Every species on earth has an environmental range in which it can live. Usually it flourishes in the central portion of this range. Organisms contain a host of adaptations that allow them to manipulate their environments to remain within their preferred range. Plants and animals differ in the nature of these adaptations, which include the control of water, temperature, pH, and ion concentration.

There is a distinct possibility that humans are currently part way through an evolutionary transition between individuals and groups. The conflict between these two units of selection and levels of organization, between biology and culture, may explain some of the tensions in modern human life. Examples of selfishness and altruism exemplify how these types of selection act on humans.

Originally, altruism and self-sacrifice were thought to be incompatible with natural selection, even by Darwin. Now we have several explanations for how altruism can increase an individual's fitness. One is kin selection, or the idea that helping relatives can help increase one's genes in the population. Another involves ecological constraints and punishments. Here, individuals contribute to the group and wait their turn to reproduce.

Breeding strategies differ both among males and females of the same species as well as among different species. The difference in breeding strategies among members of the same species can usually be linked to frequency dependence. If the species is at evolutionary equilibrium, the relative fitnesses of these different strategies will be identical. Differing strategies have been found at the level of the gamete as well as at the level of different organisms and species.

Mating systems and parental care vary tremendously from species to species. Every species differs in how it protects its young from predators and provides its young with food, if it does so at all. The physical environment as well as behavioral dynamics in intra-species relationships all influence parental care. Often the mating system, which sex is dominant in mating, and whether fertilization is external or internal will determine much of the process of parental care.

The economic concept of game theory can be readily applied to evolution and behavior. By analyzing encounters between organisms as a mathematical "game," important information such as fitness payoffs and the proportions of "strategies" played by each group within a population can be inferred. While oftentimes these games are too simplified to apply directly to actual examples in nature, they are still useful models that help to convey important concepts.

There are several ways to examine the behaviors of organisms when they forage or hunt for food or mates. These behaviors become more complex in higher organisms, such as primates and whales, which can hunt in groups. Foragers and hunters have been shown to examine the marginal cost and marginal benefit of continuing an action and then adjust their behaviors accordingly. They are also able to handle risk by hoarding resources.

One can look at biodiversity from several perspectives. An ecological point of view tries to determine how necessary diversity is for an ecosystem to function. An economic point of view tries to capture the value of the "services" nature provides for mankind. An evolutionary point of view shows how artificial the human "right" to dominance is. Finally, a personal point of view captures the emotional basis for the values that humanity place on biodiversity.

The movement of matter and energy around the planet is very important, and its study draws on geology, and meterology in addition to chemistry. Energy tends to flow upwards from plantlike producers to herbivores to carnivores before being decomposed by detritovores and cycling back into energy usable by producers, in addition to the photosynthesis or chemosynthesis used by producers to produce energy. Like energy, compounds vital to life such as carbon, nitrogen, and phosphorous flow around...

Geography is very important in ecology. Two major systems have been designed to model this, island biogeography and metapopulations. The idea of metapopulations is more recent, and has emerged as the dominant theory. Metapopulations are populations in multiple neighboring areas. The population of a species in any individual area may go extinct, but the metapopulation still survives. The theory of metapopulations has gained momentum in recent years because of its applications to epidemiology,...

The idea of ecological communities has changed tremendously over the past 40 years. The classical view stated that there were so many different species because evolution packed them tightly into the available niches. The modern view emphasizes the idea of trophic cascades, or top-down control in food chains. This emphasized the importance of predation in ecology, although it downplayed the significance of food webs, which showed the interrelated nature of ecosystems better than simple food...

Competition among species, or inter-specific competition, can have an even greater effect on selection than competition within species (intra-specific competition). This is often the case in lower density populations. Different species can have positive, neutral, or negative effects on each other's fitness, and the effect species 1 has on species 2 is not necessarily the same that 2 has on 1. The effects that cohabiting species have on each other shapes evolution the same way that selective...

The growth of populations is held in check by several factors. These can include predators, food and other resources, and density. Population density affects growth rate by determining how likely is it that an organism will interact with a member of its own species compared to an organism of a different species. Population growth studies rely on the mathematics of logs and exponents.

This lecture provides an overview of the physical aspects of earth's biomes. Temperature, water, latitude, and altitude all come into play. Regions with similar levels of these climatic features tend to have similar life-forms living there. These same climatic features can also affect weather patterns, which in turn affect life by altering habitats and ecosystems. On a large enough scale, such as El Niño, these weather patterns can affect life all over the earth.

While there are many differences between modern science and philosophy, there are still a number of lessons in modes of thought that scientists can take from philosophy. Scientists' ideas about the nature of science have evolved over time, leading to new ideas about falsifiability, creativity, revolutions, and the boundaries and limits of what can be accomplished by different types of science.

Evolution plays an important though underutilized role in medicine. Evolution guides how our bodies respond to various treatments, how pathogens will respond to treatments, and how pathogens' responses will change over time. Pathogens oftentimes will evolve to an intermediate level of virulence where they become strong enough to infect a host and reproduce, but not so strong as to kill the host before it can spread the pathogen.

Coevolution happens at many levels, not just the level of species. Organelles such as mitochondria and chloroplasts serve as good intracellular examples. Other living things make up a crucial component of an organism's environment. Coevolution can occur in helpful ways (symbiosis) and in harmful ways (parasitism). Many factors can influence coevolution, such the frequency and degree of interaction.

The fossil record holds a lot of evolutionary information that can't be seen on shorter time scales, although the more recent fossil record is more complete. Among other things, the fossil record demonstrates that extinctions can open up ecological space for new speciation and radiation, and that life forms tend to begin small and evolve to be bigger over time.

Geology and climate have shaped the development of life tremendously. This has occurred in the form of processes such as the oxygenation of the atmosphere, mass extinctions, tectonic drift, and disasters such as floods and volcanic eruptions. Life, particularly bacteria, has also been able to impact the geological makeup of the planet through metabolic processes.

The history of life and evolution has been characterized by several key events. These events can be grouped as new hierarchal levels of selection coming into play, as biological units coming together in symbiosis and specialization, or in a number of other ways. Other important events are situations of conflict resolution or information transmission, from the genetic to the cultural level.

We can use methods of genetic analysis to connect phylogenic information to geographical histories. Human migration has left genetic traces on every continent, and allows us to trace our roots back to Africa. Molecular genetic methods allow us to determine whether or not trait states were ancestral, which can have profound implications for fundamental biological ideas.

The Tree of Life must be discovered through rigorous analysis. Genetic information is crucial because appearances can be deceiving, and species that look similar can prove to be genetically very dissimilar and not share recent common ancestors. Two criteria, used to determine what the "correct" Tree is, are simplicity and whether the tree maximizes the probability of observing what we actually see.

Speciation is the process through which species diverge from each other and/or from a common ancestor. There are several definitions of species, most of which focus on reproductive isolation and/or phylogenetic similarities. This can cause some controversy. Speciation can result from geographical separation or ecological specialization. There are stages of speciation in which organisms cluster first into distinct populations before finally becoming different species.

Sexual Selection is a component of natural selection in which mating success is traded for survival. Natural selection is not necessarily survival of the fittest, but reproduction of the fittest. Sexual dimorphism is a product of sexual selection. In intersexual selection, a sex chooses a mate. In intrasexual selection, individuals of one sex compete among themselves for access to mates. Often honest, costly signals are used to help the sex that chooses make decisions.

Sex allocation is an organism's decision on how much of its reproductive investment should be distributed to male and female functions and/or offspring. Under most conditions, the optimal ratio is 50:50, but that can change under certain circumstances. Sex allocation determines what sexes sequential hermaphrodites should be at each part of their life as well as how simultaneous hermaphrodites should behave. Some species have more control over the sexes of their offspring than others, and...