Large-scale Human Intervention Research Articles

Analysis and Quantification of the Distribution of Marabou (Dichrostachys cinerea (L.) Wight & Arn.) in Valle de los Ingenios, Cuba: A Remote Sensing Approach

Cuba is struggling with a growing environmental problem: the uncontrolled spread of the allochthonous weed species marabou (Dichrostachys cinerea) throughout the country. Over the last 70 years, marabou has become a formidable invasive species that poses a threat to Cuban biodiversity and agricultural productivity. In this paper, we present a free and affordable method for regularly mapping the spatial distribution of the marabou based on the Google Earth Engine platform and ecological surveys. To test its accuracy, we develop an 18-year remote sensing analysis (2000–2018) of marabou dynamics using the Valle de los Ingenios, a Cuban UNESCO World Heritage Site, as an experimental model. Our spatial analysis reveals clear patterns of marabou distribution and highlights areas of concentrated growth. Temporal trends illustrate the aggressive nature of the species, identifying periods of expansion and decline. In addition, our system is able to detect specific, large-scale human interventions against the marabou plague in the area. The results highlight the urgent need for remedial strategies to maintain the fragile ecological balance in the region.

Morphological Response of a Highly Engineered Estuary to Altering Channel Depth and Restoring Wetlands

Estuaries are continuously adapting to anthropogenic pressure. Because of sea-level rise and reduced fluvial sediment supply, they are at risk of sediment starvation. Contrarily, some estuaries require frequent dredging after artificially deepening the channel to maintain port operations. To optimize current estuarine functions and make estuaries more resilient to future threats, improved understanding of estuarine development after system changes is essential. This paper investigates the estuarine response related to two large-scale human interventions: (1) altering channel depth, following global trends of channel deepening for port navigability; and (2) creating or restoring wetlands, a nature-based solution increasingly explored for its ecosystem services. A schematized 2D-morphological model is set up using Delft3D-FM reflecting a highly engineered estuary in a micro-tidal and wave-dominant environment. Results demonstrate how channel deepening (from 13 m to 17 m, without wetland presence) increased sedimentation in the channel by +31%. Sedimentation rates in the wetland were mostly unaffected by channel depth. After restoring the wetland area (wetland width from 0 km to 1 km, constant channel depth of 15 m), sedimentation within the channel was reduced by −72%. The wetland area not only served as sediment sink, but also increased the tidal flow, diminishing sedimentation throughout the estuarine channel. Further analysis showed that restoring wetland areas along a specific segment mostly affected channel sedimentation locally (i.e., at the channel segment along the restored wetland). As such, to alleviate dredging operations at critical locations in the navigation channel, strategic restoration of wetlands can be considered which can provide a sustainable alternative to dredging within highly engineered estuaries.

Large-scale stresses, decay of River Jamuna and resilience strategies in the Anthropocene

In the recent decades, many worlds' large rivers have been exceptionally modified by human interference. The principal objective of this study is to investigate the causes and consequences of decay of river Jamuna (distributary of river Bhagirathi-Hooghly). The entire investigation was conducted by the data of historical maps like Rennel's map of Bengal, Hunter's map, digital version of US army map, landsat satellite imageries (1980-MSS, 1990-TM, 2000-TM, 2010-ETM+ and 2020-OLI) and fluvio-hydrological study. Maximum likelihood classification algorithm was used to delineate the land use and land cover classes and Kappa based accuracy assessment indices were also used for the validation. There is no scientific work on this historically important river and afterward, millions of people are also underprivileged from this river ecosystem services due to severe degeneration. In this milieu, it is a genuine research gap. Novelty of the work is exposed the authentic causes of river decay and anthropogenic stressors. Result showed that the average width of river Jamuna has been significantly decreased whereas maximum average width of the channel was recorded in the year 1956 (319.81 m) and the present channel is flowing comparatively within narrow path (69.27 m). Rate of siltation (average rate of siltation 0.23 m/year) on channel bed has been increased due to impacts of channelization. Channel bed, natural levee and proximity floodplain have been encroached by large scale human intervention. LULC patterns showed that the urban built-up area is rapidly amplified from 2000 (22.26%) to 2020 (31.50%) whereas, agricultural and swampy land turned into built up area. Off-take of Jamuna is completely detached from the parent river Bhagirathi-Hooghly in the early 1956 and gradual anthropogenic interferences within river corridor accelerate river decaying processes. River restoration is highly required for sustainable river ecosystem health management and environmental development. Some management strategies have been recommended such as reconnecting of river Jamuna with Bhagirathi-Hooghly, dredging, decommissioning of culvert and sluice gate, cleaning of fishing pool and water hyacinth and sustainable land-use planning.

Municipal Solid Waste Management on In-depth Analysis for a Hilly area District of India

Everyone on earth faces a serious threat from municipal solid waste (MSW), but it is especially hazardous in developing countries like India where urbanization and industrial expansion are rising swiftly. Urbanization is expanding quickly and the population is gradually increasing in Almora city located in Uttarakhand. The city provides sites for a range of administrative, educational, economic, tourism, health, and recreational pursuits. In the study area, solid waste collection and management services are mostly provided by municipal organizations. Despite being a crucial service, it does not get the attention that the city’s fast growth requires. Solid waste management (SWM) and collection services are generally inadequate and lacking in this area. This situation has caused a number of problems for the urban environment and public health. Large-scale human interventions in the natural environment are the principal source of ecological and sustainability risks in the urban municipal region. Black carbon is produced during the incineration of MSW, and harmful toxins like sulfur dioxide, mercury, and carbon dioxide are also released. Particulate matter is also added to the urban environment. These elements are posing problems for people, wildlife, and vegetative plants. It is the goal of this research to identify the problems with the MSW repository, handling, and dumpsites in the chosen region so that we may work toward fixing them

Flood susceptibility zonation using advanced ensemble machine learning models within Himalayan foreland basin

Floods are considered as one of nature's most destructive fluvio-hydrological extremes because of the massive damage to agricultural land, roads and buildings and human fatalities. Rapid development of unplanned infrastructural conveniences and unplanned anthropogenic activities, the frequency and intensity of floods have been accelerated in recent years. Therefore, flood susceptibility analysis is considered as an important flood management approach. Identification of flood susceptibility areas has been performed by applying advanced machine learning (ML) algorithms (random forest (RF), support vector machine (SVM) and extreme gradient boosting (XGBoost)) at the lower part of Raidak river basin. The flood susceptibility maps have been generated based on 14 different flood conditioning factors. Models are evaluated in a conventional way using ROC (receiver operating characteristics) curve. The AUC value of ROC is above 0.80 for all models and XGBoost depicts the highest efficacy (AUC ​= ​0.92). Friedman test and Wilcoxon Signed rank test have been used to measure the statistical variances among the applied models. Models proficiently show that the upper part of Raidak river basin is a less flood probable region whereas the eastern and some middle parts have high flood probability. Around 27% area (285.39 sq.km) within the river basin is highly flood prone (based on XGBoost model) due to the fast changing dynamic landscape and large scale human intervention. The important outcomes of this research will definitely assist the local administrators to take proper sustainable management plans for the reduction of future damages.

Multidecadal Analysis of an Engineered River System Reveals Challenges for Model-Based Design of Human Interventions

Hydraulic models were used in practice to predict the effect of human intervention during extreme conditions. However, the accuracy of such predictions remains untested. In this study, we compare a simulated trend in water levels covering a twenty-year period of large-scale human intervention with a thirty-year observational record. The results show that the observed water levels display a linearly decreasing trend attributed to channel bed erosion. A deviation from this trend, which would be an indication of the effect of human intervention, was not observed. We propose that the most likely explanation for this is that any effect observable at lower discharge is hidden in the uncertainty of the rating curve. Given the inherent uncertainties associated with making predictions about a changing system for conditions with a low period of return, we argue that model uncertainty should be considered in intervention design.

Efficient Modeling of Complex Sandy Coastal Evolution at Monthly to Century Time Scales

With large-scale human interventions and climate change unfolding as they are now, coastal changes at decadal timescales are not limited to incremental modifications of systems that are fixed in their general geometry, but often show significant changes in layout that may be catastrophic for populations living in previously safe areas. This poses severe challenges that are difficult to meet for existing models. A new free-form coastline model, ShorelineS, is presented that is able to describe large coastal transformations based on relatively simple principles of (1) alongshore transport gradient driven changes as a result of coastline curvature and (2) spit formation at high-angle wave incidence. An arbitrary number of coast sections is supported, which can be open or closed and can interact with each other through relatively straightforward merging and splitting mechanisms. Rocky parts or structures may block wave energy and/or longshore sediment transport. These features allow for a rich behavior including shoreline undulations and formation of spits, migrating islands, merging of coastal shapes, salients and tombolos. The main formulations of the (open-source) model are presented. Test cases show the capabilities of the flexible, vector-based model approach, while field validation cases for a large-scale sand nourishment (the Sand Engine; 21 million m3) and an accreting groyne scheme at Al-Gamil (Egypt) show the model’s capability of computing realistic rates of coastline change as well as a good representation of the shoreline shape for real situations.

Recent adjustments of pool-riffle distribution along the channels in the Pearl River Delta, China

The adjustments of pool-riffle distribution along the deltaic channels in the Pearl River Delta (PRD) under the combined effects of human interventions and natural evolution are examined in the three periods, namely 1952–1977 period, 1977–1999 period, and 1999–2014 period, corresponding to the different dominant factors. The residual depths along the channel thalweg and their spatial autocorrelation are introduced to quantify the pool-riffle distribution. The results show that the average pool depths of the deltaic channels increased significantly and the percentages of longitudinal length occupied by riffles decreased significantly by large-scale sand excavation during the 1977–1999 period and by sediment input decrease during the 1999–2014 period. It is highlighted sand excavation has a greater impact on the pool-riffle distribution of the North River channel and sediment input decrease has a greater impact on the pool-riffle distribution of the West River channel. The changes in spatial autocorrelation of pool-riffle sequence reveal a dramatic decrease of the average pool spacing after sand excavation, reflecting a rearrangement in the pattern of pool-riffle sequence. Moreover, the rearrangement process of the North River channel is ahead of that of the West River channel. In addition, the inhomogeneity indexes of deltaic channels are decreasing during the study period, indicating a deterioration of aquatic habitats diversity. It is anticipated that these results are useful for river management and utilization in the PRD and other river deltas worldwide that are subject to large-scale human interventions.

Quantifying human error probability in independent protection layers for a batch reactor system using dynamic simulations

The batch processing facilities with features involving in large-scale human intervention are generally considered to be relatively hazardous processes due to frequent change in operating conditions. Therefore, sufficient protection layers should be implemented against the hazards inherent in the batch processing facilities, especially for batch reactor systems. The human operations involved in the batch process play an important role to maintain process production and also take responsibility for reducing risks in specific possible accident scenarios. However, in practice, a number of companies initially did not take any credits for human actions in Layer of Protection Analysis (LOPA) or were overly optimistic in a few cases, which result in unwarranted safety expenditures or inadequate risk reductions. In this study, we propose a simulation-oriented methodology for quantifying human error probability (HEP) in independent protection layers (IPLs). The methodology integrates dynamic simulations with human reliability analysis (HRA) to give a comprehensive analysis of human actions. Case study for a batch reactor system shows that risk reductions of human response are expected to be greater than that determined using other methods. The present study provides a solution for analyzing the risk reductions of human elements within the IPL and serves as a reference for improving the emergency response for operators.

Co-carcinogenic effects of vitamin E in prostate

A large number of basic researches and observational studies suggested the cancer preventive activity of vitamin E, but large-scale human intervention trials have yielded disappointing results and actually showed a higher incidence of prostate cancer although the mechanisms underlying the increased risk remain largely unknown. Here we show through in vitro and in vivo studies that vitamin E produces a marked inductive effect on carcinogen-bioactivating enzymes and a pro-oxidant status promoting both DNA damage and cell transformation frequency. First, we found that vitamin E in the human prostate epithelial RWPE-1 cell line has the remarkable ability to upregulate the expression of various phase-I activating cytochrome P450 (CYP) enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), giving rise to supraphysiological levels of reactive oxygen species. Furthermore, our rat model confirmed that vitamin E in the prostate has a powerful booster effect on CYP enzymes associated with the generation of oxidative stress, thereby favoring lipid-derived electrophile spread that covalently modifies proteins. We show that vitamin E not only causes DNA damage but also promotes cell transformation frequency induced by the PAH-prototype benzo[a]pyrene. Our findings might explain why dietary supplementation with vitamin E increases the prostate cancer risk among healthy men.

Quantifying the impacts of human interventions on relative mean sea level change in the Pearl River Delta, China

Due to the impact of both natural and human-induced changes, the hydrological regimes of many river deltas worldwide have been experienced either gradual or abrupt shifts. However, little work has explored the relative impacts of natural and human-induced changes on the natural balance of these delta systems. This study explores the overall influences of intensive human interventions (e.g., dam constructions, sand excavations, and land reclamations) on the relative mean sea level (RMSL) changes in the Pearl River Delta (PRD) in China. The analysis uses long-term measurements based on monthly averaged RMSL in 26 stations and reproduces the RMSL that would have occurred in the absence of large-scale human interventions by means of a simple bivariate linear regression model. Generally, we observe that the RMSL dynamics can be categorized into three distinct types, descending, ascending and fluctuant, according to the Mann-Kendall trend test. The analysis shows that the RMSL in the upper and central parts of the PRD displays a significant descending tendency owing to the deepening of the channels, which is primarily attributed to large-scale sand excavation. In contrast, for stations near the outlets, we observed an ascending tendency in RMSL that can be attributed to the combined effects of both the rise in global sea level and channel extension due to large-scale land reclamations. The regression model confirms that the human interventions have greater impacts in the upper and central parts of the PRD that feature river-dominated dynamics, compared with the lower parts of the PRD that are characterized by tide-dominated dynamics. In addition, the simulated results display a marked seasonal alteration in the RMSL: the alteration induced by human interventions is apparently greater during the flood season than it is during the dry season. The proposed method used here to quantify the impacts of both natural and human-induced interventions on the RMSL is particularly useful for setting scientific guidelines for water managements (e.g., flood control and salt intrusion prevention) and regulation projects (e.g., dam constructions and land reclamations) in river deltas.

Analysis of willingness for relocation of the local communities living in the Critical Tiger Habitat of the Sariska Tiger Reserve, India

ABSTRACTMany Indian Protected Areas (PAs) act as a support system for the communities living in and around them. Large-scale human interventions in these PAs have resulted in biodiversity loss, threat to wildlife and habitat fragmentation. The Sariska Tiger Reserve (STR) is no exception. In this reserve, tiger (Panthera tigris) became extinct in 2004.To create inviolate space for the reintroduced tigers, government has planned voluntary relocation of villages located inside Critical Tiger Habitat. The voluntary relocation plan will be more challenging if people are not willing to get relocated from PAs. Therefore, we have empirically analysed the identified factors influencing local communities’ willingness in getting relocated outside the STR using logit model. Results revealed that “restriction of access” and “market access” are the most influential factors and positively associated while forest dependency is negatively associated with local communities’ willingness. Based on these results, it was recommended that policy should be directed towards restriction on accessing forest resources along with reduction in forest dependency by nurturing and strengthening villagers’ livelihood to ensure successful relocation. Displacement of existed small markets around the reserve will also persuade them to relocate in areas more connected to market and other facilities.

New perspectives on bioactivity of olive oil: evidence from animal models, human interventions and the use of urinary proteomic biomarkers

Olive oil (OO) is the primary source of fat in the Mediterranean diet and has been associated with longevity and a lower incidence of chronic diseases, particularly CHD. Cardioprotective effects of OO consumption have been widely related with improved lipoprotein profile, endothelial function and inflammation, linked to health claims of oleic acid and phenolic content of OO. With CVD being a leading cause of death worldwide, a review of the potential mechanisms underpinning the impact of OO in the prevention of disease is warranted. The current body of evidence relies on mechanistic studies involving animal and cell-based models, epidemiological studies of OO intake and risk factor, small- and large-scale human interventions, and the emerging use of novel biomarker techniques associated with disease risk. Although model systems are important for mechanistic research nutrition, methodologies and experimental designs with strong translational value are still lacking. The present review critically appraises the available evidence to date, with particular focus on emerging novel biomarkers for disease risk assessment. New perspectives on OO research are outlined, especially those with scope to clarify key mechanisms by which OO consumption exerts health benefits. The use of urinary proteomic biomarkers, as highly specific disease biomarkers, is highlighted towards a higher translational approach involving OO in nutritional recommendations.

The Didymo story: the role of low dissolved phosphorus in the formation of Didymosphenia geminata blooms

We outline, in chronological sequence, the events and findings over 25 years that have shaped our understanding of Didymosphenia geminata (Lyngbye) M. Schmidt blooms. Starting with the first appearance of D. geminata mats in streams on Vancouver Island in the late 1980s and followed years later by blooms in Iceland, South Dakota and Poland, D. geminata blooms were enigmatic for nearly 20 years. Early papers exploring whether blooms were caused by environmental change consistently failed to identify any specific factor(s) associated with their onset. Following the D. geminata outbreak in New Zealand in 2004 that seemed to result from an introduction of the species, the possibility that blooms that had previously occurred elsewhere in the world might also be explained by the introduction and movement among watersheds of a new variant with a bloom-forming tendency was touted and widely accepted. Now, however, the identification of very low soluble reactive phosphorus (SRP; below ∼2 ppb) as the proximate cause of bloom formation, has led to the more likely explanation that D. geminata blooms are the result of large-scale human intervention in climatic, atmospheric and edaphic processes that favour this ultra-oligotrophic species. In this new view, blooms of D. geminata are not simply due to the introduction of cells into new areas. Rather, bloom formation occurs when the SRP concentration is low, or is reduced to low levels by the process of oligotrophication. Mechanisms that potentially cause oligotrophication on global and regional scales are identified.

Spatial relationship between climatologies and changes in global vegetation activity

Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land-cover and climate-related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982-2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate-associated effects and a spatially correlated field representing the combined influence of other factors, including land-use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large-scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land-cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology).

Abstract B68: Antioxidant activity of green tea: A phase II clinical trial in men with prostate cancer

Abstract Background: Green tea (GT) contains green tea polyphenols (GTPs) which have been shown to play a role in the regulation of cell proliferation and apoptosis in prostate cancer cells in vitro and in animal models using human prostate cancer cell xenografts. GTPs are also potent scavengers of reactive oxygen species (ROS) which play a role in tumorigenesis. While there is extensive epidemiological and basic science evidence for these effects of GTPs, data from human intervention studies is much more limited. Objective: We conducted a phase II intervention study to evaluate the anticarcinogenic and antioxidant effects of green tea in prostate cancer by administering green tea in men prior to prostatectomy. Design: 79 men, diagnosed with prostate cancer and scheduled for prostatectomy, were randomized to either 6 cups of brewed green tea (GT group, N=34) or water (control group, N=33) daily for 3-8 weeks prior to surgery. 67 men completed the intervention. Blood and urine samples were collected before and after the intervention, and a section of prostate tissue was obtained following the pathology evaluation. Serum prostate specific antigen (PSA) concentration was determined by ELISA assay and prostate tissue PSA protein concentration was measured by Western blot. The prostate concentration of GTPs and their metabolites was measured using high-performance liquid chromatography (HPLC) with CoulArray electrochemical detection. The concentration of 8-hydroxydeoxyguanosine (8-OHdG), a biomarker for oxidative DNA damage, was measured in urine by HPLC. In addition, gene expression of the antioxidant enzymes superoxide dismutase (SOD) and catalase were determined in normal and tumor prostate tissue using real-time quantitative PCR. Results: Statistical analysis within each treatment arm showed that the serum PSA concentration significantly decreased in the GT group (final vs. baseline blood) (P<0.01), while no change was observed in the control group. The comparison of percent change in serum PSA between GT and control group showed a decreasing trend (p=0.085). Prostate tissue PSA protein expression was lower in men consuming GT compared to water control (p=0.06). The major bioactive component of GTPs, epigallocatechin gallate (EGCG) and its methyl metabolite 4″-O-methyl EGCG were found in prostate tissue in similar amounts, along with a small amount of epicatechin gallate. As compared to the pre-intervention level there was a significant decrease in urinary 8-OHdG concentration after GT intervention (83 vs. 50 nmol/g creatinine), while there was no change in the control group (54 vs. 55 nmol/g creatinine). Gene expression of SOD (p=0.087) and catalase (p=0.15) in the prostate tumor tissue normalized to normal prostate tissue in each individual showed a decreasing trend in men consuming GT as compared to the water control. Conclusion: The consumption of 6 cups of GT provided antioxidant protection, which may contribute to an inhibitory effect on prostate tumor growth in humans. Large-scale human intervention studies are needed to confirm these findings. Citation Format: Piwen Wang, William Aronson, Narine Abgaryan, Catherine L. Carpenter, Jaydutt V. Vadgama, David Heber, Susanne M. Henning. Antioxidant activity of green tea: A phase II clinical trial in men with prostate cancer. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B68.

Tidal Inlet Dynamics in Response to Human Intervention

The effects of large-scale human intervention on inlet dynamics are studied. In particular, the response of the largest of the Wadden Sea inlets (Texel Inlet) to the closure of a major part of its inner basin is re-analyzed. The re-analysis is based on datasets of bathymetry, discharges and water levels that have been obtained by intensive monitoring of both the inner basin and the ebb-tidal delta. Based on this re-analyisis and modern theoretical knowledge a conceptual model is postulated that describes the morphologic adjustment of tidal inlets due to large-scale human intervention. The kernel of this model is that the morphological adjustment towards a new overall equilibrium is split into two stages related to the existence of more than one temporal response scale.

Plant foods versus compounds in carcinogenesis; observational versus experimental human studies.

The protective role of plant foods and its constituents in cancer prevention is under renewed debate since the results of recent observational studies on colorectal cancer as well as large-scale human experimental studies on colorectal adenoma recurrence are disappointing. However, most short-term experimental human studies do show that plant foods favourably modulate potential cancer-preventive mechanisms. Which methodological pitfalls may explain the inconsistencies within and between different study designs? What are the advantages and limitations of the different study approaches? Observational studies do have the advantage to study the population at large with ultimate disease as the study endpoint. These studies are limited by the difficulty to estimate intake of individual compounds by questionnaires and the lack of biological markers of relevant exposure. Controlled experimental short-term studies in humans rely on biological markers of disease as intermediate endpoints. Relatively low sensitivity and specificity of these markers may complicate extrapolation of results. In the case of long-term and large-scale human intervention studies with disease endpoints, issues such as time, dose and duration of intervention, compliance and choice of the study population influence the interpretation of results. An integrated approach combining designs, and implementing new techniques to identify biomarkers, may clarify the role of plant foods in carcinogenesis.

Epidemiologic Studies of Diet and Cancer

The hypothesis I want to discuss have to do with fats, fiber, and vitamin A. First, a word about the various methods of study, particularly in epidemiology. Experiment is the scientific instrument par excellence and as utilized in intervention trials in epidemiology has been called the most powerful epidemiologic tool. An example in dietary epidemiology is the current trial going on among American doctors whereby they are taking carotene or a placebo on a random basis. The criteria for intervention trials have to be observed very carefully: there has to be evidence in favor of a salutary effect of the substance being tried. There has to be evidence that there is no long-term toxicity, and there has to be the likelihood that the human participants will comply with the stated regimen for years, sometimes, and that the individuals on the placebo will stay on the placebo. For various reasons, past large-scale human intervention trials, although costing many millions of dollars and absorbing huge amounts of time of investigators, have yielded convincing results in only a few instances. The least powerful tool of epidemiology is the international correlational study. I don't have to dwell on the drawbacks of these. A typical study relates the mortality from colon cancer to the ingestion of fats in populations in different countries (1). Even though there is a correlation, this does not prove that fats cause colon cancer. The proportion of people involved in manufacturing can be related to colon cancer in a similar fashion. There is growing evidence that exercise reduces risk of colon cancer. We might hypothesize that those nations requiring a great deal of physical labor; that is, those nations in which large proportions are not involved in manufacturing subject their populations to much more exercise, and this could account for their low mortality from colon cancer.