Chapter 24: Evolution by Natural Selection
24.1: The Evolution of Evolutionary Thought
Plato claimed that all organisms on earth were the work of God
Aristotle proposed that species are organized into a sequence based on increase in
size and complexity
Typological thinking is based on the idea that species are unchanging types and
variations within species have no effect.
Jean-Baptiste de Lamarck first proposed that species changed through time.
o He was the first one to propose a formal theory of Evolution.
o Also claimed that organisms evolved from pre-existing species.
Lamarck’s Theory of Evolution consisted of 2 parts:
o Law of Use and Disuse
The more an organism USES a certain body part, the stronger and
better developed that part becomes. In contrast the more a
organism DISUSES a body part, the weaker it becomes.
He concluded that organisms can acquire new characteristic and
called this ACQUIRED CHARACTERISTICS.
Ex. Giraffe using its neck to reach food in high places.
o Inheritance of “Acquired Characteristics”
Lamarck thought that acquired characteristics such as muscles
could be passed onto their offspring. This part of the theory was
Population consists of organisms of the same species living in the same
Charles Darwin proposed a SECOND THEORY OF EVOLUTION.
o Concluded that organisms with favourable variations would be better
suited to survive and reproduce in their environment. He called this
Chapter 24: Evolution through Natural Selection 24.2: The Pattern of Evolution: Have Species Changed through Time?
The phrase Darwin keeps referring to is DESCENT WITH MODIFICATION.
o That phrase means that all species existing today all came from a
descendent from other preexisting species through change through time.
The theory of natural selection consist of 2 parts:
o Species change through time
o Species are all related to a common ancestry
Evidence for Change through Time (pg. 508)
Biologist especially Darwin used fossil records to observe the change on a species
Fossils is a trace of a organism that lived in the past
Fossil Records consist of all the fossils that have been found and described in the
o They used this as a backup to prove that species change through time
Based on the fossils scientist found, they organized them from oldest to youngest
and created GEOLOGIC TIME SCALE.
Geologic time scale is the time of eons, epochs and periods.
Extinction (pg. 508)
Extinct species are species that no longer exist.
Darwin interpreted that this is evidence that species are not constant, permanent
entities, unchanged since the moment of special creation.
Recent fossil records support that more species have gone extinct than exist today.
Transitional Forms (pg. 509)
Law of succession derived from the observation that certain fossils found in a
certain area had a strike resemblance to the species living in that same
Darwin stated that fossil records strongly support their hypothesis that species
change through time.
o His idea was that extinct form and living forms were related
They represent ancestors and descendants.
Transitional form is a fossil species with traits that are intermediate between
those of older and younger species.
o Ex. Humans gaining a larger brain and upright posture, snakes losing their
limbs, limbs in amphibians and other vertebrates.
Each of these transitional forms provides strong evidence that
species change through time.
Vestigial Traits (pg. 509)
Darwin was the first to provide an in-depth interpretation of vestigial traits.
Vestigial trait is a reduced or incompletely developed structure that has no
function or reduced function, but it is clearly similar to functioning organs or
structures in closely related species.
o Ex. Humans appendix, it is a reduced version of a cecum – and organ
found in other vertebrae that function in digestion.
The existence of vestigial trait is inconsistent with the theory of special creation.
Special creation a theory stating that species are made from a supernatural being
and the characteristics of species are consistent, not changing.
o Vestigial trait disproved this theory.
Chapter 24: Evolution through Natural Selection 2 Evidence That Species Are Related (pg. 510)
Traits are similar in different species because the species in question are related to each
other by common descent. If species were created independently of one another, then
these types of similarities would not occur.
Homology (study of likeness) is a similarity that exists in species descended from
a common ancestor.
o Homology can be broken down into 3 interacting levels: these levels
Genetic Homology is a similarity in the DNA sequence of different species.
Development Homology is the similarity in embryonic traits.
o This homology is constantly observed in the overall morphology, or form,
of embryos and in the fate of particular embryonic tissues.
o Due to homologous genes
Referring to Figure 24.8, it displays the embryonic development of a chick,
human and cat.
o Embryonic gill pouches are a vestigial trait in chicks, humans and cats
while the tail is a vestigial trait for humans
Structural Homology is the similarities in adult morphology.
o This homology is derived form homologous genes.
Evolution Is Change through Time (pg. 512)
Descent with modification was more successful and powerful scientific theory. It
explained the observations such as vestigial traits and the close relationship among
species on neighboring islands that special creation could not.
Chapter 24: Evolution through Natural Selection 3 24.3: The Process of Evolution: How Does Natural Selection Work?
Darwin has br