Mechanisms of Evolution
Target #3- I can explain how variation contributes to an organism’s survival
 After studying Malthus, Darwin realized that if _____________________________________________________
______________________________________, members of a population must ___________________________
to obtain food, living space, and other limited necessities
 Described as the “_____________________________________________________________________”
 _______________________________________ plays a vital role in the struggle for existence
 Individuals have natural variations among their heritable traits
 Darwin hypothesized that some of these variations are ___________________________________ to life
in their environment than others
 Ex: a lion with longer claws and higher endurance is a better hunter than a lion without those
traits
Target #4- I can describe an adaptation
 Adaptation:

Includes
 Body parts Claws, Wings
 Coloration Bright colors, Camouflage, Mimicry
 Physiological functions Photosynthesis, Brain capacity
Target #5- I can explain why organisms with greater fitness generally leave more offspring than organisms that are
less fit
 Darwin recognized that there must be a connection between the way an organism “makes a living” and the
environment.
 Differences in adaptations affect an organism’s fitness
 Fitness:


Individuals with adaptations that are well suited to their environment can survive and
reproduce __________________________________________
 Individuals with characteristics that are not well suited to their environment either die
___________________________________________ or leave ____________ offspring
 The difference in rates of survival and reproduction is called _____________________________
__________________________________________
Natural Selection
 The ________________________________ by which organisms with variations most suited to their local
environment survive and leave more offspring
 The environment influences fitness
Target #6- I can summarize how natural selection allows organisms which are more adapted survive in their
environment
 Natural selection occurs in any situation in which more individuals are ___________________________ than can
____________________________, there is a ______________________________________________________,
and there is ______________________________________________________________ among individuals



Does not make the organism “better”
Does not move in a fixed direction
A process that enables species to survive and reproduce in a local environment
 If local conditions change, some traits may become __________________________________
 If conditions change faster than a species can adapt, the species may become _______________
Target #7- I can explain how a population of organisms in a species undergoes natural selection
 Adaptations and variations among individuals in populations of species does not begin in the environment
 Step 1: a _______________________________________ occurs within the DNA of an organism
 Step 2: that mutation leads to the production of a ________________________________ that either
______________________________________________________, over functions, or has a
__________________ function than originally intended
 Step 3: the mutation is ____________________________________________ to an offspring where it is
___________________________________ in the offspring’s __________________________________
 Step 4: the mutated phenotype is _______________________________________ by the environment
as being more advantageous, and that individual has ________________________________________
than the non-mutated individuals
 Step 5: the mutation is passed down, generation to generation, until the population of organisms in that
species ____________________________________________________
 **Step 6: if enough mutations collect within a population of individuals in a given species, then a
________________________________________________________________
 Example- the Spirit Bear
 Within the species black bear (Ursus americanus), there is a subspecies (Ursus americanus kermodei)
 There are about 400 individuals in this subspecies
 About 10% of this subspecies is ____________________________________________________
for a mutation that turns their coats _________________________________
 Caused by a mutation in a pigment gene, known as __________ (Melanocortin receptor)
 MC1R is involved with the ______________________________________ of the pigment
________________________________
 A mutation in this gene in humans results in red hair
 Evolutionary Advantage
 Better at catching fish during the day than their dark bear counterparts
 Are considered sacred by the local people, the Tsimshian, so they are hunted less
Target #8- I can explain what Darwin’s mechanism for evolution suggests about living and extinct species
 Natural selection depends on the ________________________ of organisms to __________________________,
or to leave descendants
 Lineage can be traced back over many generations
 Over many generations, adaptation could successfully lead to the evolution of new species
 Darwin proposed that living species are ______________________________________________
________________________________ from common ancestors
 Known as descent with modification
 Means that life as been on earth for a ______________________________________
 Basis for the explanation of the diversity of life
 According to the principle of common descent, all species, living and extinct, are descended from ancient
__________________________________________________