The World is Perfectly Suited to Human Life

There is a common Christian argument that the Earth is perfectly suited to human life and works in perfect harmony, and therefore must have been created by an intelligent deity, with humans in mind.

At first glance, this does seem like a solid argument. After all, the Earth is in the "goldilocks zone" relative to the Sun (the goldilocks zone is the range around a star at which a planet could be capable of having liquid water on its surface. Since water is essential to life as we know it, being in the goldilocks zone is kind of a big deal for humans), the angle of its tilt give us four seasons, the speed of the rotation gives us regular day and night cycles... In a very basic sense, it does seem like the world was designed with us in mind.

That said, this argument suffers from a pair of fatal flaws:

First of all, the argument begs the question. That is, it assumes in the premise that the conclusion is true. The Christian using such an argument is aiming to prove that a deity exists, and is responsible for making the universe, but bases their argument on the assumption that the current order of the universe was a targeted outcome - which is to say, that someone (presumably the deity) intended that the universe turn out this way. However, if there is no god and the universe has come about by random chance, then we must accept that the current state of affairs of the universe is no more improbable than its being any other state of affairs that we could imagine, and therefore requires no divine guidance. (See our previous post on the alleged improbability of the universe being the way that it is for more info.)

Similarly, the Earth existed well before life. Therefore it stands to reason that, as life evolved, those organisms that were capable of surviving (or even flourishing) under the already established conditions of Earth's atmosphere survived, and those that were not capable of surviving did not. If - for example - life had evolved on a planet with liquid mercury at its surface, such a species would likely define their "goldilocks" zone as any planet capable of having liquid mercury at its surface. The conclusion thus reached is that it was not the Earth that was designed for life, but life which either adapted to meet the already existing conditions of Earth, or perished, with no deity being required.



The second and equally fatal flaw is that the picture of Earth as being "perfectly suited to human life" is blatantly false to such an extent that it should become obvious to anyone who spends any amount of time reflecting on the matter. Sure it is easy to think of yourself walking through a forest on a crisp autumn day, enjoying the colors and scent of the leaves, and thinking about what a perfect planet you live on. However, such a thought has more in common with a romantic fantasy than reality. Every year tens of thousands of people die from volcanos, earthquakes, floods, fires, hurricanes, tsunami, lightning, landslides, and extremes of temperature, among other causes. There is literally no place on Earth that is perfectly suited to human life. Every speck of dust on the Earth is susceptible to natural disaster. Similarly, there have been five major extinctions throughout history, each of which has killed some 70% of all species that existed at the time, and over 98% of every known species is now extinct.

If the odds of survival for any species are terrible for a planet that is 4.6 billion years old, they must appear far worse to a "Biblical Literalist" who thinks that the Earth is only some 6,000 years old. By such a view, a full 1% of every species ever created must have gone extinct every 61 years since the dawn of time. That is literally hundreds of thousands of species that would need to go extinct over the course of just our lifetime alone, in order for the extinctions to keep pace with what the fossil record actually shows. It paints a fairly damning picture of the deity to argue that it created one planet with the intention that it should be home to all of the life that the deity would ever create, and yet he has managed to lose 98% of his entire creation over only 6,000 years! For all of his omnipotence and omniscience he has barely managed to keep life going on that one planet that he designed to house life.

Of course, it is not only those species who have perished who stand as testimony against Earth's perfect suitability for life. Those species who have managed to survive also serve as evidence of the haphazard and non-harmonious nature of life on the Earth. Consider, for example, the over 25,000 species of Ichneumonidae wasps in the world. Almost all of these over 25,000 species of wasps reproduce by stinging their prey and depositing eggs into the prey via the stinger. As the larvae hatch they eat the host from the inside out, starting with the non-vital organs, and only moving on to the vital organs and killing the host at the very end. If all life was created by your benevolent god, who looks after the tiny sparrow and cares about all of his creation, then why did he decide to have his creatures reproduce through such a barbaric and painful process? For that matter, look at humans. Most primates walk on all fours most of the time, although they can walk on two legs. Meanwhile humans have evolved to walk upright, which is why humans typically have back, knee, and foot issues as they age. This also explains why ACL tears and other such injuries are common among athletes, yet virtually unheard of in other primates. Humans - who fancy themselves made in the image of god - are physically speaking, built barely good enough to consistently walk upright.

On a larger scale, consider the Andromeda Galaxy. It is currently on a collision course with the Milky Way which will eventually wipe out all life on Earth. How intelligent was that design? Similarly, consider all of the planets in the universe (literally billions) that are not suitable for life at all. How intelligent is a deity who doesn't know what conditions would be good for life and which won't and just drops planets everywhere as a result? (Of course, the random placement of galaxies makes sense if there is no designer.) 

To be blunt, life on Earth has not flourished because of the environmental and astronomical conditions of the Earth, but has rather flourished in spite of them! The Universe was clearly not designed for human life, and the Earth itself is only barely sufficient to sustain human life. It is not that Earth was made for us, it is that we have adapted to the preexisting conditions of Earth. If an intelligent being designed all of this as a testament to his power and perfection, then his followers need to be prepared to explain why he clearly did such a haphazard and faulty job. They need to be prepared to explain why the hallmark of the universe is that everything is barely good enough to get the job done.

Of course, if one approaches the issue without a conclusion already in mind, if one approaches the evidence with an open mind and a willingness to follow where the evidence leads, the conclusion quickly becomes obvious: The universe is so haphazard because it was created by random processes, and not by the guidance of an intelligent, supreme power.