Paleontologist Neil Shubin begins with a brief account of his role in discovering an ancient creature intermediate between a fish and a land animal. Its fossils were found on Ellesmere Island in the Canadian Arctic in 2004, and the creature was given the Inuit name Tiktaalik.
Later, Shubin pays another visit to Canada, this time the fossil beds near Parrsboro, Nova Scotia, on the Bay of Fundy. There they found rare fossils of the tritheledont, a reptile whose teeth showed mammalian characteristics.
Shubin uses these events to anchor a description of how our anatomy contains links to more primitive creatures. For example: "Tiktaalik has a shoulder, elbow, and wrist composed of the same bones as an upper arm, forearm, and wrist in a human."
Following are a number of observations that I found interesting.
Human Embryos
1. They have four gill arches, which ultimately develop into jaws, ears, larynx and throat.
2. They have a notochord, which breaks up and forms the disks that cushion our vertebrae.
3. At an early stage in their development, their elbows and knees face the same direction, as do fish and amphibians.
4. Gonads are initially located high up in the body, as in fish.
Evolution
1. Two factors may have been involved in the evolution of bodies: predation, and the rise in atmospheric oxygen.
2. "The origin of mammals involved not only new patterns of chewing...but new ways of hearing... Bones originally used by reptiles to chew evolved in mammals to assist in hearing."
Genetics
Shubin also describes some of the Dr. Moreau-like tinkering that scientists have done in order to understand how genes work. Some of the genes he mentions are Noggin, Pax 6, and Sonic hedgehog.
1. Genes from the embryo of one animal (e.g. a mouse), when grafted to the embryo of another (e.g. a shark), can perform the same function. This leads to a conclusion such as: "all appendages, whether they are fins or limbs, are built by similar kinds of genes."
2. "Inject extra amounts of frog Noggin into a frog egg, and the frog will grow extra back structures, sometimes even a second head."
3. Turning on an "eyeless" gene can result in creatures growing eyes virtually anywhere on the body. For example, "they could use the mouse gene to trigger the formation of an extra fly eye anywhere: on the back, on a wing, near the mouth."
Trivia
1. Fish have no necks.
2. Tooth replacement in reptiles continues throughout their entire lives.
3. Some creatures, like single-celled microbes, have no body at all.
4. Some creatures have no anus, they expel waste through their mouth e.g. jellyfish and corals.
