---
title: "Speciation and the Rate of Evolution"
description: "Explain how reduced gene flow can let populations diverge and how reproductive isolation can produce new species. Compare evidence from living populations and fossils, and explain why evolutionary rat"
canonical: https://lightmysky.com/learn/science/speciation-and-the-rate-of-evolution-mt_OdcdfeRyo1
source: https://lightmysky.com/learn/science/speciation-and-the-rate-of-evolution-mt_OdcdfeRyo1.md
retrieved: 2026-09-12
---

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# Speciation and the Rate of Evolution

Explain how reduced gene flow can let populations diverge and how reproductive isolation can produce new species. Compare evidence from living populations and fossils, and explain why evolutionary rates vary.

Subject: Science · Area: Genetics & Evolution · Ages 15 to 16
Page: https://lightmysky.com/learn/science/speciation-and-the-rate-of-evolution-mt_OdcdfeRyo1

## Ready when they can

- Describes a sequence from one population to two species and names the isolating step.
- Says what evidence would show that two similar-looking populations are now separate species.
- Gives one reason why evolution can be fast in one period and slow in another.

## Lesson: When one species becomes two

For sexually reproducing organisms, a biological species groups populations that can normally interbreed and produce fertile offspring. One route to speciation starts when a barrier stops gene flow, the exchange of genes through breeding. Mutation, selection, and chance can make the populations differ. If reproductive barriers develop, the groups may become separate species.

A river or mountain can be a geographic barrier. Different mating signals or breeding seasons can be reproductive barriers, as can hybrids that cannot survive or reproduce. In living populations, breeding patterns and DNA help identify species. Two sterile individuals alone prove little. For ancient fossils, breeding cannot be tested and DNA is usually unavailable, so scientists compare anatomy and other fossil evidence.

**Example.** Imagine a river that squirrels cannot cross. Their populations diverge over generations. Different breeding seasons then prevent mating even if they meet again. Geographic separation has been followed by reproductive isolation; separation alone did not guarantee speciation.

New food sources or habitats can favour rapid adaptation and speciation, as in island finches. Stable pressures can favour similar traits for long periods. Neither islands nor continents have a fixed evolutionary speed. After mass extinctions, survivors may diversify into available ecological roles, called niches. Fossils record both gradual change and faster bursts.

**Recap.** Reduced gene flow can let populations diverge. Reproductive isolation can produce new species, but neither isolation nor time guarantees a split.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Selective Breeding and Genetic Engineering](https://lightmysky.com/learn/science/selective-breeding-and-genetic-engineering-mt_a3zTtiYrR2)
- [Grouping Species Using DNA](https://lightmysky.com/learn/science/grouping-species-using-dna-mt_fqAkSv3cUE)
- [How Natural Selection Works](https://lightmysky.com/learn/science/how-natural-selection-works-mt_FuVEZ1Ac9s)
- [Evidence for Evolution](https://lightmysky.com/learn/science/evidence-for-evolution-mt_ohUnzoI_nx)

## Opens up

- [Selection Coefficients and Predicting Allele Frequency Change](https://lightmysky.com/learn/science/selection-coefficients-and-predicting-allele-frequency-change-mt__JS2XJxOXV)
- [Taxonomy, the Three Domains and What a Species Name Encodes](https://lightmysky.com/learn/science/taxonomy-the-three-domains-and-what-a-species-name-encodes-mt_12ucjuHtHE)
- [Sampling Ecosystems with Quadrats and Transects](https://lightmysky.com/learn/science/sampling-ecosystems-with-quadrats-and-transects-mt_jI8rAOYdmb)