Transcript Emerging Diseases

Emerging Diseases
Lecture 3:
Important Theories
3.1: Overview
3.2: Theory of Evolution
3.3: Cell Theory
3.1Overview: Three Important
Theories
The Theory of Evolution (late 1800s)
Through preferential reproduction of some
members, species change over time in adaptionb
to external changes such as environmental
change.
The Cell Theory (mid 1800s)
All living organisms are made up of one or more
cells.
The Germ Theory (late 1800s)
See Lecture 1.
3.2: The Theory of Evolution
theresearch
Charles Darwin
credited with the
basic idea and
the research
More individuals are born than can survive.
Individuals in a population are different from
each other.
These differences are passed down to offspring.
What determines who survives?
• The inherited differences that produce some
advantage.
• The survivors reproduce-therefore their
offspring have the advantageous
characteristics.
• This is called selection.
Natural Selection
• Natural selection is what occurs in the real
world
• Modern biology
understands
genetic changes
such as mutationthough Darwin did
not
Darwin realized that generations of natural
selection could account for the origin of new
species, biotypes, strains or races.
Artificial Selection
• Caused by humans-usually through selective
breeding-for example domestic animals.
• But also in hospital
settings
Individuals with maladaptive traits
tend not to survive and reproduce
In modern times, this is recognized by the
annual “Darwin Awards”
3.3: The Cell Theory
All living organisms are composed of at least one
fundamental building block called a cell.
This theory took almost 200 years to develop.
Became fully accepted in the 19th Century.
Modern Understanding of the Cell Theory
All modern day cells are related to one another by
descent from a common ancestor (evolution)
There are three types of cells and thus three main
groups of organisms. These groups are called
domains.
Archaea
Bacteria (aka Eubacteria)
Eukaryotes
Archaea
• Single-celled
• Harsh
environments
• Ancient form of
life
• No nucleus
(prokaryote)
• Not known to
cause disease
Bacteria or Eubacteria
• Single-celled
• Many
environments
• Very diverse and
“creative”
• No nucleus
(prokaryote)
• Many are disease
agents
Eukaryotes
• Single or multicelled
• Contain a
nucleus
(eukaryote)
• Many are disease
agents
• Humans are
Considered large and complex
eukaryotes
Evidence for Three Domains
• Lots of biochemical evidence
• The best evidence comes from studies of
genes. The genes fall into 3 main groups based
on the code that the genes contain.
• Evidence first provided by Carl Woese.
“Universal Tree” of Life