Some Assembly Required, Decoding 4 Billion Years of Life from Ancient Fossils to DNA, 2020,
Neil Shubin
How did an ancient fish crawl onto land and begin terrestrial life? This has been a controversial question for biology since the time of Darwin. Darwin was prescient in saying major transitions are “often accompanied by a change of function”. Shubin answered the question in his 2005 book “Your Inner Fish”. Way before fish walked on land, they had developed a ballast system much like the ballast tanks on submarines. Connected to the esophagus of most fish are small air sacs. When a fish wants to be nearer the surface it pushes it’s mouth above water and inflates the air sacs. Maybe you have seen fish doing this? Over time fish in oxygen depleted bodies of water expanded these air sacs into alternate lungs. What happened to the gills once these fishlike animals began life on land? In the case of many mammals they formed the inner ear structure and in humans also the structure of the voice box.
Since decoding the genome in 2000 progress in the science of genetics and paleontology has been nothing short of astounding. The cost of decoding a genome has decreased form the 3.8 billion in 2000 to just a few hundred dollars today. This has enabled the decoding of thousands of animal species, ancient human DNA, bacteria, and viruses. In the human genome we have discovered that only 2% is made up of our own genes. 10% is made up of ancient viruses that at one time infected our ancestors. 60% is duplications made up of “jumping genes gone wild”. A recent astounding discovery was that the genetic program that makes the human placenta is a genetic sequence from a virus incorporated into the mammalian genome in the transition from egg laying to placental birth. The protein that makes neuron connected memory possible also is derived from a virus invader. Amazingly both have components very similar to HIV virus. I guess we can’t be too negative on viruses, no?
What is the other 28% of our genome? These are the are linear molecular programs, consisting of on-off switches, that design and construct all complex multicellular creatures. They operate much like a digital computer. Working as a field engineer on ballistic missile submarines in the 1960’s, I was responsible for a piece of gear that checked out the missile before launch. It consisted of thousands of discreet switches that ran a group of linear subroutine programs that verified each component was working before signaling successful completion and ready for launch. What the HOX and PAX genes do in building complex bodies is somewhat similar. Each structure such as a leg, fin or hand is created by a series of switches activated in linear order to produce the required proteins in an ordered sequence. What has been discovered is that these programs are remarkably similar in all creatures ranging from flies to fish to reptiles to humans. Using Crispr, a gene editing program, researchers have changed the locations of these programs resulting in bizarre outcomes such as legs growing out of a fly’s head. As Shubin eloquently relates: “The genome at every level resembles a musical score in which the same musical phrases are repeated in different ways to make vastly different songs. In fact, if nature was a composer, she would be one of the greatest copyright violators in history- everything from DNA to entire genes and proteins is a modified copy of something else”.
What has been discovered in the last 20 years has changed the conception of humankind’s place in the universe. We can no longer be seen as somehow special or separate from the rest of life. We are a continuation of biological evolution as a product of and deeply connected to all life on Earth.
As Shubin concludes “The poet William Blake wrote of seeing “the universe in a grain of sand and a heaven in a wildflower”. When you know how to look, you can see billions of years inside the organs, cells, and DNA in all living things and relish our connections to the rest of life on the planet”.
For those of you who have read “The Tangled Tree” by David Quammen you will love this book as a perfect follow on. While that book detailed the evolution of the complex cell, this book details the evolution of complex bodies. JACK
Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA
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Last update: 07-30-2024
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