How do mutations contribute to the process of speciation?

Mutations provide the raw genetic variation; in isolated populations, different mutations will occur and be selected for, gradually making the two groups genetically incompatible.

What role does time play in the formation of a new species?

Speciation typically requires many generations for enough genetic and behavioral differences to accumulate so that interbreeding is no longer possible.

Why do different environments lead to speciation in isolated populations?

Different environments have different selection pressures, causing natural selection to favor different advantageous alleles in each population, leading to genetic divergence.

What is the primary difference between a population and a species?

A population is a group of individuals of the same species living in a specific area, while a species is the broader group of all organisms capable of interbreeding to produce fertile offspring.

How does geographic isolation differ from reproductive isolation?

Geographic isolation is a physical separation (like a mountain) that prevents mating, whereas reproductive isolation is the biological inability to produce fertile offspring even if the groups meet.

What is the difference between Darwin's and Wallace's contributions to speciation?

While both developed the theory of natural selection, Wallace is specifically noted for his pioneering work on how geographic isolation and warning coloration lead to the formation of new species.

Why is it incorrect to say that a new species forms because an organism 'needs' to adapt?

Evolution is not goal-oriented; new species form because random mutations that happen to be advantageous in a specific environment are naturally selected and passed on over time.

What is a common mistake when defining a species based only on physical appearance?

Appearance can be deceiving; some different species look nearly identical (sibling species), while members of the same species can look very different (like different dog breeds) but still interbreed.

What is the 'fertile offspring' requirement, and why is it often forgotten?

It is the rule that for two organisms to be the same species, their children must also be able to reproduce. Students often forget this and only focus on the ability to mate initially.

Speciation is the evolutionary process by which populations evolve to become distinct species that can no longer interbreed to produce fertile offspring.

Speciation | AQA GCSE Biology

Inheritance, Variation & Evolution

Speciation

Summary

Speciation is the evolutionary process by which biological populations evolve to become distinct species. It occurs when populations of the same species become reproductively isolated, leading to genetic divergence through natural selection until they can no longer interbreed to produce fertile offspring.

1. Definition & Core Concepts

Speciation is defined as the formation of one or more new species from an existing species over a long period of evolutionary time.
A species is a group of organisms that share similar characteristics and can interbreed to produce fertile offspring; if the offspring are sterile (like a mule), the parents are considered different species.
The process is driven by the accumulation of genetic changes that eventually prevent different populations from successfully mating with one another.
Alfred Russel Wallace was a key pioneer in this field, independently developing the theory of evolution by natural selection and focusing heavily on how isolation leads to new species.

Diagram showing geographic isolation where a barrier separates a population into two groups (A and B). Over time, they evolve different traits (circles vs squares) and can no longer interbreed.

2. Underlying Principles: Isolation and Selection

Geographic Isolation occurs when a physical barrier, such as a new mountain range, river, or island separation, divides a population into two or more groups.
Once isolated, the populations experience different environmental conditions, such as variations in climate, food sources, or predator types.
These different environments exert unique selection pressures, meaning different alleles (versions of genes) provide a survival advantage in each
Natural Selection ensures that individuals with advantageous alleles survive and reproduce, passing those specific traits to the next generation within their isolated group.

3. The Mechanism of Divergence

Over many generations, genetic mutations occur independently in each isolated population, increasing the genetic variation between them.
As natural selection acts on these mutations, the populations become increasingly distinct in their phenotypes (physical traits) and genotypes (genetic makeup).
Divergence can also affect behavioral traits, such as mating calls or courtship rituals, which further prevents the groups from recognizing each other as potential mates.
Eventually, the genetic differences become so significant that even if the physical barrier is removed, the two populations can no longer produce fertile offspring.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions