Lesson 2 of 10
A feature that splits cleanly
Show on a big screenA backbone is the line of bones along the back. "Has a backbone?" sorts a cow and a sparrow from an earthworm. Everyone gives the same answer.
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The rule
A good feature gives a clear yes-or-no answer for everyone. A feature that is a matter of degree draws no clear line.
Scientists sort first by big, easy features, such as a backbone. Small details come later. Animals with a backbone are vertebrates. Animals without one are invertebrates.
Step 1 of 4
- Cow, sparrow and earthworm in one pile.
- Ask: does it have a backbone?
- Cow and sparrow go right. Earthworm goes left.
- Every member gave a clear answer.
What breaks a feature
"How big is it?" draws no clear line. Big compared to what? Different people draw the line in different places.
A feature that every member shares cannot split the group either. "Is it alive?" puts a cow, a sparrow and an earthworm in one group. All three answer yes.
| Feature | Cow | Sparrow | Earthworm |
|---|---|---|---|
| Has a backbone | Yes | Yes | No |
| Is it alive | Yes | Yes | Yes |
Try the lab to finish this lesson.