Overview

• Grade Level: AP Biology / AP Environmental Science / History of Science (grades 9-12)

• Time Required: Single class (45 minutes); bell-ringer option (10 minutes); extension (2 additional class periods)

• Historical Period: 1848 to 1862, the Bates and Wallace Amazon expedition and the formulation of Batesian mimicry at the Linnean Society in London

• Modern Connection: The 2 May 2026 PLOS Biology paper by an international team led by the Wellcome Sanger Institute and the University of York titled 'Genetic parallelism underpins convergent mimicry coloration in Lepidoptera across 120 million years of evolution'

Learning Objectives

Students will be able to:

1. Describe the Bates and Wallace expedition of 1848 to 1859, including the field methods, the specimen-shipping arrangements, the duration, and the institutional structure (Samuel Stevens as London agent, the Linnean Society as publishing venue).

1. Explain in their own words what Batesian mimicry is, how Bates's 1861 paper inferred natural selection as the mechanism, and why his explanation was supported by Darwin and immediately treated as one of the first independent confirmations of natural selection outside Darwin's own domesticated-organism evidence.

1. Summarise the experimental design and key finding of the 2026 PLOS Biology paper, including the species sequenced, the two genes identified (ivory and optix), the role of regulatory switches, and the chromosomal inversion mechanism.

1. Construct an argument about why the same two genes have been re-used for 120 million years, distinguishing between the popular claim that 'evolution is not random' and the more careful claim that the space of viable molecular solutions to the warning-colouration problem is small.

Before Reading

Anticipation Questions

1. Two unrelated species of butterfly that have independently evolved the same warning colour pattern: what do you predict about whether they are using the same genes, similar genes, or completely different genes?

1. Henry Walter Bates spent eleven years in the Amazon and shipped 14,712 specimens home, of which 8,000 were new to science. Why might a self-taught working-class English naturalist have done this voluntarily?

1. If you wanted to test whether convergent evolution acts on the same genes or different genes, what would you need to compare? Predict two practical obstacles.

Key Vocabulary

• Mimicry: The phenomenon in which one species evolves to resemble another in appearance, behaviour, sound, or chemistry.

• Batesian mimicry: The specific form in which a palatable (edible, harmless) species evolves to resemble a chemically defended (unpalatable, dangerous) model.

• Convergent evolution: The independent evolution of similar features in distantly related species, usually in response to similar selective pressures.

• Regulatory element / cis-regulatory switch: A DNA sequence near a gene that controls when and where the gene is transcribed during development.

• Chromosomal inversion: A structural mutation in which a chunk of a chromosome is flipped end-to-end relative to its original orientation.

• Lepidoptera: The taxonomic order that includes butterflies and moths.

• Heliconius: A neotropical genus of brightly-patterned, chemically-defended butterflies; the model species in many Batesian mimicry systems.

• Linnean Society of London: The world's oldest active society for natural history, founded 1788; the venue at which Darwin and Wallace's joint papers were read in 1858 and at which Bates read his mimicry paper in 1861.

During Reading

Guided Questions

1. Identify the date, place, and personnel of the Bates-Wallace 1848 departure for the Amazon. What was the financial arrangement that made the expedition possible?

1. Describe in your own words the empirical observation that led Bates to the concept of mimicry. What specifically did he see in the Amazon that he could not explain?

1. Why does the story emphasise that Mendel was contemporary with Bates but unread for thirty-five years? What does Bates's lack of access to genetics tell you about what he could and could not infer?

1. Identify the two genes named in the 2026 paper. What is the evolutionary distance between the most distant lineages compared, and what mechanism does evolution use to re-deploy the two genes in different lineages?

1. The story closes with a comment that 'the space of solutions to the warning-colouration problem turns out to be very small.' What does this mean in terms of natural selection and the structure of the genome?

After Reading

Discussion Questions

1. Is the popular framing 'evolution is not random' supported by the 2026 PLOS Biology paper, or is the more careful framing 'the space of viable solutions is small' more defensible? Defend your position.

1. Bates's specimens are still in collections at the Natural History Museum in London and at other institutions. What role do museum collections play in modern genomics, and what is the case for continuing to fund them?

1. (Genuinely debatable.) The story describes Bates as having explained mimicry without having access to genetics, while the 2026 team explains the molecular mechanism. Which contribution is more important to biological theory: the original empirical insight, or the eventual mechanistic explanation?

1. The 2026 paper found that one moth lineage and one butterfly lineage independently evolved the same chromosomal inversion. What does this say about how genomes "discover" useful mutations? Is the same mechanism likely to operate in plants, vertebrates, or microbes?

1. Wallace returned from the Amazon in 1852 and lost his entire collection to a ship fire. Bates split his specimens across three vessels and lost none. What does this tell you about the role of redundancy in scientific data collection? Pick one modern parallel and defend it.

The Parallel

1. List the structural features that are similar between the 1862 Bates paper and the 2026 PLOS Biology paper. List the features that are different. Which list is longer, and which is more important?

1. Both halves of the story involve specimens of Heliconius butterflies collected in the same Amazon basin, separated by 164 years. What does it tell you about scientific continuity that the modern genomics paper used specimens descended from the populations Bates first catalogued?

1. Could there be an analogous "long-arc" story in a different field, where a Victorian-era natural-history observation was finally explained molecularly in the 21st century? Suggest one example and defend it.

Activities

Bell-Ringer (10 minutes)

Project two images side by side: a Victorian-era engraving of Heliconius butterflies from Bates's 1862 paper, and a modern fluorescence-microscope image of a Heliconius wing showing expression of the optix gene in the orange chevron. Ask students: "What did Bates see in 1862, and what do you see in the modern image that he could not have seen?" Have them write two sentences. Use the responses to introduce the lesson.

Single Class (45 minutes)

• 0 to 5 minutes: Bell-ringer recap.

• 5 to 18 minutes: Read the historical half of the story aloud. Students fill out a guided-reading organiser with three columns: "Bates and Wallace 1848 expedition," "Eleven years in the Amazon," "1861 Linnean Society paper."

• 18 to 32 minutes: Read the modern half aloud. Students extend the organiser with two more columns: "2026 PLOS Biology paper" and "What ivory and optix do."

• 32 to 42 minutes: Whole-class four-corners discussion of After Reading question 1 (is evolution random or not). Students physically move to a corner marked "Not random because of toolkit reuse," "Random at the mutation level, deterministic at the selection level," "The framing is misleading," or "Depends on the timescale."

• 42 to 45 minutes: Exit ticket. One sentence: "The most important thing Henry Walter Bates would want to know about ivory and optix is: ___."

Extension Activity

Convergent-evolution essay (3 to 5 pages, two class periods): students pick one example of convergent evolution outside of Lepidoptera (suggestions: the camera eye of vertebrates and cephalopods; echolocation in bats and dolphins; carnivorous plants on multiple continents; venom-resistance in unrelated mammal species; the streamlined body plan of sharks, ichthyosaurs, and dolphins) and write a structured essay describing what is known about whether the convergence acts on the same genes, similar genes, or completely different genes. They cite at least three primary or near-primary sources. They include a paragraph speculating about whether the 'small toolkit' principle from the Lepidoptera paper would predict the genetic answer in their chosen example.

Primary Source Connections

• Henry Walter Bates, "Contributions to an Insect Fauna of the Amazon Valley. Lepidoptera, Heliconidae," Transactions of the Linnean Society of London 23 (1862), pp. 495-566. Type: foundational scientific paper. The first description of Batesian mimicry.

• Henry Walter Bates, "The Naturalist on the River Amazons" (London: John Murray, 1863). Type: scientific travelogue. The full first-person account of the eleven-year expedition. Still in print.

• Charles Darwin's letters to Bates (1861-1862), available at the Darwin Correspondence Project, Cambridge. Type: primary correspondence. Includes Darwin's "one of the most remarkable and admirable papers" assessment.

• Bates's specimens in the Natural History Museum, London, including the Type specimens of several Heliconius and Ithomiini species. Type: museum collection / material culture.

• The PLOS Biology paper: "Genetic parallelism underpins convergent mimicry coloration in Lepidoptera across 120 million years of evolution" (2 May 2026). Open access at journals.plos.org/plosbiology.

• The Wellcome Sanger Institute butterfly genome resource, which provides whole-genome sequences for the species in the 2026 paper. Available at sanger.ac.uk.

Standards Alignment

C3 Framework

• Dimension 1 (Developing Questions): Compelling question: "What does it mean for evolution to 'find the same answer twice' across 120 million years, and what does the answer tell us about the structure of the genome?" Supporting questions about the role of selection, the structure of regulatory elements, and the relationship between empirical natural history and molecular biology.

• Dimension 2 (Applying Concepts): Biology (evolution, natural selection, gene regulation, comparative genomics, taxonomy). Geography (the Amazon basin as a centre of lepidopteran diversity). History (the Victorian institutional ecosystem of natural history: Linnean Society, John Murray, Samuel Stevens, the British Museum).

• Dimension 3 (Evaluating Sources): The story is accompanied by a populated evidence manifest with twelve verified claims and direct source URLs. Students can interrogate each claim by clicking through.

• Dimension 4 (Communicating Conclusions): The structured four-corners discussion and the extension essay both require sustained argumentation and source evaluation.

AP Alignment

• AP Biology: Big Idea 1 (Evolution) and Big Idea 3 (Information storage and transmission). Natural selection, convergent evolution, cis-regulatory elements, gene-expression patterning during development.

• AP World History: Key Concept 5.1 (Industrialisation and Global Capitalism). The Victorian global natural-history specimen trade as a feature of nineteenth-century globalisation.

• AP Research / AP History of Science: A model case for tracing how a nineteenth-century field-based natural-history observation is finally explained at the molecular level in the twenty-first century.