Fantasy literature often features creatures with lifespan significantly exceeding the lifespan of a human. In today’s post, I’ll look into some of the challenges it brings.

Warning: this post will be heavy on biological aspects of procreation. If you are afraid of science mingling with fiction, or uncomfortable around procreational topics, you might want to walk away.

A bit of biology and antropology…

As someone with some degree of interest in natural sciences (on casual curiosity level), I sometimes ponder potential connections between fantasy and reality – and how can elements of real biology be used as inspiration for additional depth in writing fantasy.

One of the major issues with fictional humanoid longevity is balance between lifespan, procreation rate, newborn and child mortality, and generational gap.

To keep it simple: ancient humans had much more children than present-time humans have, but they often died before reaching biological maturity and thus procreate. Lifespan was also shorter (30-40 years) but so was the generational gap: people had their first children earlier.

It’s biologically possible for a human to become a parent in their early teens and it’s likely this was common case with those early humans (and their predecessors) With the mentioned lifespan around 40 years, the generational gap would be roughly a third of the lifespan.

In present times, lifespan is can well exceed 70 years and reaching 100 years of age is no longer a rarity. Likewise, the age when a human has the first child is growing (close to 30 years in Europe). The generational gap thus stays at roughly third.

How this translates into fantasy, you might wonder?

…and bringing it to fiction

Let’s take the elves as the prime example of long-lived creature. Different authors use different lifespans for them – from just a few centuries to several thousands of years.

What would happen if an elf procreated at the usual human age (let’s say around 25 years) and not at the mentioned ‘third of lifespan’ point, with low children mortality?

The answer is simple: uncontrollable population expansion. The longer lifespan, the worse it would be. As with any overpopulation scenario, it’d eventually lead to wars caused by shortage of food and eventual collapse of the society.

On the other hand, elves in fantasy often age to adult at a similar rate to humans and their aging slows significantly after reaching that point. In other words, if an elf is biologically ready to procreate at 25 despite having a lifespan in centuries (or more), what’s to prevent them from doing so – and thus sending their race into a downward spiral to self-extermination through the abovementioned means?

I don’t know how many authors had thought about this, let alone dealt with it in depth. If you know of a book/series where that is the case, please let me know in the comments. Now, on to how I did so…

Bio-coding the rule of thirds

The two main characters in my books are father and son. Kraasian, aged roughly 2100, and Tyr’eshal, aged 19. The coming-of-age elements are not just the differences between their views on a situation but also about Tyr’eshal’s first forays into intimacy. Biologically, sexuality and procreation is tied to hormones that develop during adolescence and so, by the time one reaches biological maturity, it is biologically possible for them to copulate and produce an offspring. Thus, it’s out of question to make the elves unable to produce a child while being able to take part in sexual activities at the same time.

But, by the power of biology, maths, and statistics, I could dull the chances. A lot.

Yes, humans can produce an offspring at the beginning of puberty. It’s unlikely in the first years, though: ejaculate quality starts low by the time a male enters the early adolescence and increases over time. Hitting a female’s ‘fertile days’ in such an early age is likely harder as well. I took this biological fact and stretched it at pretty much the same ratio I used for elven longevity.

As the usual concepts is to drastically slow down the development of several biological traits in elves, I extended this to the procreational aspects: while the elves in my story have lifespan of roughly 6000-6500 years (I took a 60-year human and just added two zeros, lazy me!), I used a similar method for stretching out their fertility range.

Thus, elven males have very low sperm quality until they reach some 17th century and females have very long period… of their periods until the same age. This combination makes producing an offspring below reaching the ‘thirdth point’ around their 20th century extremely unlikely. With a bit of number fiddling, I set the end of their ‘fertility range’ close to the 30th century – again, to preserve the rule of thirdths.

Now, one might wonder why the hell did I go through all of this. Heck, I did not know for a long time. However, it eventually makes an impact: a pair of greedy nobles appears later in the story, nearing the end of the ‘fertile range’ yet having no heir as they focus more on their wealth and influence over their progeny as a way to point out their greed.

So, in conclusion, the usual age of having a child in my story, for an elf with ~6000 years lifespan, is somewhere between 1900 and 2200 years, though there are exceptions. I’ve also kept the usual amount of children at 1-3 which keeps the population stable – and prevents uncontrollable population growth.

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That’s all I’ll share today. I’ll welcome your thoughts on this topic.