In the name of Allah the Gracious the Merciful
Chapter 24 Evolution by Natural Selection
1) Populations and species evolve, which means that over time their heritable traits
(height, weight, abilities) change over time. Evolution is changes in allele frequencies
2) Natural selection occurs when individuals with certain heritable traits produce the
most surviving offspring in a population
3) Evolution is NOT PROGRESSIVE, and doesn’t change characteristics of individuals,
but rather only changes the characteristics of the population
24.1 The evolution of evolutionary thought
Typological thinking – based on the idea that species are unchanging and variations in the
species are irrelevant (old philosophers believed in this)
Lamarack – first to propose a formal theory of evolution
He believed that organisms are created from spontaneous generation at the base of the
chain, and then evolve and move up the chain over time, and that species change because
of the inheritance of acquired characters.
- progressive theory of evolution contrary to darwins
Darwin’s claim was that the variance among species in a population was the key for
evolution because certain individuals with certain traits will produce more surviving
24.2 The Pattern of Evolution: Have Species Changed through Time?
“Descent with modification” – used by Darwin to describe evolution
Means that the species existing today all descent from preexisting ancestors, but certain
traits have been modified through time
Pattern component makes 2 claims
1) Species change through time 2) Related by common ancestry Many of Darwin’s points make use of the fossil records
A fossil is any trace, or anything left behind (bones, branches, shells tracks) of an
organism that lived in the past.
Fossils were organized to their relative age because most were found in sedimentary
rocks that form in layers, meaning that fossils in lower layers of rock were older than
fossils found in higher layers. Fossils were relatively ordered in this fashion.
Geologic time scale was also named, in relation to these fossils
Eventually radioactivity or carbon dating was used to identify the age of fossils.
Evidence for change though time (Refutes Immutable aspect of creation theory)
Early 19 century, researches found many fossils that were al