Table of Contents
Overview of the Two Theories
Jean-Baptiste Lamarck (early 1800s) and Charles Darwin (mid–late 1800s) both proposed that species change over time, but they explained how this happens in fundamentally different ways.
To compare them, it helps to separate their ideas into:
- How variation arises
- How change is passed on to offspring
- The role of the environment
- The view of adaptation and progress
- Predictions and how well they fit observations
This chapter assumes you already know the basic outlines of Lamarck’s and Darwin’s theories from previous sections; we now put them side by side and highlight the contrasts.
Key Principles of Lamarck vs. Darwin
Source of Change in Organisms
Lamarck
- Organisms change because they actively adapt during their lifetime.
- Use and disuse:
- Frequently used organs or structures become stronger, larger, or more developed.
- Unused structures shrink or disappear.
- Change originates from the needs of the organism in a given environment.
- Example: In Lamarck’s view, the giraffe’s ancestors stretched their necks to reach high leaves; repeated stretching led to longer necks.
Darwin
- Organisms are born with small, random differences (individual variation).
- These differences are not guided by need; they simply occur.
- Variation is present before the environment “selects” among individuals.
- Example: In Darwin’s view, some ancestral giraffes were born with slightly longer necks purely by chance.
How Changes Are Inherited
Lamarck
- Acquired characteristics (traits gained during life) are inherited.
- Modifications caused by use/disuse or by responding to needs are passed directly to offspring.
- If a blacksmith builds strong arm muscles, his children would inherit more muscular arms.
- Environment → change in individual → inheritance of that acquired change.
Darwin
- Only inherited traits (encoded in what we now call genetic information) are passed on.
- Changes acquired from training, injury, or lifestyle in an individual’s lifetime do not change what is inherited.
- A bodybuilder’s children are not born muscular because of the parent’s training.
- Inheritance is independent of what the individual does with its body.
Role of the Environment
Lamarck: Environment as Direct Shaper
- Environment directly causes organisms to adapt.
- New needs created by environmental change lead to:
- Changed patterns of use/disuse.
- Altered structures.
- Inheritance of those altered structures.
- The environment acts like a “teacher” continuously reshaping organisms.
Darwin: Environment as Selector
- Environment does not directly mould individuals; it “tests” them.
- Some variants are better suited to the current environment than others.
- Natural selection:
- Better-adapted individuals survive and reproduce more.
- Poorly adapted individuals leave fewer or no descendants.
- Over many generations, advantageous traits become more common.
So, in brief:
- Lamarck: environment creates adaptations in individuals.
- Darwin: environment selects among pre-existing variations.
Direction of Evolution and “Progress”
Lamarck
- Evolution is inherently progressive and purposeful.
- He assumed a built-in tendency towards greater complexity and “perfection.”
- Simple forms continually arise and then “climb” a ladder of complexity.
- Adaptation is seen as part of a general drive upwards.
Darwin
- Evolution has no predetermined direction.
- Natural selection simply favors traits that improve survival and reproduction in a given context.
- Organisms may become more complex, simpler, or remain similar, depending on what is advantageous.
- There is no built-in drive toward “higher” forms; “fitness” is always relative to the environment.
View of Species and Their Change
Lamarck
- Species form a kind of continuous chain from simplest to most complex.
- New simple species arise spontaneously and begin their own upward development.
- Change is mostly gradual and smooth, driven by internal tendencies and environment-induced adjustments.
Darwin
- Species are real, branching lineages.
- New species arise when populations split and diverge under different conditions.
- The “tree of life” has branches and common ancestors rather than a single ladder.
- Evolution explains both diversity (branching) and adaptation (selection).
Comparative Summary Table
| Aspect | Lamarck | Darwin |
|---|---|---|
| Main mechanism | Use and disuse; inheritance of acquired traits | Variation + natural selection |
| Source of variation | Directed by needs and use/disuse | Random (undirected) variation |
| Inheritance of acquired traits | Yes | No (lifetime changes not inherited) |
| Role of environment | Directly shapes traits in individuals | Selects among pre-existing variants |
| Direction of evolution | Progressive, towards complexity/perfection | No fixed direction; context-dependent |
| Representation of history | Ladder/scale of beings | Branching tree of life |
| Origin of new species | Continuous transformation under environmental influences | Splitting of populations, divergence, speciation |
| Role of chance | Minimal; change is largely purposeful | Central; variation arises by chance |
Predictions and Evidence: Which Fits Better?
Testable Predictions of Lamarckism
If Lamarck’s model were correct, we would expect:
- Systematic inheritance of acquired bodily changes.
- Example: If many generations of humans cut their hair short, eventually shorter hair would be inherited.
- Direct, predictable changes in organisms in response to use/disuse and environment, passed rapidly to offspring.
- Less emphasis on random variation; more on uniform response within a species to the same environmental conditions.
Modern observations and experiments do not support these predictions:
- Training, learned skills, and most bodily modifications are not passed on genetically.
- Organisms in the same environment still show a wide range of inherited differences.
- Evolutionary changes can often be traced to changes in DNA sequence, not to acquired bodily changes.
Support for Darwin’s Theory
Darwin’s ideas lead to predictions that match modern findings:
- Individuals in a population show heritable variation.
- Traits that increase survival and reproduction become more common over generations.
- Fossil and genetic data show branching patterns consistent with a “tree” of common ancestry.
- Experimental evolution (e.g., in bacteria or fruit flies) demonstrates adaptation via selection on random variants.
Modern evolutionary biology has expanded and modified Darwin’s theory (e.g., incorporating genetics, mutation, genetic drift), but its core—variation plus natural selection—remains strongly supported.
Common Misunderstandings in the Comparison
“Darwin Denied Any Role for the Environment”
False. Darwin fully recognized the importance of the environment, but:
- Lamarck: environment causes inheritable changes in individuals.
- Darwin: environment filters existing variation by selection.
The difference is in how the environment acts, not whether it matters.
“Darwin Rejected All Aspects of Lamarck”
Darwin rejected the central Lamarckian mechanism (inheritance of acquired characteristics), but:
- Both accepted that species change over time.
- Both saw adaptation as a key feature to be explained.
- Early in his career, Darwin himself was not entirely sure whether some acquired traits might be inherited; only later did evidence clearly favor genetic inheritance.
“Lamarck Was Simply ‘Wrong’ and Useless”
Lamarck’s mechanism does not match modern genetics, but his work was historically important:
- He argued strongly that species change (evolve) at a time when many believed they did not.
- He tried to explain how this happened with a coherent theory.
- His ideas helped prepare the ground for later evolutionary thinking, including Darwin’s.
Modern Nuances: Any “Lamarckian” Elements Today?
Classical Lamarckism—inheritance of acquired bodily traits via use/disuse—is not supported. However, modern biology has uncovered some subtleties that sometimes revive “Lamarck-like” language:
- Epigenetics:
- Chemical marks on DNA or associated proteins can influence gene activity.
- Some of these marks can, in limited cases, be passed to offspring.
- Environmentally induced changes in gene regulation can sometimes affect the next generation.
Still, these phenomena:
- Do not operate through the simple use/disuse mechanism Lamarck proposed.
- Do not replace natural selection acting on genetic variation.
- Are integrated into, rather than overturning, the modern Darwinian framework.
Conceptual Shift: From Purposeful Change to Selection on Variation
The deep difference between Lamarck and Darwin is conceptual:
- Lamarck starts with need: organisms change because they must adapt; they develop what they need and pass it on.
- Darwin starts with variation: different forms simply exist; the environment determines which ones leave more descendants.
This shift:
- Removes the idea of built-in progress or purpose in evolution.
- Explains adaptation as an emergent result of differential survival and reproduction, not as a conscious striving or internal drive.
Understanding this contrast is central to understanding how evolutionary biology thinks about change today.