as
Diadectes
, a six-and-a-half-foot-long brute that looked like a stocky, diet-shy crocodile.
To get to be in that egg, your cell survived iterations of beasts that had, among many other things, evolved cells that produce a thicker collagen framework in their breathing organs; with this innovation the primitive lungs could support themselves without the need for water. Your cell line may well have passed through a creature like the 375-million-year-old lungfish
Rhinodipterus
, which, unlike other fish at that time, had a muscular neck, which enabled it to raise its head above the water line. These innovations allowed it to breathe air rather than suck oxygen from the seas, and maybe opened up a whole new world of food. Further back your cell line was contained within a much more fishlike thing, with fins and gills. Before that it was in one of the first vertebrates, a swimming thing that looked a bit like an eel or a lamprey. And before that it was in a much wormier thing, similar to the living two-inch amphioxus: in one of those cells a massive copying error in its genome, a quadrupling of its entire DNA, resulted not in a fatality, but in a whole genetic platform on which vertebrates began to evolve. Before that it was in a spongy thing. And before that, just a clump of cells free-floating or lodged on a rock. And back and back and back ceaselessly into the past. The lineage of your cells has survived every disaster, catastrophe, meteorite, every extinction, ice age, and hungry predatorâevery event in this solar system for almost four billion years.
The vast majority of your cells, including all of the new ones in your cut, are terminal branches in this absolute pedigree, as their story will end with your life. The only ones that survive to give rise to cells in the next generation are sperm or egg. And of the trillions of cells that have worked for you throughout your life, only a handful will go on, the lucky few that will meet a sperm or egg and make a child. But the information within all of them will be carried on. Down that line has been transmitted the DNA that builds all of those cells together to make the most efficient way of ensuring the perpetual existence of your genes: an organism. Life is an astonishingly conservative system: DNA is the same in all species; the letters of the code are all the same; the encryption in the code is the same; even the orientation of the molecules is the same. Whatâs true in bacteria is true in a blue whale. Only a system with a single root could display such conservation.
That pathway backward, retracing our steps as they become fainter and fainter over geologic time, can be applied to any creature alive today, or ever. The gaps become bigger, and itâs almost always only hypothetical. Although we have a good overall understanding of the origin of species, to claim one species was the direct ancestor of another is often overstating what we can know. But the broad sweep of evolution is well understood, and any step backward through the past from any creature drives us to a single conceptual home. The branching tree of life ultimately becomes narrower as we reverse through time until we reach a single root.
We could trace an equivalent route backward for a cell taken from the boiling mud in an Icelandic hot spring, from the flower of a sweet pea, or from a button mushroom from the supermarket, and every time we would end up back in the same place. In every cell is a perfect unbroken chain that stretches inevitably back to the origin of life. That lineage irresistibly leads back to one single entity, which we call the Last Universal Common Ancestor, or Luca. Somewhere on the infant earth, Luca split in two. Since then, the thing that we struggle to define as life has passed uninterrupted from it to you, via a colossal series of iterations. Existence is bewilderingly tenacious.
Entities that we might be able to describe as living may have emerged several times, but
Diadectes
, a six-and-a-half-foot-long brute that looked like a stocky, diet-shy crocodile.
To get to be in that egg, your cell survived iterations of beasts that had, among many other things, evolved cells that produce a thicker collagen framework in their breathing organs; with this innovation the primitive lungs could support themselves without the need for water. Your cell line may well have passed through a creature like the 375-million-year-old lungfish
Rhinodipterus
, which, unlike other fish at that time, had a muscular neck, which enabled it to raise its head above the water line. These innovations allowed it to breathe air rather than suck oxygen from the seas, and maybe opened up a whole new world of food. Further back your cell line was contained within a much more fishlike thing, with fins and gills. Before that it was in one of the first vertebrates, a swimming thing that looked a bit like an eel or a lamprey. And before that it was in a much wormier thing, similar to the living two-inch amphioxus: in one of those cells a massive copying error in its genome, a quadrupling of its entire DNA, resulted not in a fatality, but in a whole genetic platform on which vertebrates began to evolve. Before that it was in a spongy thing. And before that, just a clump of cells free-floating or lodged on a rock. And back and back and back ceaselessly into the past. The lineage of your cells has survived every disaster, catastrophe, meteorite, every extinction, ice age, and hungry predatorâevery event in this solar system for almost four billion years.
The vast majority of your cells, including all of the new ones in your cut, are terminal branches in this absolute pedigree, as their story will end with your life. The only ones that survive to give rise to cells in the next generation are sperm or egg. And of the trillions of cells that have worked for you throughout your life, only a handful will go on, the lucky few that will meet a sperm or egg and make a child. But the information within all of them will be carried on. Down that line has been transmitted the DNA that builds all of those cells together to make the most efficient way of ensuring the perpetual existence of your genes: an organism. Life is an astonishingly conservative system: DNA is the same in all species; the letters of the code are all the same; the encryption in the code is the same; even the orientation of the molecules is the same. Whatâs true in bacteria is true in a blue whale. Only a system with a single root could display such conservation.
That pathway backward, retracing our steps as they become fainter and fainter over geologic time, can be applied to any creature alive today, or ever. The gaps become bigger, and itâs almost always only hypothetical. Although we have a good overall understanding of the origin of species, to claim one species was the direct ancestor of another is often overstating what we can know. But the broad sweep of evolution is well understood, and any step backward through the past from any creature drives us to a single conceptual home. The branching tree of life ultimately becomes narrower as we reverse through time until we reach a single root.
We could trace an equivalent route backward for a cell taken from the boiling mud in an Icelandic hot spring, from the flower of a sweet pea, or from a button mushroom from the supermarket, and every time we would end up back in the same place. In every cell is a perfect unbroken chain that stretches inevitably back to the origin of life. That lineage irresistibly leads back to one single entity, which we call the Last Universal Common Ancestor, or Luca. Somewhere on the infant earth, Luca split in two. Since then, the thing that we struggle to define as life has passed uninterrupted from it to you, via a colossal series of iterations. Existence is bewilderingly tenacious.
Entities that we might be able to describe as living may have emerged several times, but
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