BIO 1M03 Chapter:24
Evolution by Natural Selection
Evidence for Natural Selection
Industrial Melanism: The prevalence of dark phenotypes of individuals brought
on by natural selection and the industrial evolution. When the industrial
environment influences the allele frequency of a species. There is molecular
variation in phenotypic variation. Ex: the moths that got darker over time due to
the coal burning on trees.
Antibiotic resistance: When Individuals take antibiotics it is to rid the body of
pathology (the infectious disease). If there are even 1 bacterium that is resistant to
the drugs, it will begin to multiply and reinfect the host and will not be affected
by the previous antibiotic.
Beak size in Galapagos: On the island the beak sizes of birds evolved due to the
drought on the island. This drought killed all the food plants for the finches and
the birds were forced to eat nuts and a variety of seeds. This environmental
change favored the finches having bigger beak size. As a result much of the
population died and the bigger beak size became selected for.
• “Selection on individuals, but evolution of populations over time”. Epigenetics is
an exception. It changes the methylation of genes changing the propensity of
offspring genes. One experience of an individual’s life can change and alter gene
expression of their offspring. This is an exception to the effects of natural
selection. These adaptions are always considered trade offs.
• Altruism : there is a benefit being gained. Individuals do not do things for the good
of the species except in the case of kinship. Natural selection changes the
characteristics of the population
Evolution of Evolutionary thought:
Plato and Typological thinking:
The Greek philosopher claimed that every organism was an example of a perfect
essence, or type that was created by God. He believed that these types would
never change. He acknowledged that types can slightly deviate away from the
perfect type but that we should only focus on the perfect type.
Typological thinking is based on the idea that species are unchanging and slight
changes are unimportant.
Aristotle and the Great Chain of Being:
Proposed a goaloriented evolution. The idea that species that could change was
developed by Aristotle.
Developed the ”Scala naturae“ or the “Great Chain of Being”. This hierarchical
ladder of nature was organized in a sequence that was based on size and
complexity with humans at the top. [Type text] [Type text] [Type text]
The major ideas of Aritstotle on this topic were 1. Species are fixed types and
2.Some species are “higher” than others. Ex: Humans are at the top.
Lamarck and the Idea of Evolution as Change through Time:
Proposed that not used characteristics are lost. This is not true because just
because we don’t use something doesn’t mean we lose the phenotype.
First to propose that species are not static. Proposed that simple organisms
originate at the base from spontaneous generation. Also that a species changes via
the inheritance of traits, and that an individual develops a response to the
environment changing its phenotype. “Giraffes have tall neck to reach high food”.
Darwin and Wallace Evolution by Natural Selection:
Described evolution as a descent with modification. Meaning that changes come from
Argued that evolution occurs because traits vary among individuals in a population and
that certain individuals with certain traits produce more offspring than others.
Darwin claimed that being unimportant is an illusion, variation among individuals in a
population was the key to understanding the nature of the species .
Law of succession: The general observations before Darwin’s theory that extinct species
in the fossil record were succeeded in the region. There were striking resemblances
between fossils under rocks and the living species in the same geographical area.
Transitional feature: is a trait in a fossil species that is intermediate between those of
older and younger species. Ex: the tetrapod limbs and fin bones. Similar sequences of
transitional features document changes that led to the evolution of feathers and flight in
birds and the vascular tissue and the stomata in plants.
Evidence for evolution: (species are dynamic not static.)
• Fossils indicate that species are not static. (change through time)
• Foot prints from 6.3 million years ago.
• Many fossils provide evidence for extinct species.
• Evidence from ancient DNA (feces). We can see variation from a molecular level.
• Transition forms have been discovered with traits that are intermediate between
earlier and later species. Examples include limb loss in tetrapod’s evolution of
feather, jaw development in fish.
• Vestigial traits: An incomplete developed structure that has no function but is
clearly similar to functioning organs or structures. Goosebumps a trait that was
inherited from chimps who had thick body hair, human coccyx (tails) and in apes.
Wales still have leg bones and pelvic spurs in pythons. There are “vestigial genes”
or (pseudo genes) that are functionless DNA.
• Speciation by hybridization offspring is isolated.
• Speciation by polypliodization. Evan’s research:[ frog has bizarre characteristics
that have duplicated genomes evolution can happen instantaneously with
hybridization.] BIO 1M03 Chapter:24
• There is geographic continuity. There are predecessors of extinct species that are
linked in geography and time.
• Sedimentary rocks and their layers, which correspond to geographical landscape.
• Mockingbird species on island: people have shown that these islands have the
most closely related birds than any other island. This shows geographic continuity
among the closely related species. Wallace was a naturalist who observed
diversity as he travelled from the west to the east (map slide)
Sumatra : many organisms
New Guinean some marsupials
There is a massive difference between species in the east and west. Geography
continuity is responsible the impeded the migration of fauna in Shanul Shelf.
Homology: a certain type of