A new study from the University of Arizona shows the primary traits that correlate with high species diversity: living on land, having a skeleton, and being a parasite.

Biologists at the University of Arizona explained in their new study why certain animal groups differ so much in their number of species, and they also drew the connection between this and the body forms of those animals as well as the way the animals survive.

For all the millennia that mankind has marveled at how unbridled Earth's diversity of animal populations is, biologists have cataloged approximately 1.5 million species, yet they have always speculated that this was the tip of the iceberg.

Every species of animal usually splits into about 30 phyla, yet those phyla drastically differ in how many species comprise them.The number of species can range anywhere from one to 1.2 million for a given phylum.Their body shapes are equally variable if not more so, taking into account varying features from eyes to skeletons (or lack thereof) to limbs, complex organs and a myriad of other things.

John Wiens and Tereza Jezkova from the University of Arizona's Department of Ecology and Evolutionary Biology put together a database focusing on 18 common traits, many of them anatomical, ecological, or reproductive.They used it as a reference to test the relationship of each trait to the number of species per phylum.

With this, they were able to publish in the academic journal, American Naturalist, their findings regarding which traits correlate to species predominance.They were able to attribute predominance to three traits in particular more than any others: having a skeleton, being a parasite and living on land.

These three traits are consistent throughout the most predominant species on the planet.These findings put much of human life into perspective, but they are based on already known species as opposed to the inclusion of species yet to be discovered, many of which may very well be in Earth's oceans.

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