This article lists notable

unsolved problems List of unsolved problems may refer to several notable conjectures or open problems in various academic fields: Natural sciences, engineering and medicine * Unsolved problems in astronomy * Unsolved problems in biology * Unsolved problems in ch ...

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

General biology

Evolution and origins of life

Origin of life Abiogenesis is the natural process by which life arises from abiotic component, non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to organism, living entities on ...

. Exactly how, where, and when did life on

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

originate? Which, if any, of the many hypotheses is correct? What were the metabolic pathways used by the earliest life forms? How did genetic code originate? What was the molecular mechanism that allows the association of the amino acids with their triplet codons? What were the biochemical paths from individual bio-building blocks like amino acids or nucleic acids to functional polymers such as proteins and DNA? * Origin of sexual reproduction. What were the fundamental selective forces responsible for the origin of sexual reproduction? * Maintenance of sexual reproduction. What are the fundamental selective forces maintaining sexual reproduction? * Origins of viruses. Exactly how and when did different groups of viruses originate? *

Morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

problem. How are neural tissues formed in specific ways in different species? The formation of neural tissues in a certain way is necessary for the formation of certain goal-directed behavior for certain species.

Developmental psychobiology Developmental psychobiology is an interdisciplinary field, encompassing developmental psychology, biological psychology, neuroscience and many other areas of biology. The field covers all phases of ontogeny, with particular emphasis on prenatal, p ...

posed this question since the lack of knowledge about the precise coordination of all cells, even those not related anatomically, in space and time during the embryonic period does not allow us to understand what forces at the cellular level coordinate four very general classes of tissue deformation, namely: tissue folding and invagination, tissue flow and extension, tissue hollowing, and, finally, tissue branching. *

Development Development or developing may refer to: Arts *Development (music), the process by which thematic material is reshaped * Photographic development *Filmmaking, development phase, including finance and budgeting * Development hell, when a proje ...

and

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. How and why did the brain evolve? What are the

molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...

determinants of individual brain development? *Origin of

Eukaryotes The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of ...

(

Symbiogenesis 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 possibl ...

). How and why did cells combine to form the eukaryotic cell? Did one or more random events lead to the first eukaryotic cells, or can the formation of eukaryotic cells be explained by physical and biological principles? How did the mitochondria's mitosis cycle come in sync with its host cell? Did the mitochondria or the nucleus develop first in eukaryotes? *

Last universal common ancestor The last universal common ancestor (LUCA) is the hypothesized common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated. The cell had a lipid bilayer; it possessed the genetic code a ...

. What were the characteristics of the Last Universal Common Ancestor of Archaea and Bacteria? *The lipid divide: How did

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

end up using membrane

glycerophospholipid Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes in eukaryotic cells. They are a type of lipid, of which its composition affects membrane structure and properties. T ...

s of the opposite chirality compared to bacteria? Why do eukaryotes have bacteria-type membrane lipids?

Biochemistry and cell biology

*Biological

homochirality Homochirality is a uniformity of chirality, or handedness. Objects are chiral when they cannot be superposed on their mirror images. For example, the left and right hands of a human are approximately mirror images of each other but are not their ow ...

. What is the origin of homochirality in living organisms? In biological organisms, amino acids appear almost exclusively in the left-handed form and sugars in the right-handed form. Homochirality is an obvious characteristic of life on Earth, yet extraterrestrial samples contain largely

racemic In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

compounds. It is not known whether homochirality existed before life, whether the building blocks of life must have this particular chirality, or whether life must be homochiral at all. *What do all the unknown proteins do? Two decades since the first eukaryotes were sequenced, the "biological role" of around 20% of proteins are still

unknown Unknown or The Unknown may refer to: Film and television Film * The Unknown (1915 comedy film), ''The Unknown'' (1915 comedy film), Australian silent film * The Unknown (1915 drama film), ''The Unknown'' (1915 drama film), American silent drama ...

. Many of these proteins are conserved across most eukaryotic species and some are conserved in bacteria, indicating a role fundamental for life. *Determinants of cell size. How do cells determine what size to grow to before dividing? *

Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

. In

cell theory In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pr ...

, what is the exact transport mechanism by which proteins travel through the

? *

Mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical Drug interaction, interaction through which a Medication, drug substance produces its pharmacological effect. A mechanism of action usually includes mention o ...

of drugs. The mechanisms of action of many drugs including

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

thalidomide Thalidomide, sold under the brand names Contergan and Thalomid among others, is an oral administered medication used to treat a number of cancers (e.g., multiple myeloma), graft-versus-host disease, and many skin disorders (e.g., complication ...

and

ketamine Ketamine is a cyclohexanone-derived general anesthetic and NMDA receptor antagonist with analgesic and hallucinogenic properties, used medically for anesthesia, depression, and pain management. Ketamine exists as its S- (esketamine) a ...

are not completely understood. *

Protein folding Protein folding is the physical process by which a protein, after Protein biosynthesis, synthesis by a ribosome as a linear chain of Amino acid, amino acids, changes from an unstable random coil into a more ordered protein tertiary structure, t ...

. What is the folding code? What is the folding mechanism? Can the native structure of a protein be predicted from its amino acid sequence? Is it possible to predict the secondary, tertiary and quaternary structure of a

polypeptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...

sequence based solely on the sequence and environmental information? ** Prediction of native structure has turned out to be the easiest of the questions, as the variety of known structures have allowed the development of prediction methods such as

Rosetta Rosetta ( ) or Rashid (, ; ) is a port city of the Nile Delta, east of Alexandria, in Egypt's Beheira governorate. The Rosetta Stone was discovered there in 1799. Founded around the 9th century on the site of the ancient town of Bolbitine, R ...

(since 1998) and the

AlphaFold AlphaFold is an artificial intelligence (AI) program developed by DeepMind, a subsidiary of Alphabet, which performs predictions of protein structure. It is designed using deep learning techniques. AlphaFold 1 (2018) placed first in the overall ...

neural network of 2020. AlphaFold is capable of predicting a protein's final shape based solely on its amino-acid chain with an accuracy of around 90% on a test sample of proteins used by the team. Accurate prediction of quaternary structure was achieved by AlphaFold3 in 2024. ** Inverse protein-folding problem ( protein design): Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions? This turned out to be tractable given a good structual prediction method, starting with the success of the small globular protein Top7 from the Rosetta team in 2002. The use of structure-prediction neural networks afforded even more complex designs.

Large language model A large language model (LLM) is a language model trained with self-supervised machine learning on a vast amount of text, designed for natural language processing tasks, especially language generation. The largest and most capable LLMs are g ...

s trained on protein sequences seem to learn a "grammar"; they represent yet another approach to the protein-design problem. ** The success of prediction and design methods still skip over ''how'' proteins end up in the final shape (folding mechanism and kinetics;

protein dynamics In molecular biology, proteins are generally thought to adopt unique structures determined by their amino acid sequences. However, proteins are not strictly static objects, but rather populate ensembles of (sometimes similar) conformations. Tran ...

Wet lab A wet lab, or experimental lab, is a type of laboratory where it is necessary to handle various types of chemicals and potential "wet" hazards, so the room has to be carefully designed, constructed, and controlled to avoid spillage and contaminatio ...

methods of the 2020s allow for microsecond-level changes to be observed and quantified. 2020s

molecular dynamics Molecular dynamics (MD) is a computer simulation method for analyzing the Motion (physics), physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamics ( ...

techniques can be used to simulate the folding behavior at the atomic level to this same timescale, though a specialized computer is needed for the simulation to finish in a reasonable amount of time. See also

Folding@home Folding@home (FAH or F@h) is a distributed computing project aimed to help scientists develop new therapeutics for a variety of diseases by the means of simulating protein dynamics. This includes the process of protein folding and the movements ...

. ** The study of

intrinsically disordered proteins In molecular biology, an intrinsically disordered protein (IDP) is a protein that lacks a fixed or ordered protein tertiary structure, three-dimensional structure, typically in the absence of its macromolecular interaction partners, such as other ...

is also not as advanced as the study of globular proteins: some sequences do not fold into a fixed shape yet still have a function. *

Enzyme kinetics Enzyme kinetics is the study of the rates of enzyme catalysis, enzyme-catalysed chemical reactions. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme' ...

: Why do some

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s exhibit faster-than-diffusion kinetics? *

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

folding problem: Is it possible to accurately predict the secondary, tertiary and quaternary structure of a polyribonucleic acid sequence based on its sequence and environment? * Protein design: Is it possible to design highly active enzymes ''de novo'' for any desired reaction? *

Biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

: Can desired molecules, natural products or otherwise, be produced in high yield through biosynthetic pathway manipulation? *What is the mechanism of allosteric transitions of proteins? The concerted and sequential models have been hypothesised but neither has been verified. *What are the endogenous

ligands In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ...

orphan receptor In biochemistry, an orphan receptor is a protein that has a similar structure to other identified receptors but whose endogenous ligand has not yet been identified. If a ligand for an orphan receptor is later discovered, the receptor is referred ...

s? *What substance is

endothelium-derived hyperpolarizing factor In blood vessels Endothelium-Derived Hyperpolarizing Factor or EDHF is proposed to be a substance and/or electrical signal that is generated or synthesized in and released from the endothelium; its action is to hyperpolarize vascular smooth muscle ...

? *Mechanism of

Golgi's method Golgi's method is a silver staining technique that is used to visualize nervous tissue under light microscopy. The method was discovered by Camillo Golgi, an Italian physician and scientist, who published the first picture made with the techni ...

: Why does this specific method stain nerve tissues? Why does it only color a random portion of the cells?

Other

*Why does

biological aging Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. Whole organism senescence involves an increase in death rates or a decrease in fecundity with increasing age, at least in the l ...

occur? There are a number of hypotheses as to why senescence occurs including those that it is programmed by gene expression changes and that it is the accumulative damage of biological structures, particularly damage to DNA. *How do organs grow to the correct shape and size? How are the final shape and size of organs so reliably formed? These processes are in part controlled by the

Hippo signaling pathway The Hippo signaling pathway, also known as the Salvador-Warts-Hippo (SWH) pathway, is a signaling pathway that controls organ size in animals through the regulation of cell proliferation and apoptosis. The pathway takes its name from one of it ...

. *Can developing biological systems tell the time? To an extent, this appears to be the case, as shown by the

CLOCK A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...

gene. *

Star jelly Star jelly (also called astromyxin, astral jelly) is a gelatinous substance sometimes found on grass and less commonly on the branches of trees. According to folklore, it is deposited on the Earth during meteor showers. It is described as a trans ...

. A complete explanation about its origins is still lacking. * Forest rings. The origin of forest rings is not known, despite several mechanisms for their creation having been proposed. Such hypotheses include radially growing fungus, buried kimberlite pipes, trapped gas pockets, and meteorite impact craters.

Human biology

Handedness In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to and causing it to be stronger, faster or more Fine motor skill, dextrous. The other hand, comparatively often the weaker, less dext ...

: It is unclear how handedness develops, what purpose it serves, why right-handedness is far more common, and why left-handedness exists. *

Laughter Laughter is a pleasant physical reaction and emotion consisting usually of rhythmical, usually audible contractions of the diaphragm and other parts of the respiratory system. It is a response to certain external or internal stimuli. Laug ...

: While it is generally accepted that laughing evolved as a form of social communication, the exact neurobiological process that leads humans to laugh is not well understood. *

Yawning A yawn is a reflex in vertebrate animals characterized by a long inspiratory phase with gradual mouth gaping, followed by a brief climax (or acme) with muscle stretching, and a rapid expiratory phase with muscle relaxation, which typically last ...

: It is yet to be established what the biological or social purpose of yawning is. *Heritable components of

homosexuality Homosexuality is romantic attraction, sexual attraction, or Human sexual activity, sexual behavior between people of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexu ...

: How to reconcile evolution with the heritable components of human homosexuality? Homosexuality is prevalent across human societies, past and present. These facts constitute an evolutionary puzzle. *Decline in average human body temperature since the 19th century: Medical data suggests that the average body temperature has declined 0.6 °C since the 19th century. The cause is unclear although it has been suggested that it has some relation with reduced inflammation from reduced exposure to microorganisms. *Why are there

blood types Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is comp ...

? It is unclear what the origin and purpose of having blood types is. It is thought that O blood may be an adaptation to malaria and that different blood types respond to different diseases but this hypothesis has yet to be proven. Why did these antigens develop in the first place? What accounts for the differences in blood type? How ancient are the differences in blood types? What accounts for the large number of rare non ABO blood types? What role do blood types have in fighting disease? * Photic sneeze effect: What causes the photic sneeze effect? Why is it so common yet not universal? * Human sex pheromones: There is contradictory evidence on the existence of human pheromones. Do they actually exist, and if so, how do they affect behavior? *Existence of the Grafenberg spot (G-spot): Does the G-spot actually exist? If so is it present in all women? What exactly is it? *Extinction of

archaic humans ''Homo'' () is a genus of great ape (family Hominidae) that emerged from the genus ''Australopithecus'' and encompasses only a single extant species, ''Homo sapiens'' (modern humans), along with a number of extinct species (collectively calle ...

: Why did archaic human species such as

Neanderthals Neanderthals ( ; ''Homo neanderthalensis'' or sometimes ''H. sapiens neanderthalensis'') are an extinction, extinct group of archaic humans who inhabited Europe and Western and Central Asia during the Middle Pleistocene, Middle to Late Plei ...

become extinct, leaving ''

Homo sapiens Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

'' the only surviving species of humans? *

Love Love is a feeling of strong attraction and emotional attachment (psychology), attachment to a person, animal, or thing. It is expressed in many forms, encompassing a range of strong and positive emotional and mental states, from the most su ...

: When did

pair bonding In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of young and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently ...

evolve? Is pair bonding an antecedent to

romantic love Romance or romantic love is a feeling of love for, or a Interpersonal attraction, strong attraction towards another person, and the Courtship, courtship behaviors undertaken by an individual to express those overall feelings and resultant ...

, or have there been other steps in the evolution of pair bonds in humans (e.g. a seasonal bond)? A theory exists that romantic love evolved by co-opting the systems for mother-infant bonding, but this does not explain when or why (under what

selection pressure Evolutionary pressure, selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection. It is a quantitative description of the amount of change oc ...

) romantic love evolved.

Neuroscience and cognition

Neurophysiology

Cognition and psychology

Non-human biology

Ecology, evolution, and paleontology

Unsolved problems relating to the interactions between organisms and their distribution in the environment include: * Paradox of the plankton. The high

diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce *Diversity marketing, marketing communication targeting diverse customers * ...

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

seems to violate the

competitive exclusion principle In ecology, the competitive exclusion principle, sometimes referred to as Gause's law, is a proposition that two species which compete for the same limited resource cannot coexist at constant population values. When one species has even the slig ...

. *

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were enigmatic tubular and frond-shaped, mostly sessile, organis ...

. How should Ediacaran biota be classified? Even what kingdom they belong to is unclear. Why were they so decisively displaced by Cambrian biota? * Cambrian explosion. What is the cause of the apparent rapid diversification of multicellular animal life around the beginning of the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

, resulting in the emergence of almost all modern animal

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phy ...

? * Darwin's abominable mystery of

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s. What is the exact evolutionary history of

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s and what is the cause of the apparently sudden appearance of nearly modern flowers in the fossil record? * Adult form of Facetotecta. The adult form of this animal has never been encountered in the water, and it remains a mystery what it grows into. * Origin of

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s. Did snakes evolve from burrowing lizards or aquatic lizards? There is evidence for both hypotheses. * Origin of

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

s. Did turtles evolve from

anapsid An anapsid is an amniote whose skull lacks one or more skull openings (fenestra, or fossae) near the temples. Traditionally, the Anapsida are considered the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Dia ...

s or

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...

s? There is evidence for both hypotheses. * '' Paleodictyon'': What is the origin of this trace fossil and its modern counterparts? Despite many theories proposed, no evidence has been found to confirm any of them. * Francevillian biota: were they early multicellular organisms? *

Snowball Earth The Snowball Earth is a historical geology, geohistorical hypothesis that proposes that during one or more of Earth's greenhouse and icehouse Earth, icehouse climates, the planet's planetary surface, surface became nearly entirely freezing, fr ...

: what was the effect of

Cryogenian The Cryogenian (from , meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran. The Cryoge ...

glaciations on the origin and evolution of early animals? * '' Eocyathispongia'': is it an early

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

? Did it have

choanocyte Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or ''cilium,'' surrounded by a collar of microvilli which are connected by ...

s? * '' Vernanimalcula guizhouena'': is this fossil organism an early

bilaterian Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–r ...

? * '' Tullimonstrum'': a taxonomic position of this fossil organism is unknown. * Adult form of ''

Planctosphaera pelagica ''Planctosphaera pelagica'' is a hemichordate Hemichordata ( ) is a phylum which consists of triploblastic, eucoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. The ...

'', a

hemichordate Hemichordata ( ) is a phylum which consists of triploblastic, eucoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and incl ...

known, as of 2023, only by its tornaria

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

. Due to differences between larvae of

acorn worm The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in th ...

s and that of ''

'', ''Planctosphaera'' is sometimes given its own

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

. *

Xenacoelomorpha Xenacoelomorpha () is a small phylum of bilaterian invertebrate animals, consisting of two sister groups: xenoturbellids and acoelomorphs. This new phylum was named in February 2011 and suggested based on morphological synapomorphies (physica ...

: are they

deuterostome Deuterostomes (from Greek: ) are bilaterian animals of the superphylum Deuterostomia (), typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, ...

s, forming a clade Xenambulacraria together with

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s and

s, or rather primitive

bilateria Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left� ...

ns and a sister group to

Nephrozoa Nephrozoa is a proposed major clade of bilaterian animals. Under this hypothesis, Xenacoelomorpha forms the earliest diverging branch of Bilateria, with all other bilaterians placed in Nephrozoa. It contrasts with the Xenambulacraria hypothesis, ...

? *'' Jennaria pulchra'': the taxonomic position of this animal is unknown and more research is needed to establish it. *

Nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

of Lobatocerebrida. Why do these simple unsegmented

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

s, which are unselective deposit feeders and lack

sense organ A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of Stimulus (physiology), stimuli. Although, in some cultures, five human senses were traditio ...

s, have a relatively complex

? * '' Diurodrilus'': is it an unusual annelid? What are the origins of morphological similarities between '' Diurodrilus'' and micrognathozoan '' Limnognathia maerski''? * Taxonomic position of pentastomids. Are they a sister group to

Argulidae The family Argulidae, whose members are commonly known as carp lice or fish lice, are parasitic crustaceans in the class Ichthyostraca. It is the only family in the monotypic subclass Branchiura and the order Arguloida, although a second famil ...

or an ancient lineage of

Panarthropoda Panarthropoda is a clade comprising the greatest diversity of animal groups. It contains the extant phyla Arthropoda (Euarthropoda), Tardigrada (water bears) and Onychophora (velvet worms), although the precise relationships among these remained ...

? * Taxonomic position of '' Tricholepidion gertschi'': is it a member of the order

Zygentoma Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order are the three long caudal filaments. The t ...

(silverfishes) or an independent ancient lineage of

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s? * How will organisms respond to complex, novel environments? Climate change is of significant relevance. * What is the relative importance of variability, across scales, and its mechanisms? * Why does intragenotypic variability persist? Striking phenotypic differences exist even among individuals with identical genotypes, and environments. * What determines

population density Population density (in agriculture: Standing stock (disambiguation), standing stock or plant density) is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geog ...

? There is disagreement over which regulatory mechanisms of population are density-dependent, or density-independent. * Why are all leaves the size they are, and not an order of magnitude larger or smaller? How is the upper limit on leaf size set? * Persistence paradox: why does the evolution of novel species almost never lead to the extinction of resident species? * Is the ecosystem a

superorganism A superorganism, or supraorganism, is a group of synergetically interacting organisms of the same species. A community of synergetically interacting organisms of different species is called a '' holobiont''. Concept The term superorganism is ...

, or a collection of organisms? Could the Earth be a superorganism, or a

unit of selection A unit of selection is a biological entity within the hierarchy of biological organization (for example, an entity such as: a self-replicating molecule, a gene, a cell, an organism, a group, or a species) that is subject to natural selection. ...

? * Why do '' Pogonomyrmex badius'' colonies cover the surface of their nests with a circular region of charcoal pieces?

Ethology

Unsolved problems relating to the behaviour of animals include: * Homing. A satisfactory explanation for the neurobiological mechanisms that allow homing in animals has yet to be found. *

Flocking (behavior) Flocking is the behavior exhibited when a group of birds, called a flock, are foraging or in flight. Sheep and goats also exhibit flocking behavior. Flocking by birds and mammals is similar to schooling in fish and these are often studied toge ...

. How flocks of birds and bats coordinate their movements so quickly is not fully understood. Nor is the purpose of large flocks like those of starlings which seem to invite predators rather than protect them. *

Butterfly migration Many populations of Lepidoptera (butterfly, butterflies or moths) migrate, sometimes long distances, to and from areas which are only suitable for part of the year. Lepidopterans migrate on all continents except Antarctica, including from or w ...

. How do the descendants of

monarch butterfly The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. I ...

all over Canada and the US eventually, after migrating for several generations, manage to return to a few relatively small overwintering spots? *

Blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known ever to have existed. The blue whale's long and slender body can ...

. There is not much data on the sexuality of the blue whale. * Gall-inducing insects. At least seven groups of insects, in six orders, have independently evolved the gall-inducing habit. Several adaptation hypotheses have been proposed, but it is largely unknown why this habit evolved and how gall-inducing insects induce gall formation in plants; chemical, mechanical, and viral triggers have been discussed.

Non-human organs and biomolecules

Unsolved problems relating to the structure and function of non-human organs, processes and biomolecules include: * Korarchaeota (archaea). The metabolic processes of this phylum of archaea are so far unclear. *

Glycogen body A glycogen body is an oval structure in the spinal cord of birds that is made of specialized cells that contain large amounts of glycogen. Housed within the synsacrum, the function of this structure is not known, but it does not seem to be rel ...

. The function of this structure in the spinal cord of birds is not known. *

Arthropod head problem The (pan)arthropod head problem is a long-standing zoological dispute concerning the Segmentation (biology), segmental composition of the heads of the various arthropod groups, and how they are evolutionarily related to each other. While the dis ...

. A long-standing zoological dispute concerning the segmental composition of the heads of the various arthropod groups, and how they are evolutionarily related to each other. *Ovaries of

basking shark The basking shark (''Cetorhinus maximus'') is the second-largest living shark and fish, after the whale shark. It is one of three Planktivore, plankton-eating shark species, along with the whale shark and megamouth shark. Typically, basking sh ...

s. Only the right ovary in female basking sharks appears to function. The reason is unknown. *Brightly colored bird eggs. It is unknown what evolutionary process would lead birds to having brightly colored eggs given the increased visibility to predators. * Stegosaur osteoderms/scutes. There is a long-standing debate over whether the primary function of the osteoderms/scutes of stegosaurs is protection from predators, sexual display, species recognition, thermoregulation, or other functions. *Function of vanadocytes, a type of

blood cell A blood cell (also called a hematopoietic cell, hemocyte, or hematocyte) is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...

s found in some

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

Vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s of vanadocytes are notable for high levels of the metal

vanadium Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

and their low pH. *

Metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

in ''

Henneguya zschokkei ''Henneguya zschokkei'' or ''Henneguya salminicola'' is a species of a myxosporean endoparasite. It afflicts several salmon and trout in the genera ''Oncorhynchus'' and ''Salmo'','' ''where it causes milky flesh or tapioca disease''. H. ...

'', a species of

myxozoa Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. ...

n. This species of

cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

n was found to lack

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

and, therefore, is incapable of

aerobic respiration Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...

. *

Mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

loricifera Loricifera (from Latin, ''wikt:lorica, lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals with 43 described species and approximately 100 more that hav ...

ns living in anoxic conditions. It is unknown whether members of the phylum

Loricifera Loricifera (from Latin, ''wikt:lorica, lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals with 43 described species and approximately 100 more that hav ...

adapted to life in anoxic conditions in the

L'Atalante basin L'Atalante basin is a hypersaline brine lake at the bottom of the Mediterranean Sea about west of the island of Crete. It is named for the French ''L'Atalante'', one of the oceanographic research vessels involved in its discovery in 1993. L'At ...

, like '' Spinoloricus cinziae'', have

Artificial life

Unsolved problems in

artificial life Artificial life (ALife or A-Life) is a field of study wherein researchers examine systems related to natural life, its processes, and its evolution, through the use of simulations with computer models, robotics, and biochemistry. The discipline ...

include: *How does life arise from the non-living? *What are the potentials and limits of living systems? *How is life related to mind, machines, and culture?

References

{{DEFAULTSORT:List Of Unsolved Problems In Biology

Unsolved problems List of unsolved problems may refer to several notable conjectures or open problems in various academic fields: Natural sciences, engineering and medicine * Unsolved problems in astronomy * Unsolved problems in biology * Unsolved problems in ch ...

Biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...