Chapter 15

Theory of Evolution

Theory of Evolution

History of Evolutionary Thought

Section 1

The Idea of Evolution

In the 1830s, Charles Darwin

visited the Galapagos Islands

and noted that groups of

animals varied on each island

Darwin was convinced that

organisms had changed over

time

Proposed the theory of

evolution – development of

new types of organisms from

preexisting types of organisms

over time

Lamarck’s Ideas on Evolution

Jean Baptiste Lamarck supported the idea that

populations of organisms change over time

His idea was the inheritance of acquired

characteristics

No supporting evidence and has been rejected

Darwin’s Ideas

Darwin published a book – On the Origin of

Species by Means of Natural Selection in 1859

proposing a new theory for the way evolution took

place

Goals of the book:

Present the large amount of evidence that evolution occurs

Explain the variety and distribution of organisms on Earth in

terms of natural selection processes that are observable

everyday

Darwin’s Ideas

Descent with Modification

Darwin reviewed evidence that every species –

living or extinct – must have descended by

reproduction from preexisting species and that

species must be able to change over time

First to argue that all species had descended

from only one or a few original kinds of life

Evidence of Descent with

Modification

Galapagos Islands are home

to 13 different species of

finches

Each has a beak that is best

adapted for a certain kind of

food

Darwin suspected that all

descended from one common

ancestor

The ancestors could have

flown from elsewhere after

the islands were formed

Natural Selection

Darwin proposed natural selection as the

mechanism for descent with modification

Natural Selection

Overproduction

More offspring can be produced than can live to

maturity

Genetic Variation

Within a population, individuals have different traits

– some can be inherited. Occasionally, new traits

may appear in a population.

Natural Selection

Struggle to survive

Individuals must compete with each other for

resources

Some variations increase and individual’s chance to

survive and reproduce

Adaptation – a trait that makes an individual successful

in its environment

Natural Selection

Differential Reproduction

Organisms with the best adaptations are most likely

to survive and reproduce

Through inheritance, the adaptations will become

more frequent in a population

Populations may begin to differ as they adapt to

different environments, even if they descended from

the same ancestor

Natural Selection

Evidence of Evolution

Section 2

The Fossil Record

Fossil – the remains or traces of an organism

that died long ago

Among the most powerful evidence of evolution

The Age of Fossils

Relative age – possible to tell a fossil’s age by

comparing it to that of other fossils

The Distribution of Fossils

From the fossil record we can infer:

Different organisms lived at different times

Today’s organisms are different from those of the

past

Fossils found closer together are more like each

other than ones found further away

Where and when different organisms existed

Transitional Species

The fossil record

shows that species

have differed in a

gradual sequence of

forms over time

Biogeography

Biogeography – the study of the locations of

organisms around the world

Darwin and Wallace observed species that

seemed closely related but were adapted to

different environments in nearby regions

They also observed animals that seemed

unrelated but had similar adaptations to similar

environments in regions that were far apart

Anatomy and Embryology

Anatomy – the study of the body structure of

organisms

Embryology – the study of how organisms

develop

As generations passed, different populations of

descendants adapted to different environments

Homologous structures- structures that occur in

different species and that originated by heredity

from a structure in the most recent common

ancestor of the species

Analogous structures – closely related functions

but do not derive from the same ancestral

structure

Anatomy and Embryology

Anatomy and Embryology

Vestigial Structures

– structures that seem

to serve no function

but that resemble

structures with

functional roles in

related organisms

Development of

animal embryos –

some stages of

vertebrate embryo

development are very

alike

Biological Molecules

In all species, DNA and RNA are the molecular

basis for inheritance of traits

Scientists can compare the DNA, RNA, and

proteins from many different organisms and look

for similarities and differences

The greater number of similarities, the more

closely the species are related through a common

ancestor

Evolution in Action

Section 3

Convergent Evolution

Convergent Evolution – the process by which

different species evolve similar traits

Example: Caribbean Anole Lizards

Convergent Evolution

Many different body types on different islands and

different species have the same body types

Lizards that live on tree trunks have stocky bodies

and long legs

Lizards that live on slender twigs have thin bodies,

short legs and tails, and large toe pads

Lizards that live in the grass are slender and have

very long tails

How did all of this happen?

Convergent Evolution

Each species evolved independently on each

island from different ancestor species

Divergent Evolution

Divergent evolution – Process in which

descendants of a single ancestor diversify into

species that each fit different parts of the

environment

Ex: Lizards with genes for large toe pads and short

legs ran so slowly on the trunk and ground that

predators often caught them

Artificial Selection

Artificial Selection –

process when a

human breeder

chooses individuals

that will parent the

next generation

Coevolution

Coevolution – when two or more species have

evolved adaptations to each other’s influence

Ex: Humans develop and use antibiotics to kill

bacteria, many populations of bacteria have evolved

to resist the effects of antibiotics