Letters to a Young Scientist (14 page)
New kinds of mussels and other novel organisms discovered in deep-sea hydrothermal vents on the Mid-Atlantic Ridge. Modified from original painting. © Abigail Lingford.
S
EARCHING FOR
N
EW
W
ORLDS ON
E
ARTH
T
O MAKE IMPORTANT DISCOVERIES
anywhere in science, it is necessary not only to acquire a broad knowledge of the subject that interests you, but also the ability to spot blank spaces in that knowledge. Deep ignorance, when properly handled, is also superb opportunity. The right question is intellectually superior to finding the right answer. When conducting research, it is not uncommon to stumble upon an unexpected phenomenon, which then becomes the answer to a previously unasked question. To search for unasked questions, plus questions to put to already acquired but unsought answers, it is vital to give full play to the imagination. That is the way to create truly original science. Therefore, look especially for oddities, small deviations, and phenomena that seem trivial at first but on closer examination might prove important. Build scenarios in your head when scanning information available to you. Make use of puzzlement.
While I’ve spent a lot of time thus far on biology, obviously because I am a biologist, I am happy to emphasize that other fields of science yield comparable treasures of discovery. I’ve worked enough with mathematicians and chemists in particular to know that their heuristics—their process of making discoveries—is closely similar. Organic chemistry, for example, to substantial degree consists of exploring the almost endless array of possible molecules, and the occurrence of this chemodiversity in the natural world, and finally the physical and combinatorial properties of each kind of molecule. Take the elementary hydrocarbon CH
4
and run it in series up through C
2
, C
3
, C
4
, and beyond, adding double and triple bonds, and sprinkle along the way the radicals S (sulfur), N (nitrogen), O (oxygen), and OH (hydroxy-), varying the form when possible into pure and branching strings, cycles, helices, and folds. The number of potential molecular “species” rises with molecular weight at a rate faster than exponential. Four million organic compounds were known by 2012, with 100,000 more being characterized each year, comparing favorably with 1.9 million biological species known and 18,000 new species added each year. Most of organic chemistry, and within it natural-products chemistry, consists of the study of the synthesis and characteristics of the molecules. Special attention is paid to those occurring in living organisms, where organic chemistry turns into biochemistry. Virtually all of life’s processes and all of living structures are but the interplay of organic molecules. A cell is like a miniature rain forest, into which biochemists and molecular biologists conduct expeditions to find and describe organic structure, variety, and function.
The mind-set of astronomers is similar. They wander through the near-infinitude of space and time to find and describe the arrays of galaxies and star systems, and the forms of energy of matter within and between them. The development of particle physics has likewise been a journey into the unknown, to explore the ultimate components of matter and energy.
Across thirty-five powers of magnitude (powers of ten, hence of magnitude 1, 10, 100, 1000, and so on), from one subatomic particle to the entirety of the universe, science rules the enterprise of the human imagination applied to the laws of reality. Even if our intellect were somehow limited to the biosphere alone, scientific research would still be an endless adventure of exploration. Life invests the planet surface totally; no square meter is entirely free of it. Bacteria and microscopic fungi exist on the summit of Mount Everest. Insects and spiders are blown there by thermal drafts; and a few, including springtails and the jumping spiders preying on them, survive on the slopes close to the very top. At the extreme opposite in elevation, the bottom of the Mariana Trench in the western Pacific, thirty-six thousand feet below the ocean surface, bacteria and microscopic fungi flourish, and, with them, fish and a surprisingly large variety of single-celled foraminiferans.
There must be by definition somewhere on Earth a site with the greatest variety of organisms. The Yasuni National Park of Ecuador, which encloses a magnificent rain forest between the Rio Napo and Rio Curaray, is reputed to be that one biologically richest place on Earth. More precisely, its 9,820 square kilometers are believed to contain more species of plants and animals than any other piece of land of comparable area. The known roster supports the claim: recorded in the whole park are 596 bird species, 150 amphibian species (more than the number in all of North America), as many as 100,000 insects, and, growing in just a single average upland hectare, 655 tree species—also more than occur in all of North America. The only question about Yasuni’s supremacy is whether there might exist some other, less explored section of the Amazon and Orinoco Basins that will prove even more diverse. At the very least, the Yasuni National Park is very close to the extreme of its kind. And outside the Amazon-Orinoco region, nothing in the world can approach it.
There is another reason to pay attention, not yet widely recognized even by most biologists: the Yasuni National Park may harbor the highest species numbers that have
ever
existed. Throughout the entire history of life, from the Paleozoic Era forward, 544 million years, the number of plant and animal species worldwide has been very slowly rising. Thus at the breakout from Africa and worldwide spread of
Homo sapiens
, beginning about 60,000 years before the present, Earth’s biodiversity was likely at its all-time maximum. Then, extinction by extinction, human activity began to whittle the number down, and today that pace is accelerating. For the time being, Yasuni holds its own, and that is why it is recognized as a world treasure. We know only a fraction of the species of animals, especially the insects, found in the Yasuni, and next to nothing of their biology. We would like to take the full measure of this place, and of others of similar extreme high diversity, and come to understand the reason for its preeminence—before it is ruined by human greed.
In extreme opposition, there exists on Earth a close outward approximation of the lifeless surface of Mars. In its own way it has been worth exploring. The place is the McMurdo Dry Valleys of Antarctica. To casual inspection the land seems as sterile as the surface of autoclaved glassware. But life is there, and it makes up the sparest and most stubborn of all of Earth’s ecosystems outside the open surface of polar ice. Even though nitrogen is at the lowest concentration of any habitat on Earth, and water is almost nonexistent, it is surprising to find bacteria in the soil of the McMurdo Dry Valleys. The rocks scattered about seem lifeless, yet some are etched with almost invisible crevices in which communities of lichens live. These organisms are minute fungi that live symbiotically with green algae. They are concentrated layers just two millimeters beneath the surface of the rocks. Farther in, other such endoliths (“living in rocks”) include bacteria capable of their own photosynthesis.
Scattered about in the McMurdo Dry Valleys are frozen streams and lakes, which contribute a small amount of moisture in the surrounding soil. The free water, which occurs in droplets and films, harbors small numbers of almost microscopic animals: tardigrades, the strange creatures sometimes called “bear animalcules” that I mentioned earlier, rotifers (“wheel animalcules”), and, most abundant of all, nematodes, also called roundworms. Although barely visible to the naked eye, the nematodes are the tigers of the land, the top of the food chain in this quasi-Martian world, and the antelope equivalents on which they feed are bacteria in the soil. In a few places can also be found rare mites and springtails, the latter a primitive form of insect. In all, sixty-seven species of insects have been recorded from the combined habitats of Antarctica, but only a few are free-living. The great majority are parasites that live in and on the warm plumage of birds and the fur of mammals.
As I write, there are many other places on the planet in which biological exploration has only begun. The greatest depths of the ocean, the abyss of eternal dark, consists of great submerged mountain ranges incised by deep unvisited valleys and intervening vast plains. The tips of many of the mountains rise above the water to form the oceanic islands and archipelagoes. Some come close but remain submerged. There are the seamounts. Their peaks are coated with marine organisms, many of whose species are unique to the location. The exact number of seamounts is still unknown. It has been estimated to run in the hundreds of thousands. Imagine the extent of human ignorance! Beneath the surface of the oceans and seas, which cover 70 percent of the Earth’s surface, there exists an all but countless number of lost worlds. Their complete exploration will occupy generations of explorers from every discipline of science.
Life on Earth remains so little known that you can be a scientific explorer without leaving home. We have scarcely begun to map Earth’s biodiversity at any level, from molecule to organism to niche in an ecosystem. Consider the following numbers of known and unknown species among different taxonomic groups of organisms around the world. They are why I like to call Earth a little-known planet. The data were pulled from global surveys made under the auspices of the Australian government in 2009.
The total number of species estimated in 2009 to have been discovered, described, and given a formal Latinized names worldwide was 1.9 million. The true number, both discovered and remaining to be discovered, could easily exceed 10 million. If the single-celled bacteria and archaea, the least known of all organisms, are added, the number might soar past 100 million. Five thousand kilograms of fertile soil contain, by one estimate, 3 million species, almost all unknown to science.
Why haven’t scientists made more progress in exploring the world of bacteria and archaea? (The latter are an important group of single-celled organisms that outwardly resemble bacteria but possess very different DNA.) One reason for our ignorance is that a satisfactory definition of “species” in these organisms remains to be made. An even more important reason is that the different kinds of bacteria and archaea are so diverse in the environments they require in order to grow, and in the food they need to eat. Microbiologists have not learned how to culture the great majority of bacteria and archaea, in order to produce enough cells for scientific study. With the advent of rapid DNA sequencing, however, the genetic code of a strain can be determined with only a few cells. As a result, the exploration of species diversity has increased dramatically.
In citing these remarkable figures on biodiversity, I am not suggesting that you plan to become a taxonomist—although for now and many years ahead that would not be a bad choice. Rather, I wish to stress how little we know of life on this planet. When we also consider that the species is only one level in the hierarchy of biological organizations, molecule to ecosystem, then the immense potential of biology, and of all of the physics and chemistry relevant to biology, becomes immediately apparent.