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This debate came up in science this past week (4th grade) in both of my classes and I just found out the teacher next door had it come up in her classes. Our science curriculum has some great trade books and hands on manipulative sets. There are sets of "Four-Limbed Animal Cards" that students observe to identify examples of variation and relatedness, then they look at a trade book and try to grow theories revolving around their comparisons. Every year, I cringe a little because the text teaches them that a limb is something that a living thing uses to help it move and/or get around. Then, they put a monkey hanging from a limb (I think a pun is intended there!) of a tree by its tail on the animal cards. And THEN, they have them view video clips of the same monkey moving from tree to tree and sometimes it would appear that it almost reaches towards new branches and grabs on with its tail. My big struggle is how I explain that the monkey isn't actually using its tail as a limb (based on the text's definition), since it is categorized as a "four-limbed animal" by the curriculum. I am curious what thoughts you all have on how best to settle the debate for this age group. Thanks!!

As a biologist, that definition does not just make me cringe...it is outright wrong. By that definition, everything that moves has limbs. Obviously not true (snakes, snails, clams, flowers- they open and close and that is movement. Locomotion is different from movement.) Please, I beg you, remove that definition and send a complaint to the publisher. This is why there are so many misconceptions. Limb isn't even a good vocab word in the first place because the definition is ambiguous and there are so many non-examples that technically fit definitions. One definition says Jointed or prehensile appendages, so the tails of old-world monkeys and opossum would count as limbs but not new-world monkeys or most animals with tails - only if they are prehensile. For fourth grade I would stick to legs and modified legs (flippers in marine mammals, wings, and arms). Tetrapod (translation: four-legged) is a better vocab word if all the animals are vertebrates.