Your Inner Fish


Neil Shubin

Teachers and parents! Our Teacher Edition on Your Inner Fish makes teaching easy.


The four bulges in a vertebrate embryo that form the head and throat of the animal. These four arches coordinate with four complicated nerves in the adult animal, and are found to create the same… read analysis of Arches


The small ball of cells that is the embryo from the first couple days after conception to about three weeks after conception. The blastocyst attaches to the uterus wall of the embryo’s mother, then begins… read analysis of Blastocyst


Close microbe relatives of simple bodied organisms like placazoans. Choanoflagellates provide a link between single-celled microbes and primitive organisms with bodies, as they have some of the properties of both kinds of life form. read analysis of Choanoflagellate


The main structural protein found in between the cells of bone and skin. Collagen is strong when it is pulled, giving skin its elasticity and bone its flexibility. read analysis of Collagen


Strange, spiky “shell” fossils with high levels of hydroxyapatite in their bone structure that confused paleontologists when they were first found. Eventually, a fossil impression of a jawless fish was found with conodonts in its… read analysis of Conodont
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Descent with modification

The process through which evolution is thought to happen. Descent with modification means that children inherit most of their physical traits and body systems from their parents, but that small changes (modifications) might happen in… read analysis of Descent with modification

Devonian Period

The geologic period of the fossil record from 420 million-years-ago to 358 million-years-ago, commonly known as the age of the fishes. During this time period, complex fish developed, including many species that are still alive… read analysis of Devonian Period

"Eyeless" gene (Pax 6)

The gene found by Mildred Hoge in the early 1900s and studied by Walter Gehring in flies. Pax 6 switches on eye formation in all animals with the complex vertebrate style eye. read analysis of "Eyeless" gene (Pax 6)

Facial nerve

One of the more complicated nerves in the human head, along with the trigimenal nerve. The facial nerve serves all the facial muscles and other muscles in the ear, which develop from the second… read analysis of Facial nerve

Hedgehog gene and sonic hedgehog gene

The gene found by Cliff Tabin, Andy MacMahon, and Phil Ingham that controls the body segments of flies so that the fly body forms properly with a head in front, body in the middle, and… read analysis of Hedgehog gene and sonic hedgehog gene

Hox gene

A gene found in any animal with a body that helps control the body orientation and body plan of the animal. The more complex the animal’s body is, the more Hox genes the animal has… read analysis of Hox gene


A mineral made partially of calcium that gives teeth and bones their strength. read analysis of Hydroxyapatite


A small amphibious animal that lived in the Late Devonian Period, about 360 million years ago. Hynerpeton walked on four legs and most likely lived in lakes and large river mouths and was able… read analysis of Hynerpeton

Malleus and incus

Two of the three bones of the mammalian inner ear, along with the stapes. The malleus and incus develop from the first arch of the mammalian embryo, and correspond to two of the jaw… read analysis of Malleus and incus


The sensory organ in fish that allows fish to be aware of the movement, speed, and direction of the water currents around the fish’s body. Neuromasts are similar to the mammalian inner ear that gives… read analysis of Neuromast


The exact fit between the teeth of the upper law and the lower jaw in mammals, unlike reptilian teeth that do not touch each other when the reptile bites down. Occlusion allows mammals to grind… read analysis of Occlusion


The protein in the eye that signals to the brain that light has entered the light-sensing molecules. Different opsins allow animals to have black and white or color vision, but all opsins perform the same… read analysis of Opsin


A patch of tissue in the blastocyst that includes tissue from all three germ layers and seems to direct the body orientation, proportions, and growth for the entire body of the embryo. The organizer was… read analysis of Organizer

Pax 2

The gene responsible for forming the inner ear in vertebrate animals. read analysis of Pax 2


One of the most primitive creatures with a body, placazoans were discovered when they developed on the walls of an aquarium in the 1880s. Though they are flat plate shaped disks that only have four… read analysis of Placazoan


Primitive worms with bristles on their body. Detlev Arendt studied these invertebrate worms to find that they have a primitive version of the complex eye found in vertebrate creatures. read analysis of Polychaete

Precambrian Era

All geologic time before 600 million-years-ago. It was originally thought that this time period held no complex organisms with bodies, until Sprigg’s creatures, the earliest known organisms with true bodies, were re-dated by Martinread analysis of Precambrian Era


A protein found in between the cells of healthy cartilage that soaks up water in bristle-like branches so that the proteoglycan can cushion the cartilage cells, and they can withstand compression force and bounce back… read analysis of Proteoglycan


One of the three bones of the mammalian inner ear, along with the malleus and incus. The stapes is the smallest bone of the inner ear—and the only bone of the inner ear in… read analysis of Stapes

Trigimenal nerve

One of the more complicated nerves in the human head, along with the facial nerve. The trigimenal nerve serves all the structures that develop from the first arch of the human embryo, including the… read analysis of Trigimenal nerve


Small to medium size reptiles from the late Triassic to Jurassic periods (around 200 million-years-ago) that show a mammalian style jaw with signs of occlusion between the teeth. The teeth are reptilian in shape and… read analysis of Trithledont

Zone of Polarizing Activity (ZPA)

The small zone at the extreme end of an embryo’s limb bud, where all of the activity of building the limb takes place. read analysis of Zone of Polarizing Activity (ZPA)