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6. Biology Revolution

Biology: Advanced Physics

Of all the advanced scientific disciplines, an emphasis on physics and scaling properties has the greatest impact on biology, as biology studies the most complex objects: living organisms.

Airplanes and many other man-made objects can be intricate creations, yet compared to the most advanced forms of life, they are relatively simple. In general, the significance of scaling properties increases with the complexity of an object or organism. When it comes to life, size matters. Beyond a solid grasp of physics fundamentals, a strong understanding of scaling properties and the process of evolution are among the most important guiding concepts for comprehending biology.

Open a standard college biology textbook and flip through the pages. Scattered throughout its thousand or so pages, you will find numerous biological concepts that depend on an understanding of the importance of size. Yet what is missing from these textbooks — just as it is from standard college physics textbooks — is a chapter near the beginning explaining Galileo's Square-Cube Law and why size matters.

How does a water strider walk on water? How does a bat navigate through a cave or stay warm at night? How does a bumblebee fly? How does a gecko walk on the ceiling? How does a tree draw water up to its highest leaves? How do nutrients pass through the walls of a cell? What determines the form of a given species?

While biology focuses on living organisms, solving biological problems ultimately relies on physics. In particular, understanding how size influences which physical principles are most relevant is key to answering the majority of biology’s questions.

The Speed of Life Determined by Size / The Fountain of Youth

Time is relative. Because Earth's 23.5-degree tilt determines the seasons, we measure time according to Earth's movement around the Sun. This perspective of time is meaningful to most plants and animals, as their growth patterns and behaviors are tied to the seasons. Yet there is another important perspective on time — one determined by the size of an animal.

Watch an ant as it moves along the ground. We can track where its body goes, but its legs move so fast that our eyes cannot keep up. Ironically, despite its tiny nervous system, the ant processes movement far more quickly than we do. Because electrical impulses travel much shorter distances in its body, the ant can coordinate its six legs with incredible speed — faster than we can even perceive. From the ant’s perspective, time moves at a much faster pace.

At the cellular level, the major differences between animals nearly disappear — except for time. Like a gas-powered engine, a cell’s metabolic rate depends on how quickly it receives fuel. Smaller animals process fuel faster, making their cells run at higher speeds. For example, a mouse’s breathing, digestion, and heart rate all function about ten times faster than ours. Additionally, the shorter distances between a mouse’s fuel-demanding cells and fuel-supplying organs allow its circulatory system to deliver nutrients about ten times more quickly. Thus, a human muscle cell and a mouse muscle cell function similarly, except the latter operates at a much higher speed.

While a faster metabolism has clear advantages, it also comes with a cost: the cells of smaller animals wear out more quickly. The smallest animals live fast but do not live long. As shown in the table below, as an animal’s mass increases, its heart rate decreases. Furthermore, as heart rate slows, lifespan increases.

Table Comparing the Speed of Life of Selected Vertebrates

Vertebrate	Metabolism	Mass (Kg)	Resting Heart Rate (BPM)	Total Heartbeats (billion)	Lifespan (yr)
Mouse	Warm	0.03	580	0.4 - 0.92	1.3 - 3
Rat	Warm	0.225 - 0.550	250	0.7	5
Macaw	Warm	0.13 - 1.7	275	over 6.0	50
Cat	Warm	2 - 9	150	1.2	15
Human	Warm	70	72	2.9	80
African Elephant	Warm	5500	28	0.25 - 0.88	17 - 60
Blue Whale	Warm	100,000	10 - 20	0.6	80
Galapagos Tortoise	Cold	250	6	0.5	over 150
Greenland Shark	Cold	1000	5	1.0	about 400

Over a century ago, researchers first investigated the relationships between size, metabolism rate, and lifespan. They discovered that vertebrates have an average lifespan of around three-quarters of a billion heartbeats. About half a century later, they began to understand why: an animal’s heart rate is a good indicator of how quickly its cells use oxygen, and oxygen damages cells over time. In the 1950s, Denham Harman formulated the oxygen free-radical theory of aging, which remains the leading hypothesis on aging today. This theory states that cells wear out because, as they metabolize nutrients and oxygen, a small percentage of oxygen molecules become free radicals — highly reactive molecules that damage cells in their quest to obtain electrons.

Since cells constantly replace themselves, this damage may not seem significant. However, the gradual destruction of cells is crucial because there is a limit to how many times they can be replaced through mitosis. After about fifty divisions, the DNA within a cell can no longer replicate accurately, leading to programmed cell death, known as apoptosis. This limit, known as the Hayflick limit, was discovered by Dr. Leonard Hayflick in 1961.

Animals do not live forever because their cells eventually wear out to the point that they stop reproducing. In general, small warm-blooded animals have the highest metabolism and race through life, while large and/or cold-blooded animals live much longer due to their lower metabolism. While we might expect the blue whale to be the longest-living vertebrate because of its massive size, the Greenland shark holds the record, as its combination of large size and cold-blooded physiology results in an exceptionally low cellular metabolism.

Still, researchers continue to investigate why there is such a broad range in the biological clocks of different species. While some animals live only a third of a billion heartbeats, others survive for several billion. For example, a macaw is relatively small, yet it can live for fifty years because its lifetime heartbeat count exceeds six billion. The wide variation in total heartbeats per lifetime raises intriguing questions about how cell damage might be reduced to extend an organism’s lifespan. If researchers can find a way to minimize cellular damage or extend the Hayflick limit on cell divisions, it may one day be possible to significantly prolong the human lifespan.

The Theory of Evolution

The resolution of the dinosaur paradox removes a major barrier to teaching Galileo's Square-Cube Law. However, this breakthrough is just one part of a broader revolution in biology. The Thick Atmosphere Solution, which resolves the dinosaur paradox, also addresses one of the obstacles preventing wider acceptance of Darwin’s Theory of Evolution. While Darwin’s theory has received better treatment than Galileo’s Square-Cube Law, few biologists would claim to be satisfied with the public’s slow acceptance of evolution.

Scientific theories are essential because they provide the conceptual tools needed to make sense of reality. Over the years, biologists have rightly emphasized that the Theory of Evolution is a true scientific theory. However, rather than merely asserting this fact, we should focus on applying the theory as a means of solving biological problems. Recognizing evolution as a scientific theory is not the finish line — it is the starting point for deeper understanding.

One of the last major challenges in biology has been the inability of the Theory of Evolution alone to explain the form of terrestrial Mesozoic animals. Yet, by combining the Theory of Evolution with the Thick Atmosphere Solution, these mysteries are resolved. With this new understanding, we can analyze any species — past or present — and gain clearer insights into its evolutionary adaptations. Given these developments and the widespread misinformation about evolution, now is an ideal time to review the process of evolution.

Explaining the Process of Evolution

A common confusion about evolution is that both natural evolution and human creativity produce functional objects. Since people easily understand how they create new things, they may mistakenly assume evolution works the same way. However, the processes behind human-made and biological objects are fundamentally different.

For human creations, the typical process begins with recognizing a need, defining its function, and designing it before construction. Builders, inventors, and engineers are always limited by time and resources, requiring careful allocation. Scientific knowledge is often essential for innovation, or at least the ability to follow designs and trade practices.

In contrast, evolution operates without forethought, master plans, or intentional design. Nature has vast time and resources to refine species, selecting the fittest individuals each generation in a gradual approach toward an optimal form.

Darwin’s first key concept of evolution is that species produce more offspring than their environment can typically support. Survival is a struggle — not only to find food but also to avoid becoming food for somebody else. As a result, not all offspring survive to reproduce, driving natural selection.

The next point is that there are always some variations among each generation of offspring in their physical and behavioral traits. This variation is the result of a reproductive genetic process that does the equivalent of shuffling a huge deck of cards and then dealing each offspring a unique hand. Add to this an occasional mutation, and the result is that each offspring matures into an adult with traits like their parents but with subtle differences.

Because there is both variation within a species and competition as to who will survive and reproduce, there is a selective process determining which genes will be passed on to each new generation. Statistically, the genes that have the best chance of being passed forward will be from those individuals that prove themselves most capable of 1) surviving to reproductive maturity and 2) reproducing. This is what is meant by the evolutionary statement “survival of the fittest.”

Like nearly all great ideas in science, at its core, the process of evolution is just a simple idea: only survivors can reproduce and so, out of every generation, the individuals that are best fitted to their environment are the ones being selected to reproduce the next generation. Because of this selective process, over several generations, a specific group of interbreeding organisms that constitutes a species will evolve in the direction of the individuals that have the superior traits.

Yet the phrases “superior traits” or “the fittest” only have meaning in terms of how the species fits into its environmental niche. The environmental niche of a species can be viewed as both its interaction with the physical environment and its interaction with other species — the biological environment.

Examples of the physical environment could include whether a species lives in the ocean or on land. Among terrestrial species, a species may attempt to find a niche in a wide variety of habitats, such as the desert, the tropics, or near the polar regions. Each physical environment presents unique challenges that the species must meet by having a physical form well suited to that environment.

Plants, animals, and other forms of life are complicated objects constructed of various biological materials. These different biological materials have physical properties in the same way that non-living objects have physical properties. For vertebrates, bone material will have a set strength, blood will flow through arteries similar to other fluids flowing in a tube, and heat will escape through the skin based on the thermal conductivity of the skin. The physical form of life, working with its available biological materials, must be correct to survive in the physical environment.

But in addition to meeting the requirements of the physical environment the various forms of life must also interact and compete in the biological environment because rarely, if ever, is a species alone in a physical environment. Flowers will bloom so that insects will help in their reproduction, and prey will run when chased by predators because their lives depend on it. The interaction between species and the achievement of reproductive goals often creates fascinating evolutionary solutions. Successful species are a product of both their physical and biological environments.

To better understand the process of evolution let us look at the example of the cheetah and the gazelle. These animals, like the vast majority of species in the wild, are well adapted to their environment. Both are physically fit, fast runners, and properly colored in dark brown to white camouflage that matches them well to their environment. That these animals are so well adapted to their environment is no accident of nature.

When a cheetah makes a kill, statistically, it is more likely that the gazelle killed is either sick or one of the slower gazelles in its group. By eliminating the least healthy or slower gazelles from the herd, only the healthier, faster gazelles remain to reproduce and produce new offspring. Unknowingly, by killing the slower young gazelles, the cheetah is ensuring the survival of only the fastest gazelles.

This interaction between the species also ensures that only the fastest and smartest cheetahs will survive from one generation to the next: if a cheetah is not successful in making kills, it will starve. The two species are locked in a perpetual battle that ensures only the fastest, healthiest, and smartest of each species survive.

Modern Homo sapiens are one of the few exceptions to this evolutionary process. Through our development of tools and our ability to communicate successful technologies to other Homo sapiens, we have achieved vast superiority over the other species on our planet. Because of this superiority, members of our species no longer need to be the fittest in order to survive and pass on their genetic code. We, and the species that we cultivate, are exceptions to the normal competitive process of evolution.

Form Follows Function: The Unique Form of Dinosaurs

Millions of people have seen displays of dinosaur skeletons. Dinosaurs fascinate children, and as kids, we may have wondered how they could be so big or why they were shaped a certain way. Perhaps we were satisfied with the answers, or maybe not. Unfortunately, if we weren’t satisfied, there wasn’t much we could do about it.

Just as paleontologists have struggled to explain the size of dinosaurs, they have also struggled to explain their form. As scientists, it is time to take a fresh look at the form of dinosaurs by applying principles of science. When we think in terms of physics and the process of evolution, we awaken from our slumber. With eyes wide open, the form of the dinosaurs screams out across the vastness of time, 'Look at me! Can you not see what I am doing?'

Let us examine the picture of the Edmontosaurus displayed at the Denver Museum of Nature and Science. This species of dinosaur has the typical shape of a dinosaur, with a long, strong tail and stronger rear legs than forward legs.

The Purpose of a Dinosaur's Tail

The most common and practical purpose of a flexible tail is to enhance an animal’s movement through a thick fluid. Animals that exist in a thick fluid, such as fish, can effectively use their flexible tail to push against the fluid as a means of propelling themselves forward. However, this type of propulsion is not possible when the animal is surrounded by a low-density fluid. Therefore, pet dogs, humans, and other modern-day terrestrial animals that live in the present low-density atmosphere tend to have either a vestigial tail or no tail at all.

A snake is effectively one long, flexible tail used for propulsion. However, the snake does not push off the atmosphere; rather, it effectively ‘swims’ over the surface of the land. The motion that a terrestrial snake uses to travel on the ground is the same motion that aquatic snakes use to swim through water.

Birds use their tails for aerodynamic guidance while flying. However, a bird’s tail is stiff rather than flexible, and birds rely on their wings, not their tails, for forward propulsion. Today’s atmosphere is too thin for a flexible tail to be effective in providing forward propulsion.

The crocodile is one of the few species that successfully transitioned from the Mesozoic to the present environment while retaining a flexible tail. It hides beneath the water, waiting to ambush thirsty animals as they stop to drink. The speed of this large animal’s ambush demonstrates the effectiveness of a strong, flexible tail in propelling an animal through a thick fluid.

While a flexible, long, muscular tail almost always indicates that an animal propels itself through a thick fluid, a few terrestrial reptilian species still drag long tails behind them with questionable value. Instead of shrinking from lack of use, these tails serve purposes such as aiding stability, acting as a defense mechanism, or storing fat for times when food is scarce.

The typical dinosaur tail is substantially larger and more developed than the vestigial tail of present-day lizards. In addition, as shown by the representative Edmontosaurus, nearly all dinosaur tails have ribs extending from the vertebrae. Notice that the bones sloping up and down from the vertebrae of the tail are similar to the rib structure of a fish — an animal that clearly uses its tail for mobility through a thick fluid. The highly evolved, flexible tail of dinosaurs is evidence that they used their tails to propel themselves through a thick fluid.

To summarize, animals with a strong, flexible tail provide evidence that they use it for propulsion through a thick fluid, while animals with no tail, only a small vestigial tail, or a stiff tail imply that the animal lives in a thin, low-density fluid environment.

Fast Dinosaurs have Mismatched Legs

Even more powerful evidence supporting the Thick Atmosphere Solution comes from the mismatched leg arrangement of dinosaurs. This arrangement, in which the rear legs of dinosaurs are much larger than their forward legs, is present in all dinosaurs except for Brachiosaurus. While this lopsided leg arrangement makes no sense in our present environment, it does make sense if a strong horizontal force is pushing back on an object.

In man-made devices, wheels often take the place of legs in providing mobility. The similarity between a tractor’s lopsided wheel arrangement and a dinosaur’s lopsided leg arrangement is no coincidence. In both cases, this mobility arrangement results from a strong horizontal force impeding forward motion.

For the purpose of breaking up hardened ground, a strong horizontal force is needed to pull a plow through the soil. When a tractor pulls a plow, the rear hitch is in tension, meaning there is both a horizontal force pulling the plow forward and an equal but opposite force pulling backward on the tractor. This backward force on the tractor produces a torque that transfers most of the tractor’s weight to the rear wheels.

A tractor has a lopsided wheel arrangement because, when working at full capacity, nearly all of its weight is on the rear wheels. With most of the tractor’s weight concentrated on the rear wheels, they are best able to generate traction with the ground to push the tractor forward. There is no need to supply power to the forward wheels or make them very large, as the only time there is significant weight on the forward wheels is when the tractor is not pulling anything.

***

Dinosaurs had a similar lopsided leg arrangement because, when moving at their fastest, nearly all of their weight was on their rear legs. During these moments, only their rear legs were effective in digging in to push the dinosaur forward.

To understand the form of dinosaurs, we need to combine our knowledge of the forces acting on them with our understanding of the process of evolution.

It may be that the mismatched legs of dinosaurs made for awkward mobility as an herbivore spent most of its time grazing on abundant vegetation. However, this day-to-day awkwardness had little impact on its chances of survival. The life-or-death moment came when a ferocious carnivore suddenly appeared out of nowhere, sprinting toward it with bad intent.

This drama of the Mesozoic world was, in many ways, similar to the chase scenes between cheetahs and gazelles that still take place on the plains of Africa today. In both cases, the survival of predator and prey often depends on who wins the foot race, and each will use whatever means necessary to gain an advantage.

For dinosaurs, their primary means of propulsion was the combination of their rear legs and tail. Unlike most large terrestrial animals today, dinosaurs had small forward legs because, during their life-or-death race, these legs would not provide much traction and would be of little use in this critical moment.

In an atmospheric density that was about sixty to eighty percent of their own body’s density, their tails effectively swam through the dense fluid. However, while the thick fluid aided propulsion, it also hindered forward movement. This horizontal resistive force explains why their weight was concentrated on their rear legs as they ran.

The Allosaurus displayed at the Visitor Center of the Cleveland-Lloyd Dinosaur Quarry demonstrates the profile of this predator in pursuit of its prey. The long, flexible vertebrae allowed the Allosaurus a snake-like movement through the extremely thick air, while its powerful rear legs worked in tandem with the flexing motion of the tail to provide maximum forward propulsion.

Among herbivores, Edmontosaurus was one of the fastest dinosaurs. It was faster than similarly shaped armored herbivores such as Stegosaurus and Ankylosaurus. With their tough, bony plates, these armored dinosaurs could have possibly survived an initial attack from a predator, but Edmontosaurus relied entirely on the speed provided by its strong, flexible tail and powerful rear legs to outpace its predators.

Brachiosaurus was the exception to the rule, having larger forward legs than rear legs, making it one of the slowest dinosaurs. Instead of fleeing like other herbivores, it likely adopted a behavioral strategy similar to that of present-day elephants, intimidating predators with its massive size. Brachiosaurus sacrificed speed in exchange for height, allowing it to reach higher foliage. Aside from Brachiosaurus, all dinosaurs had strong rear legs and powerful tails suited for moving through the dense Mesozoic atmosphere.

Until we recognize that dinosaurs moved through a thick fluid, their typical shape makes little sense. While we sometimes encounter unusual species in the modern world with features that are difficult to explain, it is flawed, lazy thinking to assume that all dinosaurs developed their distinctive shapes for no apparent reason. Our understanding of the theory of evolution — which explains how species adapt to their environment to maximize survival — demands that we account for the unique body structure of dinosaurs.

The most likely explanation — or possibly the only plausible explanation — for the distinctive form of dinosaurs is that they lived in a fluid environment that was less dense than their bodies but still comparable in density. The much larger rear legs and strong, flexible tail represent a logical adaptation for an animal striving to move as quickly as possible through a fluid that was about two-thirds its own density. The body structure of dinosaurs provides strong evidence in support of the Thick Atmosphere Solution.

Among the herbivores the Edmontosaurus was one of the fastest dinosaurs. It was faster than the similar shaped armored herbivores such as the stegosaurs and the ankylosaurs. With their tough boney plates these armored dinosaurs could have possible survived an initial attack from a predator, but the Edmontosaurus depended completely on the speed provided by its strong flexible tail and strong rear legs to outpace its predators.

The Brachiosaurus was the exception from the rule by having its forward legs larger than their rear legs and thus it was probably one of the slowest dinosaurs. Instead of fleeing like other herbivores, it took a behavioral role like present-day elephants of intimidating predators with its size. The Brachiosaurus gave up its speed to gain the advantage of height so that it could reach the higher foliage. Except for the Brachiosaurus, all dinosaurs had strong rear legs and a powerful tail for swimming through the thick Mesozoic atmosphere.

Until we recognize that the dinosaurs are moving through a thick fluid the typical shape of dinosaurs makes no sense to us. While in our present world we sometimes find unusual species with features that are difficult to explain, it is flawed lazy thinking to believe that all of these dinosaurs developed their unique shape for no apparent reason. Our understanding of the Theory of Evolution, how species within an environment evolve so as to best enhance their survival, demands that we explain the unique shape of dinosaurs.

The most likely explanation, or possible the only plausible explanation for the unique form of the dinosaurs is that they existed in a fluid that was less than, but comparable to, their own body density. The much larger rear legs and the strong flexible tail is a logical arrangement for an animal that was attempting to move as quickly as possible through a fluid that was about two thirds the density of the animal. The form of the dinosaurs is strong evidence in support of the Thick Atmosphere Solution.