# Bigger creatures live longer, travel farther for a reason

##### August 24, 2012

(Phys.org)—A biological mystery about the longer lifespans of bigger creatures may be explained by the application of a physical law called the Constructal Law.

What this law proposes is that anything that flows—a river, or highway network—will evolve toward the same basic configuration out of a need to be more efficient. And, as it turns out, that same basic law applies to all bodies in motion, be they animals or tanker trucks, says Adrian Bejan, the J.A. Jones Professor of mechanical engineering at Duke and father of the Constructal Law.

In his latest theory paper, appearing Aug. 24 in the journal Nature Scientific Reports, Bejan argues that there is a universal tendency for larger things, animate and inanimate, to live longer and to travel further.

He starts his argument with an examination of the well-known observation in biology that larger animals tend to live longer. Bejan wanted to see if this general rule might apply to inanimate systems as well and proceeded to mathematically analyze the relationship in rivers, jets of air and vehicles.

He found, as a general rule, that bigger rivers are older and that larger jets of air, such as atmospheric , last longer. By his calculations, larger vehicles should also last longer, but hard evidence of that is lacking, he says, and there are outliers of course, like Subaru Justys with 300,000 miles.

By being larger and lasting longer, all of these systems also travel farther, he says.

If you look at a moving vehicle or animal simply as a mass in motion, that is, something flowing, "the spreading of the mass of vehicles and animals is completely analogous to the flow of water in ," Bejan says. "It is the same design."

Interestingly, if the and lifespan of known species of animals are plotted on a curve, it falls on a slope of about ¼. And then, following a different line of inquiry, if you plot the frequency of breathing to body size, that is a slope of -1/4.

When combined, these two insights about animal body size work out to a constant for the number of breaths per lifetime, Bejan says. This gives most creatures about the same number of breaths in their lifetime, but the larger, slower-breathing animals use their breaths up over a longer span of time. "So bigger means a longer ," he said. "I was looking at this enigma about body size and longevity from a point of view that hadn't occurred to biologists," Bejan said.

The Constructal Law governs how big an engine a truck needs and how big a heart a whale needs. "There's no difference between a vehicle and an animal," Bejan said. "Being larger means two things, not one: you live longer and you travel farther."

There are, of course, notable exceptions to the rule: The 4-ounce Arctic Tern travels more than 44,000 miles a year.

"The size-effect on travel and life time is the same for the animate and the inanimate," Bejan argues. "Everything that moves enjoys the same design."

Explore further: New Thermodynamic Theory Will Help Engineers 'Go With the Flow'

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##### gwrede
2 / 5 (1) Aug 24, 2012
This scientist has found a couple of cases of a much bigger rule.

That rule simply states that subjective time depends on size.

Compare a 10-foot dinghy and an aircraft carrier. The dinghy completes an entire trip out fishing and back in the time it takes the aircraft carrier to turn around. Compare a car to an ant. In the time it takes to accelerate the car to highway speed, the ant went out to hunt and came back with prey.

But if you "speed up" or "slow down" your film, they suddenly start behaving alike. If you've seen the Scale of the Universe then you should consider that time is consipicuosly relevant there, too. Every "scale" of the picture has its own time scale.

At our scale birds flap wings, but for every flap, millions of molecules bend and hit each other continuously, and for each hit, electrons in an atom go "millions" of times around their nucleus. And to the outer direction, think planets and galaxies.
##### spaceagesoup
1 / 5 (1) Aug 25, 2012
"Subjective" time depends on size? Subjective anything would depend on the other thing you're using it to compare. Isn't this really just saying that when something is subjective, it's subjective... ? And what about density/energy?

And if you compare how long the ant takes to move the same radial distance the carrier moves, to your original analogy then you get an inverse subjective relationship! Amazing! Not sure if this is of any more use. What about a neutron stars rotational motion compared a planetesimal of the same size? Or would you think this constructal rule would still hold by virtue of relativistic effects?

Maybe we can try seeing how long the aircraft carrier takes to hunt and come back with dinner!
##### Mike_Massen
1 / 5 (1) Aug 25, 2012
All warm blooded animals seem to get the same number of heart beats per lifetime on average...
##### gwrede
1 / 5 (1) Aug 25, 2012
From "a galaxy's point of view", the lifetime of a star may be fleeting, but inhabitants on a planet round the star experience the star as "ancient and for ever". It's all about size. (And yes, we have outliers here, too.) I used the word "subjective" for a lack of a more precise term, since I don't remember seeing an exact formula for it.

There is, however, a place where recognition of this "law" would give unprecedented yield to all involved: business law legislation. Today, law makers don't really recognize that bigger companies move slower, need more lead time to implement changes, and can survive longer slumps than small companies.

I may not be explaining it here too well, but the concept itself is right.
##### spaceagesoup
1 / 5 (1) Aug 26, 2012
So what about the situation i put forward? I don't think the same rule would hold, nor does it in many other specific human activities, and whilst it might show some correlations in some circumstances, this isn't some broad-sweeping revolution in scientific thought.
##### ValeriaT
1 / 5 (1) Aug 26, 2012
All warm blooded animals seem to get the same number of heart beats per lifetime on average...
Being "big guy" is advantageous from many reasons. At the moment, when the weather is changing periodically, the larger animal can travel for water/rain sources longer path, so there's a positive synergy. If you buy the family pack of goods at the grocery, you will get a bulk discount. From the same reason the rich people are doing their business in cheaper way, because "money are doing money". You're paying with slower evolutionary cycle for it: when the conditions are changing fast and irregularly, being poor and small becomes an advantage instead.
##### ValeriaT
1 / 5 (1) Aug 26, 2012
BTW In my theory the species of insect are most numerous at Earth, because the life at the distance scale of CMBR radiation brings the highest complexity in the Universe: it balances the worlds of relativity and quantum mechanics. The size of human neurons and distance, at which their spikes travel correspond this dimensional scale too. We can observe this sorting inside the purely mechanical systems too: for example the size of ice particles inside of Saturn rings is the consequence of natural selection too: many repetitive collisions and fragmentation of ice particles are balanced with their gradual gravitational coalesce. It's the result of balance between fragmentation of matter with CMBR noise (which works as a shaker) and shielding of CMBR noise (which works as a glue). This balance may apply the more, the more the massive objects can persist at the single place at the Universe and the more they remain separated from another irregular influences.