Transcript Evolution Notes

Evolution Patterns
Macroevolution: changes of many different species over extremely
long periods of time.
Coevolution: A change in two or
more species in close association
with each other.
• plants and the animals that help
pollinate them
Convergent Evolution: Similar
phenotypes are selected by the
environment.
• dolphin vs. sharks – fins,
streamlined body
Evolution Patterns
Divergent Evolution:
two or more related
populations become
more and more
dissimilar.
-Often the result of
habitat change
-Can result in the
formation of a new
species
Human Intervention can
speed this up with
“Artificial Selection”
(e.g. Dog breeding)
Evolution and Populations
Variations and Trends of Natural Selection
Traits of organisms are often studied by “Populations”
Population – a collection of individuals of the same species that
routinely interbreeds. It is the smallest unit in which evolution
occurs.
Phenotypes will vary within a population.
Variations happen because of:
– Random fusion of gametes
– Recombination/crossing-over
– Mutations
If a trait is graphed for a large number of
individuals, it will follow the bell-curve
trend:
Bell Curve
Evolution & Populations
Variations and the process of natural selection can potentially
change the population’s most common phenotype and therefore
affect the bell curve. The four primary types of “selection” are
provided.
Stabilizing Selection – The individuals
in the population that have the
average form of the trait are best
adapted for the environment and
succeed in reproduction.
The center of the bell-curve is more
prominent. Something like body
size is an example.
Directional Selection – The
individuals in the population that
have one of the extreme versions of
the trait are best adapted for the
environment and succeed in
reproduction.
The hump in the bell curve shifts either
direction. Tongue length of
anteaters is an example.
Bell Curves
Evolution & Populations
Disruptive Selection – The individuals
in the population that have EITHER
extreme from the average trait are
best adapted for the environment and
succeed in reproduction.
The bell curve splits and
almost becomes 2 curves.
Shell color in limpets.
Bell Curve
Sexual Selection – The female of an
organism can choose a mate
specifically because of certain
traits.
Selection is successful reproducers, not successful survivors!
Evolution: People & Theories
Jean Baptiste de Lamarck (1744-1829)
• Acquired traits passed to offspring – the
webbed foot of a water bird being created from
stretching membranes between birds toes
would be passed on to offspring.
• Use or lose – if an organism did not use a part
of its body (tail) it would produce offspring with
smaller versions of that part until it didn’t have
that part at all.
• His theories were easy to disprove; the
described phenotypes were not always
genetically carried on. He does get credit for
saying that organisms must change over time
and the newer organisms were modified
versions of previous organisms.
Evolution: People & Theories
Charles Darwin (1809-1882)
• He provided the basis of
modern evolutionary theory.
• HMS Beagle – Darwin worked
on a 5-year voyage as a
naturalist. Traveled to South
America and the South Pacific.
He collected specimens and
took detailed notes – often
requesting to be left at ports
along the way. QUALITATIVE
OBSERVATIONS!
Galapagos Islands were especially important! Because of
GEOGRAPHIC ISOLATION, many of the plants and animals
were unique to the island.
Evolution: People & Theories
Specifically he studied
13 types of finches.
They all had
different beaks
related to their
primary food
source; all were
obviously
descendents from
an original.
Darwin understood these animals had to have changed over time. He wasn’t sure
how. The finch offspring had only been adapting for what was a relatively “short”
geologic time. He concluded: over many millions of years, large differences in
all known organisms could have occurred.
Evolution: People & Theories
Research after his journey inspired Darwin to publish:
“The Origin of Species” – 1858; which contained his ideas of evolution
and natural selection.
Summarized in two theories:
1. Decent with modification  All species had descended from one (or
a few) original types of life; a “common ancestor”.
Newer forms of the organism seen in the fossil record are modified
versions of the older species found.
2. Modification by Natural Selection  a trait is beneficial to the
reproductive success of an organism AND is inherited by offspring.
This is “adaptation” occurring; the resulting change in genes of a
population s evolution.
Evolution Theory: Natural Selection
Natural Selection – organisms best suited to their
environment reproduce more successfully than others.
Therefore, the population with the most favorable traits increases in
number.
Natural Selection is not an “active process”; favorable traits are
relative to the environment of an organism, and varied.
What’s good for some is not good for all!
Evidences of Evolution
1. Anatomy
Homologous Features (see next page)
Organisms can have parts that
look different and serve different functions
BUT are still similar in skeletal structure
and development processes. These
are called Homologous Features
Vestigial Structures – feature useful to an
organism’s ancestor but not the modern
carrier of the feature.
These were functional features at some
point. (Tail bones in humans; leg bones in
sperm whales)
Evidences of Evolution
1. Anatomy (cont.) (opposite homologous)
Analogous Features – serve identical
functions and appear similar on both
organisms.
Analogous features have very different
developmental patterns and internal
anatomy. Wings: Birds vs. Insects
2. Embryology
States that in early stages of
development, different vertebrate
embryos are very similar looking. Means
it is evidence of a common ancestry.
Evidences of Evolution
3. Macromolecules
•
Darwin hypothesized that the more similar looking organisms were, the
more recently they shared a common ancestor.
•
We can now study these similarities at a molecular level: DNA and
related proteins. For instance, proteins responsible for similar functions
(hemoglobin) are found in many similar species.
Differences in the amino acids found in homologous proteins are directly
proportional to the length of time since they shared an ancestor.
DNA works like a clock –
the more similarities
in DNA, the more
recently they shared
the common ancestor.