Some Assembly Required (DECODING FOUR BILLION YEARS OF LIFE, FROM ANCIENT FOSSILS TO DNA) by Neil Shubin
Another great science work by the discoverer of Tiktaalik. This one is more about some quirks (important ones) of evolution that defy the elementary cartoon picture of gradualism. That sometimes when it looks like a whole bunch of things have to come together for some 'leap' of evolution, that many of the enabling factors were already well in place, but now used for a new purpose.
Like lungs and limbs in the water-to-land transition, the inventions used for flight preceded the origin of flight. Hollow bones, fast growth rates, high metabolisms, winglike arms, wrists with hinges, and, of course, feathers originally arose in dinosaurs that were living on the ground, running fast to capture prey. The major change is not the development of new organs per se but the repurposing of old features for new uses and functions.
The transformation of fins to limbs is a world of repurposing at every level: genes that make hands and feet are present in fish, making the terminal end of their fins, and versions of these same genes help build the terminal end of the bodies of flies and other animals. Great revolutions in life do not necessarily involve the wholesale invention of new genes, organs, or ways of life. Using ancient features in new ways opens up a world of possibility for descendants.
Imagine a house with many rooms, each with its own thermostat. A change to the furnace will affect the temperature in every single room, but changing a single thermostat will affect only the room it controls. The same relationship is true for genes and their control regions. Just as a change in the furnace will affect the entire house, an alteration in a gene, and the protein that is produced, can affect the entire body. A global change would be catastrophic, producing dead ends in evolution. But since the genetic control regions are specific to tissues, like a thermostat in a room, a change in one organ won’t affect any others. Mutants can be viable, and evolution can work.
Or using 'tamed' viral insertions as raw material for evolution. An important gene for the mammalian placenta is derived from an ERV. A defect in the gene is what causes preeclampsia. The gene is used by the virus to sneak things across cell barriers. In the repurposed version its what allows nutrients and other molecules to pass between mother and fetus.
The genome is the stuff of B movies, like a graveyard filled with ghosts. Bits and pieces of ancient viral fragments lie everywhere—by some estimates, 8 percent of our genome is composed of dead viruses, more than a hundred thousand of them at last count. Some of these fossil viruses have kept a function, to make proteins useful in pregnancy, memory, and countless other activities