Book Review ~~ Handy Genes ~~

I recently read Handy Genes, which is the third chapter of “Your Inner Fish,” by Neil Shubin. The following essay is basically a detailed summary of the content in the third chapter:

In the mid-twentieth century, biologists were doing experiments with chicken eggs, cutting up the embryos and grafting tissues to other places to figure out what would happen if embryos’ development was interfered with. Chicken eggs were perfect for these experiments; they were large enough for biologists to carefully choose which parts to cut up and graft, protected by the eggshell, and available in large quantities everywhere. These experiments would become important to scientists studying evolution because the experiments eventually revealed that the basic genes in all animals are the same; they’re simply put to different uses in different animals.

Scientists performed a variety of experiments that eventually led to the discovery of a tissue that controlled how fingers and toes formed and made each finger different. One set of experiments, performed by a group of biologists that included Edgar Zwilling and John Saunders, revealed a tissue that controlled limb development. They removed it at different periods of development, and the earlier it was removed, the less of the limb had developed. Meanwhile, Mary Gasseling had discovered that if the tissue Zwilling and Saunders had found was moved to the opposite side, a mirror image of the limb would form. The tissue was named ZPA, and a variety of experiments were done with it to discover how it controlled the development of limbs, fingers, and toes. A variety of molecules were suggested, but none of them were capable enough.

Then, in the early 1990s, new technology became available for scientists to discover what was really going on with ZPA and how it controlled the development of fingers and toes. At that point, Tabin, McMahon, and Ingham came up with the idea of comparing the chickens to flies. One gene, called hedgehog, made one end of a fly’s body segment look different from the other, so the three laboratories began looking for a similar gene in chickens. They found one: Sonic hedgehog, which was active in the ZPA tissue. Knowing the structure of Sonic hedgehog, other researchers could look for it in animals with fingers, and they found the gene active in the ZPA tissue in every one of those animals.

At that point, Randy Dahn, who was part of Shubin’s lab, decided to connect skates, which have fins, with the fingered animals, which includes humans, to find an inner fish. He soon found a Sonic hedgehog gene in skates that did the same thing to the skates’ fins as the gene in fingered animals did to those animals’ fingers. Dahn knew that the skeletal rods in a skate fin looked alike, so would an injection of a mouse’s Sonic hedgehog gene make the rods develop differently? He tried it, putting a bead that leaked the protein in a skate embryo. After developing, the rods looked very different from one another, and the rods closer to the bead developed differently than the rods further away, just like they would for a person, meaning that the skate’s Sonic hedgehog genes were identical, or nearly identical, to a person’s Sonic hedgehog genes. Dahn had discovered that, when fish evolved into people, the genes stayed the same; they just did things in new ways.

The experiments done in the mid-twentieth century were important to the story of Your Inner Fish because they ultimately led to Dahl’s discovery that human genes and skate genes are similar and reinforce the idea that humans evolved from fish. The experiments also show that there are many connections between living animals, often in unexpected ways.

I really enjoyed reading Handy Genes and found it quite interesting as well as informative. It taught me a lot about genes and DNA, especially the genetic connection between humans and other animals, such as sharks, skates, chickens, and flies. At first, it was a bit hard to understand, since it’s filled with a variety of information, but after a while of rereading it became clear. I would recommend this chapter, and the entire book, to anyone interested in genetics, Tiktaalik, biology, evolution, or DNA and rate it 9.6/10.

Book Review ~~ The Ascent of Man — Generation upon Generation ~~

Today I read the twelfth chapter in “The Ascent of Man,” by J. Bronowski — Generation upon Generation. This chapter was about dominant and recessive genes as well as the person who thought of them, Gregor Mendel. Although he was not particularly skilled in school, he was able to conceive of the idea of the gene theory because of his observations as a naturalist and farm boy. He performed various experiments and gathered evidence supporting his idea, using peas and then lizards to test his theory. I enjoyed learning about Mendel’s success, especially because it is a delightful tale of how a simple farm boy could achieve success because of an interest of his. I also liked learning more about recessive and dominant genes — the gene for being tall may triumph over the gene for being short in the first generation, but in the second generation, there is a small possibility that the recessive gene for being short may reappear, which I found quite interesting, as it explained why people weren’t all the same if dominant traits won against recessive ones. The chapter also contained more, interesting information about DNA. I would recommend it to anyone interested in DNA or simply looking for a good read and rate it 9.8/10.

Book Review ~~ The Cooperation Instinct ~~

Recently, I read “The Cooperation Instinct,” an article in the Discover magazine. In it, Kristin Ohlson explained Martin Nowak’s analysis of why humans cooperate and don’t simply fight each other. Nowak, combining mathematics with evolution, created a scientific model of the prisoner’s dilemma, where two criminals are charged with a crime and placed in separate rooms. If both prisoners ‘defect,’ incriminating each other, they are charged with three years in prison. If neither criminal defects, both are given only a two-year sentence. However, if one criminal defects and the other doesn’t, the defector gets only one year in prison and the criminal who didn’t gets four. Clearly, defecting is more beneficial — so why do people cooperate? In the past, biologists have attributed it to inclusive fitness, the theory that people die to save their kind, to protect their genes, but Nowak suggests that people cooperate simply because species that fight amongst themselves eventually all die out, so only species that do cooperate survive. Their genes are then passed down to the next generation. Nowak and Karl Sigmund, another evolutionary biologist, created a virtual tournament where ‘criminals’ were equipped with strategies. If they won, using those strategies, then a replica of the strategy would be introduced in place of a different strategy. Prisoners that always defected prospered at first, but eventually, a strategy called ‘Tit for Tat,’ doing exactly what the other prisoner had previously done, began to win out. Then ‘Generous Tit for Tat’ was introduced, occasionally cooperating despite a previous defection. This strategy, however, was easily taken over by the ‘Always Defectors’ before the pattern repeated. Their simulation represented times of peace and war and proved that people cooperate simply because of their genes — people who fight each other tend to be killed, so more genes leaning towards cooperation appeared. I would rate this article 9.7/10 and recommend it to anyone interested in evolution.