Understanding Genetics and Evolution » Wallace and Speciation

Alfred Russel Wallace

When people talk about evolution, they usually name Charles Darwin. But Darwin was not the only scientist to work out how evolution happens. Alfred Russel Wallace came up with the theory of evolution by natural selection independently. That means he reached the same big idea on his own, without copying Darwin.

Wallace worked all over the world, gathering evidence for evolution. This is how scientists build a theory: they collect evidence from many places, then look for an explanation that fits it all.

Wallace is best known for two pieces of work:

• Warning colouration in animals
• His theory of speciation

Key terms:

• Warning colouration: bright, bold colours or patterns on an animal that warn predators it is harmful or unpleasant to eat.
• Speciation: the formation of a new species from an existing one.
• Isolation: when two groups of the same species are separated and can no longer breed together.

Two scientists, one idea

Wallace and Darwin each reached the idea of natural selection by their own route. In 1858 they published joint writings setting out the idea. These writings prompted Darwin to publish his book, On the Origin of Species, in 1859, the following year.

How new species form

Wallace did pioneering work on speciation. Over time, more evidence has built on his work and led to the theory we use today. This is a good example of how scientific ideas develop over time: one scientist makes a start, and later evidence improves the explanation.

Remember that a species is a group of organisms that can interbreed to produce fertile offspring. Speciation happens in four steps:

1. Isolation: a population of one species becomes split into two groups that are separated from each other, for example by a river, a mountain range or rising sea water that forms islands. The two groups can no longer breed together.
2. Variation: within each group, individuals show variation, because they have different alleles. The two groups also live in different conditions, so each faces different challenges.
3. Natural selection: in each group, the individuals best suited to their conditions survive and breed. They pass on the alleles that help them survive. Over many generations, each group changes in a different way.
4. No longer interbreed: in time, the two groups become so different that, even if they meet again, they can no longer interbreed to produce fertile offspring. They are now two separate species.

Notice that isolation comes first. Without it, the two groups keep breeding together and mixing their alleles, so they stay one species.

Why these ideas matter

The work of Wallace and Darwin changed biology. Natural selection and speciation gave scientists a way to explain why there are so many different species, and why living things are suited to where they live. It also showed that species are not fixed: they can change over time, and new ones can form. These ideas gave biologists a framework to explain what they saw in the living world, and they led to more investigation and more evidence.

Exam-style question

(a) Describe the work of Alfred Russel Wallace. [2 marks]

(b) Describe the steps that lead to a new species forming from a population that has become split into two groups. [4 marks]