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Darwin VS. Lamarck
Chapter 15-2
Jean Baptiste de Lamarck (1744-1829)

First to propose the
theory of evolution.

Lamarck claimed that
species are
descendents from early
ancestors.

Fossil records
supported his findings.
Lamarck’s Theory

Lamarck claimed that species changed over
time due to an acquired trait.

Acquired trait- A trait not determined by
genes but acquired through a life time.

Lamarck’s theory was later proven false.
Charles Darwin (1809-1882)

Charles Darwin came up
with a different theory to
explain how evolution takes
place.

Darwin collected evidence
for his theory on his journey
around the world on a ship
called the H.M.S. Beagle.
Natural Selection

Darwin’s theory was based on the idea of
what he called natural selection.

Natural selection- Organisms best suited to
their environment reproduce more
successfully than other organisms. Thus
passing down their favorable traits to their
offspring.
Voyage of the Beagle

One of Darwin's most famous collections
from his trip was the collection of finches
from the Galapagos islands.
The Finches

Darwin collected 13 different species of finches from the island.

Each bird had a distinct bill specialized for a particular food
source.

Darwin later concluded that these 13 species came from one
common ancestor.

Darwin thought that the original ancestors had migrated from
the nearby coast of South America.
The Origin of Species

Darwin later published his findings in a book
titled the Origin of Species.
Survival of the Fittest
We often use the term “survival of the fittest”
What does this mean?
Survival of the Fittest

Animals with favorable traits will survive and
pass those genes to the offspring.

The contribution of genes an organism gives
to the next generation is called fitness.
Fitness

As more favorable genes are contributed to the
population the organisms will change over time.

This is Darwin’s idea of natural selection.

The process by which a population becomes better
suited to its environment is known as adaptation.
THE FORMATION OF A NEW
SPECIES
Chapter 15-3 and 16-3
Notes
Homologous Structure

Homologous Structure- Similar features that
are found in a shared ancestor.
Vestigial Structures

Vestigial Structure- Structures that were
useful to ancestors now have no purpose.
Vestigial Structures
Vestigial Structures
Similarities in Embryology

The early stages of different vertebrate
embryos are strikingly similar to each other.

The similar appearance provides further
evidence that species originated from a
common ancestor.
Similarities in Macromolecules

Darwin based many of his conclusions on the
physical similarities between organisms.

Darwin was unable to examine similarities at
a molecular level.

Scientists have later studied the molecular
similarities between different organisms.
Molecular Similarities

The similarity in amino acid sequence can
determine how closely related two species
are.

And how long ago they branched off the
evolutionary chain and developed a new
species.
Analogous Structures




When organisms that vary greatly
anatomically evolve similar structures that
serve similar functions.
Example: bird wing and insect wing
Example: bird beak and giant squid beak
Share very distant relatives.
Co- Evolution

The change of two or more species in close
association with each other is called coevolution.

Example: Bat and flower
Some flowers and bees have coevolved in a way that their
existence depends on each other.
Convergent Evolution

Selection that causes two species to become
very similar to each other even though they
have very different ancestors.

Example- Dolphin and Shark
Convergent Evolution
Divergent Evolution

Two or more related populations or species
become more and more dissimilar.

Divergence is nearly always a response to
differing environmental factors and can
ultimately result in new species.

The rate of divergent evolution among dogs
has been increased by artificial selection in
humans.
Speciation
Speciation- Is the formation of new species
which results in many related populations of
organisms.
Biological Species Concept
The Biological Species Concept states- A
species is a population of organisms that can
successfully interbreed but can not breed
with other groups.
Biological Species Concept

The biological species concept works great
for living organisms but is difficult for
organisms that have since become extinct.
Speciation

In order for speciation to occur there must be
isolation.

In isolation two parts of formerly
interbreeding populations stop interbreeding.

Why is isolation important for speciation to
occur?
Speciation

Two major types of isolation frequently drive
speciation


Geographic Isolation
Reproductive Isolation
Geographic Isolation

Geographic Isolation- Is the physical
separation of members of a population.
Examples
- Canyon formation
- Shrinking ponds
- Islands
Reproductive Isolation

Reproductive Isolation- Reproductive
isolation results from barriers to successful
breeding between population groups in the
same area.
Reproductive Isolation

Examples
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Offspring does not survive to reproduce
Mating call that is not recognized
Different mating times
Selective mate