Animals all begin life similarly. A small swimming sperm fertilizes a larger egg. The fertilized egg repeatedly divides to form, in the initial stage of embryo development, a hollow sphere of cells - the animal blastula. This blastula is the defining trait of animal-hood. All animals begin as a sphere of cells. That includes all insects, all worms, all jellyfish, all birds, all lobsters, all sea urchins, all bats, all rock musicians, and on and on.
What are animals, anyway? In biology, animals share the following:
• Animals are multi-cellular (eucaryote cells), unlike bacteria (procaryotes), but like plants.
• They feed on others (heterotrophs), unlike plants, which feed themselves (autotrophs)
• In at least one life stage, animals can move spontaneously and show rapid muscular response to stimulation, unlike plants, which can move, but can't decide to move, and can't move rapidly.
This word “animal” can be confusing. There is a thinking problem called “nothing but…”
When a person says, “Human beings are animals,” people with the “nothing but” thinking problem hear “Human beings are nothing but animals.” This was not said.
People's concern, of course, is about the spirit or the soul. Saying we are animals is a description of our bodies, and says nothing about our intangible parts.
The ironic part of this confusion is this: our word “animal” derives from the Latin word “anima,” which in Latin means “soul.”
Sometimes, when people say “animal,” they mean just mammals,
which are only one kind of animal, our kind, of course, the kind that feed their babies milk.
You know a lot about animals already, of course. We all know animal stories, many of us are lucky enough to have pets. We like stuffed animals; many adults still have one from childhood.
Animals have existed for a very long time, 
first in the ocean (marine animals), eventually on land (terrestrial animals).
Size: Many animals, most roundworms and all rotifers, for example, are microscopic is size. Most life on Earth is microscopic. See Bacteria, Protists. We humans tend to be aware only of the macrolife around us, big organisms, from ants to elephants.
Animal life takes an astounding variety of shapes. Each form has its beauties. We are all members of one community. For all our wonder-filled diversity, we share a common ancestry. Over time, we share the very atoms of our flesh. In diversity there is strength and flexibility.
Our Amazing Diversity of Form and Beauty |
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sea otter |
green heron |
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polyp medusa stage |
basket star skeleton |
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deep ocean fangfish |
lubber grasshopper |
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a salp |
great egret |
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jellyfish |
beetle |
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sea snail |
American toad |
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coral polyps feeding |
scorpion |
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red squirrel |
great gray owl |
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Copyright © Morning Earth 2005
