LIFE AND NATURAL SELECTION
 The Study of Life
 Biology is the study of life
 But, what exactly is life?
 We all recognize it but defining it can be a challenge – there is no single correct definition
of life
 Some features of living things include:
o Order
o The need for energy
o Growth and development
o Regulation of one’s internal environment
o The ability to reproduce
o The ability to respond to one’s external environment
o Evolutionary adaptation
 We will begin our study of life by examining how life behaves over successive generations 
life is not static, and it changes with time
 How does life change or “evolve” as a result of natural selection?
 Natural Selection and Evolution
 Biological Evolution = change in the genetic structure of a population
o Evolution is any change across successive generations in the heritable characteristics
of biological populations
o Evolution is a very important process and reoccurring theme throughout biology and
biodiversity
o This process of evolution gives rise to the diversity of life that exists in our world at
every level of biological organization
o Evolutionary processes have shaped life’s diversity and adaptations
  natural selection leads to adaptations
 Adaptations = traits that help an organism survive in its current environment
 An evolutionary timeline of life represents the major events during the development of life
on planet Earth
o Through similarities between organisms we know that all life is related
o And can be traced back to the presence of a common ancestor from which all known
species, living and extinct, have diverged, through the process of evolution
 Since life first appeared, evolution has resulted in a continuous branching of new species
that can be described as a tree of life
o The tree of life is an ever-evolving depiction of the evolutionary relationships between
all living things on Earth
o The tree shows how all organisms are related through their descent from a common
ancestor that existed some 3.7 billion years ago
 The root/base = life’s common ancestor
 Tree’s tips = modern species
 Vast branching (between the root and the rips) = describes the history of life on the
planet
 Evolution has many facets that have contributed to the diversity of life – however, only one
process adapts life to the environment; this process is natural selection
 What is Natural Selection?
 Natural Selection = the best adapted individuals are more likely to reproduce then less
well adapted individuals – “differential reproduction”
o Natural selection is a process by which a population becomes better adapted to its'
environment over time
o However, environments are always changing causing the best adaptations in an
environment to also change
o Changing environments drive evolution via natural selection
 Genetics and genetic diversity plays an important role in understanding natural selection
o At the most fundamental level, natural selection results in changes in the frequency of
certain genes and/or alleles over successive generations within a population
o In order for natural selection to act on a population, there must be genetic variation in
the population and the genes and alleles that are selected for are the ones that result
in adaptation
 A Real Life Example of Evolution and Natural Selection – Habitat Divergence in “Evolution
Canyon”
PHOTO A
 Shows part of the “African” slope/south-facing slop of Evolution Canyon
 Characterized by light terra rossa soil with a stretch of grass cover that generates a yellowbrownish background
PHOTO B
 Part of the “European” slope/north-facing slope
 Characterized by dark terra rossa soil and shady, humus-laden dark background
o Evolution Canyons I and II are found in Israel in the Carmel and Galilee mountain ranges
o These areas are ideal for the study of evolution because each range has a north-facing slope
with relatively temperate environmental conditions and a south-facing slope with relatively
extreme UV radiation (the south-facing slopes receive 200 – 800% more solar radiation than
north-facing slopes), daily temperature variation, and arid conditions
o Scientists are interested in exploring how these different environmental conditions lead to
evolutionary changes in organisms
o An example of an evolutionary change is a change in coat color in mammals
o Many mammals, particularly prey organisms, have evolved coat coloration that matches their
environment in order to provide camouflage from predators
o Singaravelan et al (2010) investigated how hair melanin content of spiny mice (Acomys
cahirinus) has evolved in response to alternative selection pressures inflicted by contrasting
colored habitats of Evolution Canyon
o There are two main forms of melanin:
 Pheomelanin  results in yellow to brown hair color
 Eumelanin  results in gray to black hair color
1. Based on this information, do you expect mice that live on the “African” slopes to have higher
pheomelanin content in their hair or higher eumelanin? What do you expect of mice living on
the “European” slopes?
2. Explain how a change in environmental conditions can result in an evolutionary change in a
population.