Arthropods and Their Evolution (Additionally, How They Preclude A Global Flood and Young Earth Creationism)

Arthropods are an incredibly diverse group of animals, with over one million species known on our planet. How did these organisms evolve? Why are they so prolific? And how does their existence impact a "literal reading" of Genesis? Let's dive in to the wonderfully populous world of arthropods. 

Part 1, What Makes an Arthropod?

What do we mean when we say "bug"? How about "insect"? Typically when people think of arthropods, they are thinking of what we colloquially term as insects and bugs. They think of beetles and bees, or of ants and wasps. Perhaps the odd mantis blinks into someone's mind. 

But arthropods actually encompass far more than that. 

So who is apart of the not-very-exclusive arthropod club? Well, there are quite a few, and they break down in a rather interesting way! 

Below, I will paste a slide from my old entomology professor's lecture on arthropod and panarthropod classification (credit to Ray Fisher) And then we can go through what makes each group unique from one another. 
​

Of course, each group can be further broken down (arachnids contains spiders, scorpions, mites and ticks for instance) but for our purposes this is as deep as we will go. 
So first off, what makes a Panarthropod? 
These guys possess the following: 
- alpha chitin throughout the cuticle of the animal
- Metamerism (body is organized into segments that are similar in structure) 
- Tagmosis (metamere segments are organized into functional units known as tagmata)
- Gangliated nerve cord is present
- The ends of each appendage have claws

So why are we talking about panarthropods in a post about arthropods? This is because the ancestor of all arthropods was a Panarthropod. These organisms lack intense formal classification, but we will address them shortly. ​

(pictured below, the panarthropods)

We next zoom in on the arthropods. These animals can be classified in two distinct clades: 

The cheliceratans (sea spiders, horseshoe crabs and arachnids) which are characterized by:
-chelicerae (the frontal digits we refer to as their "fangs")
-pedipalps (the "mini legs" near the chelicera)
-8-14 legs
-Only two tagmata (pro/opisthsoma)

vs

The mandibulatans (myriapodans and pancrustaceans: hexapods and "true" crustceans) which are characterized by:
-Mandibles (think the chelicerae with a movable opposing "fang")
-Two pairs of maxillae
-1-2 pairs of antennae
Since we are primarily honing in on hexapods in this post, we will add that hexapods are unique from the other mandibulatans thanks to their 3 tagmata (head, thorax, abdomen) single pair of antennae and 3 pairs of walking legs. 

Hexapods can thus be further split into the 30 orders that compose the more common animals we see today:

Part 2: Panarthropods of the Past (The Evolution of Arthropods)

Arthropod evolution is heavily shrouded in mystery, in part due to the fact that they evolved so early in history. It is universally accepted that they appear in droves in the Cambrian, but many entomologists are no proposing that their first emergence was in the Ediacaran period some 555 MYA with parvancorina and spriggina (pictured below)

Certainly though, by the Early Cambrian the first organisms that looked vaguely arthropod-like were emerging on the scene (Braun, A.; J. Chen; D. Waloszek; A. Maas (2007))

(It should be noted that pikiia is considered an early chordate while the others are considered lobopods/early arthropods)

The Cambrian's conditions influenced the enormous radiation of forms that the panarthropods would experience. Warm seas with an abundance if niches for the non-sessile animal allowed strange animals to thrive, including the five-eyed opabinia or the enormous anomalocaris (pictured below)

Arthropods dominated the seas for quite some time, and when the chordates finally began to catch up to the arthropods (now diversified from the panarthropods as known from the fossil record) it was the Late Silurian and they were beginning their march onto land. This was due in part to the presence of plants who had begun their own colonization millions of years earlier in the Ordivician. The land was a habitat free of immediate predators for the first arthropods, and the plant denizens provided shelter and sustenance. They were already prepared, you see, as these animals had exoskeletons whose chitinous composition protected from desiccation and whose jointed legs could spar against gravity. Unlike the early tetrapods, water dependence was not on the forefront. 

Chordates, slow as ever, would not catch up until the Devonian and even then they would be somewhat sluggish until the Carboniferous. This left the land to the creepy crawlers, and they began to radiate out from their most basal forms. We will be examining some of the transitional Chelicerates and Mandibulates.

Chelicerates of the Silurian were some of the first to radiate as the trigonotarbid Palaeotarbus jerami, from about 420 million years ago shows us. 

This animal looks very much like a mite or a tick, which suggests that the first chelicerates likely adapted the trademark double-tagma prior to many of the specializations spiders and scorpions possess. 

Next in the Devonian we see more chelicerates emerge. Attercopus fimbriunguis is a spider-like animal closer to our modern iteration. It had the organs necessary to produce silk, but lacked the spinnerets themselves, meaning web-building (if it occured) was likely far more clumsy. 
​

Blattodeans, the order that concerns roaches and termites, sees it's beginnings in the form of Archimylacris who, like Attercopus, is also a Devonian-dweller. It differs from modern roaches in that it's ovipositor is much larger, perhaps a holdover from earlier hexapod ancestors, and it has sticky pads on it's legs which may have allowed it to cling upside-down or walk along smooth surfaces. This is not present among modern roaches.

​​

Pollen makes it's appearance in the Triassic, although the granules are heavy and more basal in comparison, their bulky form unable to easily attach itself to insects which may assist it's pollination journey.  

It should should come as no surprise then, that once pollen takes it's more lightweight form, organisms begin to specialize in nectar collection and thus pollen dispersal. 

And it is there of course, at the emergence of the pollinators, that we should begin to find some of our lepidopterans (moths and butterflies) and hymenopterans (ants, bees, wasps).

The oldest known Lepidopteran fossil is a basal moth lived during Lower Jurassic period some 190 million years ago. It had a single pair of scaled wings with a pattern of veins similar to Caddisflies. Eolepidopterix jurassica, another Jurassic lepidopteran,  was another two-winged fossil that had setae (scales) on both of its wings. Modern lepidopterans have four wings, and setae. 

The first bee fossil is found in the upper Cretaceous, and is something of a hybrid between a "flesh-eating" wasp (a specialized form) and that of a modern bee. Boasting a mixture of predatory and pollen -collecting features, it is suggested that this animal (along with the other pollinators) was partially responsible for the angiosperm boon that took place at that time. 

Finally we meet sphecomyrma, the wasp/ant mosaic. You wouldn't think it, but these animals have quite a bit in common. Both are highly euscial and work under similar colony structures. The current entomologic hypothesis is that ants evolved from wasps, as the latter appears prior to the former in the fossil record. Another hint to this is the nature of their eusociality. Eusocial animals are sometimes called "Superorganisms" as the colony behaves somewhat like a massive organism wherein the inhabitants are merely parts of a whole. 

Euscoiality is a trait seen late in evolutionary history and primarily in hymenopterans and in some blattodeans (namely termites). This is partially known from the lack of colonies and hives in the fossil record. For us to gauge which animal, ants or wasps, is more basal Eusociality may be a good place to look. 

In the modern world, there are solitary wasps. These are wasps whose species do not form colonies and instead lay eggs and guard them after mating. There are no solitary ants. 

There are also wasps which experience tense eusociality, these are species which maintain order through infighting among the females. this eusociality can result in the death of the queen or the workers and is considered a "lower" form of eusociality. There are no ants with tense eusociality. 

Finally, there are both orderly eusocial wasps and ants. This serves to complement the fossil record's claim that ants are a derivative of a wasp-like common ancestor. 

Part 3: Arthropods vs Young Earth Creationism

So now we know all about arthropods and are acquainted with many of their transitional forms. What does all this have to do with Young Earth Creationism (YEC)?

Well, YEC tends to take what they think is a "Literal" reading of the book of Genesis and use it as history. Furthermore, many (not all) YEC's believe that the inerrant nature of the Bible means it is without any error at all, in any sense. This leads to quite drastic efforts to force the text to say things it does not, such taking the verse of Isaiah 40: 22 which says "It is He (God) that sits above the circle of the Earth" and trying to force the word circle to mean sphere, thus "fixing" the fact that the writers of the bible clearly believed in a flat Earth sitting on pillars and surrounded by the firmament. There is indeed a Hebrew word for sphere, and the author opts not to use it. YEC's thus force an Ancient Near East culture to say things no other ANE culture would have said, and propose it was God's revelation (ie, God TOLD them the Earth was round). 

Of course, there is not a single time in the bible that God relates a truth to the ancient Hebrews about the natural order of science. Those who hold a faith may propose that this means God is speaking to them on their level, choosing to meet them where they are at, and that inerrancy then is about the message.  Others take the stance that this is simply proof that the Hebrews were just another ANE culture with their own god. 

Either way, they clearly were not privy to the true science: the earth is round. 

And so, the same happens when we examine Arthropods in the Old Testament book of Genesis. Let's take a look at why a "literal" reading is problematic. 

YEC Claim 1: There was no Death before the Fall of Man in Genesis 3. (AiG)

Answers in Genesis proposes that the Bible says there was no Death at all prior to the Fall of Man. First and foremost this is not a biblically sound argument to make but let's say for arguments sake that is what the author meant.

Ken might route around plant death by insisting that they lacked the breath of god (nephesh chayyah)  that humans and other animals had, but he neglects to consider the arthopods. Won't someone please consider the arthropods! 
Mites, the smallest chelicerates, breathe. As do ants, and as do all arthropods. They take in oxygen, the breath of God so proposes Ken, and they expel CO2. 
I suppose in the Garden of Eden everyone was really quite careful where they stepped. 
And I suppose all the insectivore animals chowed down on fruits. Even this guy, the humble anteater. 

YEC Claim 2: Insects WERE or WERE NOT taken on Noah's Ark (AiG)

This article by Answers in Genesis is notably wishy-washy on whether or not arthropods (although AiG only refers to insects, so I guess all the arachnids and crustaceans are toast) made it onto the Ark built by Noah and his family. 

From a standpoint of evidence based science Noah's ark either never occurred or was perhaps a local flooding event that may have been exaggerated. But the folks at AiG take this tale as 100% history. Let's examine why a literal reading of this story is fraught with Arthropod Issues. 

Genesis 6

 "I am going to bring floodwaters on the earth to destroy all life under the heavens, every creature that has the breath of life in it. Everything on earth will perish. 18 But I will establish my covenant with you, and you will enter the ark—you and your sons and your wife and your sons’ wives with you. 19 You are to bring into the ark two of all living creatures, male and female, to keep them alive with you. 20 Two of every kind of bird, of every kind of animal and of every kind of creature that moves along the ground will come to you to be kept alive. 21 You are to take every kind of food that is to be eaten and store it away as food for you and for them.”

Genesis 7

" They rose greatly on the earth, and all the high mountains under the entire heavens were covered. 20 The waters rose and covered the mountains to a depth of more than fifteen cubits.[g][h] 21 Every living thing that moved on land perished—birds, livestock, wild animals, all the creatures that swarm over the earth, and all mankind. 22 Everything on dry land that had the breath of life in its nostrils died. 23 Every living thing on the face of the earth was wiped out; people and animals and the creatures that move along the ground and the birds were wiped from the earth. Only Noah was left, and those with him in the ark."

According to a literal reading of the second chunk here, it seems to me that a literal reading NECESSITATES bringing the arthropods on the ark as EVERY living thing outside the ark perished. So taken literally this is not an optional interpretation. 

So IF Noah took arthropods, which did he take? Even if we are using the YEC concept of "kind" ratehr than species, how would Noah have cared for the Hymenopterans, whose females require many males and whose males are haploid organisms? 

What about the Odonatans (damselflies and Dragonflies) whose lifespans are short and whose mating strategies aren't always successful? Did Noah breed them?

What about the Arachnid ticks, who require bloodmeals? Or the Parasitic wasps? 

How would he care for the nectar sipping lepidopterans? Or the mate-gobbling mantises? What of the eusocial ants who require a colony?

And who will stop the mighty termites from sinking the vessel! 

It's problematic. 

YEC Problem 3: Leviticus 11: 20-23

"All flying insects that walk on all fours are to be detestable to you. There are, however, some winged creatures that walk on all fours that you may eat: those that have jointed legs for hopping on the ground. Of these you may eat any kind of locust, katydid, cricket or grasshopper. But all other winged creatures that have four legs you are to detest."

This should be self explanitory. Arthropods have at least 6 legs.

Conclusion/TL;DR

Arthropods are numerous in species today and have dominated this planet longer than we have been around. They come in many shapes and sizes and many of their transitionals track their progression to modern forms. They also create glaring problems for a literal reading of the Bible, as well as the proposed ideal of inerrency in the form of: no mistakes, ever, period.