Evolution is a change in type over time.
It connects back to that human compulsion to label and categorize
things, combined with our knowledge that the world of the past was
different than today's world. All sorts of things can
evolve, so this may be the feature of Life found most often in
things that are not alive.
Of course, for a long time it wasn't known that
Nature had ever been any different than it is today - people
accepted historical changes in cultures and societies, but their histories
didn't extend very far into the past. At the birth of modern western
science during the Renaissance, it was still widely accepted that
the Earth was only a few thousand years old, and the Nature they saw was
how things always had been. Fossils were known, but were
interpreted as representing still-living creatures currently "beyond the
map" of the known world. However,
eventually, as the map was extended and the creatures not found, a
systematic approach was taken to studying those fossils, and it was
quickly found that the deeper (and older) a layer one looked at,
the less like modern forms the fossilized animals were (fossil study is
more focused on animals because animal
hard parts fossilize much better than plants, and are much more common). In very old layers,
there were types that seemed almost totally unlike anything
existing today, such as the dinosaurs. In newer layers,
there seemed a progression of types that became more and more
similar to things living today. Attempts to explain fossils
away as some sort of bizarre rock formations found some
acceptance, and worked all right for separate bones, but it became
impossible to explain toothy skulls and near-complete skeletons that way.
Fossils and ideas from the ancients.
article connecting fossils and the monsters of mythology.
Fossils have long been used as "medical" treatments.
Most fossil beds contain the remnants of
creatures from the sea floor, since most fossil layers are sedimentary
rock that at one time was sediment in a body of water.
One of the first men to study such formations,
Lyell, became one of the most powerful influences ever on both
geology and biology. He decided that the
production of fossil beds and the nature of the fossils themselves
suggested a long, continuous process in a world not very different
from what we see around us today (this idea, which didn't originate with Lyell
but was not widely-accepted before his publications of the
1830s, is called uniformitarianism); he
rejected the idea of abrupt changes (and so rejected those who
connected hundreds of meters of sedimentary rock to deposits of
the Biblical flood), or the idea that the ancient world was significantly different
than today. He was also one of the first widely-accepted voices
to reject a Young Earth, as there was too much sediment
accumulation shown in the rocks (even without compression) to have been done in a few thousand years. His
calculations for the actual age of the Earth increased throughout
his life as more information came in - by his death, he felt that
the earth was several hundred million years old, and it is now
thought that the Earth is 4 to 5 billion years old.
A brief biography of Lyell, including how he influenced early
More about the layers.
How layers in different locations are "matched up."
The order of great eras of the past.
Two concepts arose that challenged the Word of
the Bible and were considered blasphemous in those times. The first we
might hardly recognize as controversial: extinction.
Fundamentalist reading of Scripture declared the Bible to be totally
incompatible with the idea that one of God's creations could
simply die out, although that idea has since largely been universally accepted. Some Biblical scholars
suggested that Man's world is not the first Creation, and fossils are
remnants of an earlier version, but this way of reading the text never
The second concept is evolution,
the idea that types of living things change over time, that modern
forms are significantly different from their distant ancestors,
and that ongoing influences produce continuing
change. This idea is not totally incompatible with religious
ideas, and in fact is accepted widely by people whose religious
texts might seem to say otherwise, but there are many who choose to
resist the idea. Evolution, many have decided, represents a sort of
"progressive Creation" which is all still part of God's
Plan for the world. Evolution is an actual feature of
reality - it's not reasonable to think that things have not changed
over time. When people talk about "believing in evolution," they
are really discussing the various concepts that explain how evolution
happens. It makes no more sense to talk about believing in
evolution than it would to discuss believing in gravity.
In discussions about evolution, it seems to
be that the underlying assumption that human beings have evolved
from non-human ancestors produces the biggest "sticking
point." This is understandable. Humans are strongly
invested in the idea that they are somehow special and exist apart
from the rest of the living world, and most evolutionary concepts
challenge that assumption. However, it should not be assumed
that biologists are mostly atheists, as they are not. As
humans are expert at, they usually adjust their religious concepts
to fit with the realities of their particular worlds.
timeline of controversiol evolution ideas.
A good recounting of resistance to "2 creations" in Genesis.
A transcript of an interview with a Christian biologist.
paper on the stepwise evolution of the bacterial flagellum, often
presented by Intelligent Design advocates as a system that could not have
evolved in useful stages, but must have appeared fully-formed.
Once the idea of evolution gained some momentum,
the question of how such a process works became very
important. Many prominent naturalists came up with various
explanations, but only a few are still widely remembered.
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck is
known to history as a Man With a Silly Idea, which is
unfair. Strangely enough, during his life his ideas were largely ignored by
his peers, but became influential long after his 1829
death. Two concepts that are associated with Lamarck,
neither of which turned out to be true, are:
Evolution by Inheritance of Acquired
Characteristics. Lamarck grasped that inherited changes,
influenced by the environment, were important to evolution, and he
wasn't wrong. His mistake was in believing that changes in
features developed during a lifetime (say, weightlifting to make
yourself more muscular) could be passed to offspring (the children
would themselves be born more muscular). He thought that an
organism's active adaptations to their environment could be passed
on. But would you be surprised if a world-class
bodybuilder's children were more muscular than most kids?
What we now accept, that something about that bodybuilder's genes
gave them the potential to train and to be more muscular than most, could be passed on, was
unknown in Lamarck's time, and what seemed logical then no longer
seems so now. What should also be noted is that Lamarck seemed on
the same track that Darwin wound up on in explaining evolution: how
traits that were well-adapted to the environment would be passed on and produce longterm
changes. He just was wrong about how traits got passed on.
Evolution = Improvement. A
typical philosophical approach for scientists of the 1800's was to
hypothesize as a way to investigate and describe the Perfection of
God's Creation. Part of the idea is that Modern Man, and the
world he lives in, is the culmination of that plan, and so all
evolution is a pathway, onward and upward, to that goal.
This idea, that evolution is a process of betterment working
toward some goal of perfection, still has a strong influence on
how people, even biologists, see evolution, although the
widely-accepted idea is that evolution is a
generation-to-generation adaptation to current conditions, which
change randomly and over time produce circumstantial evolutionary pathways.
A webpage about Lamarck.
What Lamarck believed.
Lamark's ideas of "use or disuse."
Basic differences between Lamarck and Darwin.
And more, including the "drive toward perfection."
Malthus. In the early 1800s, Malthus developed
his ideas about how conditions affect populations. He talked
about the Natural world, where the rate at which a population could
increase was exponential while resources remained about the same;
populations would therefore be limited by disease, famine, and
conflict, but there was a
warning embedded about growing human
populations as well (and maybe suggestions on how to use the principles to limit the numbers in the
immigrants and lower classes). These ideas were huge influences on the
evolutionary theories of both Lamarck and Darwin, who both talked
about environmental influences on groups as a basis for evolution.
Biography of Malthus.
A description of Malthus' essay.
Underlying issues of Malthus
The underlying concept for
modern evolutionary theories is the Theory of Evolution by Natural Selection.
developed originally by Charles Darwin and Alfred Russel Wallace, first
published in 1858, and has seen many adjustments and additions
by many people since. Generally, "disagreement" in
scientific circles with this theory involves a dispute about how
much Natural Selection influences evolution compared to other
factors, not whether the basic ideas are accurate.
Product of a fairly well-to-do but largely dysfunctional family,
Darwin resisted his father's ideas of what sort of career he should
have, and in 1831 took a position on the merchant ship HMS Beagle,
more or less to give the Captain someone of the same "station" for
company (the social isolation of captains over long voyages had become
quite a problem). Darwin also took on the duties of the Ship's
Naturalist, and went on a voyage around the world, with notable stops
along the coast and islands of South America. Because of
horrendous seasickness (and possibly personality clashes with the
Captain), Darwin spent as much time as possible ashore, collecting
samples and taking notes and making observations. One thing he
noticed was that the character of the animals and plants on islands
resembled those of other islands nearby and the mainland, dependent upon
how close together they were and how much the physical nature of the
environments differed. The strangest collections of creatures by
far were found by Darwin on the Galapagos Islands, a collection
of arid islands some 1000 kilometers (600 miles) from the equatorial
jungles of South America. The limited types of animals there had
obvious relatives on the mainland, but were different species
particularly suited to the different lives available on the islands.
Assuming that their ancestors were groups of mainland animals unlucky
enough to wind up there, how did they evolve into these different
species? During his travels, Darwin began to develop his
explanation for just such processes, which he came to call Evolution
by Natural Selection.
A biography of Darwin.
Dramatization of the Beagle voyage. (Video,
A map of the voyage, including inland excursions.
Darwin in the Galapagos Islands.
Darwin's Galapagos field notes.
What is Evolution by Natural
Sometimes nicknamed "Survival of the Fittest," it would
be more appropriate to call it "Reproduction by the
Fittest." Simply put, in any given group of organisms, there will be some variety
of features that directly affect how good a chance each individual
has of living to reproductive age and then successfully
reproducing - as a general trend, each generation of offspring
will, more and more, reflect features that are advantageous to
their environment. Fitness actually means how well something "fits." The important detail here is that environments
change over time - and what was a good feature in one time and/or
place may not be elsewhere / elsewhen - and these changes in environment (the
"Nature" part of Natural Selection) influence (the
"Selection" part) which individuals reproduce and what
features preferentially wind up in the offspring. Over time,
depending on an organism's suitability to the new environment, new
features and combinations of features (called adaptations,
a confusing term that does not always mean the same thing even to
biologists) may spread through the population as a whole until the
basic "type," or species has changed
significantly from the "type" of its ancestors that it
needs to be relabeled. Adaptive radiation was the
term applied to the "branching" of a family lineage in several directions,
simultaneous divergent evolution that produces many species
from a single ancestral population. Mechanisms for this will be
covered in a later chapter that also deals with the Modern Synthesis
that integrated discoveries about genetics into
evolutionary concepts. One major contribution there was the
possibility of mutations to produce rapid changes in
features or abilities, and the idea of genetic drift to
explain how different populations separated into very similar niches and
ecosystems can, over time, still become distinct species.
Darwin was strongly influenced by some knowledge
of animal husbandry - he knew that breeds of domestic animals
could be changed over time by selecting which individuals breed, a
process that has come to be called artificial selection. In Natural Selection, the "picking" of the
breeders is dependent on which individuals can survive and succeed
under the natural conditions they were born into.
Evolution is not an "ever
upward movement toward perfection," as Lamarck and many of
his time believed; species dont get better at anything
other than fitting the environment of the day, which could change
at any time. There is no target, no progress, no ultimate
peak at humans, and not everything
evolves at the same rate, partly because the rate depends both on how fast
the environment changes, which varies considerably from place to place (and
even pieces within environments, microenvironments, vary), and
on the rate of reproductive "turnover" that can give short-lived
organisms much faster potential change rates than long-lived ones.
More on natural selection.
A lecture about natural selection (video).
A simple natural selection game.
Observed evolution in Galapagos finches.
Evolution and environmental change - seen.
Modern observations in the field –
Artificial selection in dogs (Video).
When Darwin returned to England, he settled into
a role as a naturalist and went about writing up his theories,
although he seemed in no hurry to actually publish them. He
made his reputation as an expert on smaller topics, such as
earthworms, and certainly seemed comfortable discussing his ideas
with other naturalists. Perhaps he knew what sort of reaction
a widespread distribution of his theory would get from the general
Then, along came
Russel Wallace, whose travels through South America
(where virtually his entire specimen collection was destroyed in a shipwreck)
and Indonesia (perhaps the world's largest collection of islands,
presenting huge numbers of separate- but- somewhat- connected
environments) led him to essentially the same ideas that Darwin
had come up with. In the late 1850's, Wallace wrote an
article based upon his ideas and sent it off to England, where it
was brought to Darwin's attention (some account have him sending
it through Darwin, but that seems unlikely). Once published,
the concepts would from then on have been linked only to Wallace; Darwin
arranged it so that when
Wallace's paper was made public, it was accompanied by a similar
one by Darwin. They brought out the same idea
In the years that followed, Charles Darwin
became much more associated with Evolution by Natural Selection
than Wallace. There are many reasons for this: Darwin
was in England, where he was well-known in certain circles, while
Wallace, who would not return from Indonesia for a few years, was
less well-known or respected. Also, Darwin's ideas were soon
presented in a book,
On the Origin of Species, which was
widely-read and discussed and became the particular reference source on the
Speciation, the development of a new species, was met with
opposition. Changes within a "type" was acceptable, but not to
the extent that the type changed into a new one. The lack of
logic seems inescapable now, but the immutability of species
was a concept that was hard to shake.
A list of Darwin's publications - he kept busy...
Possible explanations for the delay in publication.
A page devoted to Alfred Russel Wallace.
More on Wallace and his influence on the publication.
On the Origin of Species completely available online.
Darwin also developed a theory of
Evolution by Sexual Selection to explain traits that
had obvious advantages in the competition for mates but which
might actually be disadvantages from a survival standpoint, traits such
as a peacock's tail. This was not difficult to integrate
into his ideas, since it is actually mating success that
ultimately decides which traits get passed on and affect the
nature of descendants. Evolution may be a balance between
what helps you survive long enough to reproduce and what helps you
actually accomplish the reproduction. And, in an example of an established
term broadening into a confusing area, "sexual selection" can be applied to
any feature that aids reproduction success - it should even apply to asexual reproducers,
which makes it quite the confusing term. Keep in mind that the process
of asexual reproduction was not really understood when the term was coined.
Lecture on classic sexual selection theory (video).
Misconceptions about evolution.
Not surprisingly, Darwin's ideas were
controversial and remain so to this day. What also shouldn't
be surprising is that, although the idea of natural selection has
great explanatory power for evolution, there are parts that Darwin
couldn't explain because no one knew how certain processes
work. Like any great, descriptive theory, the years since
its release have seen a long procession of tinkerers that have
adjusted it here and there. As we continue through the
history of biology, we will investigate the impact of later
One side-note to the theory:
the French translation of On the Origin of Species tended to include
"interpretations," including a subtitle, that suggested that the whole idea
confirmed Lamarck's ideas. Even the word "selection" was replaced with
the word "election," implying more purpose and plan. That version was
used widely in Europe; its difficult to assess how that affected
later developments there.
New research suggests that some acquired characteristics
might be heritable.