Speciation: how new species arise — Biology, 14–17 years
A new species can arise when populations become separated and change until they can no longer successfully reproduce with one another.
Idea
Speciation is the formation of a new species from an existing population. Usually, a barrier first stops groups from breeding together, such as a mountain, island, or different breeding season. Over many generations, mutation, selection, drift, and new behaviours can make the groups reproductively separate.
Why it matters
Evolution does not only change traits within a species; it can also split one lineage into separate species. The problem is deciding when a visibly different population is truly separate, because appearance alone can mislead. Reproductive isolation gives a useful test: genes are no longer regularly exchanged between the groups.
Worked example
Suppose one bird population reaches two islands. On island 1, birds prefer smaller seeds and sing a short song; on island 2, larger seeds and a long song are common. After many generations, the songs and mating preferences differ so much that the birds no longer choose one another, even if brought together. Gene flow has stopped: speciation may be underway.
Common trap
A common mistake is to think that two populations become different species as soon as they look different. That feels natural because we often classify objects by appearance. But colour or body shape can change while interbreeding continues, and some very similar-looking organisms cannot produce fertile offspring together.
Outside school
Biologists use reproductive isolation when identifying and protecting species. It matters in conservation because a rare population may be a separate species, not just an unusual form of a common one. It also helps explain why island animals often have close relatives on nearby land but differ in behaviour, shape, or breeding.
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