Transcript Example #3: Artificial Selection

Examples of
Evolution:
Archeopteryx: A transition
fossil between reptiles and
birds.

A famous example from England that demonstrates natural
selection is the Pepper Moth.

Two different species of moths, one light colored and one dark.
 Before the 1850’s the dark one was very rare, after the 1850’s
the light color became rare.
What happened in the 1850’s?
INDUSTRIAL REVOLUTION
Coal fired plants produced lots
of soot that covered the trees
and buildings, making
everything dark. So where once
the birds preferentially picked
off and ate the dark moths, they
now saw and ate the light ones
instead.

As the use of
antibiotics have
become widespread
many disease-causing
bacteria have
developed resistance
against known
antibiotics.
 Only the resistant
bacteria will survive
and reproduce


This means that if you
become infected with
these bacteria,
treatment with
antibiotics will not
cure you and the
disease may become
fatal.

This is more likely to occur when a small dose
of antibiotics is used over a short time.
It will kill some of the bacteria but not all.
 Next time antibiotics are used, these bacteria may be
less vulnerable and more survive.
 Repeated small dosages can produce very resistant
strains.

http://www.usatoday.com/story/news/nation/2013/
03/05/superbugs-infections-hospitals/1965133/

In the USA,

half the livestock is fed
antibiotics to increase the
growth of the animals.
○ This leads to strains of
antibiotic resistant bacteria
being discovered in the gut
of these animals and then in
human guts.
○ The runoff from the waste
and feed contains the
antibiotic resistant strains
that can get out to the rest
of the world.

There are numerous examples of humans
performing their own type of selection
(hence: artificial) on desired, heritable
traits belonging to a variety of organisms.
Since we seem to like the #3,
we have…
3 examples:
#1 Dog breeding
#1:
The domestication of the wolf (or
domestication of any animal) is a
good example:
Further selection of favored
traits resulted in the varied
amount of dog breeds we have
today.
#2: Selective breeding
transformed teosinte’s few
fruitcases into modern corn’s
rows of kernels.
#3:
By selecting various traits of the common wild
mustard plant to breed for, we have created
many common vegetables we use today such as
broccoli, cauliflower and brussels sprouts.
Artificial selection is also important as it acts
as an experiment on natural selection.
Experimentation is the ultimate test of a
scientific hypothesis, without it you can never
be sure that a correlation (i.e. the
environment selecting for traits) you observe
is significant.
In artificial selection,
humans are the
manipulators (we are the
environment)- we choose
which individuals get to
reproduce.
We would expect to see
what is found in nature- that
the individuals who
reproduce pass on their
genes/traits, and that is
exactly what we see.
Artificial Selection can also be used as
evidence of evolution.
We will discuss more forms of evidence next.
“Those who cavalierly reject the Theory of
Evolution, as not adequately supported by facts,
seem quite to forget that their own theory is
supported by no facts at all”
-Herbert Spencer, Essay Scientific,
Political and Speculative, 1891.
Fossils do show intermediate
stages, despite their rarity.
And geological strata (layers)
consistently reveal the same
sequence of fossils!
A quick and simple way to
debunk the theory of evolution
would be to find a fossil horse
in the same stratum as a
trilobite.
For example, there
are now at least
eight intermediate
fossil stages
identified in the
evolution of whales.

An organ present in the organism but either
reduced in size or has no use.
Ex.
 Femur in some whales
 Dewclaw in dogs
 Eyes in blind mole rats
 Fake sex in virgin Whiptail lizard
 Wings on flightless birds
The Appendix
Wisdom Teeth
Human Coccyx (Tailbone)
Body Hair and Erector Pili (Goosebumps)
Ear Muscles
Third Eyelid

Homologous Structures

Similar structures in very different organisms
is evidence of a common ancestor.
An example of this is the
similarity of the skeleton
between all mammals.
Every bone in a bat has is its
own identifiable counterpart
in a human. Identifiable,
because of the order in which
they join up. Only the
proportions are different.
from Ernst Haeckel's 1904 work
Kunstformen der Natur

Embryonic
Development
Physical similarities
between embryos of
different species at
different stages.
In 1866, Ernst Haeckel
proposed his theory
that the embryonic
development of an
individual organism
followed the same
path as the
evolutionary history of
its species.

Haeckel’s theory has
largely been rejected
today.
Though humans share
common ancestors
with other animals,
stages of human
embryonic
development are not
functionally
equivalent to the
adults of these
shared ancestors.
In other words, just because
we develop a tail and gill slits
embryonically does not mean
that they are functional like
they are in fish.
Darwin's view: that
early embryonic
stages are similar to
the same embryonic
stage of related
species but not to the
adult stages of these
species, has been
confirmed by modern
evolutionary
developmental
biology

Similarity of Genetic
Code (DNA)


All organisms share the
same genetic code, based
on the series of bases: A,
T, G, and C.
The more similar two
species are the more alike
the sequence of bases in
their DNA are.
First we need to look at what the word theory means.
The Oxford English Dictionary gives two meanings:
Theory, Definition 1: A scheme or system of ideas or statements
held as an explanation or account of a group of facts or phenomena; a
hypothesis that has been confirmed or established by observation or
experiment, and is propounded or accepted as accounting for the known facts;
a statement of what are held to be the general laws, principles, or causes of
something known or observed.
Theory, Definition 2: A hypothesis proposed as an explanation;
hence, a mere hypothesis, speculation, conjecture; an idea or set of ideas
about something; an individual view or notion.
Darwin’s Theory, as with all scientific theories follow the first definition.
Having your explanation for a group of observations being called a theory is an
honor in the scientific field; it means that it is the best explanation we have for
why something happens.
Does being a scientific law mean you have more evidence to support your
explanation than a theory?
Not at all… laws and theories are used to describe different things in science.
In general, Scientific Laws describe what is happening. Examples include:
Newton’s Laws of Gravity, Kepler’s Laws of Planetary Motion, Law of
Conservation of Energy, Laws of Thermodynamics….
Scientific Theories explain why something happens. Examples
include: The Big Bang Theory, Cell Theory, Theory of Relativity, String Theory…
NO!
Evolution points to humans sharing a common ancestor with
chimpanzees and other great apes around 7-8 million years ago.
Chimps have continued to evolved alongside us since then.
The ancestor you
share between
yourself and the
chimpanzee at the
zoo probably did look
something like this
though:
Sahelanthropus tchadensis
In fact we have shared the Earth with many other human like
species (called hominids).
We even shared the Earth
at
the same time with other
hominid species such as
Homo Neanderthalensis.
And this recent find:
Homo Floresiensis, the
hobbit
people on the island of
Flores
in Indonesia.
Courtesy of Smithsonian, 03/10
The first step in the evolution of the eye, would be a set of
photoreceptor proteins that sense light called photoreceptors.
Photoreceptors can sense ambient brightness, and distinguish
light from dark.
These allowed unicellular organisms to move toward where they
sensed light, probably to use for photosynthesis.
Example of a photoreceptor
in a Euglena
The next step would be indenting the tissue
behind the eye to make a cup behind the
photoreceptor cells. This enlarges the area of
photoreceptor cells as well, now known as the
retina.
These primitive eyes are called eyespots.
Example of an eyespot in a
planarian (flat worm)
The “pinhole camera” eye stage was next. This is where the
eyespot hollows out more and reduces the size of the hole where
the light comes through. This gave the organism true imaging,
allowing for directional and shape sensing.
Example of a pinhole eye in
a nautilus.
Next came eyes that were fully enclosed, fluid-filled chambers.
A refractive lens has also evolved over the pin-hole.
Refraction is when light waves change speed as they enter a new
medium. This bends the angle of the light, and in the case of an
eye (or camera) directs the light into a single beam on one spot.
The refractive lens in most
animals is known as the
cornea.
The iris later evolved, which
allows the organism to
adjust the “pin-hole”,
controlling the amount of
light that enters the eye.
So if we remember that evolution is an accumulation of heritable
changes, the evolution of complex structures like they eye, though
remarkable, isn’t all that unrealistic.