|| Gathering Evidence
The Scientific Process
Science provides an organized way to answer questions and find natural explanations about the world. Because of scientific research, we have a rudimentary understanding of how endocrine disrupting chemicals (EDCs) can alter hormones and other endocrine functions and affect health. Through science, we continue to learn and understand how EDCs function.
The science process, and its governing rules of the scientific method, developed from our ancient curiosity to understand ourselves, the world, and the universe. Today, the scientific method still provides a time-tested, coordinated way to gather information or evidence that supports, explains, or disproves an original prediction or hypothesis. Rarely do true or false/right or wrong answers emerge in isolation. Rarely are cause and effect proven rapidly and without periods of doubt. Rarely is the process quick or immediate. But, over time, enough evidence may be gathered to support and explain the biological or physical event in question.
Good science, though, involves more than curiosity. Researchers must use their knowledge, interest, creativity, imagination, and logic to build on past results. In their work, they are guided by, and rely upon, the scientific method, which involves:
For example, James Watson, Francis Crick, and Maurice Wilkins used the scientific method to piece together the chemical structure and double-helix shape (two spiral staircases twisted together) of DNA, or deoxyribonucleic acid. They formed their double-helix hypothesis after studying results from earlier chromosomal and x-ray diffraction studies. Years of experiments tested and confirmed the prediction, which won them the 1962 Nobel Prize for physiology and medicine and led to modern genetics.
Skepticism and Flexibility
After data are gathered and analyzed, scientists publicize new findings in journals or at meetings.
Several checks and balances ensure scientific quality. Foremost of these is skepticism. Researchers review new findings with a critical eye looking for sound conclusions based on the available evidence. Healthy suspicion is important because, like in any human endeavor, wrong conclusions can be drawn, vital information can be overlooked, or experiments can be faulty.
To ensure scientific quality, results are usually peer reviewed, or scrutinized by other experts in the field, before being published in peer-reviewed journals. Unpublished results can be presented at scientific meetings where colleagues question and criticize the study’s methods and conclusions.
Once publicized, scientists with differing views and interests debate the data at meetings, in scientific journals, and through the media. Sometimes, other scientific groups repeat the experiments to validate results.
If the research holds up to scrutiny, the scientific process is flexible enough to embrace the new conclusions and modify or change theories to more accurately represent what is now known about the subject.
It Keeps Happening
For example, the discovery of microscopic spores and eggs in the 17th century explained how maggots got into decaying flesh, putting an end to the theory of spontaneous generation (animals and plants emerge spontaneously from other matter). In the early 1970s, geologists replaced all other theories and embraced the theory of plate tectonics to explain continental drift and other geological activity. The discovery that chromosomes carry genetic information in the pattern of DNA's nucleotide subunits (made up of sugars, phosphates, and nitrogen-containing base rings) revolutionized genetics and replaced the belief that chromosomes were made from protein.
In some cases, the research doesn't hold up and ideas are abandoned. For instance, in 1989, two chemists declared they had done something nobody thought was possible: fusion at room temperature. Fusion, the union of atom nuclei, usually occurs only at very high temperatures, like those inside the sun or during an atomic explosion. Although the research received tremendous attention from scientists and the public, the claims were eventually dismissed because no one could reproduce the results.
Currently, EDCs and global climate change are under scrutiny. The scientific, political, and public debates will no doubt continue as more evidence accumulates and adds to our knowledge about their pervasiveness, causes, effects, and prevention.
It is sometimes difficult to understand how experts can disagree about what data mean. Or how one study can contradict another study's findings. But, uncertainty, differing opinions, and conflicting evidence are part of the scientific process. By letting others critique experiments, conclusions, and implications, ideas are challenged, knowledge is gained and, hopefully, a better, more accurate understanding is reached.
Evidence for Endocrine Disruption
Everything from ecosystems to molecules is studied to answer perplexing questions. One looming conundrum is endocrine disruption. How do synthetic chemicals and natural compounds interfere with hormones? How do environmental disrupters (EDs) affect the endocrine, immune, and neurological systems and with what, if any, health consequences?
To find answers, researchers gather evidence through wildlife studies, laboratory experiments (cells, tissues, and nonhuman animals), observations and anecdotal reports, and human clinical and health trend data.
Wildlife studies and laboratory animal research
No one assay can test all of these at the same time. However, many compounds are identified as estrogenic, antiestrogenic, antiandrogenic, or antithyroid based on one or more of them.
Observations and anecdotal reports
Human clinical and health trend data
The decade-long debate over declining human sperm quality is a case in point. A 1992 study evaluating human sperm quality used 40 years of data gathered from clinics around the world. Researchers found a statistically significant trend towards lower sperm quality (lower volume, numbers and motility) that could be linked to environmental estrogens (Carlsen et al. 1992; Sharpe and Skakkenbaek 1993). In response, other scientists published contrary clinical data studies directly challenging the idea that declining sperm quality is pervasive in the modern world (Safe 1995). Further studies definitely confirmed significant declines in human sperm quality in Europe and North America but not in other world regions (Swan et al. 1997, 2000, 2003a). International efforts to track human sperm quality and to investigate potential causes of significant declines revealed that environmental exposure to some chemicals is strongly associated with low sperm quality (Duty et al. 2003; Hauser et al. 2003; Swan et al. 2003b).
The EDC Controversy
Scientific evidence is not always straightforward and certain, especially with complex biological systems. That's why skepticism and flexibility are built into the scientific process. Once data are published, other scientists review the findings and agree with or challenge the author's conclusions. The review process leads to scientific and public debates that help to shape our understanding of science and interpret, apply, and use scientific results.
The issue of EDCs is no exception. Its complexities lend itself to controversy. Debates center around which chemicals, in what combinations, at what doses, and exposed at what ages may cause what health problems. Can the risks be estimated and contained?
Some believe that research studies prove there are real and dangerous health effects for wildlife and humans. Others admit there may be health effects but think the results are only applicable to wildlife, and even then, only where high doses exist. They also acknowledge the need for further scientific verification. Still others believe the results are sketchy, mainly correlative, and without substance.
Less overt, long-term health threats - like those posed by EDCs - are modifying the way we define toxicity and determine public health risk. Finding answers to increasingly complicated and interrelated problems with environmental, health, economic, and political consequences is no easy matter. In response, regulatory agencies, industry, and universities are devoting time, money, and research to learn how and to what degree EDCs affect wildlife and human health.
In addition, ongoing research efforts to better understand long-term health effects continues to:
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