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
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
• 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:
• Differences (variation) exist between individuals
• Some of these differences are passed down to
offspring
• Differences matter when change in environment
(selective pressure) occurs
• Those individuals with favorable traits have an
advantage over those who do not
•
•
More likely to survive, reproduce, and pass on those
traits to offspring
Environmental context (nature) determines which
traits are advantageous
Natural Selection, cont.
• Favorable traits increase while less
favorable traits decrease
• Over long periods of time, successful
variations/traits accumulate such that later
populations may become distinct from
ancestral ones, hence, new species evolve
• Populations are adaptable & can change
over time in response to changing
environments
What is 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
Lamarck vs. Darwin
Lamarck:
Variation when need
Darwin:
Variation already present
Natural Selection, 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
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
The “–isms” and “schisms” of
Darwin’s Theory
“-isms”
1. Implies a “belief system,” like
Hinduism, absolutism, etc.
2. Ideas associated with Nat. Sel.
used to explain & justify
social differences (Social
Darwinism) or “survival of the
fittest” – Not Darwin’s doing
3. Darwinism used synonymously with “Evolution”
4. Darwin’s name & ideas used
by others to advance their own
agendas
“schisms”
1. Seemed to contradict
religious explanations
2. Led to Eugenics movement,
including the Holocaust;
Darwin never used term
“survival of fittest”
3. Process of evolution
includes much more than
Darwin ever explained or
understood (in 19th century)
4. Darwin would never have
supported those agendas
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
Natural Selection in Action:
Darwin’s Finches Revisited
Beak of the Finch