Shared traits at Higher Level: The same statement as SL. HL builds on it with the problems of the biological species concept and with clades, so keep the two concepts apart: looks for Linnaeus, breeding for the biological concept.
Practise this as you read
- Outline Linnaeus's morphological concept of a species.
- State why looks alone can mislead.
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The big idea: A species is a group of organisms that share traits. Linnaeus decided species by the traits he could see.
The points to remember
- Carl Linnaeus (1707-1778) was a Swedish biologist who named thousands of species.
- He put organisms that share visible traits into one species.
- Visible traits are the organism's morphology.
- So this is called the morphological species concept: the original way of defining a species.
- Members still vary a little; they are grouped by what they share.
Remember it as: Looks alike? Same species, said Linnaeus.
Real example: the lion: In 1758 Linnaeus named the lion Felis leo. He placed it with the other cats because of the body features they share, such as their teeth, claws and body shape.
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The big idea: Looks can mislead: one species can look like two, and two species can look like one.
The points to remember
- Males and females of one species can look very different.
- Young and adults can look nothing alike: a caterpillar and a butterfly.
- Look-alike species can share almost every visible trait.
- So biologists later added a test of breeding: the biological species concept.
One species, looks different
- Male and female mallards
- A caterpillar and its butterfly
- Forms of one ladybird
Two species, look alike
- Chiffchaff and willow warbler
- Some sibling beetles
- Told apart by song or breeding
Real example: two warblers: The chiffchaff and the willow warbler look almost the same, yet they are two species. In the 1700s, Gilbert White told them apart by their different songs.
How it is tested: Paper 1B can set a short Outline [1] inside a data question: say what Linnaeus based a species on.
IB-style questionOutline[1 mark]
A collector sorted pinned beetles in a museum drawer into groups by their body shape, size and spot pattern.
Outline Linnaeus's morphological concept of a species. [1]
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Not the breeding test: Interbreeding and fertile offspring is the biological species concept. Linnaeus's concept is about looks only.