Evolution: Evidence,Evolution: Evidence,Selection and AdaptationSelection and Adaptation

One of the key words of our modern time is Evolution

OutlineOutlineu 1. Key concepts

u 2. Early Beliefs, and New Discoveries

u 3. Darwin developed the theory of evolution

u based on his observations and other evidence

a. Darwin’s observations

b. Factors that influenced Darwin’s thinking

u 4. Natural selection: A mechanism of evolution

u 5. Conclusions

Key Concepts:Key Concepts:

Evolutionary theories gave early scholars new

ways to interpret the occurrences in the world

Today, biological evolution is interpreted as

heritable changes

Darwin and Wallace explained evolution on the

basis of Natural Selection

The traits that characterize a population can

change over time

Early Beliefs, and New DiscoveriesEarly Beliefs, and New DiscoveriesAristotle – believed that each kind of organism was

distinct from all the rest

“Chain of Being”- fourteenth century (A chain of Being

was seen to extend from the “lowest” forms of life to

humans.

Biogeography – until the fifteenth century, naturalists

were not aware that the world is much bigger than

Europe, a few scholars began to examine the world

distribution of organisms

Comparative Anatomy – eighteenth

Fossils – from the late 1600s on geologists added to the

growing confusion.

Chain of Chain of BeingBeing(1579)(1579)

A Flurry of New TheoriesA Flurry of New Theories

Lamarck

Theory of Inheritance of Acquired

Characteristic

Darwin

Voyage of the Beagle - 1831

LamarckLamarck’’ss TheoriesTheories

According to Lamarck's theory, life created long

ago in a simple state gradually improved.

For example, the ancestor of giraffes could have

been a short-necked animal. Pressed by the

need to find food, the animal stretched its neck,

which permanently lengthened. This acquired

characteristic (a long neck) was then passed on

to the giraffe's offspring.

Lamarck inferred, correctly, that environment is a

factor in evolution.

LamarckLamarck’’ssTheoriesTheories

Charles Darwin

[1809-1882] called evolution “Descent with modification”

DarwinDarwin’’s Voyages VoyageAt age 22, Charles Darwin began a five-year,

round-the-world voyage aboard the Beagle

He collected and examined the species that inhabited the regions the ship visited

EQUATOR

Galapagos

Islands

DarwinDarwin’’s observationss observations

Prevailing ideas about species: they did not change or interbreed

Darwin’s evidence for change came from:1. his observations of living organisms

2. geologic evidence and fossil record

3. theories of population growth

DarwinDarwin’’s observationss observationsWhat the evidence showed:

• Relationship between living and fossil organisms (distinct yet similar)

• Among living organisms: distinct yet similar organisms occur in

� Similar climates – S. Africa, Chile, Australia

� Isolated populations of same species –species often change slightly due to geographical isolation

� Island v. mainland populations – Island species often resembles to mainland species

DarwinDarwin’’s Theory Takes Forms Theory Takes Form

Armadillo – 10 pounds

Glyptodont – fossil from S. A. (2 tons!)

Three Species Native to Three Three Species Native to Three Geographic RealmsGeographic Realms

Ostrich

of Africa

Rhea of

S. America

Emu of

Australia

DarwinDarwin’’s Theory Takes Forms Theory Takes Form

Variations in traits

Survival

Reproduction

Four finch

species from the

Galapagos

Islands

Galapagos Islands todayGalapagos Islands today

Factors that influenced Factors that influenced DarwinDarwin’’s thinkings thinking

• Geology: as Earth changed, so did types of fossil organisms in rock strata

• Population studies: many organisms are produced; only a few survive to reproduce [Thomas Malthus (1766-1834) Essay on Disease, Famine, and Population Size]

• Artificial breeding experiments: humans “select” desirable traits in plants and animals; so does “nature”

Natural selection: A Natural selection: A mechanism of evolutionmechanism of evolution

Darwin’s explanation for species diversity:

Nature “selects” organisms which have inheritable traits (adaptations) suited to their environment which allow them to survive to reproductive age

Survivors then breed and pass on these characteristics to their offspring

Variation in a Snail SpeciesVariation in a Snail Species

Shell color and

banding patterns

differ due to

different alleles

for the genes for

that trait

Adaptation and Natural Adaptation and Natural SelectionSelection

Mutation (Lethal mutation, Neutral mutation,

Good mutation) – no purpose, no direction

Fitness

Adaptation to the environment

Natural Selection

Result of differences in survival and reproduction

among individuals that differ in heritable traits

An example of natural An example of natural selection: Darwinselection: Darwin’’s finchess finches

Showed relatively rapid evolution:

• Ancestral finches from mainland reached islands, underwent adaptive radiation and populated many diverse habitats

• Ancestral species became groups of closely related yet diverse populations

An example of natural An example of natural selection: Darwinselection: Darwin’’s finchess finches

Natural SelectionNatural Selection

Selection can increase the frequency of a trait in a

population

Environment may favor a trait over another

Alfred Wallace

Developed same theory as Darwin

Origin of Species

1859 - Darwin

Evidence for the Theory of Evolution

In ConclusionIn Conclusion

The Theory of Evolution by Natural Selection

states

More offspring are produces than the environment can

support

Variant forms of a trait may be more or less adaptive

under environmental conditions

An adaptive trait allowed organisms to survive and

reproduce more frequently. The frequency of that

adaptive trait increases in a population

In ConclusionIn Conclusion

Comparative anatomy, biogeography,

fossils, and a lot of other evidence showed

changes in lines of descent

Natural Selection results in modification of

traits and can bring about the evolution of

a new species