"Do we not therefore perceive that by the action of the laws of organization . . . nature has in favorable times, places, and climates multiplied her first germs of animality, given place to developments of their organizations, . . . and increased and diversified their organs? Then. . . aided by much time and by a slow but constant diversity of circumstances, she has gradually brought about in this respect the state of things which we now observe. How grand is this consideration, and especially how remote is it from all that is generally thought on this subject!"Text of a lecture given by Lamarck at the Musée National d'Histoire Naturelle, Paris, May 1803
Lamarck's scientific theories were largely ignored or attacked during his
lifetime; Lamarck never won the acceptance and esteem of his colleagues
Buffon and
Cuvier, and he died
in poverty and obscurity. Today, the name of Lamarck is associated merely with
a discredited theory of heredity, the "inheritance of acquired traits." However,
Charles Darwin, Lyell, Haeckel, and other
early evolutionists acknowledged him as a great zoologist and as a
forerunner of evolution. Charles Darwin wrote in 1861:
Biography of Lamarck
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck was born on
August 1, 1744, in the village of Bazentin-le-Petit in the north of France.
He was the youngest of eleven children in a family with a centuries-old
tradition of military service; his father and several of his brothers were
soldiers. The young Lamarck entered the Jesuit seminary at Amiens around 1756,
but not long after his father's death, Lamarck rode off to join the French
army campaigning in Germany in the summer of 1761; in his first battle, he
distinguished himself for bravery under fire and was promoted to officer. After
peace was declared in 1763, Lamarck spent five years on garrison duty in the
south of France, until an accidental injury forced him to leave the army. After
working as a bank clerk in Paris for a while, Lamarck began to study medicine
and botany, at which he rapidly became expert; in 1778 his book on the plants
of France, Flore Française, was published to great acclaim, in
part thanks to the support of Buffon.
On the strength of the Flore Française (and Buffon's patronage),
Lamarck was appointed an assistant botanist at the royal botanical garden,
the Jardin des Plantes, which was not only a botanical garden but a center
for medical education and biological research.
Aside from a stint as tutor to Buffon's son during a tour of Europe in 1781,
Lamarck continued as an underpaid assistant at the Jardin du Roi, living
in poverty (and having to defend his job from cost-cutting bureaucrats in
the National Assembly) until 1793.
That year, the same year that Louis XVI and Marie
Antoinette went to the guillotine, the old Jardin des Plantes was reorganized
as the Musée National d'Histoire Naturelle (National Museum of
Natural History), which was to be run by twelve professors in twelve different
scientific fields. Lamarck, who had called for this reorganization,
was appointed a professor -- of the natural history of
insects and worms (that is, of all invertebrates), a subject he knew nothing
about.
To be fair to Lamarck, we should mention that since the time of
Linnaeus, few naturalists had considered the
invertebrates worthy of study. The word "invertebrates" did not even exist at
the time; Lamarck coined it. The invertebrate collections at the Musée
were enormous and rapidly growing, but poorly organized and classified. Although
the professors at the Musée were theoretically equal in rank, the
professorship of "insects and worms" was definitely the least prestigious.
But Lamarck took on the enormous challenge of learning -- and creating
-- a new field of biology. The sheer number and diversity of invertebrates
proved to be both a challenge and a rich source of knowledge. As Lamarck
lectured his students in 1803, after ten years of research on invertebrates:
But Lamarck's works never became popular during his lifetime, and Lamarck
never won the respect or prestige enjoyed by his patron Buffon or his colleague
Cuvier.
While Cuvier respected Lamarck's work on invertebrates, he
had no use for Lamarck's theory of evolution, and he used his influence to
discredit it. Most of Lamarck's life was a constant struggle against poverty;
to make matters worse, he began to lose his sight around 1818, and spent his
last years completely blind, cared for by his devoted daughters (he had been
married four times). When he died, on December 28, 1829, he received a poor
man's funeral (although his colleague Geoffroy
Saint-Hilaire gave one of the orations) and was buried in a rented grave;
after five years his body was removed, and no one now knows where his remains
are.
Lamarck's Scientific Thought
Beginning in 1801, Lamarck began to publish details of his evolutionary
theories. Where men like Buffon had hinted at the possibility of evolutionary
change, Lamarck declared it forthrightly. In 1801 he wrote:
While the mechanism of Lamarckian evolution is quite different from that
proposed by Darwin, the predicted result is the same: adaptive change in
lineages, ultimately driven by environmental change, over long periods of time.
It is interesting to note that Lamarck cited in support of his theory of
evolution many of the same lines of evidence that Darwin was to use in the
Origin of Species. Lamarck's Philosophie zoologique mentions the
great variety of animal and plant forms produced under human cultivation
(Lamarck even anticipated Darwin in mentioning fantail pigeons!); the presence
of vestigial, non-functional structures in many animals; and the presence of
embryonic structures that have no counterpart in the adult. Like Darwin and
later evolutionary biologists, Lamarck argued that the Earth was immensely old.
Lamarck even mentions the possibility of natural selection in his writings,
although he never seems to have attached much importance to this idea.
It is even more interesting to note that, although Darwin tried to refute
the Lamarckian mechanism of inheritance, he later admitted that the heritable
effects of use and disuse might be important in evolution. In the Origin
of Species he wrote that the vestigial eyes of moles and of cave-dwelling
animals are "probably due to gradual reduction from disuse, but aided
perhaps by natural selection." Lamarckian inheritance, at least in the sense
Lamarck intended, is in conflict with the findings of genetics and has now
been largely abandoned -- but until the rediscovery of Mendel's laws
at the beginning of the twentieth century, no one understood the mechanisms of
heredity, and Lamarckian inheritance was a perfectly reasonable hypothesis.
Several other scientists of the day, including
Erasmus Darwin, subscribed to the theory of
use and disuse -- in fact, Erasmus Darwin's evolutionary theory is so close
to Lamarck's in many respects that it is surprising that, as far as is known
now, the two men were unaware of each other's work.
In several other respects, the theory of Lamarck differs from modern
evolutionary theory. Lamarck viewed evolution as a process of increasing
complexity and "perfection," not driven by chance; as he wrote in
Philosophie zoologique, "Nature, in producing in succession every
species of animal, and beginning with the least perfect or simplest to end her
work with the most perfect, has gradually complicated their structure."
Lamarck did not believe in extinction:
for him, species that disappeared did so because they evolved into different
species. If this goes on for too long, it would mean the disappearance of
less "perfect" organisms; Lamarck had to postulate that simple organisms, such
as protists,
were constantly being spontaneously generated.
Yet despite these differences, Lamarck made a major contribution to evolutionarythought, developing a theory that paralleled Darwin's in many respects.
Rediscovered in the middle part of the 19th century, his theories finally
gained the attention they merited. His mechanism of evolution remained a
popular alternative to Darwinian selection until the beginning of the 20th
century; prominent scientists like Edward
Drinker Cope adopted Lamarckianism and tried to apply it to their work.
Though his proposed mechanism eventually fell out of favor, he broke ground
in establishing the fact of evolution.
Lamarck was the first man whose conclusions on the subject excited much
attention. This justly celebrated naturalist first published his views in
1801. . . he first did the eminent service of arousing attention to the
probability of all changes in the organic, as well as in the inorganic world,
being the result of law, and not of miraculous interposition.
Who was this man, and why did he inspire such conflicting attitudes?
. . . we perceive that, relative to the animal kingdom, we should chiefly
devote our attention to the invertebrate animals, because their enormous
multiplicity in nature, the singular diversity of their systems of
organization, and of their means of multiplication, . . . , show us, much
better than the higher animals, the true course of nature, and the means which
she has used and which she still unceasingly employs to give existence to all
the living bodies of which we have knowledge.
Lamarck published a series of books on invertebrate zoology and paleontology.
Of these, Philosophie zoologique, published in 1809, most clearly states
Lamarck's theories of evolution. The first volume of
Histoire naturelle des Animaux sans vertèbres was published in
1815, the second in 1822. Aside from Lamarck's contributions to evolutionary
theory, his works on invertebrates represent a great advance over existing
classifications; he was the first to separate the Crustacea,
Arachnida,
and Annelida
from the "Insecta." His
classification of the mollusks was far in advance of anything proposed
previously; Lamarck broke with tradition in removing the
tunicates
and the barnacles from the Mollusca.
He also anticipated the work of Schleiden & Schwann in cell theory in stating
that:
. . . no body can have life if its constituent parts are not cellular tissue
or are not formed by cellular tissue.
Lamarck even found time to write papers
on physics and meteorology, including some annual compilations of weather data.
. . . time and favorable conditions are the two principal
means which nature has employed in giving existence to all her productions.
We know that for her time has no limit, and that consequently she always has
it at her disposal.
What was the mechanism for evolution?
"Lamarckism" or "Lamarckianism" is now often used in a rather derogatory sense
to refer to the theory that acquired traits can be inherited. What Lamarck
actually believed was more complex: organisms are not passively altered by
their environment, as his colleague Geoffroy
Saint-Hilaire thought. Instead, a change in the environment causes
changes in the needs of organisms living in that environment, which in turn
causes changes in their behavior. Altered behavior leads to greater or lesser
use of a given structure or organ; use would cause the structure to increase
in size over several generations, whereas disuse would cause it to shrink or
even disappear. This rule -- that use or disuse causes structures to enlarge
or shrink -- Lamarck called the "First Law" in his book Philosophie
zoologique. Lamarck's "Second Law" stated that all such changes were
heritable. The result of these laws was the continuous, gradual change of
all organisms, as they became adapted to their environments; the physiological
needs of organisms, created by their interactions with the environment,
drive Lamarckian evolution.
Scientists at the beginning of the 1800s know of some kinds of fossils, and they were very aware of homologous and vestigial structures. Many scientists suspected that some kind of evolution had given rise to living things around them. However, they had no unifying theory to explain how evolution might have occurred. Two scientists led the way in the search for a mechanism of evolution. The first was Jean Lamarck. The second was one of the greatest figures in biology, Charles Darwin.
Assume that there were salamanders living in some grasslands. Suppose, Lamarck argued, that these salamanders had a hard time walking because their short legs couldn't trample the tall grasses or reach the ground. Suppose that these salamanders began to slither on their bellies to move from place to place. Because they didn't use their legs, the leg muscles wasted away from disuse and the legs thus became small. Lamarck's theory said that the salamanders passed this acquired trait to their offspring. In time the salamander's legs were used so rarely that they disappeared. Thus, Lamarck argued, legless salamanders evolved from salamanders by inheriting the acquired characteristic of having no legs. Lamarck presented no experimental evidence or observation and his theory fell out of scientific favor. The next significant idea came from the British scientist Charles Darwin.
Charles Darwin (1809-1882), like many people of genius,
did not at first appear to have extraordinary talents. From a young age Darwin disliked school and preferred
observing birds and collecting insects to study. He was sent to medical school in Scotland when he was 16.
Young Darwin found medicine "intolerably dull." He was much more interested in attending natural history
lectures.
Seeing that Darwin lacked enthusiasm for becoming a doctor, his father suggested he study for the clergy. Darwin was agreeable to the idea and enrolled in the university at Cambridge, England, in 1827. Here again, Darwin admitted, "My time was wasted, as far as the academic studies were concerned."
However, Darwin found that his friendship with John S. Henslow, professor of botany, made life in Cambridge extremely worthwhile. Through long talks with Henslow, Darwin's knowledge of the natural world increased. Henslow encouraged Darwin in his studies of natural history. In 1831 Henslow recommended that Darwin be chosen for the position of naturalist on the ship the HMS Beagle.
The Beagle was chartered for a five-year mapping and collecting expedition to South America and the South Pacific. Darwin's job as ship naturalist was to collect specimens, make observations, and keep careful records of anything he observed that he thought significant.
At the beginning of the voyage Darwin read a geology book given to him by Henslow. This book, Principles of Geology by Charles Lyell, spurred his interest in the study of land forms. In Chile Darwin observed the results of an earthquake: the land had been lifted by several feet. In the Andes he observed fossil shells of marine organisms in rock beds at about 4,300 m. He came to agree with Lyell that over millions of years earthquakes and other geologic processes could change the geology of the land. Because the land changed, new habitats would form. Darwin realized that animals would have to adapt to these changes.
During the Beagle's five-year trip the captain often dropped Darwin off at one port and picked him up months later at another. One reason that Darwin was so eager to study life on land was that he suffered from terrible seasickness and couldn't wait to get off the Beagle. During his time on land Darwin trekked hundreds of miles through unmapped region. He observed thousands of species of organisms and collected many different types of fossils. On the long sea voyages he used his time to catalog his specimens and write his notes.
In 1837 Darwin began his first notebook on evolution. For several years Darwin filled his notebooks with facts that could be used to support the theory of evolution. He found evidence from his study of the fossil record: he observed that fossils of similar relative ages are more closely related than those of widely different relative ages. Comparing homologous structures, vestigial organs, and embryological development of living species gave him additional evidence of evolution. He consulted animal and plant breeders about changes in domestic species. He ran his own breeding experiments and also did experiments on seed dispersal.
Resources such as food, air and water cannot increase at the same rate, Malthus argued. Thus human beings are involved in an intense "struggle for existence," competing for the limited resources. This idea helped Darwin uncover the mechanism he needed.
Combining the idea of competition with his other observations, Darwin explained how evolution could occur. First, he stated that variation exists among individuals of a species. Second, he stated that scarcity of resources in a burgeoning population would lead to competition between individuals of the same species because all use the same limited resources. Such competition would lead to the death of some individuals, while others would survive. From this reasoning Darwin concluded that individuals having advantageous variations are more likely to survive and reproduce than those without the advantageous variations.
Darwin coined the term natural selection to describe the process by which organisms with favorable variations survive and reproduce at a higher rate. An inherited variation that increases an organism's chance of survival in a particular environment is called an adaptation. Over many generations, an adaptation could spread throughout the entire species. In this way, according to Darwin, evolution by natural selection would occur.
As an example Darwin noted that the ptarmigan turns white in winter. This color change, he inferred, helped protect it from predators, which would have a hard time spotting the bird in snow. Ptarmigans that didn't change color in winter would be spotted easily and eaten. In this way, Darwin implied, ptarmigans that turned white in winter would be more likely to survive, reproduce, and pass this adaptation to future generations.
However, the publication of Darwin's book The Origin of Species in 1859 changed biology forever. The first printing of the book sold out in one day. Darwin clearly and logically presented the idea that natural selection is the mechanism of evolution. In Darwin's own lifetime many scientists became convinced that evolution occurs by means of natural selection. Today this theory is the unifying one for all biology.