Transcript EvolutionPPtSE2016

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
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 all
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 morefit 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.