Tortoises Reach High, Finch Beaks Diverge

Published Wednesday, September 16, 2026

by Violet shen & Ming Chuong

Editor’s Note :

Travel is more than movement—it is a way of reading the world.

Cultural Express launches Hidden Pattern, a new column by USC professor Cheng-Ming Chuong and Violet Shen, former Director of Clinical Research at Children’s Hospital of Orange County.

Through words and images, they explore landscape, culture, nature, and science—revealing the traces of time, the path of evolution, and the hidden order of the world.

Introduction:

Born of fire and sea, the Galápagos reveals evolution in motion:Giant tortoises’ shells record drought and rain, finch beaks answer hunger, marine iguanas brave cold waters, and blue-footed boobies dance for love.

The authors set foot on the Galápagos, tracing Darwin’s footsteps to create the Galápagos Discovery Trilogy—a journey in words and photos through fire, sea, and evolution’s wonders. (Part 2 of 3)

In a Galápagos forest, a giant tortoise slowly emerged from the shade of trees. Its massive shell seemed to carry the islands’ ancient past; each step moved at the pace of time itself.

We crouched nearby and watched in silence. It raised its long neck and calmly crossed the rocks, its weathered eyes seemingly witness to volcanoes rising and vegetation withering and flourishing.

The name Galápagos comes from the Spanish word galápago, a word linked to the islands’ giant tortoises and their saddle-shaped shells.

Yet what fascinates scientists is not simply their size, but how tortoises on different islands evolved distinctly shaped shells.

Shells Match, Necks Reach

In general, domed giant tortoises inhabit wetter highlands rich in vegetation. Their shells slope low in front, allowing them to graze easily on ground-level grasses.

On drier islands, where vegetation is sparse and food is often found grows higher, saddleback tortoises have upturned front shells and longer necks that reach elevated cacti and shrubs.

No individual tortoise lengthens its neck during its lifetime simply by stretching for higher leaves. Instead, natural selection acts on existing variations within a population.

Traits better suited to the environment improve survival and reproductive success; over generations, those advantages accumulate into distinct forms.

When Darwin reached Floreana Island in 1835, Vice Governor Nicholas Lawson told him he could identify a tortoise’s home island by its appearance.

Darwin remembered the remark, though he did not immediately grasp its evolutionary significance.

Beaks Feed, Species Split

What truly puzzled Darwin was a group of seemingly ordinary birds—the Darwin’s finches we later spotted among the trees and cacti.

Though similar in appearance, their beaks differ dramatically.

Thick, powerful beaks crack hard seeds; slender, pointed beaks catch insects; longer, narrower beaks reach cactus flowers, fruit, and seeds. Each beak is a built-in utensil, revealing how its owner survives.

Today, this process is called adaptive radiation: descendants of a common ancestor enter a new environment, occupy different ecological niches, and—through isolation and natural selection—gradually diverge into multiple species.

A tortoise shell and a finch beak may seem unrelated, yet both reveal the same truth: life is not fixed forever, Over time populations can follow different evolutionary paths as they respond to different environments .

Islands Question, Years Answer

Darwin’s story is often reduced to a sudden flash of insight: he saw different beaks and instantly discovered evolution.

Real science discovery was far less dramatic.

Darwin left the Galápagos not with answers, but with specimens and questions.

Why did animals on remote islands still bear the imprint of South American ancestry? Why were species on neighboring islands so similar, yet distinctly different?

Those questions followed him home. He organized specimens, compared species, and drew upon knowledge from geology, selective breeding, population studies, and other fields.

Only 24 years later, with the 1859 publication of On the Origin of Species, did natural selection emerge as a central scientific explanation for biological evolution.

The Galápagos did not hand Darwin the answer. It compelled him to ask the right questions—and pursue them further.

Forms Observed, Mechanisms Revealed

Darwin saw differences in outward form. Modern science asks a deeper question: how do genes and embryonic development create them?

Avian evolution later became a major focus of my own interdisciplinary research.

In recent decades, Peter and Rosemary Grant at Princeton, Clifford Tabin at Harvard, and Leif Andersson in Sweden have brought genetics and developmental biology into the study of Darwin’s finches.

Their work allows us to trace the patterns and principles of evolution at the level of genes and developmental biology.

In the laboratory, I studied beak development in chicken and duck embryos and identified zones of cell proliferation along the beak’s growing edge.

In chickens, these zones merge earlier and stop extending; in ducks, growth continues longer, producing an elongated beak.

Changes in growth direction can even create the curved beak of a parrot.

These studies also show that molecular signals involved in embryonic development—including BMP4—are closely tied to beak shape.

Evolution does more than alter outward appearance: by fine-tuning when, where, and how developmental signals act, it can sculpt beaks of remarkably different shapes and sizes.

Nearly two centuries ago, Darwin studied finch beaks and wondered why species differed. Today, scientists look inside genes and cells to discover how those differences arise.

Giant tortoises still move slowly through the woodland, and finches still feed among the branches.

As we walk across the Galápagos, the story of evolution written into these islands remains unfinished—its pages still turning. (Part Two of Three)

Note: BMP4 (Bone Morphogenetic Protein 4) is one of the molecular “growth signal" that helps determine the thickness and width of Darwin’s finch beaks during embryonic development.

Next Week | Boobies’ foot colors hide survival secrets. Our Galápagos trilogy finale takes you inside the story.