Evolutionary physiology is the study of physiological evolution, which is to say, the manner in which the functional characteristics of individuals in a population of organisms have responded to selection across multiple generations during the history of the population.
It is a subdiscipline of both physiology and evolutionary biology. Practitioners in this field come from a variety of backgrounds, including physiology, evolutionary biology, ecology and genetics.
Accordingly, the range of phenotypes studied by evolutionary physiologists is broad, including but not limited to life history, behavior, whole-organism performance, functional morphology, biomechanics, anatomy, classical physiology, endocrinology, biochemistry, and molecular evolution. It is closely related to comparative physiology and environmental physiology, and its findings are a major concern of evolutionary medicine.

As the name implies, evolutionary physiology is the product of what was at one time two distinct scientific disciplines. According to Garland and Carter,evolutionary physiology arose in the late 1970s, following "heated" debates concerning the metabolic and thermoregulatory status of dinosaurs (see physiology of dinosaurs) and mammal-like reptiles.
This period was followed by attempts in the early 1980s to integrate quantitative genetics into evolutionary biology, which had spill-over effects on other fields, such as behavioral ecology and ecophysiology. In the mid- to late-1980s, phylogenetic comparative methods started to became popular in many fields, including physiological ecology and comparative physiology. An 1987 volume titled "New Directions in Ecological Physiology" had little ecology but a considerable emphasis on evolutionary topics. It generated vigorous debate, and within a few years the National Science Foundation had developed a panel titled Ecological and Evolutionary Physiology.
Shortly thereafter, selection experiments and experimental evolution became increasingly common in evolutionary physiology. Most recently, "macrophysiology" has emerged as a subdiscipline, in which practitioners attempt to identify large-scale patterns in physiological traits (e.g., patterns of covariation with latitude) and their ecological implications.

As a hybrid scientific discipline, evolutionary physiology provides some unique perspectives. For example, an understanding of physiological mechanisms can help in determining whether a particular pattern of phenotypic variation or covariation (such as an allometric relationship) represents what could possibly exist or just what selection has allowed.Similarly, a thorough knowledge of physiological mechanisms can greatly enhance understanding of possible reasons for evolutionary correlations and constraints than is possible for many of the traits typically studied by evolutionary biologists (such as morphology).

Areas of Research

Important areas of current research include:
Organismal performance as a central phenotype (e.g., measures of speed or stamina in animal locomotion)
Role of behavior in physiological evolution
Physiological and endocrinological basis of variation in life history traits (e.g., clutch size)
Functional significance of molecular evolution
Extent to which species differences are adaptive
Physiological underpinnings of limits to geographic ranges
Role of sexual selection in shaping physiological evolution
Magnitude of "phylogenetic signal" in physiological traits
Role of pathogens and parasites in physiological evolution and immunity
Application of optimality modeling to elucidate the degree of adaptation
Role of phenotypic plasticity in accounting for species differences
Mechanistic basis of trade-offs and constraints on evolution (e.g., putative Carrier's constraint on running and breathing)
Limits on sustained metabolic rate
Origin of allometric scaling relations or allometric laws (and the so-called metabolic theory of ecology)
Individual variation (see also Individual differences psychology)
Functional significance of biochemical polymorphisms
Analysis of physiological variation via quantitative genetics
Paleophysiology and the evolution of endothermy
Human adaptational physiology
Darwinian medicine
Evolution of dietary antioxidants


The Archaea are a group of single-celled microorganisms with no cell nucleus nor any other membrane-bound organelles.
They show many differences in their biochemistry from other forms of life and have an independent evolutionary history.
In the three-domain system, they are classified as a separate domain from the phylogenetically distinct
Bacteria and Eukaryota.
Archaea are divided into four recognized phyla,but many more phyla may exist. Of these groups the Crenarchaeota and the Euryarchaeota are most intensively studied. Classification is still difficult, since the vast majority have never been studied in the laboratory. Archaea and bacteria are quite similar in size and shape,
but a few archaea have very unusual shapes. Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes: notably the enzymes involved in transcription and translation. Initially,archaea were seen as extremophiles that lived in harsh environments,such as hot springs and salt lakes, but they have since been found in a broad range of habitats, including soils, oceans, and marshlands.

Archaea are now recognized as a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle.

Archaea have, in the past, been classed with bacteria as prokaryotes (or Kingdom Monera), this classification is regarded by some as outdated.
Other aspects of archaean biochemistry are unique, such as their reliance on ether lipids in their cell membranes. Archaea reproduce asexually and divide by binary fission, fragmentation, or budding; in contrast to bacteria and eukaryotes, no known species form spores.
Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet.  No clear examples of archaeal pathogens or parasites are known, but they are often mutualists or commensals. One example are the methanogens that inhabit the gut of humans and ruminants, where their vast numbers aid digestion. Methanogens are used in biogas production and sewage treatment, and enzymes from extremophile archaea that can endure high temperatures and organic solvents are exploited in biotechnology.

Although probable prokaryotic cell fossils date to almost 3.5 billion years ago, most prokaryotes do not have distinctive morphologies and fossil shapes cannot be used to identify them as Archaea.Instead, chemical fossils of unique lipids are more informative because such compounds do not occur in other organisms.Some publications suggest that archaean or eukaryotic lipid remains are present in shales dating from 2.7 billion years ago;such data have since been questioned.Such lipids have also been detected in Precambrian formations. The oldest such traces come from the Isua district of west Greenland, which include Earth's oldest sediments, formed 3.8 billion years ago.The archaeal lineage may be the most ancient that exists on earth.Eukaryotes are colored red, archaea green and bacteria blue. Adapted from Ciccarelli et al.
Woese argued that the bacteria, archaea, and eukaryotes represent separate lines of descent that diverged early on from an ancestral colony of organisms.A few biologists, however, argue that the Archaea and Eukaryota arose from a group of bacteria. In any case it is thought that viruses and archaea began relationships approximately two billion years ago, and that co-evolution may have been occurring between members of these groups.It is possible that the last common ancestor of the bacteria and archaea was a thermophile, which raises the possibility that lower temperatures are "extreme environments" in archaeal terms, and organisms that live in cooler environments appeared only later.Since the Archaea and Bacteria are no more related to each other than they are to eukaryotes, the term prokaryote's only surviving meaning is "not a eukaryote", limiting its value.

Nutritional types in archaeal metabolismNutritional typeSource of energySource of carbonExamples Phototrophs  Sunlight  Organic compounds  Halobacteria  Lithotrophs Inorganic compounds Organic compounds or carbon fixation FerroglobusMethanobacteria or Pyrolobus  Organotrophs Organic compounds  Organic compounds or carbon fixation  PyrococcusSulfolobus or Methanosarcinales