Chapter 4
Origins of Life
Development of Life on the Primitive Earth: The Big Picture
 Scientific evidence indicates that the earth’s life is the result of about 1 billion
years of chemical change to form the first cells, followed by about 3.7 billion
years of biological change to produce the variety of species we find on the earth
today
 Biological evolution: the description of how earth’s life changes over time
 Natural selection: survival traits that would be more prevalent in future
populations of species; individuals in a population with some edge over other
individuals are more likely to survive, reproduce, and have offspring with similar
survival skills
o Charles Darwin and Alfred Russel Wallace both came up with this on their
own, but Darwin was the first one to mention it and purpose it
 Life on earth developed in two phases
o The first phase involved chemical evolution of the organic molecules,
biopolymers, and systems of chemical reactions needed to form the first
cells. This took about 1 billion years
o Followed by biological evolution by natural selection from single-celled
bacteria to multi-cellular protists, plants, fungi, and animals. This phase
has been going on for about 3.7 billion years
How Do we know Which Organisms Lived in the Past?
 Our knowledge about past life comes from fossil, chemical analysis, cores drilled
out of buried ice, and DNA analysis
 Fossils: mineralized or petrified replicas of skeletons, bones, teeth, shells, leaves,
and seed, or impressions of such items found in rocks
o Provide physical evidence of ancient organisms and revel what their
internal structures looked like
 Also drill cores from glacial ice and examine the kinds of life found at different
layers
 Also compare the DNA of past and current organisms
 Fossil record: the world’s cumulative body of fossils found
o This record is incomplete and uneven
o Difficult to reconstruct the development of life with so little evidence
Evolution, Natural Selection, and Adaptation
Genetic Mutations: Changes in a Population’s Gene Pool
 The most widely accepted idea is that biological evolution by natural selection
results from changes in a population’s genetic makeup overtime
 Biological evolution by natural selection involves the change in a population’s
genetic makeup through successive generations
 Important: Populations, not individuals, evolve by becoming genetically different
 Mutations: random changes in the structure or number of DNA molecules in a
cell that can be inherited by offspring

Mutations can occur in two ways
o By exposure of DNA to external agents such as radioactivity, X-rays, and
natural and human-made chemicals (called mutagens)
o From random mistakes that sometimes occur in coded genetic instructions
when DNA molecules are copied each time a cell divides and when an
organisms reproduces
 Some mutations are harmless, and some are lethal
o Every so often, a mutation can be beneficial
 If beneficial, it gives the organisms a better chance of survival and
reproduction under existing environmental conditions or when
such conditions change
Natural Selection and Adaptation: Leaving More Offspring with Beneficial Genetic
Traits
 Some members of a population may have genetic traits that enhance their ability
to survive and produce offspring with these traits
 Natural selection is the next step in conventional biological evolution
o survival traits that would be more prevalent in future populations of
species; individuals in a population with some edge over other individuals
are more likely to survive, reproduce, and have offspring with similar
survival skills
 Natural selections explains how populations adapt to changes in environmental
conditions
 Three conditions are necessary for biological evolution by natural selection
o First, there must be enough genetic variability for a trait to exist in a
population
o Second, the trait must be heritable, meaning that it can be passed from one
generation to another
o Third, the trait must lead to differential reproduction: is must enable
individuals with the trait to leave more offspring than other members of
the population
 Natural selection acts on individuals, but evolution occurs in populations
 Adaptation/adaptive trait: is any heritable trait that enables an organism to
survive through natural selection and reproduce better under prevailing
environmental conditions
o Natural selection tends to preserve beneficial adaptations in populations
and discard harmful ones
 When faces with an environmental change species have three possibilities
o Adapt to the new conditions through natural selection
o Migrate (if possible) to an area with more favorable conditions
o Become extinct
 Genes mutate, individuals are selected, and populations evolve that are better
adapted to survive and reproduce under existing environmental conditions
Coevolution: A Biological Arms Race
 Interacting species can engage in a back-and-forth genetic contest in which each
gains a temporary genetic advantage over the other

Coevolution: when populations of two different species interact over a long time,
changes in the gene pool of one species can lead to changes in the gene pool of
the other
o Each species is in a genetic race to produce the largest number of
surviving offspring
 The species develop new traits so they can beat the other species at their own
game, one set of species is always trying to do something to outsmart the species
Hybridization and Gene Swapping: Other Ways to Exchange Genes
 Sometimes different species can crossbreed to form hybrids that can survive and
reproduce, and some species can exchange genes without sexual reproduction
 Hybridization: when individuals of two distinct species crossbreed to produce an
individual or hybrid that in some cases has better ability to survive tan
conventional offspring of the two parent species
 Horizontal Gene Transfer: when some species (mostly microorganisms) can
exchange genes without sexual reproduction
 These two things can occur rapidly compared to the thousands to millions of years
required for the conventional Darwinian evolution
Limits on Adaptation Through Natural Selection
 A population’s ability to adapt to new environmental conditions through natural
selection is limited by its gene pool and how fast it can reproduce
 Limits to adaptations in nature through conventional conditions natural selection
o First, a change in environmental conditions can lead to adaptation
through conventional natural selection only for genetic traits already
present in a population’s gene pool
o Second, even if a beneficial heritable trait is present in a population,
the population’s ability to adapt may be limited by its reproductive
capacity
 Even if there is a beneficial trait in a population, everyone else in the population
has to die out, so the beneficial trait predominates the population to pass the trait
on through natural selection
 These limitations do not apply to development of new species through
hybridization and the exchange of genes between different species without sexual
reproduction
Common Myths about Evolution through Natural Selection
 Evolution through natural selection is about leaving the most descendants;
organisms do not develop certain traits because they need them or want them; and
there is no master plan leading to genetic perfection
 Three common misconceptions
o “Survival of the fittest” means “survival of the strongest”, fitness is a
measure of reproductive success, not strength; the fittest are the ones who
leave the most descendants
o Organisms develop certain traits because they need or want them
o This evolution involves some grand plan of nature in which species
become more perfectly adapted; no plan or goal of genetic perfection has
been identified in the evolutionary process
Geological Processes, Climate Change, Catastrophes, and Evolution
Geological Process and Evolution by Natural Selection
 The very slow movement of huge solid plates making up the earth’s surface,
volcanic eruptions, and earthquakes can wipe out existing species and help form
new ones
 Tectonic plates: a series of gigantic solid plates, have very slowly drifted back
and forth across the planet’s surface over thousands to millions of years
 Tectonic plates has two important effects on the evolution and location of life on
the earth
o First, the locations of consistent and oceanic basic greatly influence the
earth’s climate and this help determine where plants and animals can live
o Second, the movement of continents has allowed species to more, adapt to
new environments, and form new species through natural selection. When
continents join together populations can disperse to new areas and adapt to
new environmental conditions. An when continents separate, populations
must evolve under isolated conditions or become extinct
 Volcanic eruptions can also affect biological evolution by destroying habitats and
reducing or wiping out populations of species
 Earthquakes can separate and isolate populations of species. Over long periods of
time, this can lead to the formation of new species as each isolated population
changes genetically in response to new environmental conditions
Clime Change and Natural Selection
 Changes in climate through the earth’s history have shifted where plants and
animals can live
 Long-term climate changes have a major effect on biological evolution by
determining where different types of plants and animals can live and thrive and by
changing the locations of different types of ecosystems
 Some existing species became extinct because the climate changed too rapidly for
them to survive and new species evolved
Catastrophes and Natural Selection
 Asteroids and meteorites hitting the earth and large upheavals of the earth’s crust
from geological processes have wiped out large numbers of species and created
opportunities for the evolution by natural selection of new species
 Each major catastrophe resulted in long periods of extreme environmental stress
o This changed the course of evolution by wiping out large numbers of
existing species
o Such mass extinctions also have opened up opportunities for the evolution
by natural selection of new species and shift in the locations of different
types of ecosystems
Ecological Niches and Adaptation
Ecological Niches: How Species Live and Coexist
 Each species in an ecosystem has a specific role or way of life
 Ecological niche: is a species’ way of life or role in a community or ecosystem
and includes everything that affects its survival and reproduction

Each species has a distinct niche or role to plat un the ecosystems where it is
found
 Fundamental niche: consists of the full potential range of physical, chemical,
and biological conditions and resources it could theoretically use if it could avoid
direct competition from other species
o Of course, different species often compete with one another for the same
resources
o The niches of competing species overlap
 Realized Niche: to survive and avoid competition for the same resources, a
species usually occupies only part of its fundamental niches in a particular
community or ecosystem
Generalists and Specialists Species: Broad and Narrow Niches
 Some species have broad ecological roles and other have narrow or more
specialized roles
 Generalist Species: have broad niches; can live in many different places, eat a
variety of foods and tolerate a wide range of environmental conditions
 Specialists Species: occupy narrow niches; may be able to live in only one type
of habitat, use one or a few types of food, or tolerate a narrow range of climatic
and other environmental conditions
 Specialists are more prone to extinction when environmental conditions change
 When is it better to be one or the other?
o If the environmental conditions are fairly constant specialists have an
advantage because they have fewer competitors
o Under rapidly changing environmental conditions, the generalists usually
is better off
 Natural selection can led to an increase in specialized species when several
species must compete intensely for scarce resources
o Over time one species may evolve into a variety of species with different
adaptations that reduce competitions and allow them to share limited
resources
 Evolutionary Divergence: starting with a single ancestor, the species begin to
evolve different types of traits in order to survive in their specific habitat, to
access certain resources
Speciation, Extinction, and Biodiversity
How Do New Species Evolve?
 A new species can arise when members of a population are isolated from other
members for so long that changes in their genetic makeup prevent them from
producing fertile offspring if the get together again
 Speciation: two species arise from one
o For sexually reproducing species, a new species, is formed when some
members of a population cannot longer breed with other members to
produce fertile offspring
 The most common mechanism of speciation takes place in two phases:
geographic isolation and reproductive isolation
o Geographic Isolation: occurs when different groups of the same
population of a species become physically isolated from one another for
long periods of time
 Separation by physical barrier, by a change such as a volcanic
eruption or earthquake, or by few a few individuals being carries to
a new area by wind or flowing water
o Reproductive Isolation: mutation and change by natural selection operate
independently in the gene pools of geographically isolated population
 After these two phases have happened, speciation has occurred
Extinction: Lights Out
 A species become extinct when its populations cannot adapt to changing
environmental conditions
 Extinction: when an entire species ceases to exist
 Endemic Species: species that are only found in one area in the world and are
especially vulnerable to extinction
Background Extinctions, Mass Extinction, and Mass Depletion
 All species eventually become extinct, but drastic changes in environmental
conditions can eliminate large groups of species
 Background extinction: as local environmental conditions change, a certain
number of species disappear at a low rate
 Mass extinction: is a significant rise in extinction rates above the background
level, widespread (often global) event, large groups of existing species are wiped
out in a geological period lasting up to 5 million years
o Evidence shows that there has been 5 mass extinctions during the past 500
million years
 Mass Depletion: in which extinction rates are higher than normal but not high
enough to classify as a mass extinction
 During times of mass extinction and depletion, it is an opportunity for other
species that can fill unoccupied niches or newly created ones
Effects of Human Activities on the Earth’s Biodiversity: Are We a Wise Species?
 The scientific consensus is that human activities are decreasing the earth’s
biodiversity
 Speciation minus extinction equals biodiversity, the planet’s genetic raw material
for future evolution in response to changing environmental conditions
 Extinction is a natural process, but humans have become a major force in the
premature extinction of a growing number of species
 We are also destroying and degrading ecosystems that are centers for future
speciation
Genetic Engineering and The Future of Evolution
Artificial Selection and Genetic Engineering
 We selectively breed members of populations to produce offspring with certain
genetic traits and use genetic engineering to transfer genes from one species to
another

Artificial selection: to change the genetic characteristics of populations with
similar genes
o We select one or more desirable genetic traits in the population of a plant
or animal
o Then we use selective breeding to end up with populations of the species
containing large numbers of individuals with the desired traits
 Today scientists use genetic engineering to speed up our ability to manipulate
genes
 Genetic Engineering, or Gene Splicing: is the alteration of an organism’s
genetic material through adding, deleting, or changing segments of its DNA, to
produce desirable traits and eliminate negative ones
o This allows scientists to transfer genes between different species that
would not interact in nature
 Recombinant DNA: (key tool used in genetic engineering) which is DNA that
has been altered to contain genes or portions of genes from organisms of different
species
 Genetically Modified Organisms (GMOs) or transgenic organisms: organisms
that have been genetically engineered by use of recombinant DNA technology
Synthetic Biology and Cloning
 Biologists are learning to rebuild organisms from their cell components and to
make identical copies or clones of organisms
 Synthetic biology: to go beyond conventional genetic engineering, spate cells
into their fundamental components, and use them to rebuild new organisms
 Clone: a genetically identical version of an individual in a population
Some Concerns about the Genetic Revolution
 Genetic engineering has great promise for improving the human condition, but it
is an unpredictable process and raises a number of privacy, ethical, legal, and
environmental issues
Controversy over Genetic Engineering
 There are arguments over how much we should regulate genetic engineering
research and development
Case Study: How did We Become Such a Powerful Species so Quickly?
 We have thrived as a species mostly because of our strong opposable thumbs,
ability to walk upright, and complex brains