In the Beat of a Heart by John Whitfield
Thompson believed that still deeper investigation would dissolve the distinction between biology, chemistry, and physics. Only then would we have a true understanding of biology. (p. 15)
Thompson wanted to convince his readers that, in contrast to vitalist philosophy, the laws of physics apply to living organisms and that life does nothing that breaks these laws. (p. 18)
Where previous biologists had taken it for granted that organisms were well adapted to their environment, Thompson demonstrated what this meant. (p. 19)
When he turned his attention to physics and mathematics in biology, Thompson decided that there were already quite enough facts available --- what was needed was a synthesizer to tease the threads of an argument from the disparate work of other researchers. (p. 23)
This fire stolen from heaven, this torch of Prometheus, does not only represent an ingenious and poetic idea. It is a faithful picture of the operations of nature, at least for animals that breathe: one may therefore say, with the ancients, that the torch of life is lighted at the moment the infant breathes for the first time, and is extinguished only on his death. (p. 33. By Antoine Lavoisier, in 1789)
One of the most reliable rules of conservation is that it is
bad to be big. Across the animal kingdom, big species are more at risk than
their smaller brethren. Orangutans and elephants are disappearing more quickly
than rats and rabbits. Rhinos are more endangered than antelopes. Large birds,
such as albatrosses and eagles, are in more trouble than warblers and finches. Whales
are more endangered than porpoises. This rule holds even for reptiles and
insects: The planet’s largest known earwig, a 3-inch-long giant from the
Atlantic
It is easy to see what makes large species more prone to extinction. They need more food and so more land. They are often found high up in the food chain and so depend everything below them staying in good shape. All of this means that there are fewer of them to start with. Big animals take longer to reach breeding age, breed less often, and produce smaller numbers of young when they do. The fossil records show that, throughout history, carnivorous mammals, such as cats and dogs, have experienced a high degree of evolutionary churn. Species come along, dominate for a few million years, and then disappear, at which point a new group comes along to do the same job. There are obvious benefits to a predator in being big and fierce, but this might also paint a species into an evolutionary corner. (p. 95)
Lotka was not the first person to have this idea, but he pursued it harder and farther, and with greater mathematical rigor, than anyone else. Also like Thompson, he worked outside the academic mainstream and had little contact with other scientists. A quarter of century of such work culminated in his book, Elements of Physical Biology. In the book he imagines physical biology, which he defines as “the application of physical principles in the study of life-bearing systems,” as analogous to the then-voguish physical chemistry. Scarcely any life-bearing system escaped his gaze. He tackled growth and population dynamics, the cycling of chemical elements from the environment into life and back again, behavior, the senses, communication, travel and consciousness. Often he tok examples from economics and sociology. … Lotka wanted to build an intellectual framework that would unify physics, biology, and the study of human society, (p. 97)
As well as trying to understand biology in terms of physical principles, Lotka sought to solve biological problems using the tools of physics. He drew analogies between evolution and thermodynamics, but he also thought that organisms were far too complicated to be understood simply by the application of thermodynamics. It would be “like attempting to study the habits of an elephant by means of a microscope.” But the mathematical techniques of physics could still be used in studying life, by treating plants and animals as if they were particles: “What is needed is an altogether new instrument, one that shall envisage the units of a biological population as the established statistical mechanics envisage molecules, atoms and electrons.”
The world, said Lotka, is an engine, and although it is useless --- all its work is used internally to feed and repair itself --- the world engine’s great trick is its ability to improve its working as it goes along, through evolution. (p. 98)
Brown had become frustrated with ecology’s emphasis on small spatial scales and short periods. The typical experiment tracked, say, the plants in one field over three years or the mollusks on a single beach over a single summer. A great many of the published studies focused on 1 square meter of land or less. (p. 98)
That this mechanism is the best possible under all the circumstances of the case, that its work is done with a maximum of efficiency and at a minimum of cost, may not always lie within our range of quantitative demonstration, but to believe it to be so is part of our common faith in the perfection of nature’s handiwork … To prove that it is the best of all possible modes of transport may be beyond our powers and beyond our needs; but to assume that it is perfectly economical is a sound working hypothesis. (p. 106, quote from D’Arcy Thompson’s On Growth and Form)
Growth involves myriad constantly varying chemical reactions, and every individual of every species will be different at every moment. But, he reasoned, just as we regard a company’s statement of profit and loss as a meaningful generalization, even though it conceals a host of individual transactions, so it ought to be possible to make generalization about animal growth. (p. 124)
There is more to growth and development than energy. A builder with a generator but no bricks would build nothing. Likewise, organisms need material as well as calories: A body won’t work properly without a balanced diet and what it can do depends on what chemicals it gets. Just as they vary in size and temperature, organisms also vary in their chemical composition, and this variation can explain another tranche of their biological differences. (p. 129)
Entropy can count both energy and material scarcity.
Metabolism sets the boundaries of reproductive choices, too. The rate at which animals can seize energy for themselves limit the rate at which they can pass it on to their offspring. So, not surprisingly, many aspects of reproduction march in step with metabolism, and an animals’ size is its best guide to its reproductive biology. Bigger animals produce bigger young, but they devote a smaller proportion of their resources to their offspring. The clutch of a 100-kilogram ostrich consists of thirteen 1-kilogram eggs, totaling about one-eighth of the mother’s body weight. A 3-gram hummingbird can lay two eggs that each weighs a s much as itself. Big fish and reptiles also lay proportionally lighter clutches than small ones. The mass of mammals’ litters shows a similar trend, and big mammals’ milk contains less protein than that of small species. All these properties are more or less proportional to the body mass raised to the power of ¾, although there is much variation about this number. One thing that does vary between groups is the way these resources are divided up: Birds and mammals produce relatively few large offspring, in which they invest considerable resources, both before and after birth. Many reptiles, fish, and invertebrates go for quantity rather than quality, producing many small young, each of which stands only a small chance of survival. Bigger animals also breed less often --- the interval between litters or clutches is proportional to body mass raised to the power of ¼ --- and so produce a smaller number of offspring over their lifetime. (p. 131)
Countries’ birth rates fall as their economies grow. Less developed countries typically have both
high birth and death rates. As health improves, the dezth
rates falls, and population rises quickly. But eventually birth rate falls too,
and the population stabilizes. In parts of
In fact, humans reproduce exactly as much as their
metabolisms predict. It’s just that, unlike every other species, biological
metabolism makes up only a small fraction of human energy consumption. We also
use energy in our heating, air-conditioning, cars, appliances
and so on. Our societies use it is manufacturing, airplances, communications, and road building. Jim Brown
and his student Melanie Moses compared per capita energy consumption and birth
rates for more than 100 countries. They found that birth rates falls smoothly
as energy consumption rises. The average
Metabolism sets the pace, and balances and scales, for the beginning of life, the course of life, and in reproduction for the purpose of life, at least in evolutionary terms. …
In the inanimate world, putting a lot of energy through a thing is a good way to wear it out. The harder you work a machine, the quicker it falls apart. We talk about running things into ground; people who work and play hard say they are burning the candle at both ends, and the candle that burns twice as brightly burns half as long.
First appearances suggest that the same is true for living organisms. Large animals with relatively slow metabolisms live longer. The match is striking: metabolic rate per cell declines proportional to body mass to the power of -1/4, and life span increases proportional to body mass to the power of ¼. This means that every cell, be it rat or rhino, burns approximately the same amount of energy in its lifetime. Heart rate also declines in line with relative metabolic rate, as the -1/4 power of body mass. …
This means that every mammal should get about the same number of heart … Fruit flies reared at 30ºC live on average 14 days, those at 10 ºC live for 120 days. … Rats that live sedentary lives live longer than those that are forced to exercise. All this evidence made a deep impression on the man who would become most associated with the idea that tolive fast is to die young … (p. 135)
Oxygen is a mixed blessing because it is highly reactive. This property makes it perfect for releasing energy from food but also makes it liable to react with and damage the rest of the body’s molecules --- just as a fire can both warm your house and burn it down. When two oxygen atoms are joined in an O2 molecule, they are relatively harmless. The trouble starts up when the molecule is broken up for use in respiration. Such reaction creates free radicals, lone oxygen atoms with spare electrons. It is these free radicals that make the free radical so reactive and so noxious. The free radical careens around the cell, damaging any protein molecule or DNA it bumps into. DNA damages is particularly bad because it is passed on to the cell’s descendents. … This is why dieticians recommend food rich in small molecules, such as omega-3 fish oils, that mop up free radicals before they can cause harm. (p. 137)
It now looks as though it’s not how quickly you burn energy
that influences the aging process but the way that you burn it. Long-lived mice
do not simply have faster metabolism than their shorter lived counterparts.
They also have different mitochondrial chemistry. Mitochondria can do two
things with food: turn it into cellular fuel, in the form of ATP, or burn it
off as heat. The chemical reaction that turn food into
heat produce fewer free radicals than those that produce ATP. Cells have protein that switch their mitochondria from ATP mode into
heat mode, a process called mitochondrial uncoupling. The long-lived
energy-hungry mice in the
Some researchers, including Speakman, are on the trail of drugs that might increase life span by uncoupling mitochondria. We already know some chemicals that do that, but they tend to have some unfortunate side effects. (p. 140)
This shows that systems doing useful works will get damaged easier. This is no way to get around it.
Perhaps, then, it’s the quality of the climate, not the quantity of energy, that’s important. As well as being warmer and wetter, the climate in the tropics is … more stable, lacking the seasonal fluctuations in temperature found in temperate regions.
This stability might encourage diversity by letting species be more specialized, making their niches narrower and allowing a finer division of natural resources. If an animal in a temperate forest live on fruit, or leaves, or insects, it has a problem. These food source disappears for some of the year. The animal must either broaden its diet, hibernate, or migrate. But in the tropics it can eat leaves, fruit, or bugs all year round, leaving more resources for other species. Perhaps stability promotes diversity in general. Some other highly variable environments, such as estuaries, which alternate between saltwater and freshwater twice daily, have relatively low number of species.
But while weather in the tropics might be more agreeable, the biological environment is as cutthroat as anywhere else, perhaps more so. This too has been suggested as the cause of abundant tropical diversity. Freed from the stress of coping with the inclement or unpredictable, tropical species might instead evolve to exploit each other by becoming better competitors, or predators, or parasites. If tropical species faced fiercer struggles with their enemies, or with others of their own kind, than temperate ones, they might compete less with their neighbors over resources --- the force that drives species out. Thus might more tropical species coexist. (p. 216)