Transcript Darwin’s Theory of Evolution

The Theories of Evolution
Species change over time!!!
• Species evolve (change) over time.
• Evolution is the consequence of the interactions of
– (1) the potential for a species to increase its numbers
– (2) the genetic variability of offspring due to mutation and
recombination of genes
– (3) a finite supply of the resources required for life
– (4) the ensuing selection by the environment of those
offspring better able to survive and leave offspring
Evolutionary Foundation
• Hutton and Lyell helped scientists recognize that Earth is
many millions of years old, and the processes that changed
Earth in the past are the same processes that operate in the
present.
• Lamarck proposed that by selective use or
disuse of organs, organisms acquired or lost
certain traits during their lifetime. These traits
could then be passed on to their offspring.
Over time, this process led to change in a
species = Adaptation
• Malthus reasoned that if the human population continued to
grow unchecked, sooner or later there would be insufficient
living space and food for everyone.
Introducing Evolutionary Theory
• We share Earth with millions of other organisms
(variety of living things) = Biological Diversity
– How is everything so different?
• Evolution = change over time leading to modern
organisms that have descended from ancient
organisms
• Theory = well-supported testable explanation of
phenomena that have occurred in the natural
world
Introducing… Charles Darwin!
• In 1831, Darwin set sail on the Beagle for a voyage around the
world
• During his travel, Darwin
made numerous
observations and collected evidence that
led him to propose a revolutionary
hypothesis about the way life changes over
time = The Theory of Evolution
• Darwin used these observations to scientifically explain the
diversity of life on this planet.
The Galapagos Islands
• Darwin observed that the characteristics of
many animals and plants varied noticeably
among the different islands.
Pinta Island
Intermediate
shell
Hood Island
Saddlebacked shell
Isabela Island
Dome-shaped shell
Natural Variation & Artificial Selection
• Natural Variation = differences among
individuals of a species
– Variations can be inherited from one
generation to the next
• Selective breeding = humans select desirable
traits and breed based on natural variation (to
improve crops/farms)
– Darwin called this artificial selection = nature
provides variation among different organisms,
and humans select variations they found
useful.
Evolution by Natural Selection
• Living things evolve as the result of:
– The struggle for existence
– The survival of the fittest
– The descent with modification
Peacock tail evolution:
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
Struggle for Existence
• Darwin was convinced artificial selection
worked in nature as the result of overproduction
and competition for resources = struggle for
existence (members of each species compete
regularly to obtain food, living space, and other
necessities of life)
– Depends on an individual’s ability to survive
and reproduce = fitness
– Fitness results from adaptations = inherited
characteristics that increase an organism’s
chance of survival
Natural Selection
• Survival of the fittest = Natural Selection!
– Traits are being selected and increasing over
time (over many generations without human
influences)
• Over time, natural selection results in
changes in the inherited characteristics of
a population. These changes increase a
species’ fitness in its environment.
Descent with Modification
• Over time, natural selection
produces organisms with different
structures or functions resulting in
species that look different from
their ancestors
– Each living species has
descended with changes
from other species over
time = Descent with
Modification
• Then, all living things must be
related!
– There’s a common ancestor of
all living things = Common
Descent
Evidence of Evolution
• Living things have been evolving on Earth
for millions of years. Evidence of this
process could be found in:
– The fossil record
– The geographical distribution of living
species
– Homologous structures of living organisms
– Similarities in development
Geographic Distribution
• Populations in different
places adapted to different
environments… different
species descended with
modification from a common
ancestor.
• Different species living in
similar environments in
different parts of the world
sometimes have similar
structures and functions
because they experienced
similar pressures of natural
selection
Homologous Structures
• Some vertebrates have similar bone structures that develop
from a specific group of cells in an embryo, but the structures
adapted different functions so the organism can survive in
different environments providing evidence of descent with
modification from common ancestors
• Homologous Structures = they appear and
function differently, but develop from the same
embryonic tissues
• Some homologous structures provide little or
no function in some organisms = vestigial
organs
Similarities in Development
• Embryos of many
vertebrates look very
similar in the early
stages of
development.
• The same groups of
embryonic cells
develop in the same
order and in similar
patterns producing
homologous
structures