Science

Why, God, did you have to make me peak at 18?

Intelligence tests show it's all downhill from here, but perhaps don't place enough merit in wisdom

As I write this, death and resurrection are occurring inside of me at a constant pace. In you, too, as you read this.

In the 1950s, it was discovered that approximately 98% of our body’s atoms die and are replaced each year. Our DNA essentially remains the same (although areas of chromosomes, such as telomeres, can erode), but most cells in the human body replace each other every 7-10 years. Cells move on at different speeds. Red blood cells are typically replaced in a span of four months, while most skin cells only last up to four weeks. Cells that line much of our GI system may only last five days, while liver tissue may last from 1.5 to 2.5 years. Bones generally don’t fully revamp for 10 years.  

But as the divine design would have it, not every cell resurrects. While the cornea can regenerate in a day, lenses stay around for a lifetime. And deep within the cerebral cortex are the neurons that help us think, remember, speak, and organize. These remain with us for life even as other more primitive neurological features regenerate on a regular basis.  

The question remains: Why, God?

A few weeks ago, I sat down with a very bright 5-year-old boy. As I went through a battery of intellectual tests, it was quickly clear that he had a mastery of language uncanny for his young age. As we moved into a visual-spatial reasoning task, he again showed an ability to solve a number of difficult problems. But when it came time to score up the subtests, I found myself surprised even though I have been giving similar tests for years. As I expected, his verbal abilities were at the 99th percentile. But what appeared to be quite an advanced performance on the visual task turned out to be nothing more than average for his age.  

As I reflected on these results and my knowledge of the lifespan development of intellectual skills, I again found myself reflecting on the question: Why, God?

Something curious emerges when we look at four primary intellectual skills all humans possess—verbal, visual-spatial, working memory, and processing speed—and how they evolve in life. Using 4 tasks from the WAIS intelligence test looking at each of these skills, we find that the average performance of an 18- to 19-year-old gradually gives way to an erosion of skills in the latter three areas (starting with processing speed in the mid-to-late 20s) although working memory decreases at a slightly slower rate. By the time an individual reaches 65-69, the average performance at 18-19 becomes the high end of average to superior performance; by 85-89, the average performance at the start of adulthood becomes superior to very superior (95th percentile and above) in all three domains.

In other words, if you could just maintain performance as you grew older like you did as an 18-year-old, you would eventually excel when compared to peers your age.

Meanwhile, though, the average performance in vocabulary abilities of an 18- to 19-year-old is actually worse than that of a 75- to 79-year-old, i.e. while all other intellectual skills are declining, verbal abilities are still improving into our 70s. In fact, by the time a person reaches 85-89 years of age, the very score that was perfectly average when adulthood began is the same score that results in a perfectly average score as 90 quickly approaches. 

Certainly experience and exposure has something to do with this phenomenon. But in the midst of everything, we must ask again: Why, God? Why is Your design this way? Are we living Your resurrection each day more than we ever know? But in living death and resurrection each hour of our day, does our word as Your Word remain ever viable and important to us and those around?  

It seems that as people age, what they offer is not measured in speed or indelible memory or feats of agility. But we do look to our elders for the proclaimed wisdom from what they have seen and come to know—created in God’s dynamic design.  

Pedro Santana

Jim Schroeder

Jim Schroeder is a married father of six children, a pediatric psychologist, and an endurance athlete.  He writes a monthly column entitled “Just Thinking” at www.stmarys.org/articles.  He is the author of “Wholiness:  The Unified Pursuit of Health, Harmony, Happiness, and Heaven”, “Into the Rising Sun”, and “Forty Days of Hopeful Prayer.”