Download Natural Selection

Natural Selection
Life Science Unit 8 Lesson 3
Attendance link: http://goo.gl/forms/1yzOHFdnMy
EXPECTATIONS
Required Class Connects
Tuesday, Wednesday, & Thursday
1:30-2:30 pm
Be active and participate in class.
Be respectful to your classmates
Be positive in the chat box and use it correctly.
Have a working microphone!
You will need it during the lessons and break out rooms.
If you have a question, please place it in the chat box and
repost it if I don’t see it.
2
2
Objectives
 Explain the process of natural selection.
 Recognize that environmental changes
may affect the survival of particular
organisms and entire species.
 Identify specific adaptations that favor
the survival of certain organisms in their
environment.
Evolution is a Theory –
Just like Gravity!
• Evolution is a well supported explanation of
phenomena that have occurred in the natural
world
• A theory in science is a well tested hypothesis,
not just a guess or random idea.
Selective Breeding
 nature provides variation, humans select
variations that are useful.
 Example - a farmer breeds only his best
livestock
Natural Selection
 The traits that
help an organism
survive in a
particular
environment are
“selected” in
natural selection
Natural Selection and Species
Fitness
 Overtime, natural selection results in
changes in the inherited
characteristics of a population.
 These changes increase a species
fitness (survival rate)
Natural Selection
The unequal survival and reproduction of organisms
due to environmental forces, resulting in the
preservation of favorable adaptations.
It is a two step process:
1. The Production of variation in a population
2. Non-random aspects of survival and reproduction
Natural Selection is a two step
process:
Step One: The Production of Variation. (Chance)
Mutations
Meiosis:
recombination due to crossing-over in 1st division
random movement of chromosomes in 2nd division
Random mate selection & fertilization
Step Two: Non-random aspects of survival and
reproduction
Superior success of certain phenotypes
Nonrandom mate choice
Do we see variation within different wild species ?
Lemurs of Madagascar
Amazonian Frogs
Humans select traits for dogs, pigeons and other animals
when they breed them.
Bred Pigeons came from a single original species
Who selects the traits for wild plans & animals?
NOBODY!!
There is no agent involved in natural selection.
Natural selection is a process of elimination
INDIVIDUALS THAT HAVE TRAITS THAT ARE BEST ADAPTED
FOR THE CURRENT ENVIRONMENT ARE THE ONES THAT
SURVIVE TO BREED AND PASS ON THEIR GENES TO THE
NEXT GENERATION.
Organisms not possessing the beneficial traits
either die or don’t have as many offspring.
Natural Selection is Survival of the fittest
Natural Selection is a mixture of both Chance and necessity
Natural Selection is not goal directed. It does not have a long term
goal.
Descent
with
Modification
Each living
species has
descended
with changes
from other
species over
time
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than
survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass
those advantages to their children
5. Species alive today are descended with
modifications from common ancestors
Evidence for Evolution:





Fossil Record
Homologous Body Structures
Vestigial Organs
Embryology
Biochemical Evidence
The Fossil Record
 Fossils: a record of the history of life
on Earth
Evidence of
Evolution
Fossil Record provides
evidence that living
things have evolved
Fossils show the history
of life on earth and
how different groups
of organisms have
changed over time
Archaeopteryx
 Missing link between
reptiles and birds
Homologous Body Structures
 Homologous
Body Structures:
similar anatomy in
different types of
animals because
of common
ancestor
Evidence of Evolution
Homologous Body Structures

Structures that have different mature forms
but develop from the same embryonic tissues
e.g. Wing of bat, human arm, leg of turtle
Homologous Body Structures
Biochemical Evidence
 Biochemistry: DNA with more similar
sequences suggest species are more
closely related
 EX: Humans and chimpanzees share
more than 98% of identical DNA
sequences
Vestigial Organs
 Traces of homologous organs in other species
 Organ that serves no useful function
e.g. Appendix (may be a holding place for bacteria)
Vestigial Organs
 Vestigial Organs: “leftover” traces of
evolution that serve no purpose
Embryology
 Embryology: embryos of all
vertebrates are very similar early on
Similarities in
Embryology

In their early
stages of
development,
chickens,
turtles and rats
look similar,
providing
evidence that
they shared a
common
ancestry.
Theory of Evolution
 Evolution: The process of change
over time
 Specifically, a change in the frequency
of a gene or allele in a population over
time
What acts as a selection pressure on a population?
• Competition for food
• Competition for a mate
• Changes in the environment
• Predators
• Parasites
Darwin’s Finches
Natural Selection
 Natural Selection: Organisms that are
best adapted to an environment survive
and reproduce more than others
 Darwin’s Theory of Natural Selection
occurs in four steps:




Overproduction
Variation
Competition
Selection
Overproduction
 Each species produces more
offspring that can survive
Variation
 Each individual has a
unique combination of
inherited traits.
 Adaptation: an inherited
trait that increases an
organism’s chances of
survival
Why is Variation Important?
 Because the environment changes.
 The more variation within a species,
the more likely it will survive
 EX: If everyone is the same, they are all
vulnerable to the same environmental
changes or diseases
 The more variation of types of
species in an habitat, the more likely
at least some will survive
 EX: Dinosaurs replaced by mammals
Competition
 Individuals COMPETE for limited
resources:
 Food, water, space, mates
 Natural selection occurs through
“Survival of the fittest”
 Fitness: the ability to survive and
reproduce
 Not all individuals survive to adulthood
Selection
 The individuals with the best traits /
adaptations will survive and have the
opportunity to pass on it’s traits to
offspring.
 Natural selection acts on the phenotype
(physical appearance), not the genotype
(genetic makeup)
 Ex: When a predator finds its prey, it is due to
the prey’s physical characteristics, like color or
slow speed, not the alleles (BB, Bb)
 Individuals with traits that are not
well suited to their environment
either die or leave few offspring.
 Evolution occurs when good traits
build up in a population over many
generations and bad traits are
eliminated by the death of the
individuals.
Coral Snake
(Poisonous)
Milk Snake
(Not
poisonous)
Stick Mantid
Flower Mantid
Assignment
 OLS
 Part 1 – online – 4 questions
 Part 2 – offline – 1 question
 Make sure you are mastering your lessons!
 We will go over Unit 8.4 next Thursday.
 No CC on Tue. Or Wed. because of M-STEP
for the 3rd/6th. I will be out of the office.