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Chapter 4
Evolution & Biodiversity
• 1 billion years of chemical change to form
the first cells, followed by about 3.7 billion
years of biological change.
• Mutations, random changes in the DNA of
a cell, can occur at any time
• These small changes have provided the
means for genetic variability
• How have these small changes in a single
organism’s DNA led to the abundant
amount of biodiversity that exists today?
• Natural Selection
• According to Charles Darwin, natural
selection is a biological mechanism for
evolution.
• Some organisms have particular traits, or
genes that give them an increased chance
for survival in their environment.
• They are more likely to reproduce more
often than other organisms lacking these
genes
• Those will increase the percent of the
population who express this successful
trait
• Any organism that is better suited for their
environment will be fit to reproduce and
pass down the favorable trait
• The genetically inheritable traits that make
an organism more likely to survive and
reproduce are adaptations
• Adaptations lead to differential
reproduction because they will leave more
offspring than other individuals in the
population
Natural Selection and Adaptation:
Leaving More Offspring With
Beneficial Traits
• Three conditions are necessary for
biological evolution:
1. Genetic variability 2. traits must be heritable,
3. trait must lead to differential
reproduction.
• An adaptive trait is any heritable trait that
enables an organism to survive through
natural selection and reproduce better
under prevailing environmental conditions
Why won’t our lungs evolve to deal
with air pollution?
• Limits to adaptation:
– A change in the environment can only lead to adaptation
for traits already present in the gene pool
– Reproductive capacity may limit a population’s ability to
adapt
• If you reproduce quickly (insects, bacteria) then your population can
adapt to changes in a short time
• If you reproduce slowly (elephants, tigers, corals) then it takes
thousands or millions of years to adapt through natural selection
– Most individuals without trait would have to die in order for
the trait to predominate and be passed on
How Can Geologic & Climatic
Events Impact Natural Selection
• Environmental Changes can cause differential
reproduction to stop
• Geologic Events like tectonic activity, movement
of continents, earthquakes and volcanoes.
• Climatic events= Periods of warming and cooling
(ice ages) have shaped earth’s ecosystems.
• Organisms unable to adapt to changing
conditions have become extinct and replaced
with organisms better suited for the new
environment
How do New Species Evolve?
• Geographic Isolation= Geological and
climatic events can physically separate
populations for long periods of time.
• Since these populations are exposed to
different environmental pressures, the
traits that make one population successful
will not make the other successful.
• This causes reproductive isolation
• These types of isolation events can lead to
one species into evolving into two distinct
species= speciation event
• When an entire organism disappears from
earth its known as extinction
• Mass extinctions have opened ecological
roles or niches
• A niche is an organisms way of life including
everything that would effect its survival and
reproduction
• Generalist Species= have broad niches
• Specialist Species= have narrow niches