Part 1      Animals are 100% committed to multi-cellular living so learn to love it

Remember the kingdom of the protoctists? As you know, life can be so very different. All those unicells experimenting with many lifestyles.  A number of them also make use of something quite powerful. They make more of themselves when they coordinate as a group of unicells. That group work is now a trait that characterizes the animal kingdom: being multi-cellular.

Each and every animal is a community of many eukaryote cells . (here is link to a review diagram of an eukaryote cell) Their growth is coordinated over a lifetime. The cells are often grouped together as organs, each with their own patterns of development and activities.

All of this is in synchrony with the life and death of the animal itself. This unspoken and unshakable commitment by every cell in each animal is to be a member of the whole organism, doing whatever is required.  It's a powerful way to live.

Starting from a single egg

Every animal begins life as a fertilized egg, known as a zygote, which rapidly divides into a coalition of cells shaped as a hollow ball. This ball is known as the blastula. It is unique to the animal kingdom. The cells continue to multiply. They move around the sphere and begin to differ from each other. They specialize in ways which lead to more cells which also differ in still more ways. (See the colour diagram about this cascade effect.)

This growth commits some cells to become one type while others become something else. All the cells constantly communicate with each other. They pass molecules through the pores in their membranes, as do living beings from the bacteria and protoctist kingdoms. They also send messages using electrical impulses.

Although the cells of one body all have the same DNA, each cell only uses certain parts of that DNA. They are only creating and using the molecules as suit their role in the entire body. Each cell’s individual life cycle is timed, with its death and replacement within the organs cycling right up to the final death of the animal as a whole.

That process from fertilization through development is both inherited and changeable. There are fixed steps and set patterns but every action and pathway is influenced in real time by the unique conditions of every present moment. You can see how the fixed and the variable interact across space and time by looking at the differences in animals around you.

Having a backbone is optional

You, as an animal with a skeleton and a backbone, are likely to first think of other animals like yourself, who also have bones and a spine. As vertebrates, you all have limbs and a trunk, a head with a mouth, a rear end with an anus. A tail is optional. You have a front, a ventral side, your soft spot. You also have a back, a dorsal side, with that stiff backbone housing the spinal cord inside. You can see these similarities and variations as you look at the development of every vertebrate animal.

But of some forty phyla, (that’s one level below that of kingdom), you and these other vertebrates are only one. Thirty nine others, all without backbones, make up the majority of animals on the earth. (Have a quick look at all them by scrolling through all these animal phyla).

It is a habit to think more highly of vertebrates, but that’s all it is. The old idea that all of the living beings on earth could be lined up from grand to lowly is long gone. (Here's more about our relatives, which include certain worms and seastars.)

What makes an animal

Without sharing the same multi-cellular body plan, all animals are still recognizable because of five basic traits.  They all develop from zygotes, which become blastula and then embryos. All their bodies depend on using oxygen. They have different senses to assess their environments. They nourish themselves by eating other living beings. At some stage in their lives, they are mobile, roaming the world.

The other very popular animal body plan is that of the invertebrate, the animals without backbones. The variety of forms that are possible when you give up a backbone is enormous. Some of the more familiar plans are those used by many worms, snails, jellyfish, spiders and insects.

Long before robots, there were arthropods

Insects are part of a larger group officially known as arthropods (having “jointed legs”). Instead of bones inside their bodies, they have hard external shells. Attached to the main body are different sets of limbs, all held together as jointed segments. These animals are as wildly different as beetles and shrimps. The shrimps themselves are related to lobsters, crayfish and crabs.

If you take a close look at crabs, you see they are very much shrimps with altered “tails”. What are called their “tails” are actually their abdomens. In crabs, these are not very fleshy and are tucked up underneath, against the main part of their bodies.

As you already know, crabs begin life as zygotes. But you may be surprised that unlike the direct development that vertebrates follow, crabs take an indirect pathway. So do many other invertebrates.

Crabs take three different shapes at three different stages in their development.

The three stages are swimming stages that make them part of a mobile marine life, quite separate from the homes and food sources of the adult crabs. They join communities of plankton as suit their particular size class. In this way, they are influenced by different factors than those affecting their parents.

Finally, when crab larvae become adults, they grow larger but stay in the same form, molting their hard shell regularly. Often, from one molt to the next, they are able to regrow a lost limb.

This indirect development is a great advantage. The juveniles of a species can grow away from the adults. They can make the best of new food, travel and eventually new home places and sex partners. These can also work against them, as changed circumstances at any stage can doom an entire generation. (Take a look at this in-depth PDF Life cycle of the Australian mud crab.)

Unity in diversity

All these bewildering life cycles and body plans can distract you from the unity in the animal kingdom. You can glimpse not only this but also something about evolution itself by going back to the blastula and its growth. Remember how the cells would commit to one form rather than another?

The commitment happens as genes turn on and off. This sends waves of messenger molecules flowing through the entire collection of cells. The messengers direct the actual development of each cell. A major coordinator sending these messages is a special set of genes known as Hox (slang for homeotic).

Somehow, the Hox genes set off a timed cascade of reactions which commit cells to becoming parts such as eyes, antennae, limbs and tails. The Hox genes appear in many animals as repeated genes organized in clusters of various sizes. These clusters activate development sequences unique to each species. (Here is more about how Hox genes work)

More and more evidence shows that these unique sequences spell out the variations in body plans. Acting together with cues from the environment, the sequence influences the cells from one species to make one type of a body rather than another.

As a specific example, remember all the variously shaped jointed legs of shrimps and crabs? They appear in pairs along the length of the different bodies according to the development tune orchestrated by their Hox genes.

Commitment leads on to consciousness

These Hox genes, influenced in ways still unclear, set off large effects. They have been the sheet music for animal development since the Cambrian time, 540 million years ago and may well have evolved before then.

Somewhere, back in our earth’s history, some cells, with certain DNA, in a favourable situation, made commitments to group living. This multi-cellular experience managed to continue from one generation to the next. The process caught on and the kingdom of animals branched out in many directions.

The animal kingdom has many intimate links with the other unicells. They have many types of bacteria, protoctists and fungi living in and on themselves. But, by becoming multi-cellular, the animals experience life on earth in a way that is much more complex.

In the animal blend of earthly materials and activities, there emerges a certain wealth of consciousness. That awareness varies from species to species but key elements are there throughout all of the multi-cellular animal experience. We are not sure how to adequately describe it in different animals. We try and extrapolate from what we do know and imagine what consciousness may be in other kingdoms.

But that awareness is an enormous treasure which is still developing. There seem to be many shortcomings, especially with human consciousness. But for all our dilemmas as a species, we are an integral part of that evolution. Who can predict what shapes consciousness on earth will continue to take?

It’s worth repeating:

Animals are 100% committed to multi-cellular living so learn to love it

We look forward to your comments! Please tell us

What do YOU think? How could nature "need" the awareness or consciousness of animals including humans?

If you want to READ MORE by Mary Gardner about animals and related topics there are over 30 such stories in the three eBooks. Some of the titles are listed below.

From eBook 1 Bats, Pollinators, Maggots, Four Beetles

From eBook 2 Pythons, Jellyfish, Sand bubbler Crabs

From eBook 3 Bee eaters, Purple Swamp Hens, Marine Tube Worms

If you want to READ MORE online about animals, try the selected links at cool links and blogs on this website