Lucky you, sailing for 10 days with 3,000 people aboard a luxury cruise ship from California nonstop to Japan. You’re swimming in the heated pool, relaxing in the sauna, sipping iced tea, always knowing there’s an ample supply of clean, healthy water. That abundant fresh water for everyone aboard starts as salty sea water full of unpleasant chunks and chemicals. The ship’s desalinization system filters and boils the water, collecting the steam that condenses into pure distilled water. Your ship also treats that water with chlorine to kill any possible germs. Like most others, your ship carries about 500,000 gallons of fresh water. Cool.

Before you board the vessel, however, you might wonder if you can trust the ship’s ability to provide clean fresh water. You could ask: (1) How reliable is the freshwater system? (2) If that system breaks down, how quickly could the crew restore it to service?

How likely to fail and how quick to fix?

To figure out the reliability of the system, you need to know the average time between failures for every necessary integrated component: the intake pumps, the boiling system, the condensing system, the purification system, and all the interconnecting pipes. Within each component are subsystems, each with parts that must be more reliable than the system as a whole. To be reliable, parts must be selected and engineered for fit, function, and durability.

Still, if one of the necessary component systems fails while the ship is cruising the sea, your second question arises: How fast can the problem be repaired? Here’s where maintainability comes in. What is the average time to complete a critical repair to the water system? The challenges are many. Are spare parts readily available? If not aboard the ship, how soon can they be obtained? Does the crew know how to make the repair, or must a specialist be brought in? What else can cause delays or go wrong during the responses to failure?

For systems comprised of subsystems, it is not enough to engineer a merely working version of every element. Engineering each element, from entire subsystem to component, must consider both reliability and maintainability.  Every part of a system must work for more than enough time to fulfill the mission, and if anything breaks down, it must be fixable before the mission fails.

The human body must be reliable and maintainable, too

If the cruise ship’s fresh water supply system seemed crucial and complex, the human body raises that a million times over. Your Designed Body (2023) (“YDB”), by Steve Laufmann (engineer) and Howard Glicksman (physician), explains how the human body is a system of subsystems, the smallest discrete unit being the cell. Every one of about 30 trillion cells must have working solutions to a complicated set of problems: containment, gates, controls, framing, transport, energy, information, and reproduction. To support every cell there must be a set of working subsystems: respiratory, gastrointestinal, renal/urinary, cardiovascular, skin, skeletal, motor, nervous, immune/lymphatic, and endocrine.

Every subsystem must be engineered to include:

Specialization – The right parts performing the right functions, made with the right materials, all fine-tuned to precise tolerances, and effectively interfacing with the other parts.

Organization – All parts in their right places, arranged and interconnected to enable the function of the integrated whole.

Integration – All parts must be precisely built and interface so they all work together. Subsystems may require structural support, alignment, shock absorption, gating, and transport systems, electrical signaling, chemical signaling, exchange of complex information, and integrated logic.

Coordination – All parts must coordinate to carry out their functions at the right time, which usually requires control systems, sensing, communications, and feedback loops.

Just looking at the many categories of interlocking challenges leads to realizing the human body must have been engineered. Undirected forces banging into inert matter can’t do the job of making the working body. As the authors of YDB summed up:

As all working engineers know, it’s hard to build a coherent interdependent system that actually functions. Designing, building, and fine tuning such a system takes a combination of creative problem-solving and plain old hard work. For such a system to work, many parts need to come together at the same time. These parts must be specialized, organized to fit and work together, and the whole must be operated in strictly orchestrated processes. There’s a reason companies employ thousands of engineers to make complicated products like Atlas 5 rockets or iPhones.

Oh, shoot, yeah … those pesky details

Nicely written for the lay person, YDB shows what it takes to engineer a human body. Getting it down plausibly on paper, or working in the design lab, is one thing. Getting it to work for an extended time in the real world requires more: choosing materials, connectors, and operational functions so that every subsystem in the body is both reliable and maintainable.

Another book, The Miracle of the Cell (2020), by biochemist and physician Michael Denton, identifies the highly specific materials necessary to build a cell. When choosing those materials and fashioning them into parts and subsystems, the engineer must always be thinking: How long will this item work before it degrades or fails? How will the system repair itself, and will it do it fast enough and well enough to survive?

Fortunately, the human body, from cells to subsystems, already has threat- and failure-detection systems along with defense and repair mechanisms. Also fortunately, these mechanisms usually work speedily enough to keep us alive and thriving most of the time.

Dr. Geoffrey Simmons, author of What Darwin Didn’t Know (Harvest Publishers 2004), has identified these criteria to find intelligent design: purpose, plan, engineering, and foresight. All four criteria underlie building a human body that’s both reliable and maintainable. Undirected forces acting on chemicals — the materialist view of life’s origins and existence — cannot begin to do that engineering job.