Title: A (Very) Short History of Life on Earth: 4.6 Billion Years in 12 Pithy Chapters

Author: Henry Gee

Completed: August 2023 (Full list of books)

Overview: This was an unusual book to me. It started off covering vast swaths of early prehistory at breakneck speed. Often only discussing one species long enough to note the name, what it evolved from, and what species followed after it. It was reminiscent of sections of Genesis (Adam begat Seth; Seth begat Enos; etc). At this stage, I almost stopped reading, which I rarely do. I’m glad I opted to continue on. Several of the later chapters were much more interesting to me. The last chapter also looked ahead in a way that was both reassuring and alarming at once. He argues that we need to continue to all we can to fight climate change and our impact on the environment, but no matter what we do, humans will be extinct in 1000 years. After that, the Earth will quickly (geologically speaking) wipe away any trace we were ever here. The planet doesn’t need “saving”; it will be fine. Life will continue. There will be no people or most of the species we currently know, but that’s the way life has been for billions of years, constantly changing.

Highlights:

• Stromatolites—as we have seen, the first visible signs of life on Earth—were colonies of different kinds of bacteria. Bacteria can even swap portions of their own genes with one another. It is this easy trade that means, today, that bacteria can evolve resistance to antibiotics. If a bacterium doesn’t have a resistance gene for a particular antibiotic, it can pick it up from the genetic free-for-all of other species with which it shares its environment.
• Sponges have no distinct organs or tissues. A live sponge pushed through a sieve and back into the water will pull itself together into a different shape but one just as alive, just as functional. It is a simple life that requires little energy—and little oxygen.
• Some of the armored heirs of Saccorhytus created their own distinctive suits of chain mail, each link sculpted from a single crystal of calcite. In doing so they became the echinoderms—the spiny-skinned ones—the ancestors of the starfishes and sea urchins of today. All modern echinoderms have a distinctive body shape based on the number five, entirely different from any other animal. In the Cambrian, however, their shapes were more varied. Although some were bilaterally symmetrical, a few were triradial (that is, with a symmetry based on the number three), and yet others were completely irregular.
• The evolution of the seed, like the evolution of the amniote egg, allowed plants to break away from the tyranny of water.
• As pterosaurs evolved, they grew, until the last of their kind—at the end of the Cretaceous period—were as large as small airplanes and barely flapped at all. Light in build but with enormous wings, all they needed to do to take off was to spread their wings into a light breeze and physics would do the rest. Their success was abetted by a delicate construction, their skeletons modified into rigid, boxy airframes made of bones hollowed almost to paper-thinness.
• But dinosaurs also excelled at being small. Some were so small they could have danced in the palm of your hand. Microraptor, for example, was the size of a crow and weighed no more than a kilogram; the peculiar, bat-like Yi, diminutive in name as well as size, weighed less than half that.
• A sizable beneficiary was the liver, which generated a lot of heat and, in a large dinosaur, was the size of a car. The air-cooled internal workings of dinosaurs were more efficient than the liquid-cooled mammalian version. This allowed dinosaurs to become much larger than mammals ever could, without boiling themselves alive.
• Although vertebrates in general have always laid eggs—a habit that allowed the final conquest of the land by the first amniotes—many vertebrates have reverted to the ancestral habit, found in the earliest jawed vertebrates, of bearing live young. It is all a matter of finding a strategy that protects the offspring without incurring too onerous a cost on the parent. Mammals started by laying eggs. Almost all of them became live-bearers, but at terrible cost. Live-bearing demands vast expenditures of energy, and this sets limits on the sizes that mammals can achieve on land.16 It also limits the number of offspring they can produce at once.
• Madagascar, then as now, was a haven for the exotic. In the Cretaceous, many ecological niches there, even vegetarianism, were occupied by crocodiles.40
• The dinosaurs’ card had been marked long before. Around 160 million years ago, in the late Jurassic, a collision in the distant asteroid belt produced the forty-kilometer-diameter asteroid now known as Baptistina, along with a magazine of more than a thousand fragments, each more than a kilometer across, some much larger. These harbingers of doom dispersed into the inner solar system.
• We humans, at least in childhood, can hear notes as high as 20 kHz, much higher than the highest song of the skylark.6 But humans are cloth eared compared with many other mammals, such as dogs (45 kHz7), ring-tailed lemurs (58 kHz8), mice (70 kHz9), and cats (85 kHz10), and they are profoundly deaf compared with dolphins (160 kHz11). The evolution of the chain of three bones in the mammalian middle ear opened up to mammals an entirely new sensory universe inaccessible to other vertebrates.
• When the backbone evolved half a billion years ago, it was a structure held horizontally, in tension. In hominins, it moved through ninety degrees, to be held vertically, in compression. No more radical alteration in the engineering requirements of the backbone has happened since it first evolved, and it can only be regarded as maladaptive; witness that back problems constitute one of the most costly and frequent causes of illness in humans today. Dinosaurs made a huge success of being bipeds but did so in a different way; they held their backbones horizontally, using their long, stiff tails as counterbalances. But hominins, like apes, have no tails and achieved bipedality the hard way.
• they took a step that would be as revolutionary as standing upright had been to their now-distant forest ancestors: they learned how to run.
• Half a million years ago, Britain was buried under ice a mile thick. In contrast, the climate was so warm 125,000 years ago that lions hunted deer on the banks of the Thames, and hippos wallowed as far north as the River Tees. Forty-five thousand years ago, Britain was a treeless steppe where reindeer roamed in winter and bison in summer.4 Twenty-six thousand years ago, it was too cold even for reindeer.
• The hand axe is so distinctive because it has more or less the same design wherever it is found, irrespective of its age or the material from which it is made. Its association with a particular species—Homo erectus—suggests that hand axes, for all their undeniable beauty, were made according to a hardwired, stereotypical design. They were created as thoughtlessly as birds make their nests. If, when creating a hand axe, the maker made a mistake in the sequence of strokes required to chip it from a blank flint, they would not try to fix it or perhaps turn it to some other purpose. They would simply discard the mistake and start again from the beginning with a fresh blank.
• Within the next few thousand years, Homo sapiens will have vanished. The cause will be, in part, the repayment of an extinction debt, long overdue. The patch of habitat occupied by humanity is nothing less than the entire Earth, and human beings have been making it progressively less habitable. The main reason, though, will be a failure of population replacement. The human population is likely to peak during the present century, after which it will decline. By 2100, it will be less than it is today.