theSIGNAL SCIENCE
27 July 2026
"The eye has to see its own limitation before it can transcend it."
NEWSBUSINESSTECHNOLOGYWORLDSCIENCECULTUREENVIRONMENTSPORT
Science

Your Ancestor Had One Eye — and It's Still Inside You

New research suggests vertebrates descended from a single-eyed, worm-like creature, and a remnant of its ancient vision system may still sit inside your skull.

Picture a tiny, worm-shaped animal drifting on an ancient seafloor nearly 600 million years ago. It does not hunt. It does not chase. It simply sits, filtering plankton from the water — and peering at the world through a single eye planted squarely on top of its head.

According to a striking new study from Lund University in Sweden and the University of Sussex in the UK, this cyclops-like creature may be the common ancestor of every vertebrate alive today, including you. The research proposes something wonderfully strange. The ancestor probably once had paired eyes — the kind shared by almost every moving animal, from goldfish to giraffes — because paired vision helps creatures judge distance and direction. But when this particular lineage settled into a slow, stationary lifestyle, those paired eyes became redundant.

Over generations, they faded away. What remained was a cluster of light-sensitive cells at the centre of the head, which gradually became a single median eye. It likely could not form sharp images, but it could probably tell light from dark and up from down — enough to stay alive in the open ocean. Here is the part that should make you pause.

Photo: EJ Strat / Unsplash
A reconstruction of the ancient single-eyed ancestor that may have shaped vertebrate vision and the modern brain.
Discuss
  • Why might a stationary lifestyle cause paired eyes to disappear over many generations?
  • The pineal gland regulates sleep in humans today — what does this suggest about evolution's approach to repurposing old structures?
  • Is it surprising that vertebrate eyes may have re-evolved from a single central eye rather than being retained from the beginning? Why or why not?
Science

Weight-loss drugs are reshaping marriages

Jennifer lost 40 kilograms on Mounjaro. She expected her marriage to improve. Instead, it began to crack in ways neither she nor her husband had imagined. GLP-1 drugs like Mounjaro and Ozempic are now used by millions, with Australian prescriptions rising nearly ten-fold since 2020. Doctors warn patients about nausea and fatigue — but rarely about desire, emotional distance, or identity. Researchers suspect these drugs rewire dopamine reward pathways in the brain. That may suppress more than just hunger.…
  • Should doctors be required to discuss relationship risks before prescribing GLP-1 drugs?
∞
They turn our understanding of the evolution of the eye and the brain upside down.
Dan-E Nilsson, Professor Emeritus in Sensory Biology, Lund University
Science

Why teen brains aren't broken

A 15-year-old hits back after an insult in a school corridor. Adults call it impulsive. Evolution calls it rational. Research in evolutionary criminology argues that punishing rule-breakers is what allowed human cooperation to survive at all. Groups that ignored cheaters eventually fell apart — so the urge to retaliate is ancient, and it is wired deep. During adolescence, the brain's reward system peaks in sensitivity while the prefrontal cortex — the part that applies the brakes — is still under construction into a person's late twenties. The teenage brain is not broken; it is tuned for a specific, genuinely difficult task: leaving family, winning peers, defending a reputation. The cost teenagers are calculating when they "fail to think ahead" is almost always social. Walking away in front of an audience can destroy the standing they need most.…
  • Should schools be taught about evolutionary reasons behind teenage behavior?
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theSIGNAL IN THE LAB
1VOCABULARY
redundantstationary
lineagerewireprefrontal cortex
retaliateregulate
2GRAMMAR FOCUS
Wish and if only — expressing regret
Use 'wish' or 'if only' + past perfect (had + past participle) to express regret about past events, or + simple past / would to express regret about present situations.
had · knew · hadn't · could · would · were · had known
  1. Jennifer wishes she understood how Mounjaro might affect her emotional life before she started taking it.
  2. If only doctors warned patients about the impact of GLP-1 drugs on desire and identity, not just nausea.
  3. The researchers wish they explain exactly which other reward pathways are being switched off by these drugs.
  4. If only the ancient ancestor kept its paired eyes — vertebrate vision might have evolved along a very different path.
  5. Jennifer wishes her marriage stronger now, but the distance between her and her husband keeps growing.
  6. If only the teenager in the corridor walked away before retaliating — the consequences might have been far less serious.
3IDIOMS
Define each idiom in your own words. Then write one sentence of your own using one idiom of your choice.
  1. peering at the world (article 1)
  2. change its job description (article 1)
  3. apply the brakes (article 3)
  4. under construction (article 3)
  5. wired deep (article 3)
4CRITICAL THINKING
The teenage brain article argues that adolescent retaliation is 'surprisingly logical' given social priorities, while the eye-evolution article shows that structures once considered useless were actually repurposed. Do these two findings together challenge the idea that biology ever produces genuine mistakes — or are there clear limits to that argument?
5CREATIVE · HEADLINES
Write a headline for the top story in each of the following styles. One line each, no explanation:
  • TABLOID NEWSPAPER
  • LUXURY MAGAZINE
  • ACTIVIST BLOG
6WRITING
A character in a short story discovers that a physical feature they were ashamed of has an unexpected ancient origin — write the moment they find out and how it changes how they see themselves.
7DEGREES OF EXTREMITY
Complete each ladder from mild to strong. Choose from the box or use your own words where marked *.
  • useful→→
  • changed→→
  • noticed→→
  • odd→→
  • quieter→→
  • risky→→
8SPEAKING
  1. Can a physical change like weight loss genuinely alter someone's personality?
  2. Is social reputation a fair reason for a teenager to retaliate?
  3. Should evolutionary biology change how courts treat adolescent offenders?
  4. Which matters more: what an organ does now or where it came from?