Darwinism vs Lamarckism, and Macro vs Micro Evolution

By the time Darwin published his theory, Lamarck’s ideas had already been circulating for decades. Both men tried to answer the same fundamental question: how do species change over time? Yet they reached remarkably different conclusions about what actually drives that change. Understanding where their ideas overlap and where they split apart is essential for grasping how evolutionary thought grew and matured. Beyond this classic debate, there is another crucial distinction in evolutionary biology: the difference between small changes happening within a species and the sweeping transformations that give rise to entirely new ones.

Two Pioneers, One Question: Comparing Lamarck and Darwin

Lamarck, a French naturalist, presented his ideas on evolution in the book “Philosophie Zoologique” (Zoological Philosophy). His central claim was that changes in the environment trigger bodily modifications in individual organisms, driven by an internal force he called elan vital (an inner vital urge pushing organisms toward greater complexity). These acquired changes, he argued, are then handed down to the next generation. This is why his theory is also known as the theory of inheritance of acquired characters. For Lamarck, the individual is the unit of evolutionary change.

Darwin saw the process very differently. In his book “On the Origin of Species” (1859), he proposed that environmental change does not directly reshape individual bodies. Instead, organisms within a population naturally vary from one another. The environment selects which individuals survive and reproduce, and over time this shifts the genetic makeup of the entire group. For Darwin, the population is the unit of evolutionary change.

In 1982, the evolutionary biologist Ernst Mayr published a detailed side-by-side comparison of the two theories in the Biological Journal of the Linnean Society. His analysis revealed both surprising areas of agreement and sharp points of difference.

Where They Agreed: Shared Ground Between Two Theories

Despite proposing very different mechanisms, Lamarck and Darwin shared several core convictions:

• Evolution as a real process — Both thinkers rejected the idea that the natural world is fixed and unchanging. They each argued that species transform over time, which was itself a radical claim in their respective eras.
• Gradual change over time — Neither believed that new species appear suddenly. Both insisted that evolution is slow and gradual, with change accumulating step by step across many generations. They both discarded essentialism (the belief that each species has a fixed, unchangeable essence).
• Use and disuse of organs — Both used the idea that organs grow stronger with repeated use and weaken with neglect to explain certain physical changes. An organ that an organism relies on heavily tends to develop further, while one that goes unused may shrink or disappear across generations.
• Role of the environment — Both recognised that the surrounding environment plays a central role in shaping how organisms evolve. Where they disagreed was the mechanism: Lamarck believed the environment directly causes bodily changes, while Darwin believed it acts as a selective filter on variation that already exists.

Where They Parted Ways: Key Differences

The similarities are real, but the differences between these two theories are far more significant:

• Evolution by common descent — Darwin proposed that related species share common ancestors, meaning all life is connected through a branching family tree. This idea of common descent (the proposition that related groups of organisms descended from shared ancestral populations) was entirely absent from Lamarck’s framework. Lamarck did not think in terms of shared ancestry linking different species together.
• What drives diversity — For Lamarck, the cause of evolutionary change was an internal driving force, the elan vital, pushing organisms toward greater complexity. For Darwin, diversity arose from the struggle for existence, natural selection, and the survival of the fittest. The driving force was external, rooted in competition and environmental pressure, not an internal urge.
• Vertical vs horizontal evolution — Lamarck focused mainly on vertical evolution (a single lineage becoming progressively more complex over time). Darwin addressed both vertical and horizontal evolution (the branching and splitting of one species into multiple new ones), though he concentrated more on the horizontal aspect, explaining how one ancestral population can give rise to several different species.
• Scientific evidence — Lamarck’s theory was largely speculative and lacked rigorous, observation-based evidence. Darwin’s theory, by contrast, was grounded in extensive field observations, detailed data from the Galapagos Islands, breeding experiments, and the fossil record. This is why Darwinism is often called the first scientific theory of evolution.

Both Lamarck and Darwin, each in their own way, laid the groundwork for our modern understanding of how life changes over time. Their ideas sparked debate, inspired further research, and ultimately guided others toward developing the Modern Synthetic Theory, which brought together Darwin’s natural selection with Mendelian genetics and insights from population biology.

Two Scales of Change: Macro vs Micro Evolution

Evolution, at its core, means change in a progressive direction, change with modification, or simply change and adaptation. In genetic terms, evolution is understood as a change in gene frequency (the shift in how common a particular gene variant is within a population) over time. But not all evolutionary change happens at the same scale. Some changes are small and subtle, visible within a single species over a short stretch of time. Others are sweeping transformations that play out across millions of years and produce entirely new groups of organisms. Biologists distinguish between these two scales using the terms microevolution and macroevolution.

Microevolution: Small Changes Within a Species

The term microevolution was introduced by Richard Goldschmidt in 1940 to describe evolutionary changes that occur within a species. These are the small mutations (random changes in DNA) that gradually accumulate in a population, producing subtle shifts in traits without creating a fundamentally new kind of organism.

Microevolution operates on a relatively small scale and over relatively short periods of time. You can study it directly by observing living populations. A well-known example is the sickle cell trait ($HbS$): in certain populations, a single mutation in the haemoglobin gene has increased in frequency because carriers gain some resistance to malaria. The population’s gene frequency has shifted, but humans remain humans. That is microevolution in action. It can lead to the formation of new races or sub-species, but not to the emergence of an entirely new species.

Macroevolution: Large Changes Above the Species Level

Macroevolution refers to evolution at the level of species and higher taxonomic groups (the classification categories above species: genera, families, orders, and beyond). These are large-scale changes that unfold over vast stretches of geological time and result in the appearance of fundamentally new kinds of organisms.

You cannot study macroevolution by observing only living populations. It requires looking at the fossil record and working within the field of palaeoanthropology (the study of ancient human and primate ancestors through their fossil remains). The transition from Homo erectus to Homo sapiens, for example, is a macroevolutionary event: an entirely new species emerged with distinctive physical and cognitive traits.

Comparing the Two Scales

Feature	Macroevolution	Microevolution
What changes	Broad modifications across genera, species, and higher taxonomic groups	Changes within a single species
Scale and time	Large-scale changes over long geological time periods	Small-scale changes over relatively short time periods
How it is studied	Requires fossil evidence and palaeoanthropology; cannot rely on living populations alone	Can be studied directly on living populations
What it can produce	New species (e.g., Homo erectus to Homo sapiens)	New races or sub-species (e.g., sickle cell trait, $HbS$)

Two Sides of the Same Coin

These two scales of evolution are not separate, disconnected processes. The genetic variations that accumulate through microevolution, the small mutations and shifts in gene frequency happening in populations right now, are the very building blocks that eventually lead to macroevolution. Given enough time, the small changes within a species add up until the population has transformed so significantly that it constitutes an entirely new species. Microevolution and macroevolution are best understood as complementary aspects of a single continuous process of evolutionary change.