Resistance to new ideas seems to be an enduring human characteristic, and scientists —despite extolling the virtues of objectivity— have often proved themselves very human in this respect. Many of the great breakthroughs of modern science were initially rejected or ignored, sometimes for decades, and mainly because of bias. It is instructive to consider a few examples of scientific advances that were originally rejected.

The Atom. In the late 1800s, when Ludwig Boltzmann, the great Austrian physicist, proposed that all matter was comprised of atoms and molecules, the suggestion seemed entirely strange to most of his contemporaries. Although the concept of the atom was familiar in Western science, it was not taken seriously at that time. Boltzmann more or less stumbled on the probability of atoms as the basis of matter when he developed a theory of gases. But he had no way to actually prove that atoms existed.

Many prominent scientists of the time, especially Ernst Mach, scoffed at the idea of an unimaginably small and invisible structure as the basis of matter. The proof emerged in 1906, when Albert Einstein noticed the movement of pollen grains in still water. He was able to explain that this movement, called "Brownian motion" for the botanist who originally noticed the phenomenon, was due to the activity of atoms in the water. Einstein's proof vindicated Boltzmann a year after Boltzmann's death. Unfortunately, Boltzmann did not witness the rapid acceptance of the atom after 1906 and its role in the development of modern physics.

The Big Bang. Today the instantaneous emergence of the cosmos from a singularity known as the Big Bang is the preferred theory of the origin of the universe. But when this concept evolved as an explanation for Edwin Hubble's discovery that the galaxies were moving rapidly away from each other, the Big Bang seemed unscientific, almost religious. This was in the 1920s when the orthodox view, held by most astronomers and physicists, was that the universe had existed in a "steady state" forever; there was no beginning.

The notion of the universe springing from nothing was immediately ridiculed by leading astronomers including Fred Hoyle, who originated the term "big bang" as a pejorative. Hoyle followed up with a very public radio tirade against the theory. Other physicists, including Einstein, opposed the Big Bang, even when their equations implied an abrupt beginning of the universe. It became the theory of choice only gradually, and only because no other explanation could explain the cosmos that scientists were beginning to study in the 1920s and 1930s. Today, other theories of the universe's origin exist, but have not gained widespread support. Advanced methods and technology are expected to confirm or reject the Big Bang theory in the near future.

Exoplanets. Now that hundreds of planets have been discovered beyond the Milky Way, it is difficult to imagine why the possibility of such solar systems elsewhere in the universe was originally controversial. But in the conventional astronomy of the late 1980s, the idea of exoplanets was close to science fiction. When two unknown astrophysicists, Geoffrey W. Marcy (UC-Berkeley) and R. Paul Butler (Carnegie Institution for Science) decided to look for exoplanets, they were warned that their careers would be destroyed. The scorn from their contemporaries was coupled with the technical challenge of locating planets beyond our own solar system. It took Marcy and Butler almost ten years to locate their first exoplanet orbiting a distant star. After that, progress was rapid; Marcy and Butler discovered more than 100 planets in the next decade and other scientists added more to the count. Today there are hundreds of known exoplanets. Marcy and Butler initiated a whole new, and now respectable, field of astrophysics.

Evolution. In biology, the best known example of initial rejection is Darwin's theory of evolution. Because the theory was introduced in the mid-1800s when the Biblical view of creation still reigned, Darwin anticipated the hostility his theory (and that of Alfred Russell Wallace) would inevitably draw. The antagonism was not confined to the general public. Very prominent scientists attacked Darwin's theory and rejected the evidence he so carefully assembled. Even now when evolution is an established fact, there is still resistance among religious conservatives.

Symbiogenesis. The opposition to the theory of evolution might be considered understandable in the context of the mid-1800s. But resistance among scientists to the theory of cell evolution known as symbiogenesis is more difficult to explain.

Lynn Margulis, the distinguished biologist who formulated this modern theory of cell evolution, had to endure years of antagonistic rejection from her peers before the evidence simply forced the scientific establishment to accept her view.

Symbiogenesis is the process by which different types of microbes combine to form a single cell. Each participating microbe in such a union retains its own DNA while contributing a specific function. The net result is a much more sophisticated cell that performs as a community. In animal cells, the most significant partner is the mitochondria, which performs the crucial function of cell metabolism. In plant cells the symbiont partner is the chloroplast, which takes care of the photosynthesis function.

Early versions of symbiogenesis were worked out in the late 1800s and early 1900s, and especially by Konstantin Mereschovsky in Russia. From the 1960s onward, Lynn Margulis expanded significantly on the theory, and with modern tools of microbiology she was able to develop evidence that would have been inaccessible to her progenitors.

A key point of symbiogenesis theory is that many evolutionary developments are due not to single adaptive mutations but to more sudden restructuring of cells that are able to capture and exploit other cells. These unions, according to the theory, result in evolutionary changes that are much faster and more advanced than the standard —and much slower—adaptations associated with traditional evolutionary theory. Today, after many years, symbiogenesis is no longer controversial.

An Ancient Earth. The theory of Earth's development and age was the result of astute observations by a small number of people. Indications that the planet was much, much older were evident well before geology became a science. The discovery of layers of rock and layers that strongly suggested ancient processes, plus the discovery of many fossils in those layers contradicted the Biblical age of the Earth of some 4000 years.

As early as the 1700s a Swiss, Horace-Benedict de Saussure, examined formations in the Alps that contradicted the widely held Biblical account of Earth's origin and age. In the 1800s James Hutton in Scotland and William Smith in England analyzed rock types and formations and the fossil distribution in rock layers. Both men methodically recorded the evidence that would shatter the mythical view of Earth's history.

The geological evidence for an ancient Earth accumulated around the time of the natural science investigations of Charles Darwin, Russell Wallace and others who would establish a scientific account of the evolution of Earth and its life forms. Resistance to both the geological and evolutionary facts was predictable. In the Biblical view, Earth and its life forms were created in a week. The creation myth disallowed the species extinctions that the fossil record clearly indicated. Only gradually was the geological antiquity of the Earth accepted. As the technical ability to estimate the age of rocks and strata improved, the true age, some 4.6 billion years, was determined.

Continental Drift. The explanation for the distribution of the continents was formulated in 1912 by Richard Wegener, a German meteorologist and explorer, in 1912. The idea, backed up with substantial evidence, was met with opposition for almost 50 years.

Wegener's careful analysis included the observation that the continents resembled a jigsaw puzzle that suggested they had split over time from a single landmass. In addition, he listed unique geological similarities between areas of different continents that suggested those areas were once joined. Further, there were similar flora and fauna (including fossils) in South America and Africa, for example, indicative of a common origin in an ancient setting. These similarities had been noted also by early scientists in the 1700s and 1800s.

Because of his training in meteorology and physics, Wegener was able to construct a very good theory to explain what he called "continental drift" —the breakup of an original single landmass and the slow drift over eons of what became the modern continents. However, it was not until after World War II that scientists were able to investigate the deep ocean. For that reason, Wegener could not determine the underlying structure of the oceans that would allow them to float. The cause of both the breakup of the continents and the force that moved them was not established until the 1960s, when an understanding of tectonic plates developed. It took from 1912 until the 1960s for Wegener's idea to gain credibility.

Prions. When Stanley Prusiner was awarded the 1997 Nobel Prize for Medicine/Physiology for his discovery of the prion, the event was a great personal triumph. For years before the award Prusiner worked to understand the cause a strange brain wasting disease. In animals the condition was known as scrapie or "mad cow" disease, and the human version was called Crutzfeld-Jakob disease. Initially Prusiner and others thought the source was a virus and they made elaborate attempts to locate it. However, over time —and much to his surprise— Prusiner discovered that the disease agent lacked the nucleic acid that was a component of any virus. He realized that the brain wasting disease was caused by what he called an "infectious protein." This was a completely alien concept and the medical research community disparaged Prusiner's research. It took years to prove beyond doubt the link between the prion and the brain wasting diseases, but in the end Prusiner was triumphant.

In our time resistance to new scientific facts is still quite common, despite the effort of most scientists to be objective. Examples include the denial of the hazards of tobacco, DDT, endocrine disrupters many other toxins. There were widespread denials about ozone depletion before the problem was too obvious to ignore, and there is still denial of climate change, although not among scientists. In all of these cases, part of the denial has been shaped by disinformation campaigns on the part of vested interests. But as the public becomes better informed this situation is likely to change.

Where new ideas in science are largely theoretical, caution is understandable. Current examples include string theory and multiple universes, both of which are exciting but still unprovable. But while experts in physics and cosmology are far from agreement on such theories, the advocates have not suffered greatly. Other new ideas that do not fit the prevailing mindset, especially in the fields of medicine and environment, may still struggle for recognition.