Many feel as has been the case throughout history that the major international wars to be fought in the future will continue to be over natural resources. Power conflicts and self-interest will perhaps mean that there will be gross violation of basic rights and death or misery for millions of innocent people. Throughout history, most wars have had trade and resources at their core leading to ideological battles fueled by imperialistic motives. In the future, while this pattern is likely to continue, as resources get depleted and wasted in these wars hot and coldadditional conflicts and contention will arise through access to even more limited resources.
All relevant data are within the paper.
Introduction. The phenomena of human population growth and its impacts are all too apparent; is the ecological community willing to ignore the most pressing social and scientific issue of all time?--Pulliam and Haddad, Regardless of criticisms against the theory that population is a function of food availability, the human population is, on the global scale, undeniably increasing, as is the net quantity of human food produced — a pattern that has been true for roughly 10, years, since the human development of agriculture. Population Media Center knows the planet and its resources are finite, but if men, women, and children are empowered with information, health, human rights, information about the environment, and economic opportunity – population dynamics will change, improving the health and prosperity of .
Abstract Explaining the evolution of human life history traits remains an important challenge for evolutionary anthropologists. Progress is hindered by a poor appreciation of how demographic factors affect the action of natural selection.
I review life history theory showing that the quantity maximized by selection depends on whether and how population growth is regulated. To concretely show how demography-free life history theory can lead to errors, I reanalyze an influential model of human life history evolution, which investigated the coevolution of a long lifespan and late age of maturity.
This analysis suggests that progress in human life history theory requires better understanding of the demography of our ancestors. Introduction The unusual life history characteristics of humans provide a unique challenge to evolutionary anthropologists. Humans have a distinctive life history even among our closest living relatives: This pronounced life course has attracted the attention of many theorists, and consequently some novel, human-specific theories have been proposed [ 1345 ] alongside more species-general life history theory [ 267 ].
Theorists often use optimization methods to understand how selection acts on life histories. The general method is to maximize a fitness function with respect to some physiological tradeoff.
For example, we might assume that energy devoted to immune function cannot be devoted to gamete production or any other biological function. A life history theorist might ask: The maximization method is widely used in introductory life history textbooks on which empirical researchers strongly rely e.
One of the major difficulties with optimization methods arises in the first step: As I demonstrate here, this problem is usually solved by specifying a complete model of demography and inheritance, from which one can derive a quantity which natural selection maximizes.
Unfortunately, traditional life history theory often does not begin with the construction of complete population models, but rather with the theorist simply choosing a common fitness quantity. The chosen maximand is usually only valid under particular demographic conditions [ 1112 ], but, without full justification from a population model, most readers never know these conditions.
This paper aims to clarify the role of demography in life history theory, with a focus on how demographic assumptions determine the correct fitness maximand.
First, I review two general models of selection on age-structured populations, showing which quantities are maximized under density-independent and density-dependent population growth. These conditions do not appear to be widely appreciated among anthropologists.
In particular, zero population growth alone is not sufficient to justify R as a fitness maximand. Then, to concretely show how demographically vague models can lead to premature conclusions, I reanalyze the model in an influential paper on the evolution of human life histories: This sensitivity to the precise form of population regulation implies that we need to better understand the demographic history and prehistory of our species if our models are to provide specific, realistic predictions.
What does selection maximize? Here I review how different forms of population regulation lead to different maximization procedures.
There are an infinite number of possible demographic scenarios one could assume, but much can be learned from studying the two broad categories of density-independent or -dependent growth. The latter usually implies that population growth rates decrease as the population becomes more dense, via increased competition for resources.
To simplify matters, I assume asexual, haploid genetic inheritance and no frequency-dependent selection, as is often done in fitness maximization models.
The extension to sexual reproduction is usually straightforward [ 13 ]. The goal, for each case, is to find the quantity that natural selection maximizes, and to briefly explain how a theorist can apply the results to specific problems.
Maximization under density-independent growth First, consider a population of individuals whose survival and reproduction is not affected by population density. Specifically, the probability of surviving to age x is l xand the average number of offspring produced by an individual of age x is m x.
Under some fairly lenient demographic assumptions [ 14 ], such a population will approach growth rate of r, which is found by solving the equation 1.during the s population growth, on average, acted as a brake on economic growth as measured by the growth rate of per capita gross domestic product, or GDP.
4 (This is a standard measure of a nation¹s total output of goods and services by residents and. Human population growth challenges efforts toward sustainability. People who are concerned about the environment, development, and sustainability are in a position to stress the importance of human population and to encourage people to choose small family size (Grossman, in Conserv Biol, 24(6), pp.
"Go Forth And Multiply!" That's what the human population has successfully been doing for thousands and thousands of years, expanding, exploring, migrating, conquering, utilizing, evolving, civilizing, industrializing, and now, destroying the very land upon which we live.
The IPAT equation, first devised in the s, is a way of determining environmental degradation based on a multiple of factors.
At its simplest, it describes how human impact on the environment (I) is a result of a multiplicative contribution of population (P), affluence (A) and technology (T).
Human population issues - urbanization Geographical distribution of people affects impact of population growth throughout recent history, people have increasingly migrated to cities.
Population Media Center works to enhance health, human rights, environmental protection, and economic equity, all of which impact population and protect the environment. is not only a crucial human rights issue that must be addressed, it's also intricately connected with the world’s population and the creation of a sustainable planet.