Chapter 1
1. The author and his colleagues chose to focus on rocks from 375 million years ago
because it is the most likely point in time when the first limbs started developing. There
is strong evidence of diverse life-forms from 365 million years ago in Greenland but only
fossils of fish are found from 385 million years ago. Shubin and his team found these key
fossils in the Arctic Circle in sedimentary rocks which apply pressure and preserve the
fossils.
2. Shubin thinks that Tiktaalik says something about our bodies because it represents the
transition and the evolution of fish-like organisms to amphibians that have multiple
limbs. Tiktaalik shows how and where humans started and why our anatomy is like this
today.
Chapter 2
1. Owen described a pattern in the arm where there is one bone that connects to two bones,
followed by lots of small bone blobs and finally the digits. The exceptional similarity is
that all, although sizes and shapes vary greatly, this blueprint is used by most, if not all,
limbs.
2. Darwin explained Owen’s research by suggesting that all animals with this pattern have a
common ancestor that gave them this structure.
Chapter 3
1. To find the two patches of tissue that controlled development, Edgar Zwilling and John
Saunders observed chicken embryos by cutting and moving various tissues to discover
the effect upon the embryos’ development. This patch of tissue controlled all limb
development. They removed the tissue and saw that development would come to a stop.
When it was removed early, only the upper arm developed; when it was removed later,
the arm almost completely developed with the exception of shorter, deformed digits in
the chicken’s wing.
Chapter 4
1. Teeth are “as hard as rocks” because they contain the molecules hydroxyapatite, which
causes the infrastructure of teeth to be resistant to stress. In addition, the outer layer of
enamel has the highest concentration of hydroxyapatite, making the teeth even sturdier.
2. Conodonts were small, shelly organisms from 250 to 500 million years ago, and some of
the most common fossils in ancient oceans today.
3. Teeth are made of two layers of tissue that fold together, with the outer layer becoming
the enamel and the inner layer becoming the dentine and pulp of the tooth. This two-layer
process is also used in the development of all body structures that form within the skin,
such as scales, fur, hair, or feathers.
Chapter 5
1. Cranial nerves only have one function- to attach to one muscle or organ, and they serve
one purpose- to conduct information back and forth. However, the trigeminal and the
facial cranial nerve are very complex, branching out into an array of networks, very much
unlike the other cranial nerves. The reason for this complexity is because these two
nerves can carry both sensation and action. Other fibers end up being consolidated into
the trigeminal and facial nerves, and then break up again. The nerves control muscles,
trigeminal in carrying sensory information from the face to the brain, and the facial nerve
controlling facial muscles and expressions.
2. The first arch forms the upper and lower jaws, ear bones called the malleus and the incus,
and all the muscles and vessels that supply them. The second arch forms a small ear bone
called the stapes, a small throat bone, and most of the muscles involved in facial
expressions. The third arch forms bones, muscles, and nerves that are deeper in the throat
that will allow us to swallow. The fourth arch forms the deepest parts of the throat,
including the larynx and the muscles and vessels around it.
3. Amphioxus is an important species to study because, if looked at closely, there are very
similar patterns between the Amphioxus worm and hums. The worm has a nerve cord
that runs along the backbone, as well as a “support” rod, the notochord, that runs parallel
to the nerve cord. Humans have the notochord as well, but it breaks up and becomes part
of the disks that lie between our vertebrae.
Chapter 6
1. Ectoderm (Outer Layer) - The ectoderm forms the skin and the nervous system.
Endoderm (Inner Layer) - The endoderm forms the inner structures of the body, including
the digestive tract and the glands associated with it. Mesoderm (Middle Layer) - The
mesoderm forms the tissue between the guts and the skin, including our skeleton and our
muscles.
2. The sperm fertilizes the egg and a zygote forms. Cell division continues and this creates a
ball of cells called a blastocyte. There does not appear to be any body plan, meaning there
is no front or back, left or right. The blastocyte attaches to the mother’s uterus to share
the mother’s bloodstream and receive nutrients.
3. Ontogeny recapitulates phylogeny is the idea that an embryo that is far up an
evolutionary tree will pass through each species in its evolutionary history during
development.
4. Noggin is a type of HOX gene that helps with the body plan (such as the axes) but it is
also involved with other organs. It is associated with another gene called BMP-4 when
determining the top-bottom axis, where BMP-4 is the bottom gene (ventral side) and
Noggin is the top gene (dorsal side). Whenever Noggin is active, BMP-4 is suppressed.
Therefore, Noggin is a suppressor.
5. Sea anemones have a long central stump that branches off into tentacles. Although sea
anemones have radial symmetry while humans have bilateral symmetry, they still have a
head-anus axis and similar belly-to-back genes as humans. Although the end product of
humans and sea anemones may appear quite different, both are based on the same basic
recipe, and a long time of modification accounts for the visible difference between the
body plans of a human versus a sea anemone.
Chapter 7
1. The most surprising thing about the timescale is how late humans came into existence in
the bigger scope of things. The events that we learn about in a history class seem so old
and distant like humans have been there since the beginning.
2. The most common protein in the body is collagen. Collagen is a protein that is shaped
like a 3-D brush, with branches extending out of it. It is much of what fills the space
between cartilage and is 90% of all of the body’s protein by weight.
3. Small molecular rivets allow cells to stick together. Yet, cells have many different
methods of sticking. In some cases, one molecule will attach to the outer membrane of
another cell which then attaches to the outer membrane of another cell endlessly. Some
tissues have cells in organized strips or columns, while others have cells that are
randomly scattered or loosely attached to each other. For example, the molecules in
between bone cells determine the strength of the bone and more loosely attached proteins
in eyes make them more squishy and yielding.
4. Choanoflagellates are single-celled microbes; they are the most recent common ancestor
of animals with bodies as well as placozoans and sponges. Biologists study
choanoflagellates because most of this microbe's active genes also operate and are active
in animals. The choanoflagellate controls such functions as cell adhesion and cell
communication.
5. Some scientists believe that the body developed as a defense mechanism. When microbes
learned to eat each other, the body, big in form, provided a defense to avoid being eaten.
Microbes attach to other microbes and invade them as a food source; the molecules that a
microbe uses to engulf their prey show similarities to the molecules that are rivet
attachments for body cells. Thus, it is likely that the microbe increased the production of
this molecule. Under different experiments, scientists found that when a unicellular
organism fears a predator, often, it may divide to become cell clumps.
Chapter 8
1. We perceive smell in through a large chain of steps. First, when we breathe in through
our nose, we suck tiny odor molecules into our nostrils. On the lining of the nostrils, there
are millions of nerve cells, and each odor molecule attaches to one of the receptors. An
impulse is sent up to the brain based on the molecules captured by the nerve receptors,
each receptor sending up a different signal. The combination of these signals creates the
appearance of an odor.
Chapter 9
1. Like humans, Old World monkeys use three different light receptors to respond to
various light frequencies. Both humans and old monkeys possess this detailed color
vision. While two of the human's three receptors are more like one of the two in other
mammals, our vision is stronger and more complete like Old World monkeys. The reason
for the ability of humans and the old world monkeys to perceive color is based around the
change in plant life. Increased diversity in plant life gave the old world monkeys an
evolutionary benefit to being able to perceive different colors in order to differentiate
different fruits, berries, and other plant life. Likely, Old World monkeys have these three
receptors due to a mutation that also increased fitness.
2. Eyeless and Pax 6 genes help control the formation of tissues and organs. The eyeless and
Pax 6 genes control eye development. When the DNA sequence appears for these genes,
eyes form, but, when it does not, they do not develop. Scientists attribute the eyeless and
Pax 6 genes to being the major components of eye formation. When the gene is mutated,
small eyes or no eyes appear. The Pax 6 and eyeless genes have the ability to form an eye
anywhere the gene is found, regardless of the section of the body.
Chapter 10
1. Of the three parts of the ear, the external part of the ear, or the pinna, is unique to
mammals.
2. The Pax 2 gene is active in the ear and starts a chain reaction that allows for inner ear
formation. If a mutation in humans or mice knows this gene out the inner ear cannot
properly form. This is a major gene that is essential for proper development.
Chapter 11
1. With his “Bozo” example, Shubin is trying to convey the meaning of descent with
modification. The characteristics that are shown in Bozo are recognizable features such
as a red nose and big feet that reflect previous generations of clowns. Shubin’s final point
is that living things show traces of their parental DNA and genetic information. Though
the parental generation and second generation look vastly different in the Bozo example,
the lineage is traceable through characteristics.
2. Obesity: Obesity has become one of the leading causes of death in humans today and
much of it is due to the fact that humans have a body for an active animal; however,
humans live a sedentary lifestyle. Our ancestors were hunter-gatherers who lived with a
cycle of feast and famine. Our bodies were made to store food for times of need. This
leads to obesity as humans eat excessive amounts of food with no periods of famine to
use up the saved fat, causing humans to then become overweight and obese.
Heart Disease: Heart disease is a disease that is stimulated by obesity. Therefore, heart
disease is so prevalent in our society due to the increased rates of obesity.
Sleep Apnea: Though human embryos never use their gill arches to breathe, the
developmental path that follows humans back to fish means that these gill structures are
still in place in the human. Humans then simply repurposed old structures that other
animals already had for other reasons. When humans speak, the muscles in the back of
the throat contract to control how rigid or flexible the throat, making it possible to
produce a wide range of speech sounds. Yet this flexibility means that the throat can
collapse so much while a human sleeps that no air can pass through, a breathing problem
called sleep apnea.
Afterword: Tiktaalik
1. The operculum is the flap that covers the gills of bony fish, allowing a push and pull
motion to move water. However, Tiktaalik does not have this, showing that the animal
relied on its mouth for breathing.
2. A true neck allowed Tiktaalik to move its head independent of its body. This meant that
the animal could support itself on the ground/on land.
3. Tiktaalik was not able to withstand the cold; it lived in a warm environment. Shubin
uncovered the fact that the climate then was completely different from the climate today.