•	22 of the 29 species of birds on the Galapagos are endemic 
•	found only on these islands
•	collected specimens of all
•	One particular group…
•	at first, he paid little attention to a series of small birds
•	some were woodpecker-like, some warbler-like, & some finch-like
Darwin’s finches
•	Darwin was amazed to find out they were all finches
•	14 species
•	but only one species on South American mainland 
•	500 miles away
•	all the birds had to originally come 
from mainland 
species
Correlation of species to food source
Darwin’s finches
•	Differences in beaks 
•	associated with eating different foods
•	adaptations to foods available on islands
Darwin’s finches
•	Darwin’s conclusions 
•	small populations of original South American finches reached islands
•	variation in beaks enabled some to obtain food successfully in the different environments
•	over many generations, the populations of finches changed anatomically & behaviorally
•	accumulation of advantageous traits
•	emergence of different species

Correlation of species to food source

Unique species
Artificial selection
Selective breeding
Selective breeding
Lots of hidden variation comes out!
A Reluctant Revolutionary 
•	Returned to England in 1836
•	wrote papers describing his collections & observations
•	long treatise on barnacles
•	draft of his theory of 
species formation in 1844
•	instructed his wife to 
publish this essay upon 
his death
•	reluctant to publish but 
didn’t want ideas to die 
with him
And then came the letter….
The time was ripe for the idea!

November 24, 1859, Darwin published 

Essence of Darwin’s ideas
Natural Selection
•	Darwin referred to all of these factors together as natural selection
•	variation
•	production of more offspring than can survive
•	competition
•	for food, for mates & nesting 
spots, to escape predators
•	differential survival based
on traits
•	successful traits = adaptations
LaMarckian vs. Darwinian view
•	LaMarck
•	in reaching higher 
vegetation giraffes 
stretch their necks & transmits the acquired longer neck to offspring
•	Darwin
•	longer-necked giraffes survive better & leave more offspring who inherit their long necks
•	genes
"Nothing in biology makes sense except in the light of evolution."
-- Theodosius Dobzhansky
March 1973
Geneticist, Columbia University
(1900-1975)