Transcript EVOLUTION and NATURAL SELECTION

Jean Baptiste Lamarck (1744-1829):
• Noted fossils resembled
living species
• Suggests fossils were
ancestors of living
species
• Features had modified
over time in response to
changing climates &
geography
• Called this modification,
“Transformational
evolution”
Lamarck’s Theory of the Inheritance
of Acquired Characteristics
• Living things make adjustments to their
environment during their lifetime that can
be passed down to their offspring, making
the offspring, better adapted to the
environment
Based on Use/Disuse of Body Parts
• Some organs or body parts may be used
more than others during process of
adaptation
• Those “used” more are enhanced
• Those “not used” are reduced
• Believed these physical changes could be
passed down from one generation to the
next
Significance of Larmarck’s Theory
• Recognized crucial relationship between living
things and the environment
• Modern genetic research tells us genes can be
influenced by the environment & changes in
genes CAN be passed on to offspring (The
Epigenome)
Charles Darwin (1809-1882)
• British naturalist
• First studied medicine,
then ministry for Church
of England
• 5 year voyage around the
world on the H.M.S.
Beagle as naturalist
• Observations from
Galapagos Islands critical
to formulation of theory
“The Most Powerful Idea in Science”:
Evolution by Natural Selection
• Developed by Charles Darwin and Alfred
Russell Wallace
Pre-Darwin
• Is the cornerstone of modern evolutionary
theory because it explains how biological
change & adaptation occurs
NATURAL SELECTION
• Darwin & Wallace recognized that variation in
populations already existed
• This variation (genetic diversity) provided the
“raw material” for natural selection; some
individuals would have traits that gave them
an advantage to surviving & reproducing over
others
Darwin observed that:
As populations expand generation by generation, they
run into limits on food, space, right kind of habitat
– These natural pressures limit which individuals are able to
survive & reproduce
Not all individuals in a population are exactly alike
Some will have traits that give them and advantage in
surviving, mating & passing on their traits
These differences are known as variation
A change in the environment can lead to an advantage
for some individuals & disadvantage for others
If selective pressure acts against or upon these
differences, you get natural selection
Natural Selection in a Nutshell
Natural selection is the process by which NATURE
(i.e. the environment), selects better adapted
individuals for more successful reproduction
Variation----Selection-----Variation-----Selection
Lamarck vs. Darwin
Lamarck:
Variation when needed
Darwin:
Variation already present
How does this lead to diversity of
species?
• Over long periods of time, successful variations/traits
accumulate such that later populations may become
distinct (physically, behaviorally) from ancestral ones
What defines a population?
• A group of individuals that:
– is reproductively isolated (of the same species)
– occupies a specific area
Natural selection operates on or “selects” individuals,
but it is the population that evolves
Diversity of species, cont.
• If no interbreeding (sharing of genes) occurs,
they may eventually become separate species
• Populations are adaptable & can change over
time in response to changing environments
Diversification of species, cont.
• Geographical isolation can fuel speciation
as populations respond to different
selective pressures (different environmental
circumstances that influence reproductive
success)
• Sexual selection also affects the process of
natural selection; female preference for
specific male qualities
In Sum
• Natural selection is a process of elimination
– “Survival of the fittest”: to be “fit” means to
possess certain characteristics that increase the
probability of survival & reproductive success
• Natural selection is essentially, the differential
reproductive success of individuals in a
population, mediated by the environment
Evolution of Hudson River Tomcod
BEGINNING POPULATION (Fish w/red outline = resistant gene)
Evolution of Hudson River Tomcod
Evolution of Hudson River Tomcod
Peppered Moths:
Natural selection in action
• Common variety of moth is
spotted gray (peppered)
– Also a dark colored moth of same
species (less common)
• Peppered moth better
camouflaged when resting on
lichen-covered trees; dark moths
more visible to predators, are
eaten more frequently (producing
fewer offspring than light colored
moths)
Peppered Moths, cont.
• Coal dust from factories kills lichen on trees
and turns the bark a dark gray
• Light gray (peppered) moths are more
visible; dark gray moths better camouflaged
• Dark gray variety increase in number, light
gray population declines
Peppered Moths, cont.
• Pollution control enables lichen to grow back
on trees
• Peppered moths once again better
camouflaged, darker variety declines
• Natural Selection Short
Pesticide resistance among beetles
Natural Selection in Action:
Darwin’s Finches Revisited
Beak of the Finch
The “–isms” and “schisms” of Darwin’s
Theory
“schisms”
Implies a “belief system,” like 1. Seemed to contradict
Hinduism, absolutism, etc.
religious explanations
Ideas associated with Nat. Sel. 2. Led to Eugenics movement,
used to explain & justify social
including the Holocaust;
differences (Social Darwinism)
Darwin never used term
or “survival of the fittest” –
“survival of fittest”
Not Darwin’s doing
3. Process of evolution
Darwinism used synonyincludes much more than
mously with “Evolution”
Darwin ever explained or
Darwin’s name & ideas used
understood (in 19th century)
by others to advance their
4. Darwin would never have
own agendas
supported those agendas
“-isms”
1.
2.
3.
4.
What Evolution & Natural Selection
ARE NOT:
• Evolution means that organisms are
“progressing” or getting better.
What it IS:
• Natural selection does weed out individuals
that are unfit in a particular environment
• What’s “good” or “better” in one place or
time, may not be in another
• Fitness (reproductive success) is linked to
the environment not progress
Example: Chimps are chimps because the
features they have are perfectly adapted to
their environment & niche
Misconception: Natural Selection
involves organisms “trying” to adapt
Adaptation doesn’t involve “trying”
• Nat. Sel. leads to adaptation
• Stems from variation (genetic diversity) in the
population (no two individuals are exactly
alike)
• Some individuals will have genes
(characteristics) that will enhance its chances
of survival, and others won’t
Misconception: Evolution means
that life has changed “by chance”
• There is an element of chance (mutations,
genetic processes, movement of
populations, etc.) and of luck
• Selection of/for specific traits is not random
• Nat. Sel. favors characteristics that confer
an advantage to survival, thereby
increasing the frequency of that trait in the
population to keep it adapted to its
environment