Transcript Evolution

Evolution
Introduction
Charles Darwin
 Born in England in 1809
 Enrolled in divinity school at Cambridge; graduated
in 1831
 In 1831, Darwin signed on the naturalist on the
HMS Beagle & traveled around the world for the
next 5 years
 He gathered data during his travel; that data
was used as the basis for his books and
ideas on evolution
Bozeman Biology: Evolution
(9.22 min.)
Evolution Defined
 The change that has
occurred in a species
of organism with the
passage of time.
 The passage of time is
used here to mean
from the distant past
to the present.
 Diversity of living
things is a direct result
of biological evolution.
 Traits in species and
organisms developed
overtime by evolution.
 Evolution unifies all
the different areas of
study of biology.
Fossil Evidence for Evolution
 Fossils are the remains of organisms that lived in
the distant past.
 Countless organisms have lived and died since life
began; many left behind remains.
 Examining structures in a fossil species &
comparing them to similar species today, evolution
can be seen.
 Examples of fossils and their
method of formation are
hard parts, imprints,
molds, petrifaction,
refrigeration, amber
and tar pits.
Hard Parts
 Hard parts are bones, teeth, or shells of organisms
that lived in the past.
 Hard parts often survive the natural process of
decay.
 Evolution is change, for
example fossil skeletons
of horses show how this
organism has evolved
from a small horse to
the modern day large
horse.
Imprints
 Imprints are impressions made by
plants and animals in soft soil or mud,
that with the passage of time harden
to become rock
 Example: dinosaur footprints & outlines
of leaves in rocks
Molds
 An organism suddenly dies in the ocean & sinks to
the bottom becoming covered with mud, as it
decays its outline remains, forming a mold of that
organism
 The sand and mud harden to form rock, then
millions of years later the rock can be opened to
reveal the mold of that organism
Petrifaction
 Minerals in water that covered trees and
bones of organisms diffused into the cells of
the organism, forming rock that resembles
the organic tissue that was replaced
 Examples: petrified forests & petrified wood
Refrigeration
 Occurs when an organism is preserved by cold
temperatures or ice
 Mammoths have been found preserved in ice, in
remarkably good condition
Amber

A form of fossilized resin from trees that lived
millions of years ago

As the resin dripped down from the tree, it often
trapped and surrounded an insect or part of a plant

As the resin hardened, the organism that was
trapped inside was preserved

Most amber comes from the Dominican Republic

Amber is prized by jewelers for its gem-like quality &
by scientists for any organism that might be trapped
inside
Tar Pits
 Accumulation of oil or asphalt that seeped up to the
earth’s surface.
 Animals often became trapped in the sticky asphalt,
resulting in the soft parts of the animal decayed, but
the hard parts were preserved by the asphalt
 The La Brea tar pits in Los Angeles are famous for
fossils of dire wolves, saber-toothed tigers,
mammoths, horses, camels and other organisms
 Other tar pits have been found in Iran, Peru, Poland &
Russia
Dating of Fossils
 Two different techniques used to date fossils
 Relative dating & absolute dating
Relative Dating
 Method used to determine the age of a fossil by
comparing its location relative to fossils in nearby rock
layers
 An exact age is not assigned to a fossil
 When a rock formation is examined, the oldest fossils
are found in the bottom layer & the youngest are found
in the top
 Some species of organisms were once found all over the
world, but lived for a short time. Fossils of these
organisms are called index fossils.
Absolute Dating
 Method used to determine the approximate age of a
fossil by relying on the radioactivity of certain elements
& their half lives
 Half life is the amount of time that it takes for an
element to decay into half of its original amount
 The older the fossil, the more the radioactive element
has decayed
 Fossils of organisms that lived up to 50,000-70,000
years ago can be dated using Carbon-14
Sedimentary Rock
 Most fossils are found in sedimentary
rock, which is formed by the deposition of
very small particles of rock, clay or silt.
 It forms in layers, often in water & takes
millions of years to form
Igneous Rock
 Formed by volcanic activity & never
contains fossils
 The high temperature associated with the
formation of this rock incinerates any
organism unfortunate enough to be caught
in the lava flow
Metamorphic Rock
 Formed by tremendous heat and pressure
applied to igneous & sedimentary rock
 Fossils are not found in metamorphic rock
Additional Evidence of Evolution
 A common ancestor is an individual from which 2 or
more related species could have evolved
 With time, organisms change and diverge from their
common ancestor to form new species
Comparative Anatomy
 Anatomy is the body structure
 Evolutionary relationships based on comparative
anatomy depend on homologous structures
 Homologous structures are similar in construction &
evolutionary development but dissimilar in function
 Analogous structures are similar in function but
dissimilar in construction & evolutionary development &
are not used in comparative anatomy
 Vestigial structure at one time had a function in the
evolutionary history of an organism but now does not
have a function
Comparative Embryology
 Similarity exists between vertebrate embryos
 As the embryos develop, they begin to acquire the
unique characteristics of their species
 The similarity of embryological development supports
the concept of the common ancestor
Comparative Biochemistry
 DNA, RNA, the genetic code & protein synthesis are
similar in all organisms
 The greater the genetic and molecular similarity
between species, the closer the common ancestor
 Humans & chimpanzees have 98% of their genes in
common
 Hemoglobin in humans is almost identical to hemoglobin
in all other vertebrates.
 The similarity in chemical structure demonstrates that al
vertebrates can be traced back to a common ancestor
Theories of Evolution
 Naturalists tried to explain the changes they
observed in the fossil record through the
concepts of acquired characteristics and use
and disuse
 In 1859, Charles Darwin published his view on
evolution in his book On the Origin of Species
 He proposed the theory of natural selection
 Hugo De Vries ( early 1900’s) updated the
theory of natural selection by suggesting that
mutations are a source of variation in a
population
Natural Selection
 Natural selection explains how evolution takes
place
 Overproduction: When members of a species
reproduce, they produce more offspring than is
necessary
 Struggle for survival: Overproduction results
in competition for scarce resources such as food,
water & territory
 Variation: Within every population, members of
a species show variation (differences) in their
traits
Natural Selection
continued
 Natural Selection: Nature selects
those variations that are most fit.
Organisms with the best variation
survive the struggle for existence &
reproduce & are then passed on to
the next generation
 Formation of new species: The
most fit variations become the norm
within the population. The less fit
variations are eliminated. Eventually,
a new species of organism evolves,
that is significantly changed from
that of its ancestor.
Natural Selection
(10.16 min.)
Mutation
 A source of variation in a population that can lead to
the formation of new species with the passage of
time
 Hugo De Vries noted sudden changes in the evening
primrose, he called the changes mutations
The Rate of Evolution
 Can be explained by gradualism & punctuated
equilibrium
 Gradualism: evolution is a slow and gradual process
that proceeds in numerous small steps, taking many
years and generations for new species to form
 Punctuated equilibrium: biologists believe that
evolutionary change occurs in sudden spurts during
which many new species are formed, followed by long
periods of stability with no speciation
The Hardy-Weinberg Law
 Discovered by G.H. Hardy & W. Weinberg in 1908
 It predicts how gene frequencies are maintained from one
generation to the next
 This law states that in a population the frequency of an
allele remains constant from generation to generation, as
long as five conditions are met
 It can be stated in mathematical terms
In order for the Hardy-Weinberg
Law to work, these 5 conditions
must be met
 The gene pool must be large to provide statistical
accuracy of the Hardy-Weinberg Law
 No migrations can be allowed into or out of the
population because this changes the frequency of alleles
 Mating must be random to ensure that the laws o
probability work. The organisms decide who their mates
are without restrictions or interference
 No mutations can occur because mutations can change
the frequency of an allele within a population
 No natural selection can be present because it tends
to favor individuals within the population that have
more-fit alleles
Geographic & Reproductive
Isolation
 Geographic isolation is caused by geographical barriers
such as mountains, deserts, oceans, and rivers
 It results in the physical separation of individuals within
a population, preventing random mating between
individuals
 Eventually, the organisms become reproductively
isolated and are no longer able to mate and produce
fertile offspring
 When that happens, two new species have developed
 Reproductive Isolation also occurs when species
reproduce during different times of the year, have
different mating rituals, or have reproductive structures
that prevent mating between the male and female
Environmental Factors
 They can favor one variation of a trait over another,
resulting in a change in the frequency of an allele within
a population
The Origin of Life on Earth
 A.I. Oparin & J.B.S. Haldane proposed the heterotroph
hypothesis to explain how the first cells might have
originated on earth
 According to this hypothesis, the first cells on earth were
heterotrophs and most likely originated in the ocean
The Heterotroph Hypothesis
 A modern explanation states that the earth’s early
atmosphere was a reducing atmosphere (one with little
or no oxygen).
 Among the gases that were probably present were:
water vapor, nitrogen, carbon monoxide, carbon dioxide,
& some hydrogen
 UV radiation, high temperature & lightning were energy
sources for chemical reactions between the gases
 These reactions may have resulted in the production of
simple organic compounds such as simple sugars, amino
acids, fatty acids, glycerol and nucleotides
Complex Organic Compounds
 Took place in oceans
 Producing complex carbohydrates, proteins, lipids &
nucleoproteins
 Compounds grouped together and formed the first
primitive prokaryotic heterotrophic cells
 These early heterotrophs used organic compounds in the
ocean as a source of energy, producing alcohol & carbon
dioxide as waste products
 The first autotrophs were primitive prokaryotic cells
 They used carbon dioxide & water to produce glucose &
oxygen by photosynthesis
 The early autotrophs introduced oxygen to the
atmosphere
 Modern heterotrophs are eukaryotic & developed the
ability to use oxygen for respiration
 Aerobic respiration produces more energy than
anaerobic respiration
As the saying goes;
the rest is evolutionary
history.
Endosymbiotic theory
 Heterotrophic and autotrophic eukaryotic cells developed
from a symbiotic relationship between prokaryotic
organisms
 Prokaryotic organisms with the ability to produce energy
from organic molecules were ingested by a larger
prokaryote, were incorporated into the cell, then evolved
to become the mitochondria of modern heterotrophs
 Other prokaryotic organisms with the ability of
photosynthesis were ingested by a prokaryote and
evolved into the chloroplasts of modern autotrophs
 The theory is supported by the fact that mitochondria
and chloroplasts have their own DNA & reproduce
independently of the cell by binary fission
 Eukaryotic cells reproduce by mitosis
 Mitochondria & chloroplasts have ribosomes that are
similar to prokaryotic organisms