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Natural Science - Year I

Unit 12: Biological Classification and Invertebrates

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History Weblecture for Unit 12

This Unit's Homework Page History Lecture Science Lecture Lab Parents' Notes

History Lecture for Unit 12:
Biological Observation and Invertebrate Classification

For Class

Scientific Methods

Last week we concentrated on the general problems of classification, and Aristotle's position as one of the first recorded scientists to try to classify organisms. This week we look briefly at Aristotle's overall scheme, and then at a sample of his observations. Most of our effort, however, will be spent on the modern classification of invertebrates.

Classification of Animals

Aristotle proposed a "ladder of nature", which organized matter from simplest to most complex forms. His ladder included all matter, both non-living (the basic elements) and living organisms.

Reptiles and Fish
Octopuses and Squids
Jointed Shell Fish
Jelly Fish and Sponges
Higher Plants
Lower Plants
Inanimate Matter: Earth, Fire, Water, Air

Our modern schema includes microscopic organisms Aristotle couldn't see, and many plants and animals that he could not observe in Mediterranean Greece. But two concepts are at the basis of both Aristotle's scheme and the modern one:

Observing Crustaceans

Aristotle based his classifications on the close observation of over 500 species of animals. His work in marine biology is still considered among the best and most reliable set of observations available for species of the Aegean.

Read an example of Aristotle's observation and description of the Crustaceans and Cephalopods from On the Parts of Animals, Book IV Part 5 (you'll need to click on book IV then scroll down to part 5).

  • What details does Aristotle include about the structure of urchins?
  • What details does he include about their behavior?

Study/Discussion Questions:

Further Study/On Your Own