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 honey bee: In 1758 Linnaeus named the honey bee Apis mellifera. He placed it with other bees because of the body features they share, such as a hairy body and two pairs of wings.
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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: the mallard: A male mallard has a green head; the female is brown all over. By looks alone they could be sorted into two species, but they are one.
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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 museum holds hundreds of pressed leaves, which an early botanist sorted into groups by their shape and edges.
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.