雅思阅读 067 — Do Octopus Brains Work Like Humans'?

改编自 Scientific American / Nature（2026-05，Liam Drew）。

🎧 课文朗读音频（约 1 分半）

Reading Passage

Three hearts; blue blood; no skeleton; arms like tongues. These are just some of the alien features of octopuses, squid and cuttlefish — members of the cephalopod family. The outlandish list continues. Cephalopod skin can taste chemicals, sense light and change colour and texture rapidly. In many species, the sucker-covered arms can even regenerate.

These invertebrates have evolved independently from the vertebrate lineage for more than 600 million years. Their last common ancestor was probably a worm-like creature with a rudimentary nervous system and eye-like patches of light-sensitive cells. Despite this evolutionary gulf, vertebrates and these highly specialised molluscs share strange similarities. Their eyes, for example. "It's eerie how similar they ended up," says Cristopher Niell, a neuroscientist at the University of Oregon. "The convergent evolution of the eye still blows my mind."

Now, one similarity is spurring a boom in cephalopod neuroscience. Around 400 million years ago, cuttlefish, squid and octopuses diverged from the only other living cephalopods — the nautiluses. They then lost their protective shells and evolved brains that are uniquely large among invertebrates. These brains bestow the soft-bodied cephalopods with high intelligence. Cuttlefish, squid and octopuses have excellent memories, use tools and are adept problem-solvers; they have a concept of time and are capable of delayed gratification.

Cephalopods are the only non-vertebrate animals that have big, smart brains, says Cliff Ragsdale, a comparative neuroscientist at the University of Chicago. That presents a unique opportunity. Neuroscientists have gained a wealth of knowledge about how vertebrate brains work, but are increasingly looking to cephalopods for insights into ways to build large, high-functioning nervous systems.

Building a brain differently

A rudimentary look at the cephalopod nervous system reveals that there is more than one way to construct a large, smart brain. Cephalopod brains are doughnut-shaped organs built around the oesophagus. Moreover, a large number of a cephalopod's neurons — more than half in the case of octopuses — are located in the eight nerve cords, or "minibrains", that control the arms.

Even systems that perform recognisable functions are mystifying. Although octopus eyes resemble those of vertebrates, the visual system in the brain does not. "It's hard to convey how different it is," says Niell. "We just have no idea of how it functions."

When you look at the octopus-arm nerve cord, says Robyn Crook, a cephalopod neurobiologist at San Francisco State University, "it is just — we call it horrible grey spaghetti. Everything is tiny. There are no bundles. There are no big cells and small cells. It's just horrifically disorganised. And yet, obviously, it makes beautiful sense."

As well as looking different, these neurons also communicate in strikingly different ways. In a recent study, William Schafer and Amy Courtney of the MRC Laboratory of Molecular Biology in Cambridge showed that the octopus visual system contains a dopamine receptor that works differently from those of vertebrates. The octopus receptor is an ion channel opened directly by dopamine, allowing ions to flow through, whereas the vertebrate receptor is activated when dopamine binds to its surface, triggering biochemical signalling inside neurons.

A classic model, revived

Neuroscience already owes cephalopods a debt of gratitude. In 1929, zoology graduate John Zachary Young, working at the Zoological Station in Naples, discovered a cluster of nerve cells in squid that give rise to nerve fibres up to one millimetre wide. This insight meant that scientists could implant electrodes into these fibres and decipher the fundamentals of how neurons fire electrical impulses.

Yet, despite Young's celebrated work, octopuses never became a widespread model for studying cognition. One reason was that studying cephalopod brains was a huge technical headache. Boycott, for example, tried and failed for 17 years to make stable neural recordings in living animals, eventually leaving the field.

That has changed. The first item in the modern cephalopod toolkit was the sequence of an octopus genome, published in 2015 by Carrie Albertin, Ragsdale and their colleagues. "I think when we published the genome, it led a lot of people who'd been interested in these creatures to say, 'Gee, it's safe to go in the water now,'" Ragsdale says. The octopus had entered its molecular-biology era.

Whether cephalopod brains ultimately turn out to share the same principles as ours, or operate on entirely different ones, the result is a win-win, says Tessa Montague, a cuttlefish neurobiologist at Columbia University. "Either it tells us there are fundamental principles shared by all brains, or it tells us there are different ways to build a complex, functional brain."

Questions

Questions 1–5: TRUE / FALSE / NOT GIVEN

1. Cephalopods and vertebrates share a common worm-like ancestor from 600 million years ago.
2. Octopuses have more than half of their neurons in their arms.
3. Octopus visual systems are organised identically to those of vertebrates.
4. The octopus dopamine receptor works by directly opening an ion channel.
5. John Zachary Young discovered the squid giant axon in 1929.

Questions 6–10: Choose the correct letter, A, B, C or D.

6. The last common ancestor of cephalopods and vertebrates was

   • A. a fish
   • B. a worm-like creature with a simple nervous system
   • C. an early mammal
   • D. unknown

7. Around when did cuttlefish, squid and octopuses diverge from nautiluses?

   • A. 600 million years ago
   • B. 400 million years ago
   • C. 100 million years ago
   • D. 100 years ago

8. The octopus brain is described as doughnut-shaped because it

   • A. is soft and edible
   • B. surrounds the oesophagus
   • C. has no neurons
   • D. is split into two halves

9. Why did octopuses not become a mainstream model organism earlier?

   • A. They were considered too intelligent.
   • B. Technical difficulties in neural recording made them hard to study.
   • C. They are protected by law.
   • D. They are too expensive to buy.

10. The octopus genome was sequenced in

    • A. 1929
    • B. 1970
    • C. 2015
    • D. 2025

Questions 11–13: Complete the sentences. Choose NO MORE THAN TWO WORDS.

11. Cephalopods have three hearts and __________ blood.
12. In octopuses, more than half of neurons are found in the eight arm __________.
13. The 2015 publication of the octopus genome opened its __________-biology era.

Answers

1. TRUE
2. TRUE
3. FALSE (视觉系统组织方式非常不同)
4. TRUE
5. TRUE
6. B
7. B
8. B
9. B
10. C
11. blue
12. nerve cords
13. molecular

Glossary

• cephalopod /ˈsefələpɒd/ n. 头足类动物
• convergent evolution /kənˈvɜːdʒənt/ n. 趋同进化
• invertebrate /ɪnˈvɜːtɪbrət/ n. 无脊椎动物
• oesophagus /iːˈsɒfəɡəs/ n. 食道
• dopamine /ˈdəʊpəmiːn/ n. 多巴胺
• ion channel /ˈaɪən ˈtʃænl/ n. 离子通道
• genome /ˈdʒiːnəʊm/ n. 基因组
• mollusc /ˈmɒləsk/ n. 软体动物
• cognition /kɒɡˈnɪʃn/ n. 认知