Transcript Principles of Evolution

Principles of Evolution
What is Evolution?
• Evolution is the change in inheritable
traits in a population over generations.
• Change in traits is caused by changes in
the genes (in DNA) that code for those
traits.
• Natural selection tends to increase
favorable traits in a population and
decrease unfavorable traits.
What Evolution is NOT
• Many people argue against evolution
based on statements they have heard.
Yet many of those statements are ideas
that are not part of evolutionary theory.
Evolution is NOT about things
getting “better and better” or
more and more complex.
Evolution is NOT about
organisms “trying” to adapt.
Evolution does NOT give
organisms what they “need.”
Evolution does NOT mean
that individuals in a
population slowly change.
Evolution is NOT a theory
of how life began.
Early Ideas
• While many people associate evolution
with Darwin, other scientists were talking
about organic change long before
Darwin published his theory of natural
selection.
Aristotle (384-322 B.C.)
viewed the living world as
fixed and unchanging. All
living things could be
arranged in a ladder from
inferior to superior, with
humans on top. Aristotle’s
views influenced thought for
over 2000 years.
Curiosity about fossils around the 16th century led to
new questions.
Were fossils the
remains of
organisms?
If they were, what
did this say about
species being
unchanging?
James Hutton
(1726 - 1797)
Charles Lyell
(1797 - 1875)
These two naturalists are best known for the theory of
Uniformitarianism, proposed by Hutton and expanded by
Lyell. Uniformitarianism states that the physical laws that
now shape the earth have always done so, and that the
past can be understood by studying the present. Both
suggested that the Earth is very old.
Jean-Baptiste de Lamarck (1744 1829)
Lamarck sought a naturalistic explanation
for the diversity of modern organisms and
the animals seen in the fossil record.
Lamarck used the theory of Inheritance of
Acquired Characteristics, a widely-held
belief at the time, to explain change in
organisms. Blacksmiths, for example, were
thought to pass their well-developed right
arms on to their sons.
Lamarck’s Theory of Development
Organisms are shaped by their
environment.
Change is goal-directed -organisms have an internal drive
to become more and more
complex.
Use and disuse of parts causes
change that is passed on from
generation to generation.
Charles Darwin
(1809 - 1882)
and
Alfred Russell
Wallace
(1823 - 1913)
Darwin and Wallace, working separately, devised a model
for organic change that was based on their observations of
living and fossil organisms over many years. Natural
Selection was the first evidence-based mechanism for
evolution that was proposed.
Darwin and Wallace observed that change did not
happen equally to all members of a population, as
Lamarck and others had thought.
Instead, Darwin and Wallace proposed that selection
happens each generation. Some individuals have traits that
help them survive and reproduce, while others have traits
that put them at a disadvantage.
Over generations, the number of individuals with favorable
traits increases while those with unfavorable traits
decrease.
Natural Selection
• Process by which individuals with
inherited characteristics well-suited to
the environment leave more offspring
• 4 Principles of Natural Selection
• Variation
• Heritability
• Overproduction
• Reproductive Advantage
Natural Selection
Variation
Within any population,
individuals differ from
one another in many
ways.
Natural Selection
Heritability
Some differences
between
individuals are
inheritable, and
can be passed
from parent to
offspring.
X
Natural Selection
Overproduction
In most populations,
more young are born
than can survive. Many
of the young will die. A
few will live long
enough to reproduce.
Natural Selection
Reproductive
Advantage
While random accidents
do happen, an
individual’s survival
depends mainly on the
individual’s traits. Those
that are better suited to
their environment may
pass their traits to the
next generation.
Evidence for Evolution
• Darwin spent over 20 years collecting
evidence and reading research by others
before he wrote On the Origin of Species.
• He found many features of organisms that
suggested they were related by ancestry.
Fossils
Fossils showed that
species existed in
the past that no
longer exist today,
and species exist
today that did not
exist in the past.
In many groups of organisms, fossils demonstrated
change from one form to another over long periods
of time.
Homologous Structures
Four-limbed vertebrate animals all have the same bones in
the forelimbs, but the bones are shaped differently. In
modern terms, this suggests a shared set of genes (for the
bones) arising from common ancestry.
Common structure – different function
Vestigial Structures
Vestigial organs are remnants of structures that may have
had important functions in an ancestral species, but have
no clear function in some of the modern descendents.
Embryological Similarities
Lemur
Pig
Human
Similar structures and similar developmental processes in
embryos demonstrate a shared set of genes between
groups of organisms, suggesting common ancestry.
Note: Humans do not become fish or grow gills during
development. We do share several embryological
features with other vertebrate animals.
Biochemical and Genetic Analysis
Darwin inferred
shared ancestry from
shared traits.
Modern analysis of
DNA demonstrates
shared genes for
many traits between
related species,
suggesting descent
from a common
ancestor.
Mice and humans both have the gene
for the protein Cytochrome c. Small
differences show changes over time
as the two groups diverged.
Recap
• Evolution is the change in inherited traits
in a population over generations.
• Fossils, molecular data, and other
evidence shows that the genetics of a
population do change over time.
• Natural Selection, one mechanism for
change, is well-supported by evidence.
Evidence for Selection
• In order to construct his theory, Darwin
had to gather and examine evidence to
discover whether selection happens in
nature.
Natural Selection
Selection favors organisms that
are best adapted to the
environment.
Biological “fitness” is about
survival, and those organisms
with traits that help them
survive are more likely to
reproduce.
Artificial Selection
Darwin knew from his studies of pigeon breeding that
selection can change organisms, sometimes rapidly.
Human selection created many breeds of dogs from wild
dogs or wolves as humans chose to breed those
animals with traits that the humans wanted.
Selection acts on variations
Studies have shown that
guppies living in ponds
with few predators are
more brightly colored than
those living with many
predators.
In both populations there are guppies with genes for
bright colors. Why are dull colors favored in ponds with
many predators? Why are bright colors favored in ponds
with few predators?
Selection does not cause new variations.
Studies on Anole lizards showed
that long, fast-moving legs were
favored where trees had thicker
branches, while shorter, more
agile legs were favored where
trees were flimsier.
If lizards from places where trees had thin branches were
moved to a place where trees had thick branches, those
with the longest legs survived better. Each generation had
more individuals with longer legs because the genes for
longer legs were already in the population.