Your Inner Fish


Neil Shubin

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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 full term analysis)


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 full term analysis)


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 full term analysis)


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 full term analysis)


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 full term analysis)
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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 full term analysis)

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 full term analysis)

"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 full term analysis)

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 full term analysis)

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 full term analysis)

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 full term analysis)


A mineral made partially of calcium that gives teeth and bones their strength. (read full term analysis)


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 full term analysis)

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 full term analysis)


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 full term analysis)


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 full term analysis)


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 full term analysis)


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 full term analysis)

Pax 2

The gene responsible for forming the inner ear in vertebrate animals. (read full term analysis)


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 full term analysis)


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 full term analysis)

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 Martin(read full term analysis)


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 full term analysis)


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 full term analysis)

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 full term analysis)


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 full term analysis)

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 full term analysis)