Saturday, October 25, 2014

Classification of Living Things

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Classification of Living Things
Classification of living things is called "Taxonomy." This is when scientists put organisms into groups when they have things in common. The first groups they use are the Kingdoms. There are five kingdoms:
  • Animal Kingdom
  • Plant Kingdom
  • Fungi Kingdom
  • Protist Kingdom
  • Moneran Kingdom
Each Kingdom is then split into smaller groups, called Phyla. Each Phylum is split into smaller groups called Classes, each Class is split into Orders, each Order is split into Families, each Family is split into Genera, and each Genus is split into Species. A Species is a single organism, not a group. Some examples of species would be Southern Leopard Frog, Honey Mushroom, or White Oak. All seven types of groups go in order from largest to smallest, like this:
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
As each group is split into smaller groups, the organisms are more and more alike. For instance, a White-tailed Deer, an Eastern Gray Squirrel, and an Eastern Chipmunk are all in the Mammal Class together. This is because they have more in common with each other than with other animals, such as turtles, birds, or insects. However, it is easy to notice that there are some big differences between a deer and squirrels and chipmunks. The White-tailed Deer is in the Aritiodactyla Order (Even-toed Hoofed Mammals), while squirrels and chipmunks are both in the Rodentia Order (Rodents).

In fact, squirrels and chipmunks have so much in common, they are also in the same Family, the Sciuridae Family. However, even though squirrels and chipmunks are very much alike, they still have differences. The Eastern Gray Squirrel is in the Sciurus Genus, while the Eastern Chipmunk is in the Tamias Genus.

Did you notice that these groups have funny names? Scientists from around the world agreed to use the ancient language of Latin to give organisms, and their groups, names. Sometimes a group will have a "Common Name" and a fancy, scientific Latin name. For example, there is a Family of frogs called "Ranidae" (Scientific Latin name). This Family's common English name is "True Frogs." Sometimes this gets confusing.

Every Species gets a fancy scientific Latin name. A Bullfrog is also known as "Rana catesbeiana." A White-tailed Deer is known as "Odocoileus virginianus." A Monarch butterfly is known as "Danaus plexipus."

One thing that makes it easier to understand all these names is to know that a Species always has a first and a last name; and that the first name is also the name of the Genus group that Species is in. So the Monarch butterfly is known as Danaus plexipus and it is in the Danaus genus. Notice that the first name of a Species is always capitalized, while the second name is not.

Here is the classification of a Bullfrog, so you can see all the groups it is in:
Bullfrog (Rana catesbeiana)
  • Kingdom: Animal
  • Phylum: Chordate
  • Class: Amphibians
  • Order: Salientia
  • Family: Ranidae
  • Genus: Rana
  • Species: Rana catesbeiana (Bullfrog)

Linnaean system of classification used in the biological sciences to describe and categorize all living things. The focus is on finding out how humans fit within this system. In addition, you will discover part of the great diversity of life forms and come to understand why some animals are considered to be close to us in their evolutionary history.

How many species are there?
This is not an easy question to answer. About 1.8 million have been given scientific names.  Thousands more are added to the list every year. Over the last half century, scientific estimates of the total number of living species have ranged from 3 to 100 million. The most recent methodical survey indicates that it is likely to be close to 9 million, with 6.5 million of them living on the land and 2.2 million in the oceans. Tropical forests and deep ocean areas very likely hold the highest number of still unknown species. However, we may never know how many there are because it is probable that most will become extinct before being discovered and described. The tremendous diversity in life today is not new to our planet. The noted paleontologist Stephen Jay Gould estimated that 99% of all plant and animal species that have existed have already become extinct with most leaving no fossils. It is also humbling to realize that humans and other large animals are freakishly rare life forms, given that 99% of all known animal species are smaller than bumblebees.

Why should we be interested in
learning about the diversity of life?
In order to fully understand our own biological evolution, we need to be aware that humans are animals and that we have close relatives in the animal kingdom. Grasping the comparative evolutionary distances between different species is important to this understanding. In addition, it is interesting to learn about other kinds of creatures.

When did scientists begin classifying living things?
Before the advent of modern, genetically based evolutionary studies, European and American biology consisted primarily of taxonomy, or classification of organisms into different categories based on their physical characteristics and presumed natural relationship. The leading naturalists of the 18th and 19th centuries spent their lives identifying and naming newly discovered plants and animals. However, few of them asked what accounted for the patterns of similarities and differences between the organisms. This basically non-speculative approach is not surprising since most naturalists two centuries ago held the view that plants and animals (including humans) had been created in their present form and that they have remained unchanged. As a result, it made no sense to ask how organisms have evolved through time. Similarly, it was inconceivable that two animals or plants may have had a common ancestor or that extinct species may have been ancestors of modern ones.

One of the most important 18th century naturalists was a Swedish botanist and medical doctor named Karl von Linné. He wrote 180 books mainly describing plant species in extreme detail.  Since his published writings were mostly in Latin, he is known to the scientific world today as Carolus Linnaeus, which is the Latinized form he chose for his name.

In 1735, Linnaeus published an influential book entitled Systema Naturae in which he outlined his scheme for classifying all known and yet to be discovered organisms according to the greater or lesser extent of their similarities. This Linnaean system of classification was widely accepted by the early 19th century and is still the basic framework for all taxonomy in the biological sciences today.

The Linnaean system uses two Latin name categories, genus and species , to designate each type of organism. A genus is a higher level category that includes one or more species under it.  Such a dual level designation is referred to as a binomial nomenclature or binomen (literally "two names" in Latin). For example, Linnaeus described modern humans in his system with the binomen Homo sapiens , or "man who is wise". Homo is our genus and sapiens is our species.

Linnaeus also created higher, more inclusive classification categories. For instance, he placed all monkeys and apes along with humans into the order Primates. His use of the word Primates (from the Latin primus meaning "first") reflects the human centered worldview of Western science during the 18th century. It implied that humans were "created" first. However, it also indicated that people are animals.

While the form of the Linnaean classification system remains substantially the same, the reasoning behind it has undergone considerable change. For Linnaeus and his contemporaries, taxonomy served to rationally demonstrate the unchanging order inherent in Biblical creation and was an end in itself. From this perspective, spending a life dedicated to precisely describing and naming organisms was a religious act because it was revealing the great complexity of life created by God.

This static view of nature was overturned in science by the middle of the 19th century by a small number of radical naturalists, most notably Charles Darwin. He provided conclusive evidence that evolution of life forms has occurred. In addition, he proposed natural selection as the mechanism responsible for these changes.

Late in his life, Linnaeus also began to have some doubts about species being unchanging.  Crossbreeding resulting in new varieties of plants suggested to him that life forms could change somewhat. However, he stopped short of accepting the evolution of one species into another.

Why do we classify living things today?
Since Darwin's time, biological classification has come to be understood as reflecting evolutionary distances and relationships between organisms. The creatures of our time have had common ancestors in the past. In a very real sense, they are members of the same family tree.

The great diversity of life is largely a result of branching evolution or adaptive radiation. This is the diversification of a species into different lines as they adapt to new ecological niches and ultimately evolve into distinct species. Natural selection is the principal mechanism driving adaptive radiation.

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