AP Biology

Lecture #39Introduction to Evolution

Descent with Modification: A Darwinian View of Life

Evolution• Evolution: the change over time of the

genetic composition of populations• Natural selection: populations of

organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success)

• Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction

November 24, 1859

Life’s Natural History is a record of Successions & Extinctions

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Ediacaran

Precambrian,Proterozoic,

&Archarozoic

Anae

robi

c Ba

cter

ia

Inse

cts

Repti

les

Din

osau

rs

Mam

mal

s

Bird

s

Land

Pla

nts

Seed

Pla

nts

Plan

ts

Arth

ropo

ds

Chor

date

s

Jaw

less

Fis

h

Tele

ost F

ish

Amph

ibia

ns

Phot

osyn

theti

c Ba

cter

ia

Gre

en A

lgae

Mul

ticel

lula

r Ani

mal

s

Mol

lusc

s

1.5

4500

700

63

135

180

225

280

350

400

430

500

570

Flow

erin

g

mya

Evolutionary history• Linnaeus: taxonomy• Hutton: gradualism• Lamarck: evolution• Malthus: populations• Cuvier: paleontology

• Lyell: uniformitarianism• Darwin: evolution• Mendel: inheritance• Wallace: evolution

Mid-Eighteenth-Century ContributionsCarolus Linnaeus and Taxonomy

a. Taxonomy is the science of classifying organisms;.

b. Carolus Linnaeus (1707–1778) was a Swedish taxonomist.

1) Linnaeus developed a binomial system of nomenclature (two-part names for each species [e.g., Homo sapiens]).

2) Like other taxonomists of his time, Linnaeus believed in the ideas ofa) special creation—each species had an “ideal” structure and function; andb)fixity of species—each species had a place in the scala naturae, a sequential ladder of life.

2. Georges Louis Leclerc

a. Georges Louis Leclerc, known by his title, Count Buffon (1707-1788), was a French naturalist.b. He wrote on the natural history of all known plants and animals, provided evidence of descent with modification.c. His writings speculated on influences of the environment, migration, geographical isolation, and the struggle for existence.

In the course of his examination of the animal world, Buffon noted that despite similar environments, different regions have distinct plants and animals, a concept later known as Buffon's Law, widely considered the first principle of biogeography.

3. Erasmus Darwin 

a. Erasmus Darwin (1731-1802) was Charles Darwin's grandfather.

b. He was a physician and a naturalist whose writings on both botany and zoology contained many comments that suggested the possibility of common descent.

c. He based his conclusions on

1) changes undergone by animals during development,2) artificial selection by humans3) the presence of vestigial organs 

Erasmus Darwin offered no mechanism by which evolutionary descent might occur.

Late Eighteenth-/Early-Nineteenth Century Contributions

1. Cuvier and Catastrophism 

a. George Cuvier (1769-1832), a French vertebrate zoologist, was the first to use comparative anatomy to develop a system of classifying animals.b. He founded the science of paleontology-the study of fossils-and suggested that a single fossil bone was all he needed to deduce the entire anatomy of an animal.

c. To explain the fossil record, Cuvier proposed that a whole series of catastrophes (extinctions) and repopulations from other regions had occurred.

d. Catastrophism is the term applied to Cuvier's explanation of fossil history: the belief that catastrophic extinctions occurred, after which repopulation of surviving species occurred, giving an appearance of change through time.

2. Lamarck's Acquired Characteristicsa. Lamarck (1744-1829) was the first to state that descent with modification occurs and that organisms become adapted to their environments.b. Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's.c. Lamarck mistakenly saw "a desire for perfection" as inherent in all living things.

d. Inheritance of acquired characteristics was Lamarck's belief that organisms become adapted to their environment during their lifetime and pass these adaptations to their offspring.e. Experiments fail to uphold Lamarck's inheritance of acquired characteristics

         

How could you test Lamarck's theory?

What We Know So Far

1.  Taxonomy and classification emphasize similarities among species  (common descent)2.  Fossils show extinct species (paleontology)3.  Isolated species are distinct (biogeography)4.  Organisms have adaptations to help them survive

*At this point, no mechanism has been proposed to explain how these adaptations come to be

* Special creation is still strongly held, but offers no explanation for the appearance of new species (like on an island)

........................Enter Charles Darwin............................

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• Invited to travel around the world

– 1831-1836 (22 years old!)– makes many observations of nature

• main mission of the Beagle was to chart South American coastlineStopped in Galapagos Islands

500 miles off coast of Ecuador

Darwin found… birds

Finch? Sparrow?

Woodpecker? Warbler?

Collected many different birds on the Galapagos Islands.

Thought he found very different kinds…

Darwin was amazed to find out: All 14 species of birds were finches…

Sparrow?

Woodpecker? Warbler?

But Darwin found… a lot of finches

Large Ground Finch

Small Ground Finch

Warbler Finch Veg. Tree Finch

But there is only one species of finch on the mainland!

How didone species of finches becomeso many differentspecies now?

Warbler finch

Woodpecker finch

Small insectivoroustree finch

Largeinsectivorous

tree finch

Vegetariantree finch

Cactus finch

Sharp-beaked finch

Small groundfinch

Mediumground finch

Large ground finch

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finc

hes Ground finches

Darwin’s finches• Differences in beaks

– associated with eating different foods– survival & reproduction of beneficial adaptations

to foods available on islands

Darwin’s finches• Darwin’s conclusions

– small populations of original South American finches landed on islands• variation in beaks enabled individuals to gather food

successfully in the different environments

– over many generations, the populations of finches changed anatomically & behaviorally• accumulation of advantageous traits in population• emergence of different species

Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends.

• Differences in beaks allowed some finches to…– successfully compete – successfully feed– successfully

reproduce• pass successful traits

onto their offspring

Darwin’s finches

Correlation of species to food source

Whoa,Turtles, too!

More observations…

Essence of Darwin’s ideas• Natural selection

– variation exists in populations– over-production of offspring

• more offspring than the environment can support

– competition• for food, mates, nesting sites, escape predators

– differential survival• successful traits = adaptations

– differential reproduction• adaptations become more

common in population