Biological hypotheses

life that does not originate from Earth

paradigm that living organisms interact with their surroundings in a self-regulating system

thumb |upright=1.3 |Panspermia proposes that organisms such as [[bacteria, complete with their DNA, could be transported by means such as comets through space to planets including Earth.]] Panspermia () is the hypothesis that life exists throughout the universe, distributed by cosmic dust, meteoroids, asteroids, comets, and planetoids, as well as by spacecraft carrying unintended contamination by microorganisms, known as directed panspermia. The theory argues that life did not originate on Earth, but instead evolved somewhere else and seeded life as we know it.

hypothetical phase of the history of life, in which self-replicating RNA proliferated

disproven theory of life arising from nonliving matter

thumb|upright=2.2|In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria; a second merger added [[chloroplasts, creating the green plants. The original theory by Lynn Margulis proposed an additional preliminary merger, but this is poorly supported and not now generally believed.]] Symbiogenesis (endosymbiotic theory, or serial endosymbiotic theory) is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possi

thumb|3D representation of a living cell during the process of mitosis, example of an autopoietic system

hypothesis about human evolution

hypothesis that humans possess an innate tendency to seek connections with nature and other forms of life

multi-location related human origins

theory regarding lack of alien contact

possible alternative biochemicals used by life forms

hypothesis in medicine that early childhood exposure to certain microorganisms (e.g. gut flora, helminths) protects against allergies

In biology, Archezoa is a term that has been introduced by several authors to refer to a group of organisms (a taxon). Authors include Josef Anton Maximilian Perty, Ernst Haeckel and in the 20th century by Thomas Cavalier-Smith in his classification system. Each author used the name to refer to categories of organisms described by different sets of shared characteristics. This reuse by later authors of the same taxon name for different groups of organisms is problematic in taxonomy because the inclusion of the name in a sentence such as "Archezoa have no olfactory organs" does not make sense u

intelligent extraterrestrial beings

hypothetical geoclimactic event

assumption that the chemical processes of hypothetical extraterrestrial life must be constructed primarily from carbon

theory about the origin of petroleum

Hypothesis about the origin of life

Hypothesis in evolutionary biology

hypothesis that multicellular life, understood as a superorganism, is suicidal, and that microbial-triggered mass extinctions are attempts to return the Earth to a microbial-dominated state

proposed evolutionary event in the history of metazoa

causes and mechanism of the extinction of the Neanderthal people

hypothesis that human evolution was influenced by hunting

postulate in biology

thumb|right|200px|Gamma-ray bursts might have regulated the advent of intelligent life Neocatastrophism is the hypothesis that life-exterminating events such as gamma-ray bursts have acted as a galactic regulation mechanism in the Milky Way upon the emergence of complex life in its habitable zone. It is one of several proposed solutions to the Fermi paradox since it provides a mechanism which would have delayed the advent of intelligent beings in local galaxies near Earth.

human evolution hypothesis

Hemolithin (sometimes confused with the similar space polymer hemoglycin) is a proposed protein containing iron and lithium, of extraterrestrial origin, according to an unpublished preprint. The result has not been published in any peer-reviewed scientific journal. The protein was purportedly found inside two CV3 meteorites, Allende and Acfer-086, by a team of scientists led by Harvard University biochemist Julie McGeoch. The report of the discovery was met with some skepticism and suggestions that the researchers had extrapolated too far from incomplete data.

nineteenth century hypothesis that males have a greater range of ability than females

hypothesis regarding ecology in formerly glaciated regions

hypothesis about human childbirth