Download Natural Selection

Natural Selection
YOLO! Survival of the Fittest
What is the ultimate goal of all living things?
To reproduce more offspring and for those
offspring to survive means you are the
FITTEST!
Why? More offspring means survival of YOUR
specific traits and hopefully the survival of
your entire species!
Artificial Selection is when people select
the traits that we want passed on to the
next generation
• People are the choosers
Artificial Selection
• First animal to be domesticated by humans
• About 12,000 years ago hunter-gatherers in Israel placed a
body in a grave with its hand cradling a pup. Whether it was
a dog or a wolf can’t be known. Scientists know the process
was under way by about 14,000 years ago but do not agree
on why.
• At the molecular level not much changed at all: The DNA
makeup of wolves and dogs is almost identical.
Scenario 1: "Humans adopted wolf pups and
natural selection favored those less aggressive
and better at begging for food."
• Scenario 2: "Dogs domesticated themselves by
adapting to a new niche—human refuse dumps.
Scavenging canids that were less likely to flee
from people survived in this niche, and
succeeding generations became increasingly
tame."
https://www.haikudeck.com/foxes-anddomestication-education-presentationiWVY2vzVx0#
(read on your own)
Many things have been artificially selected for
human’s benefit, such as…
Wild Banana
Domesticated Banana
Also…
Wild Maize
Domesticated Corn
In natural selection, nature is selective force!
In Natural Selection
the environment is
the chooser
Natural selection is a
NONRANDOM
process by which
traits are selected for
by nature because
they provide some
survival benefit.
Woolly BEAR!
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
selection.
Genetic Variation of heritable traits (due to meiosis and
mutations)-variety in genes create unique combinations in
offspring that allow some traits to be more successful than
others in a particular environment. “Variety is the spice of life”—
exact clones are prone to failure and extinction!
– Overproduction and struggle for survival-organisms don’t
control reproduction rate to ensure that some offspring will survive
and compete for resources.
– Adaptation favorable traits arise over many generations in
a population and not in one individual due to selective
pressure from environment.
– Descent with modification—offspring share characteristics and
genetic traits with common ancestor, but there is a change in gene
frequency over time.
Descent with modification
occurs on a species level
Source: Berkeley Evolution
• Descent with modification — a change in gene frequency
over time
Beetles of a different color
• Most of the beetles in the population (say 90%) have the
genes for bright green coloration and a few of them (10%)
have a gene that makes them more brown. First Generation
• Some number of generations later, things have changed:
brown beetles are more common than they used to be and
make up 70% of the population. Second Generation
• Fitness is the measure of survival ability and
ability to produce offspring that survive.
Natural selection acts on existing variation.
• Natural selection can act only on traits that already
exist (the genetic combo that was randomly assigned
before fertilization).
• Structures take on new functions in addition to their
original function. (example: homologous structures).
five digits
wrist bone
Natural Selection
Got milk? Lactase mutation
• Nomadic-hunter-gatherer ancestors were
lactose-intolerant.
http://www.hhmi.org/biointeractive/natural
-selection-lactose-tolerance
• When cattle were domesticated and cow milk
became readily available, the mutation for
lactase enzyme production (LCT gene)
became favorable and became more common
in the genotype of future generations.
Got Milk?
• Remember “linked-genes”? Lactose
intolerance mutation is a mutation that is
passed on with other certain traits because
of its proximity to those genes.
• The LCT lactase mutation is found on
chromosome 2! 
Pedigrees show short-term
descent with modification
Cladograms show descent
with modification
Dormaalocyon latouri
ancestor
Cladogram
Shows
Speciation:
Descent
from
Ancestor(s)
http://www.nature.co
m/scitable/topicpage/
interpreting-sharedcharacteristics-theplatypus-genome44568#
Cladogram
• A clade is a group of species that includes an
ancestral species and all of its descendants.
Clades, like species, are formed by the process
of descent with modification.
This Cladogram Shows Descent
from Ancestor(s) on a MACRO
scale (whole tree of animal life)