Human population size

Daily, G.C., Ehrlich, A.H., and Ehrlich, P.R., 1994, "Optimum Human Population Size," Population and Environment, A Journal of Interdisciplinary Studies 15 469. 

Years ago Period Human population size Technology or event Effect on the biosphere... 

The impact of chemical pollution on the reproductive success and population sizes of wildlife species is often difficult to assess. In many cases, environmental factors such as habitat restriction, stress due to human intrusion and changes in natural food supplies owing to hunting, fishing and restocking policies may have a significant, even predominant, effect on population size. This makes it difficult to determine to what extent, if any, environmental endocrine disrupters may be contributing to observed effects on reproduction or population size in wildlife species. 

Exposure of the general population to higher concentrations of methyl parathion may result from contact with, or ingestion of, contaminated hazardous waste site media, principally soils and water. No information was found in the available literature regarding the size of the human population potentially exposed to methyl parathion through contact with contaminated waste site media. 

The threshold for the human population is estimated by dividing the NOAEL (or, alternatively, the BMD), by an uncertainty factor (UF), the size of which depends upon the nature and quality of the toxicity data and the characteristics of the human population. (The estimated human threshold dose has several different names, depending upon the regulatory context, see later.)... 

Is the amino acid sequence absolutely fixed, or invariant, for a particular protein No some flexibility is possible. An estimated 20% to 30% of the proteins in humans are polymorphic, having amino acid sequence variants in the human population. Many of these variations in sequence have little or no effect on the function of the protein. Furthermore, proteins that carry out a broadly similar function in distantly related species can differ greatly in overall size and amino acid sequence. 

Why would a predominantly meat-based diet be a severe restriction on the possible size of the human population ... 

Exposure assessment An identification and evaluation of the human population exposed to a toxic agent, describing its composition and size, as well as the type, magnitude, frequency, route and duration of exposure. 

The growth of population size and trends in civilization development bring with them many problems of global ecodynamics, especially the impact of society on climatic trends. The broader issues of the ecological, economic, and human effects of climate change were considered by Hardy (2003). The following aspects of the climate change problem were explained ... 

The application of human data in risk assessment for children has been detailed in a number of publications (USEPA, 1991 Richter-Reichhelm et al., 2002 IPCS, 2005 Kimmel et al., 2006). In general, the risk assessor should evaluate each human study for its power and potential bias. The power of the study is the study s ability to detect an effect. It is dependent on the size of the study population, the frequency of the effect or the exposure in the population, and the level of risk to be identified. The greater the population size and the effect or exposure frequency, the greater the power of the study. In studies of low power, it is generally not possible to establish the lack of an association between an exposure and an effect, and even positive findings may be difficult to support. Metaanalysis, which combines populations from different studies, may increase the power of the overall database, but the potential for the combination of dissimilar populations must be considered in any risk assessment. 

After assessing the nature and quantities of toxins present, one must evaluate their potential for human exposure. Even when materials known to be toxic are present, human exposure may not have occurred or may be only remotely possible. Before exposure can be evaluated, the means of exposure (for example, direct contact, contaminated water, or contaminated air) must be determined, and the size of human populations potentially exposed and their degree of proximity to the toxic materials must be defined. 

The application of probability theory makes it possible to proceed on the basis of incomplete knowledge. However, the extrapolations must be as precise as possible. The IND does not propose a blanket approval of the administration of the new drug in any form at any dose to any number of sick or healthy people simply because it happened that none, or very few, of the laboratory animals died. Instead, the IND proposes specific doses, a specific regimen over a named period in a human population of a size determined through statistics to be necessary to minimize the likelihood of error in reaching conclusions about safety (phase 1). 

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