Evolution Ch 22, U202PP

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Evolution- Ch 22, U202PP
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• Concept 22.3 Darwins theory explains a wide
  range of observations
• Darwins theory of evolution
• Continues to be tested by how effectively it can
  account for additional observations and
  experimental outcomes

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Evidence for evolution by natural selection? (or,
in Darwins words, descent with modification)

• What did Darwin use to support his ideas?

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Homology

• Homology
• Is similarity resulting from common ancestry

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Anatomical Homologies

• Homologous structures between organisms
• Are anatomical resemblances that represent
  variations on a structural theme that was present
  in a common ancestor

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Comparative embryology

• Reveals additional anatomical homologies not
  visible in adult organisms

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• Vestigial organs
• Are some of the most intriguing homologous
  structures
• Are remnants of structures that served important
  functions in the organisms ancestors

In the first chapter of The Descent of Man,
Charles Darwin identified roughly a dozen
anatomic traits that he gleefully described as
useless, or nearly useless, and consequently no
longer subject to natural selection. The list
included body hair, wisdom teeth, and the
coccyxsuperfluous features that served as
Exhibit A in his argument that humans did not
descend from demigods but rather from a long
line of fur-insulated, plant-chewing creatures
that sported tails.
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Other human vestigial structures to add to the
list

• PARANASAL SINUSES- The nasal sinuses of our early
  ancestors may have been lined with odor receptors
  that gave a heightened sense of smell, which
  aided survival. No one knows why we retain these
  perhaps troublesome mucus-lined cavities, except
  to make the head lighter and to warm and moisten
  the air we breathe.

VOMERONASAL ORGAN - A tiny pit on each side of
the septum is lined with nonfunctioning
chemoreceptors. They may be all that remains of a
once extensive pheromone-detecting ability.
EXTRINSIC EAR MUSCLES - This trio of muscles
most likely made it possible for prehominids to
move their ears independently of their heads, as
rabbits and dogs do. We still have them, which is
why most people can learn to wiggle their
ears. WISDOM TEETH- Early humans had to chew a
lot of plants to get enough calories to survive,
making another row of molars helpful. Only about
5 percent of the population has a healthy set of
these third molars. NECK RIBS- A set of cervical
ribspossibly leftovers from the age of
reptilesstill appear in less than 1 percent of
the population. They often cause nerve and artery
problems. THIRD EYELID- A common ancestor of
birds and mammals may have had a membrane for
protecting the eye and sweeping out debris.
Humans retain only a tiny fold in the inner
corner of the eye. DARWINS POINT - A small
folded point of skin toward the top of each ear
is occasionally found in modern humans. It may be
a remnant of a larger shape that helped focus
distant sounds.- SUBCLAVIUS MUSCLE - This small
muscle stretching under the shoulder from the
first rib to the collarbone would be useful if
humans still walked on all fours. Some people
have one, some have none, and a few have
two. PALMARIS MUSCLE - This long, narrow muscle
runs from the elbow to the wrist and is missing
in 11 percent of modern humans. It may once have
been important for hanging and climbing. Surgeons
harvest it for reconstructive surgery.
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And still more.

• MALE NIPPLES  - Lactiferous ducts form well
  before testosterone causes sex differentiation in
  a fetus. Men have mammary tissue that can be
  stimulated to produce milk.
• ERECTOR PILI - Bundles of smooth muscle fibers
  allow animals to puff up their fur for insulation
  or to intimidate others. Humans retain this
  ability (goose bumps are the indicator) but have
  obviously lost most of the fur.
•  APPENDIX  - This narrow, muscular tube attached
  to the large intestine served as a special area
  to digest cellulose when the human diet consisted
  more of plant matter than animal protein. It also
  produces some white blood cells. Annually, more
  than 300,000 Americans have an appendectomy.
• BODY HAIR - Brows help keep sweat from the eyes,
  and male facial hair may play a role in sexual
  selection, but apparently most of the hair left
  on the human body serves no function.
• PLANTARIS MUSCLE  - Often mistaken for a nerve by
  freshman medical students, the muscle was useful
  to other primates for grasping with their feet.
  It has disappeared altogether in 9 percent of the
  population.
• THIRTEENTH RIB- Our closest cousins, chimpanzees
  and gorillas, have an extra set of ribs. Most of
  us have 12, but 8 percent of adults have the
  extras.
• MALE UTERUS- A remnant of an undeveloped female
  reproductive organ hangs  off the male prostate
  gland.
•  FIFTH TOE- Lesser apes use all their toes for
  grasping or clinging to branches. Humans need
  mainly the big toe for balance while walking
  upright.
• FEMALE VAS DEFERENS  - What might become sperm
  ducts in males become the epoophoron in females,
  a cluster of useless dead-end tubules near the
  ovaries.
• PYRAMIDALIS MUSCLE - More than 20 percent of us
  lack this tiny, triangular pouchlike muscle that
  attaches to the pubic bone. It may be a relic
  from pouched marsupials.
• COCCYX - These fused vertebrae are all thats
  left of the tail that most mammals still use for
  balance and communication. Our hominid ancestors
  lost the need for a tail before they began
  walking upright.

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The Fossil Record

• The succession of forms observed in the fossil
  record
• Is consistent with other inferences about the
  major branches of descent in the tree of life

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• The Darwinian view of life
• Predicts that evolutionary transitions should
  leave signs in the fossil record
• Paleontologists
• Have discovered fossils of many such transitional
  forms

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Homologies and the Tree of Life

• The Darwinian concept of an evolutionary tree of
  life
• Can explain the homologies that researchers have
  observed

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Biogeography

• Darwins observations of the geographic
  distribution of species, biogeography
• Formed an important part of his theory of
  evolution

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• Some similar mammals that have adapted to similar
  environments
• Have evolved independently from different
  ancestors

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Homology, Biogeography, and the Fossil Record

• Evolutionary theory
• Provides a cohesive explanation for many kinds of
  observations

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Additional evidence to support evolution by
natural selection (unavailable to Darwin at the
time)
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Molecular Homologies

• Biologists also observe homologies among
  organisms at the molecular level
• Such as genes that are shared among organisms
  inherited from a common ancestor

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• Anatomical resemblances among species
• Are generally reflected in their molecules, their
  genes, and their gene products

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More molecular

• Immunological testing
• Injecting human blood serum into rabbits forms
  antibodies against human blood serum. When rabbit
  antibodies are mixed with human blood a
  precipitate is formed. By comparing the amount of
  precipitate formed when the antihuman antibodies
  react with a foreign blood serum hints at
  biological relatedness - the greater the
  reaction, the closer the supposed relationship.
• Man versus Man 100Man versus Chimpanzee
  97Man versus Baboon 50 Man versus the dog 0

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Well, even more molecular.

• Similarity of sequences that are presumably
  closely related
• Humans and chimpanzees share 95-98 of their DNA
  (depending on the study)
• Humans and gorillas share less
• Humans and lemurs share even less
• Humans and other mammals share even less
• Humans and ..
• Humans and

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Continental Drift

• In the early 1900's Alfred Wegener proposed the
  idea of Continental Drift. His ideas centered
  around continents moving across the face of the
  earth. The idea was not quite correct - compared
  to the plate tectonics theory of today - but his
  thinking was on the proper track.

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New evidence

• February 24, 2006 New Evidence That Natural
  Selection Is A General Driving Force Behind The
  Origin Of Species
• The famous scientist would be pleased because a
  study published this week finally provides the
  first clear evidence that natural selection, his
  favored mechanism of evolution, drives the
  process of species formation in a wide variety of
  plants and animals. But he would be chagrined
  because it has taken nearly 150 years to do so.
• What Darwin did in his revolutionary treatise "On
  the Origin of Species" was to explain how many of
  the extraordinary biological traits possessed by
  plants and animals arise from a single process,
  natural selection. Since then a large number of
  studies and observations have supported and
  extended his original work. However, linking
  natural selection to the origin of the 30 to 100
  million different species estimated to inhabit
  the earth, has proven considerably more elusive.
• In the last 20 years, studies of a number of
  specific species have demonstrated that natural
  selection can cause sub-populations to adapt to
  new environments in ways that reduce their
  ability to interbreed, an essential first step in
  the formation of a new species. However,
  biologists have not known whether these cases
  represent special exceptions or illustrate a
  general rule.
• The new study, published online in the
  Proceedings of the National of Sciences,
  provides empirical support for the proposition
  that natural selection is a general force behind
  the formation of new species by analyzing the
  relationship between natural selection and the
  ability to interbreed in hundreds of different
  organisms ranging from plants through insects,
  fish, frogs and â and finding that the overall
  link between them is positive.

"We have known for some time that when species
invade a new environment or ecological niche, a
common result is the formation of a great
diversity of new species. However, we haven't
really understood how or whether the process of
adaptation generally drives this pattern of
species diversification." The specific question
that Funk and his colleagues set out to answer is
whether there is a positive link between the
degree of adaptation to different environments by
closely related groups (termed ecological
divergence) and the extent to which they can
interbreed (termed reproductive isolation.) Funk
and his colleagues saw a way to address this
question by extending a method pioneered by Jerry
A. Coyne, University of Chicago, and H. Allen
Orr, University of Rochester in a now classic
study of speciation in fruit flies published in
1989. Coyne and Orr were interested in exploring
how the process of species formation develops
over time. To measure this process, known as
speciation, they developed an index of
reproductive isolation. For a measure of time,
they used the fact that genetic mutations
accumulate over time. So if the percent
difference in the genomes of species A and B
differs by five percent while the difference
between A and C differs by 10 percent, then the
time since A and C diverged is about twice that
since A and B split apart.
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The Evolution of Drug-Resistant HIV

• In humans, the use of drugs
• Selects for pathogens that through chance
  mutations are resistant to the drugs effects
• Natural selection is a cause of adaptive evolution

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• Researchers have developed numerous drugs to
  combat HIV
• But using these medications selects for viruses
  resistant to the drugs

Patient No. 1
Patient No. 2
Percent of HIV resistant to 3TC
Patient No. 3
Weeks
Figure 22.13
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• The ability of bacteria and viruses to evolve
  rapidly
• Poses a challenge to our society

The issue of HIV drug resistance impacts greatly
on treatment regimens for HIV and AIDS patients,
therefore impacting
The number of deaths linked to hospital superbug
MRSA has risen by nearly a quarter, statistics
show.
INCREASE IN ANTIBIOTIC-RESISTANT GONORRHEA.
Gonorrhea rates did not change much in the
United States between 1988 and 1989, but the
percentage of gonorrhea strains with antibiotic
resistance increased at the 21 sexually-transmitte
d-disease clinics monitored by the Centers for
Disease Control.
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What Is Theoretical about the Darwinian View of
Life?

• In science, a theory
• Accounts for many observations and data and
  attempts to explain and integrate a great variety
  of phenomena

• Darwins theory of evolution by natural selection
• Integrates diverse areas of biological study and
  stimulates many new research questions