More than 150 years after "The Origin of Species," we explore how evolutionary science has transformed - and enriched - Darwin's legacy.
More than 150 years ago, Charles Darwin published "On the Origin of Species," a book that forever changed our understanding of life on Earth. His theory of evolution by natural selection constituted an unprecedented scientific revolution that not only transformed biology but also deeply challenged established conceptions about humanity's place in nature 4 .
But what remains of the original Darwinism in contemporary biology? Are Darwin's postulates still valid or have they been replaced by new theories?
In this article, we explore how evolutionary science has transformed - and enriched - Darwin's legacy, demonstrating that his theory not only survives but has strengthened over time, albeit with important nuances and corrections.
Publication of "On the Origin of Species"
Voyage of HMS Beagle around the world
The core of Darwin's ideas can be summarized in three fundamental principles that, at the time, represented a radical shift in scientific thinking:
Darwin observed that individuals of the same species present heritable variations that arise naturally 4 .
Darwin proposed that all life forms share a common ancestor at some point in evolutionary history 4 .
| Principle | Description | Evidence Observed by Darwin |
|---|---|---|
| Genetic Variation | Heritable differences between individuals | Observation of variations in Galápagos finches, tortoises and other organisms |
| Natural Selection | Differential survival of advantageous variations | Comparison of adaptations in island vs. continental species |
| Common Ancestry | All species related through descent with modification | Anatomical similarities between different species, geographic distribution of species |
After his voyage on the Beagle, Darwin spent decades conducting meticulous experiments at his home in Kent, seeking evidence to support his theory 2 .
"Darwin had health problems and only someone who truly loved studying nature would have persevered as he did through decades of careful experiments and observations. The theory of natural selection, with all its importance, can be seen as a consequence of Darwin's intense love and curiosity for the natural world."
Darwin's curiosity knew no bounds. Here are some of his most revealing experiments:
Darwin discovered that grass shoots bent toward light, but when he covered the tip with an opaque "hat," the plant no longer curved. He correctly deduced that the part that perceives the stimulus (the tip) is not the same as the one that responds (the base), anticipating the discovery of plant hormones 2 .
In 1857, he marked 357 weed seedlings; within months, 277 had perished, mainly due to slugs. This high mortality supported his idea that there must be a "struggle for existence" where only the fittest survive 2 .
To respond to critics who saw species distribution as divine design, Darwin demonstrated that seeds could survive long periods in salt water and then germinate, showing the possibility of transoceanic dispersal 2 .
Among Darwin's numerous experiments, his research on phototropism (plant response to light) stands out for its elegant simplicity and conceptual depth 2 :
Darwin noticed that grass shoots (Phalaris canariensis) consistently bent toward the light of a lamp.
He speculated that the upper part of the shoot (the coleoptile) was responsible for detecting the direction of light.
He selectively covered different parts of the seedlings with small "hats" of opaque material, mainly tin foil.
He kept uncovered seedlings to compare normal behavior versus experimental behavior.
The results were revealing: when the tip of the shoot was covered, the plant completely lost its ability to bend toward light, even though the lower part (where the differential growth that produces curvature occurs) remained exposed. This led Darwin to a fundamental conclusion: the perception of the stimulus and the response occur in different parts of the plant 2 .
"Darwin's key idea is that the part of a plant that responds to a stimulus, in this case light, is not necessarily the same part that perceives the stimulus. And that realization leads to an inevitable conclusion: something carries those signals from one part of the plant to another. Darwin had in effect discovered plant hormones."
| Experimental Condition | Number of Seedlings | Curvature Toward Light | Interpretation |
|---|---|---|---|
| Uncovered (control) | 12 | 12/12 | Normal behavior toward light |
| Tip covered | 15 | 0/15 | Tip is necessary for detecting light |
| Base covered | 14 | 14/14 | Base does not intervene in detection |
| Completely covered seedling | 13 | 0/13 | Confirmation of light's crucial role |
Modern biology has confirmed Darwin's central ideas but has revealed more complex mechanisms than he imagined:
Besides natural selection, we now recognize genetic drift (random changes in small populations), gene flow (gene exchange between populations) and population bottlenecks, among others 8 .
| Aspect | Original Darwinism (1859) | Contemporary Evolutionary Theory |
|---|---|---|
| Inheritance Mechanisms | Ignored; hypothesis of pangenesis | Well-established genetic and molecular bases |
| Source of Variation | Unknown | Mutations, genetic recombination, gene duplication |
| Speed of Evolutionary Change | Strict gradualism | Punctuated gradualism (interrupted equilibria) |
| Unit of Selection | Individual | Gene, individual, population, species |
| Main Evidence | Fossils, geographic distribution, comparative anatomy | All of the above plus genomics, developmental biology, comparative biochemistry |
Ernst Mayr, a prominent 20th century evolutionary biologist, noted that the term "Darwinism" has had at least nine different uses throughout history 9 . Initially, it simply meant "anti-creationism," but over time its meaning has been refined.
Contemporary biology fully accepts the three theoretical axes central to Darwinism 9 :
Species change their characteristics over time gradually.
All species are related and diversify through adaptation.
As the main, though not exclusive, mechanism of adaptive change.
However, important limitations have been identified in Darwin's original thinking, particularly regarding:
Darwin proposed the erroneous "theory of pangenesis," suggesting that cells throughout the body produced "gemmules" that transmitted characteristics to offspring 7 .
Darwin was more "Lamarckian" than usually admitted, believing to some extent in the inheritance of adaptations acquired during an organism's lifetime 7 .
Contemporary evolutionary biology employs a sophisticated set of tools that go far beyond the meticulous observation that characterized Darwin:
Allows comparing genes between species and reconstructing evolutionary relationships with unprecedented precision 4 .
Analyze vast genomic datasets to identify patterns of molecular evolution.
Provide direct evidence of evolutionary changes through geological time.
Field and laboratory studies that observe evolution in action, such as Richard Lenski's famous experiments with E. coli bacteria.
Investigates how changes in embryonic development generate new forms and structures.
Reveals inheritance mechanisms beyond DNA sequence, modifying how genes are expressed 7 .
At 150 years since "On the Origin of Species," we can affirm that contemporary biology is Darwinian in essence, but not in its original form. Darwin's fundamental principles - common descent with modification and the role of natural selection - have withstood the test of time and accumulated evidence. However, the theoretical edifice has become considerably more complex and enriched.
The current evolutionary theory is more pluralistic than strict Darwinism, incorporating mechanisms that Darwin could not anticipate. As noted in an academic article on the fate of Darwinism, "the development of the modern synthesis in the 20th century, incorporating natural selection with population genetics and Mendelian genetics, revived Darwinism in an updated form" .
Most notably, far from weakening Darwin's legacy, subsequent discoveries have strengthened and deepened his fundamental vision: that all life forms are connected through a shared evolutionary history, and that biological diversity is the result of natural processes operating over immense time scales.
Contemporary biology is not less Darwinian for having surpassed Darwin; it precisely honors him by using the scientific method he himself employed so brilliantly: observe, question, experiment, and not be afraid to follow the evidence wherever it leads.
Natural selection and common descent remain foundational to modern biology.
Modern synthesis incorporates genetics, epigenetics, and new evolutionary mechanisms.
DNA sequencing and bioinformatics provide unprecedented insights into evolutionary processes.