A multicellular organism is an organism that consists of more than one cell , unlike unicellular organisms . All species of animals , land plants and most fungi are multicellular, as are many algae , whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium .
122-418: Animals are multicellular , eukaryotic organisms in the biological kingdom Animalia ( / ˌ æ n ɪ ˈ m eɪ l i ə / ). With few exceptions, animals consume organic material , breathe oxygen , have myocytes and are able to move , can reproduce sexually , and grow from a hollow sphere of cells, the blastula , during embryonic development . Animals form a clade , meaning that they arose from
244-615: A deist . The philosopher of biology Michael Ruse described Lamarck, "as believing in God as an unmoved mover, creator of the world and its laws, who refuses to intervene miraculously in his creation." Biographer James Moore described Lamarck as a "thoroughgoing deist". The historian Jacques Roger has written, "Lamarck was a materialist to the extent that he did not consider it necessary to have recourse to any spiritual principle... his deism remained vague, and his idea of creation did not prevent him from believing everything in nature, including
366-416: A gastrula with a digestive chamber and two separate germ layers , an external ectoderm and an internal endoderm . In most cases, a third germ layer, the mesoderm , also develops between them. These germ layers then differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within a population due to
488-455: A botany book by James Francis Chomel. With a reduced pension of only 400 francs a year, Lamarck resolved to pursue a profession. He attempted to study medicine, and supported himself by working in a bank office. Lamarck studied medicine for four years, but gave it up under his elder brother's persuasion. He was interested in botany , especially after his visits to the Jardin du Roi , and he became
610-545: A clade Xenambulacraria for the Xenacoelamorpha + Ambulacraria; this is either within Deuterostomia, as sister to Chordata, or the Deuterostomia are recovered as paraphyletic, and Xenambulacraria is sister to the proposed clade Centroneuralia , consisting of Chordata + Protostomia. Eumetazoa , a clade which contains Ctenophora and ParaHoxozoa , has been proposed as a sister group to Porifera . A competing hypothesis
732-435: A eulogy to denigrate Lamarck: [Cuvier's] éloge of Lamarck is one of the most deprecatory and chillingly partisan biographies I have ever read—though he was supposedly writing respectful comments in the old tradition of de mortuis nil nisi bonum . While he was working on Hydrogéologie (1802), Lamarck had the idea to apply the principle of erosion to biology. This led him to the basic principle of evolution, which saw
854-543: A force adapting animals to their local environments and differentiating them from each other. He believed that these forces must be explained as a necessary consequence of basic physical principles, favoring a materialistic attitude toward biology. Lamarck referred to a tendency for organisms to become more complex, moving "up" a ladder of progress . He referred to this phenomenon as Le pouvoir de la vie or la force qui tend sans cesse à composer l'organisation (The force that perpetually tends to make order). Lamarck believed in
976-475: A major work on the classification of invertebrates. In the work, he introduced definitions of natural groups among invertebrates. He categorized echinoderms , arachnids , crustaceans , and annelids , which he separated from the old taxon for worms known as Vermes . Lamarck was the first to separate arachnids from insects in classification, and he moved crustaceans into a separate class from insects. In 1802, Lamarck published Hydrogéologie , and became one of
1098-444: A more well-established alternative. Lamarck is usually remembered for his belief in the then commonly held theory of inheritance of acquired characteristics , and the use and disuse model by which organisms developed their characteristics. Lamarck incorporated this belief into his theory of evolution, along with other common beliefs of the time, such as spontaneous generation. The inheritance of acquired characteristics (also called
1220-457: A motile single-celled propagule ; this single cell asexually reproduces by undergoing 2–5 rounds of mitosis as a small clump of non-motile cells, then all cells become single-celled propagules and the clump dissolves. With a few generations under Paramecium predation, the "clump" becomes a persistent structure: only some cells become propagules. Some populations go further and evolved multi-celled propagules: instead of peeling off single cells from
1342-449: A role for use and disuse as an evolutionary mechanism subsidiary to natural selection, most often in respect of disuse . He praised Lamarck for "the eminent service of arousing attention to the probability of all change in the organic... world, being the result of law, not miraculous interposition". Lamarckism is also occasionally used to describe quasi-evolutionary concepts in societal contexts, though not by Lamarck himself. For example,
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#17328522265331464-418: A separation between a sterile somatic cell line and a germ cell line evolved. However, Weismannist development is relatively rare (e.g., vertebrates, arthropods, Volvox ), as a great part of species have the capacity for somatic embryogenesis (e.g., land plants, most algae, many invertebrates). One hypothesis for the origin of multicellularity is that a group of function-specific cells aggregated into
1586-531: A single common ancestor . Over 1.5 million living animal species have been described , of which around 1.05 million are insects , over 85,000 are molluscs , and around 65,000 are vertebrates . It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs . The scientific study of animals
1708-410: A single cell organism to one of many cells. Genes borrowed from viruses and mobile genetic elements (MGEs) have recently been identified as playing a crucial role in the differentiation of multicellular tissues and organs and even in sexual reproduction, in the fusion of egg cells and sperm. Such fused cells are also involved in metazoan membranes such as those that prevent chemicals from crossing
1830-404: A single opening, which serves as both mouth and anus. Animals in both phyla have distinct tissues, but these are not organised into discrete organs . They are diploblastic , having only two main germ layers, ectoderm and endoderm. Multicellular Multicellular organisms arise in various ways, for example by cell division or by aggregation of many single cells. Colonial organisms are
1952-414: A single species. Although such symbiosis is theorized to have occurred (e.g., mitochondria and chloroplasts in animal and plant cells— endosymbiosis ), it has happened only extremely rarely and, even then, the genomes of the endosymbionts have retained an element of distinction, separately replicating their DNA during mitosis of the host species. For instance, the two or three symbiotic organisms forming
2074-407: A slug-like mass called a grex , which moved as a multicellular unit. This is essentially what slime molds do. Another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a coenocyte . A membrane would then form around each nucleus (and the cellular space and organelles occupied in the space), thereby resulting in a group of connected cells in one organism (this mechanism
2196-506: A small element of his theory of evolution, and was in his time accepted by many natural historians. Lamarck's contribution to evolutionary theory consisted of the first truly cohesive theory of biological evolution, in which an alchemical complexifying force drove organisms up a ladder of complexity, and a second environmental force adapted them to local environments through use and disuse of characteristics, differentiating them from other organisms. Scientists have debated whether advances in
2318-592: A student under Bernard de Jussieu , a notable French naturalist. Under Jussieu, Lamarck spent 10 years studying French flora. In 1776, he wrote his first scientific essay—a chemical treatise. After his studies, in 1778, he published some of his observations and results in a three-volume work, entitled Flore française . Lamarck's work was respected by many scholars, and it launched him into prominence in French science. On 8 August 1778, Lamarck married Marie Anne Rosalie Delaporte. Georges-Louis Leclerc, Comte de Buffon , one of
2440-460: Is a consumer–resource interaction where the predator feeds on another organism, its prey , who often evolves anti-predator adaptations to avoid being fed upon. Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various antagonistic/ competitive coevolutions . Almost all multicellular predators are animals. Some consumers use multiple methods; for example, in parasitoid wasps ,
2562-431: Is a stage in embryonic development that is unique to animals, allowing cells to be differentiated into specialised tissues and organs. All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins . During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised, making
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#17328522265332684-413: Is also considered probable in some green algae (e.g., Chlorella vulgaris and some Ulvophyceae ). In other groups, generally parasites, a reduction of multicellularity occurred, in the number or types of cells (e.g., the myxozoans , multicellular organisms, earlier thought to be unicellular, are probably extremely reduced cnidarians ). Multicellular organisms, especially long-living animals, face
2806-558: Is also typically considered to involve cellular differentiation . The advantage of the Colonial Theory hypothesis is that it has been seen to occur independently in 16 different protoctistan phyla. For instance, during food shortages the amoeba Dictyostelium groups together in a colony that moves as one to a new location. Some of these amoeba then slightly differentiate from each other. Other examples of colonial organisation in protista are Volvocaceae , such as Eudorina and Volvox ,
2928-448: Is debatable: The vast majority of living organisms are single celled, and even in terms of biomass, single celled organisms are far more successful than animals, although not plants. Rather than seeing traits such as longer lifespans and greater size as an advantage, many biologists see these only as examples of diversity, with associated tradeoffs. During the evolutionary transition from unicellular organisms to multicellular organisms,
3050-450: Is disputed, as they might be water-escape or other structures. Animals are monophyletic , meaning they are derived from a common ancestor. Animals are the sister group to the choanoflagellates , with which they form the Choanozoa . The dates on the phylogenetic tree indicate approximately how many millions of years ago ( mya ) the lineages split. Ros-Rocher and colleagues (2021) trace
3172-670: Is inexact, as living multicellular organisms such as animals and plants are more than 500 million years removed from their single-cell ancestors. Such a passage of time allows both divergent and convergent evolution time to mimic similarities and accumulate differences between groups of modern and extinct ancestral species. Modern phylogenetics uses sophisticated techniques such as alloenzymes , satellite DNA and other molecular markers to describe traits that are shared between distantly related lineages. The evolution of multicellularity could have occurred in several different ways, some of which are described below: This theory suggests that
3294-450: Is known as zoology , and the study of animal behaviour is known as ethology . The animal kingdom is divided into five infrakingdoms / superphyla , namely Porifera , Ctenophora , Placozoa , Cnidaria and Bilateria . Most living animal species belong to the infrakingdom Bilateria, a highly proliferative clade whose members have a bilaterally symmetric body plan , and the vast majority of bilaterians belong to two large superphyla :
3416-410: Is now called soft inheritance , the inheritance of acquired characteristics, or simply "Lamarckism", though it forms only a part of Lamarck's thinking. However, in the field of epigenetics , evidence is growing that soft inheritance plays a part in the changing of some organisms' phenotypes; it leaves the genetic material ( DNA ) unaltered (thus not violating the central dogma of biology ) but prevents
3538-533: Is observable in Drosophila ). A third hypothesis is that as a unicellular organism divided, the daughter cells failed to separate, resulting in a conglomeration of identical cells in one organism, which could later develop specialized tissues. This is what plant and animal embryos do as well as colonial choanoflagellates . Because the first multicellular organisms were simple, soft organisms lacking bone, shell, or other hard body parts, they are not well preserved in
3660-794: Is often used to refer only to nonhuman animals. The term metazoa is derived from Ancient Greek μετα ( meta ) 'after' (in biology, the prefix meta- stands for 'later') and ζῷᾰ ( zōia ) 'animals', plural of ζῷον zōion 'animal'. Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular . Unlike plants and algae , which produce their own nutrients , animals are heterotrophic , feeding on organic material and digesting it internally. With very few exceptions, animals respire aerobically . All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle , but some animals, such as sponges , corals , mussels , and barnacles , later become sessile . The blastula
3782-420: Is only produced by sponges and pelagophyte algae. Its likely origin is from sponges based on molecular clock estimates for the origin of 24-ipc production in both groups. Analyses of pelagophyte algae consistently recover a Phanerozoic origin, while analyses of sponges recover a Neoproterozoic origin, consistent with the appearance of 24-ipc in the fossil record. The first body fossils of animals appear in
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3904-425: Is presumed land-evolved - multicellularity occurs by cells separating and then rejoining (e.g., cellular slime molds ) whereas for the majority of multicellular types (those that evolved within aquatic environments), multicellularity occurs as a consequence of cells failing to separate following division. The mechanism of this latter colony formation can be as simple as incomplete cytokinesis , though multicellularity
4026-407: Is remembered, at least in malacology , as a taxonomist of considerable stature. The modern era generally remembers Lamarck for a theory of inheritance of acquired characteristics , called Lamarckism (inaccurately named after him), soft inheritance, or use/disuse theory, which he described in his 1809 Philosophie zoologique . However, the idea of soft inheritance long antedates him, formed only
4148-419: Is sometimes regarded as believing in a teleological (goal-oriented) process where organisms became more perfect as they evolved, though as a materialist, he emphasized that these forces must originate necessarily from underlying physical principles. According to the paleontologist Henry Fairfield Osborn , "Lamarck denied, absolutely, the existence of any 'perfecting tendency' in nature, and regarded evolution as
4270-535: Is the Benthozoa clade, which would consist of Porifera and ParaHoxozoa as a sister group of Ctenophora . Several animal phyla lack bilateral symmetry. These are the Porifera (sea sponges), Placozoa , Cnidaria (which includes jellyfish , sea anemones , and corals), and Ctenophora (comb jellies). Sponges are physically very distinct from other animals, and were long thought to have diverged first, representing
4392-506: The Cambrian explosion shortly after the Marinoan. The predation hypothesis suggests that to avoid being eaten by predators, simple single-celled organisms evolved multicellularity to make it harder to be consumed as prey. Herron et al. performed laboratory evolution experiments on the single-celled green alga, Chlamydomonas reinhardtii , using paramecium as a predator. They found that in
4514-555: The Cambrian explosion , which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived about 650 Mya during the Cryogenian period. Historically, Aristotle divided animals into those with blood and those without . Carl Linnaeus created
4636-476: The Cryogenian period and consisted of two global glaciation events known as the Sturtian and Marinoan glaciations. Xiao et al . suggest that between the period of time known as the " Boring Billion " and the snowball Earth, simple life could have had time to innovate and evolve, which could later lead to the evolution of multicellularity. The snowball Earth hypothesis in regards to multicellularity proposes that
4758-577: The Ediacaran is not necessary for complex life and therefore is unlikely to have been the driving factor for the origin of multicellularity. A snowball Earth is a geological event where the entire surface of the Earth is covered in snow and ice. The term can either refer to individual events (of which there were at least two) or to the larger geologic period during which all the known total glaciations occurred. The most recent snowball Earth took place during
4880-558: The Ediacaran , represented by forms such as Charnia and Spriggina . It had long been doubted whether these fossils truly represented animals, but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes their nature. Animals are thought to have originated under low-oxygen conditions, suggesting that they were capable of living entirely by anaerobic respiration , but as they became specialized for aerobic metabolism they became fully dependent on oxygen in their environments. Many animal phyla first appear in
5002-464: The Muséum national d'Histoire naturelle in 1793, Lamarck became a professor of zoology . In 1801, he published Système des animaux sans vertèbres , a major work on the classification of invertebrates , a term which he coined. In an 1802 publication, he became one of the first to use the term " biology " in its modern sense. Lamarck continued his work as a premier authority on invertebrate zoology . He
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5124-480: The Wnt and TGF-beta signalling pathways which may have enabled animals to become multicellular by providing a pattern for the body's system of axes (in three dimensions), and another 7 are for transcription factors including homeodomain proteins involved in the control of development . Giribet and Edgecombe (2020) provide what they consider to be a consensus internal phylogeny of the animals, embodying uncertainty about
5246-636: The Xenophyophorea that can reach 20 cm. Multicellularity has evolved independently at least 25 times in eukaryotes , and also in some prokaryotes , like cyanobacteria , myxobacteria , actinomycetes , Magnetoglobus multicellularis or Methanosarcina . However, complex multicellular organisms evolved only in six eukaryotic groups: animals , symbiomycotan fungi , brown algae , red algae , green algae , and land plants . It evolved repeatedly for Chloroplastida (green algae and land plants), once for animals, once for brown algae, three times in
5368-665: The evolutionary relationships between taxa . Humans make use of many other animal species for food (including meat , eggs , and dairy products ), for materials (such as leather , fur , and wool ), as pets and as working animals for transportation , and services . Dogs , the first domesticated animal, have been used in hunting , in security and in warfare , as have horses , pigeons and birds of prey ; while other terrestrial and aquatic animals are hunted for sports, trophies or profits. Non-human animals are also an important cultural element of human evolution , having appeared in cave arts and totems since
5490-467: The fossil record during the Cambrian explosion , starting about 539 million years ago, in beds such as the Burgess shale . Extant phyla in these rocks include molluscs , brachiopods , onychophorans , tardigrades , arthropods , echinoderms and hemichordates , along with numerous now-extinct forms such as the predatory Anomalocaris . The apparent suddenness of the event may however be an artifact of
5612-429: The fungi ( chytrids , ascomycetes , and basidiomycetes ) and perhaps several times for slime molds and red algae. The first evidence of multicellular organization, which is when unicellular organisms coordinate behaviors and may be an evolutionary precursor to true multicellularity, is from cyanobacteria -like organisms that lived 3.0–3.5 billion years ago. To reproduce, true multicellular organisms must solve
5734-493: The lobe-finned fish Tiktaalik started to move on to land in the late Devonian , about 375 million years ago. Animals occupy virtually all of earth's habitats and microhabitats, with faunas adapted to salt water, hydrothermal vents, fresh water, hot springs, swamps, forests, pastures, deserts, air, and the interiors of other organisms. Animals are however not particularly heat tolerant ; very few of them can survive at constant temperatures above 50 °C (122 °F) or in
5856-407: The memetic theory of cultural evolution is sometimes described as a form of Lamarckian inheritance of nongenetic traits. During his lifetime, Lamarck named a large number of species, many of which have become synonyms. The World Register of Marine Species gives no fewer than 1,634 records. The Indo-Pacific Molluscan Database gives 1,781 records. Among these are some well-known families such as
5978-561: The placenta and the brain body separation. Two viral components have been identified. The first is syncytin , which came from a virus. The second identified in 2002 is called EFF-1 , which helps form the skin of Caenorhabditis elegans , part of a whole family of FF proteins. Felix Rey, of the Pasteur Institute in Paris, has constructed the 3D structure of the EFF-1 protein and shown it does
6100-495: The protostomes , which includes organisms such as arthropods , molluscs , flatworms , annelids and nematodes ; and the deuterostomes , which include echinoderms , hemichordates and chordates , the latter of which contains the vertebrates . The much smaller basal phylum Xenacoelomorpha have an uncertain position within Bilateria. Animals first appear in the fossil record in the late Cryogenian period and diversified in
6222-504: The Academie for financial assistance. Lamarck was buried in a common grave of the Montparnasse cemetery for just five years, according to the grant obtained from relatives. Later, the body was dug up along with other remains and was lost. Lamarck's books and the contents of his home were sold at auction, and his body was buried in a temporary lime pit. After his death, Cuvier used the form of
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#17328522265336344-695: The Cambrian explosion, possibly as early as 1 billion years ago. Early fossils that might represent animals appear for example in the 665-million-year-old rocks of the Trezona Formation of South Australia . These fossils are interpreted as most probably being early sponges . Trace fossils such as tracks and burrows found in the Tonian period (from 1 gya) may indicate the presence of triploblastic worm-like animals, roughly as large (about 5 mm wide) and complex as earthworms. However, similar tracks are produced by
6466-706: The Cnidaria) never grow larger than 20 μm , and one of the smallest species ( Myxobolus shekel ) is no more than 8.5 μm when fully grown. The following table lists estimated numbers of described extant species for the major animal phyla, along with their principal habitats (terrestrial, fresh water, and marine), and free-living or parasitic ways of life. Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of
6588-517: The Cryogenian period in Earth's history could have been the catalyst for the evolution of complex multicellular life. Brocks suggests that the time between the Sturtian Glacian and the more recent Marinoan Glacian allowed for planktonic algae to dominate the seas making way for rapid diversity of life for both plant and animal lineages. Complex life quickly emerged and diversified in what is known as
6710-576: The Paris Basin, he grew convinced that transmutation or change in the nature of a species occurred over time. He set out to develop an explanation, and on 11 May 1800 (the 21st day of Floreal , Year VIII, in the revolutionary timescale used in France at the time), he presented a lecture at the Muséum national d'histoire naturelle in which he first outlined his newly developing ideas about evolution. In 1801, he published Système des Animaux sans Vertèbres ,
6832-468: The Royal Garden, and also other objects of natural history, such as minerals and ores, that were not found in French museums. On 7 January 1786, his second son, Antoine, was born, and Lamarck chose Antoine Laurent de Jussieu , Bernard de Jussieu's nephew, as the boy's godfather. On 21 April the following year, Charles René, Lamarck's third son, was born. René Louiche Desfontaines , a professor of botany at
6954-404: The Royal Garden, was the boy's godfather, and Lamarck's elder sister, Marie Charlotte Pelagie De Monet, was the godmother. In 1788, Buffon's successor at the position of Intendant of the Royal Garden, Charles-Claude Flahaut de la Billaderie, comte d'Angiviller , created a position for Lamarck, with a yearly salary of 1,000 francs, as the keeper of the herbarium of the Royal Garden. In 1790, at
7076-475: The appearance of metazoans are deregulated in cancer cells, including genes that control cell differentiation , adhesion and cell-to-cell communication . There is a discussion about the possibility of existence of cancer in other multicellular organisms or even in protozoa . For example, plant galls have been characterized as tumors , but some authors argue that plants do not develop cancer. In some multicellular groups, which are called Weismannists ,
7198-528: The ark clams ( Arcidae ), the sea hares ( Aplysiidae ), and the cockles ( Cardiidae ). The International Plant Names Index gives 58 records, including a number of well-known genera such as the mosquito fern ( Azolla ). The honeybee subspecies Apis mellifera lamarckii is named after Lamarck, as well as the bluefire jellyfish ( Cyaneia lamarckii ). A number of plants have also been named after him, including Amelanchier lamarckii (juneberry), Digitalis lamarckii , and Aconitum lamarckii , as well as
7320-585: The army after being injured in 1766, and returned to his medical studies. Lamarck developed a particular interest in botany, and later, after he published the three-volume work Flore françoise (1778), he gained membership of the French Academy of Sciences in 1779. Lamarck became involved in the Jardin des Plantes and was appointed to the Chair of Botany in 1788. When the French National Assembly founded
7442-415: The assembly of professors for the museum for a period of one year. In 1797, Charlotte died, and he married Julie Mallet the following year; she died in 1819. In his first six years as professor, Lamarck published only one paper, in 1798, on the influence of the moon on the Earth's atmosphere. Lamarck began as an essentialist who believed species were unchanging; however, after working on the molluscs of
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#17328522265337564-425: The challenge of cancer , which occurs when cells fail to regulate their growth within the normal program of development. Changes in tissue morphology can be observed during this process. Cancer in animals ( metazoans ) has often been described as a loss of multicellularity and an atavistic reversion towards a unicellular-like state. Many genes responsible for the establishment of multicellularity that originated around
7686-445: The classical four elements . During Lamarck's lifetime, he became controversial, attacking the more enlightened chemistry proposed by Lavoisier . He also came into conflict with the widely respected palaeontologist Georges Cuvier , who was not a supporter of evolution. According to Peter J. Bowler , Cuvier "ridiculed Lamarck's theory of transformation and defended the fixity of species." According to Martin J. S. Rudwick : Cuvier
7808-704: The clump, the clump now reproduces by peeling off smaller clumps. Multicellularity allows an organism to exceed the size limits normally imposed by diffusion : single cells with increased size have a decreased surface-to-volume ratio and have difficulty absorbing sufficient nutrients and transporting them throughout the cell. Multicellular organisms thus have the competitive advantages of an increase in size without its limitations. They can have longer lifespans as they can continue living when individual cells die. Multicellularity also permits increasing complexity by allowing differentiation of cell types within one organism. Whether all of these can be seen as advantages however
7930-449: The composite lichen , although dependent on each other for survival, have to separately reproduce and then re-form to create one individual organism once more. This theory states that a single unicellular organism, with multiple nuclei , could have developed internal membrane partitions around each of its nuclei. Many protists such as the ciliates or slime molds can have several nuclei, lending support to this hypothesis . However,
8052-454: The dark sea floor consume organic matter produced through chemosynthesis (via oxidizing inorganic compounds such as hydrogen sulfide ) by archaea and bacteria . Animals evolved in the sea. Lineages of arthropods colonised land around the same time as land plants , probably between 510 and 471 million years ago during the Late Cambrian or Early Ordovician . Vertebrates such as
8174-448: The earliest times, and are frequently featured in mythology , religion , arts , literature , heraldry , politics , and sports . The word animal comes from the Latin noun animal of the same meaning, which is itself derived from Latin animalis 'having breath or soul'. The biological definition includes all members of the kingdom Animalia. In colloquial usage, the term animal
8296-459: The expression of genes associated with reproduction and survival likely changed. In the unicellular state, genes associated with reproduction and survival are expressed in a way that enhances the fitness of individual cells, but after the transition to multicellularity, the pattern of expression of these genes must have substantially changed so that individual cells become more specialized in their function relative to reproduction and survival. As
8418-413: The expression of genes , such as by methylation to modify DNA transcription ; this can be produced by changes in behaviour and environment. Many epigenetic changes are heritable to a degree. Thus, while DNA itself is not directly altered by the environment and behavior except through selection, the relationship of the genotype to the phenotype can be altered, even across generations, by experience within
8540-598: The field of transgenerational epigenetics mean that Lamarck was to an extent correct, or not. Jean-Baptiste Lamarck was born in Bazentin , Picardy , northern France, as the 11th child in an impoverished aristocratic family. Male members of the Lamarck family had traditionally served in the French army. Lamarck's eldest brother was killed in combat at the Siege of Bergen op Zoom , and two other brothers were still in service when Lamarck
8662-425: The final necessary effect of surrounding conditions on life." Charles Coulston Gillispie , a historian of science, has written "life is a purely physical phenomenon in Lamarck", and argued that Lamarck's views should not be confused with the vitalist school of thought. The second component of Lamarck's theory of evolution was the adaptation of organisms to their environment. This could move organisms upward from
8784-565: The first hierarchical biological classification for animals in 1758 with his Systema Naturae , which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa , single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics , which are effective at demonstrating
8906-446: The first multicellular organisms occurred from symbiosis (cooperation) of different species of single-cell organisms, each with different roles. Over time these organisms would become so dependent on each other that they would not be able to survive independently, eventually leading to the incorporation of their genomes into one multicellular organism. Each respective organism would become a separate lineage of differentiated cells within
9028-400: The first theoretical frameworks of organic evolution . While this theory was generally rejected during his lifetime, Stephen Jay Gould argues that Lamarck was the "primary evolutionary theorist", in that his ideas, and the way in which he structured his theory, set the tone for much of the subsequent thinking in evolutionary biology, through to the present day. Developments in epigenetics ,
9150-408: The first to use the term biology in its modern sense . In Hydrogéologie , Lamarck advocated a steady-state geology based on a strict uniformitarianism . He argued that global currents tended to flow from east to west, and continents eroded on their eastern borders, with the material carried across to be deposited on the western borders. Thus, the Earth's continents marched steadily westward around
9272-417: The fluids in organs inheriting more complex forms and functions, thus passing on these traits to the organism's descendants. This was a reversal from Lamarck's previous view, published in his Memoirs of Physics and Natural History (1797), in which he briefly refers to the immutability of species. Lamarck stressed two main themes in his biological work (neither of them to do with soft inheritance). The first
9394-445: The formation of complex structures possible. This may be calcified, forming structures such as shells , bones , and spicules . In contrast, the cells of other multicellular organisms (primarily algae, plants, and fungi ) are held in place by cell walls, and so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions , gap junctions , and desmosomes . With few exceptions—in particular,
9516-514: The fossil record, rather than showing that all these animals appeared simultaneously. That view is supported by the discovery of Auroralumina attenboroughii , the earliest known Ediacaran crown-group cnidarian (557–562 mya, some 20 million years before the Cambrian explosion) from Charnwood Forest , England. It is thought to be one of the earliest predators , catching small prey with its nematocysts as modern cnidarians do. Some palaeontologists have suggested that animals appeared much earlier than
9638-715: The fossil record. One exception may be the demosponge , which may have left a chemical signature in ancient rocks. The earliest fossils of multicellular organisms include the contested Grypania spiralis and the fossils of the black shales of the Palaeoproterozoic Francevillian Group Fossil B Formation in Gabon ( Gabonionta ). The Doushantuo Formation has yielded 600 million year old microfossils with evidence of multicellular traits. Until recently, phylogenetic reconstruction has been through anatomical (particularly embryological ) similarities. This
9760-718: The giant single-celled protist Gromia sphaerica , so the Tonian trace fossils may not indicate early animal evolution. Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals. Objects such as sediment-filled tubes that resemble trace fossils of the burrows of wormlike animals have been found in 1.2 gya rocks in North America, in 1.5 gya rocks in Australia and North America, and in 1.7 gya rocks in Australia. Their interpretation as having an animal origin
9882-417: The globe. That year, he also published Recherches sur l'Organisation des Corps Vivants , in which he drew out his theory on evolution. He believed that all life was organized in a vertical chain, with gradation between the lowest forms and the highest forms of life, thus demonstrating a path to progressive developments in nature. In his own work, Lamarck had favored the then-more traditional theory based on
10004-473: The height of the French Revolution , Lamarck changed the name of the Royal Garden from Jardin du Roi to Jardin des Plantes , a name that did not imply such a close association with King Louis XVI . Lamarck had worked as the keeper of the herbarium for five years before he was appointed curator and professor of invertebrate zoology at the Muséum national d'histoire naturelle in 1793. During his time at
10126-407: The herbarium, Lamarck's wife gave birth to three more children before dying on 27 September 1792. With the official title of "Professeur d'Histoire naturelle des Insectes et des Vers", Lamarck received a salary of nearly 2,500 francs per year. The following year, on 9 October, he married Charlotte Reverdy, who was 30 years his junior. On 26 September 1794 Lamarck was appointed to serve as secretary of
10248-501: The highest forms of life, was but the result of natural processes." Lamarck is known largely for his views on evolution, which have been dismissed in favour of developments in Darwinism . His theory of evolution only achieved fame after the publication of Charles Darwin 's On the Origin of Species (1859), which spurred critics of Darwin's new theory to fall back on Lamarckian evolution as
10370-1078: The increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding . Some animals are capable of asexual reproduction , which often results in a genetic clone of the parent. This may take place through fragmentation ; budding , such as in Hydra and other cnidarians ; or parthenogenesis , where fertile eggs are produced without mating , such as in aphids . Animals are categorised into ecological groups depending on their trophic levels and how they consume organic material . Such groupings include carnivores (further divided into subcategories such as piscivores , insectivores , ovivores , etc.), herbivores (subcategorized into folivores , graminivores , frugivores , granivores , nectarivores , algivores , etc.), omnivores , fungivores , scavengers / detritivores , and parasites . Interactions between animals of each biome form complex food webs within that ecosystem . In carnivorous or omnivorous species, predation
10492-420: The ladder of progress into new and distinct forms with local adaptations. It could also drive organisms into evolutionary blind alleys, where the organism became so finely adapted that no further change could occur. Lamarck argued that this adaptive force was powered by the interaction of organisms with their environment, by the use and disuse of certain characteristics. The last clause of this law introduces what
10614-438: The larvae feed on the hosts' living tissues, killing them in the process, but the adults primarily consume nectar from flowers. Other animals may have very specific feeding behaviours , such as hawksbill sea turtles which mainly eat sponges . Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers ) through photosynthesis . Herbivores, as primary consumers , eat
10736-453: The latter of which consists of up to 500–50,000 cells (depending on the species), only a fraction of which reproduce. For example, in one species 25–35 cells reproduce, 8 asexually and around 15–25 sexually. However, it can often be hard to separate colonial protists from true multicellular organisms, as the two concepts are not distinct; colonial protists have been dubbed "pluricellular" rather than "multicellular". Some authors suggest that
10858-410: The lieutenancy. Lamarck's company was left exposed to the direct artillery fire of their enemies, and was quickly reduced to just 14 men—with no officers. One of the men suggested that the puny, 17-year-old volunteer should assume command and order a withdrawal from the field; although Lamarck accepted command, he insisted they remain where they had been posted until relieved. When their colonel reached
10980-500: The lifetime of an individual. This has led to calls for biology to reconsider Lamarckian processes in evolution in light of modern advances in molecular biology. In his book Philosophie zoologique , Lamarck referred to God as the "sublime author of nature". Lamarck's religious views are examined in the book Lamarck, the Founder of Evolution (1901) by Alpheus Packard . According to Packard from Lamarck's writings, he may be regarded as
11102-740: The most extreme cold deserts of continental Antarctica . The blue whale ( Balaenoptera musculus ) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long. The largest extant terrestrial animal is the African bush elephant ( Loxodonta africana ), weighing up to 12.25 tonnes and measuring up to 10.67 metres (35.0 ft) long. The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus , which may have weighed as much as 73 tonnes, and Supersaurus which may have reached 39 meters. Several animals are microscopic; some Myxozoa ( obligate parasites within
11224-408: The movements of fluids in living organisms naturally drove them to evolve toward ever greater levels of complexity: The rapid motion of fluids will etch canals between delicate tissues. Soon their flow will begin to vary, leading to the emergence of distinct organs. The fluids themselves, now more elaborate, will become more complex, engendering a greater variety of secretions and substances composing
11346-637: The multicellular organism emerged, gene expression patterns became compartmentalized between cells that specialized in reproduction ( germline cells) and those that specialized in survival ( somatic cells ). As the transition progressed, cells that specialized tended to lose their own individuality and would no longer be able to both survive and reproduce outside the context of the group. Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck ( / l ə ˈ m ɑːr k / ; French: [ʒɑ̃batist lamaʁk] ),
11468-453: The newly created species. This kind of severely co-dependent symbiosis can be seen frequently, such as in the relationship between clown fish and Riterri sea anemones . In these cases, it is extremely doubtful whether either species would survive very long if the other became extinct. However, the problem with this theory is that it is still not known how each organism's DNA could be incorporated into one single genome to constitute them as
11590-614: The oldest animal phylum and forming a sister clade to all other animals. Despite their morphological dissimilarity with all other animals, genetic evidence suggests sponges may be more closely related to other animals than the comb jellies are. Sponges lack the complex organization found in most other animal phyla; their cells are differentiated, but in most cases not organised into distinct tissues, unlike all other animals. They typically feed by drawing in water through pores, filtering out small particles of food. The comb jellies and Cnidaria are radially symmetric and have digestive chambers with
11712-404: The ongoing spontaneous generation of simple living organisms through action on physical matter by a material life force. Lamarck ran against the modern chemistry promoted by Lavoisier (whose ideas he regarded with disdain), preferring to embrace a more traditional alchemical view of the elements as influenced primarily by earth, air, fire, and water. He asserted that once living organisms form,
11834-477: The organs. He argued that organisms thus moved from simple to complex in a steady, predictable way based on the fundamental physical principles of alchemy. In this view, simple organisms never disappeared because they were constantly being created by spontaneous generation in what has been described as a "steady-state biology". Lamarck saw spontaneous generation as being ongoing, with the simple organisms thus created being transmuted over time becoming more complex. He
11956-517: The origin of multicellularity, at least in Metazoa, occurred due to a transition from temporal to spatial cell differentiation , rather than through a gradual evolution of cell differentiation, as affirmed in Haeckel 's gastraea theory . About 800 million years ago, a minor genetic change in a single molecule called guanylate kinase protein-interaction domain (GK-PID) may have allowed organisms to go from
12078-524: The origins of animals to unicellular ancestors, providing the external phylogeny shown in the cladogram. Uncertainty of relationships is indicated with dashed lines. Holomycota (inc. fungi) [REDACTED] Ichthyosporea [REDACTED] Pluriformea [REDACTED] Filasterea [REDACTED] [REDACTED] [REDACTED] The most basal animals, the Porifera , Ctenophora , Cnidaria , and Placozoa , have body plans that lack bilateral symmetry . Their relationships are still disputed;
12200-412: The other way round. To be deemed valid, this theory needs a demonstrable example and mechanism of generation of a multicellular organism from a pre-existing syncytium. The colonial theory of Haeckel , 1874, proposes that the symbiosis of many organisms of the same species (unlike the symbiotic theory , which suggests the symbiosis of different species) led to a multicellular organism. At least some - it
12322-497: The oxygen available in the atmosphere of early Earth could have been the limiting factor for the emergence of multicellular life. This hypothesis is based on the correlation between the emergence of multicellular life and the increase of oxygen levels during this time. This would have taken place after the Great Oxidation Event but before the most recent rise in oxygen. Mills concludes that the amount of oxygen present during
12444-516: The plant material directly to digest and absorb the nutrients, while carnivores and other animals on higher trophic levels indirectly acquire the nutrients by eating the herbivores or other animals that have eaten the herbivores. Animals oxidize carbohydrates , lipids , proteins and other biomolecules, which allows the animal to grow and to sustain basal metabolism and fuel other biological processes such as locomotion . Some benthic animals living close to hydrothermal vents and cold seeps on
12566-645: The presence of this predator, C. reinhardtii does indeed evolve simple multicellular features. It is impossible to know what happened when single cells evolved into multicellular organisms hundreds of millions of years ago. However, we can identify mutations that can turn single-celled organisms into multicellular ones. This would demonstrate the possibility of such an event. Unicellular species can relatively easily acquire mutations that make them attach to each other—the first step towards multicellularity. Multiple normally unicellular species have been evolved to exhibit such early steps: C. reinhartii normally starts as
12688-773: The problem of regenerating a whole organism from germ cells (i.e., sperm and egg cells), an issue that is studied in evolutionary developmental biology . Animals have evolved a considerable diversity of cell types in a multicellular body (100–150 different cell types), compared with 10–20 in plants and fungi. Loss of multicellularity occurred in some groups. Fungi are predominantly multicellular, though early diverging lineages are largely unicellular (e.g., Microsporidia ) and there have been numerous reversions to unicellularity across fungi (e.g., Saccharomycotina , Cryptococcus , and other yeasts ). It may also have occurred in some red algae (e.g., Porphyridium ), but they may be primitively unicellular. Loss of multicellularity
12810-487: The remains of their company, this display of courage and loyalty impressed him so much that Lamarck was promoted to officer on the spot. However, when one of his comrades playfully lifted him by the head, he sustained an inflammation in the lymphatic glands of the neck, and he was sent to Paris to receive treatment. He was awarded a commission and settled at his post in Monaco . There, he encountered Traité des plantes usuelles ,
12932-399: The result of many identical individuals joining together to form a colony . However, it can often be hard to separate colonial protists from true multicellular organisms, because the two concepts are not distinct; colonial protists have been dubbed "pluricellular" rather than "multicellular". There are also macroscopic organisms that are multinucleate though technically unicellular, such as
13054-425: The simple presence of multiple nuclei is not enough to support the theory. Multiple nuclei of ciliates are dissimilar and have clear differentiated functions. The macro nucleus serves the organism's needs, whereas the micro nucleus is used for sexual reproduction with exchange of genetic material. Slime molds syncitia form from individual amoeboid cells, like syncitial tissues of some multicellular organisms, not
13176-724: The sister group to all other animals could be the Porifera or the Ctenophora, both of which lack hox genes , which are important for body plan development . Hox genes are found in the Placozoa, Cnidaria, and Bilateria. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian . 25 of these are novel core gene groups, found only in animals; of those, 8 are for essential components of
13298-403: The smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova . These fuse to form zygotes , which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form
13420-471: The sponges and placozoans —animal bodies are differentiated into tissues . These include muscles , which enable locomotion, and nerve tissues , which transmit signals and coordinate the body. Typically, there is also an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians). Nearly all animals make use of some form of sexual reproduction. They produce haploid gametes by meiosis ;
13542-410: The structure at the base of the tree (dashed lines). Porifera [REDACTED] Ctenophora [REDACTED] Placozoa [REDACTED] Cnidaria [REDACTED] Xenacoelomorpha [REDACTED] Ambulacraria [REDACTED] Chordata [REDACTED] Ecdysozoa [REDACTED] Spiralia [REDACTED] An alternative phylogeny, from Kapli and colleagues (2021), proposes
13664-565: The study of cellular and physiological traits that are heritable by daughter cells and not caused by changes in the DNA sequence, have caused debate about whether a "neolamarckist" view of inheritance could be correct: Lamarck was not in a position to give a molecular explanation for his theory. Eva Jablonka and Marion Lamb , for example, call themselves neolamarckists. Reviewing the evidence, David Haig argued that any such mechanisms must themselves have evolved through natural selection. Darwin allowed
13786-510: The subsequent Ediacaran period in what is known as the Avalon explosion . Earlier evidence of animals is still controversial; the sponge -like organism Otavia has been dated back to the Tonian period at the start of the Neoproterozoic , but its identity as an animal is heavily contested. Nearly all modern animal phyla became clearly established in the fossil record as marine species during
13908-448: The theory of adaptation or soft inheritance) was rejected by August Weismann in the 1880s when he developed a theory of inheritance in which germ plasm (the sex cells, later redefined as DNA), remained separate and distinct from the soma (the rest of the body); thus, nothing which happens to the soma may be passed on with the germ plasm. This model allegedly underlies the modern understanding of inheritance. Lamarck constructed one of
14030-446: The top French scientists of the day, mentored Lamarck, and helped him gain membership to the French Academy of Sciences in 1779 and a commission as a royal botanist in 1781, in which he traveled to foreign botanical gardens and museums. Lamarck's first son, André, was born on 22 April 1781, and he made his colleague André Thouin the child's godfather. In his two years of travel, Lamarck collected rare plants that were not available in
14152-461: The total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011. 3,000–6,500 4,000–25,000 Evidence of animals is found as long ago as the Cryogenian period. 24-Isopropylcholestane (24-ipc) has been found in rocks from roughly 650 million years ago; it
14274-417: The work of linking one cell to another, in viral infections. The fact that all known cell fusion molecules are viral in origin suggests that they have been vitally important to the inter-cellular communication systems that enabled multicellularity. Without the ability of cellular fusion, colonies could have formed, but anything even as complex as a sponge would not have been possible. This theory suggests that
14396-478: Was a French naturalist , biologist , academic, and soldier. He was an early proponent of the idea that biological evolution occurred and proceeded in accordance with natural laws . Lamarck fought in the Seven Years' War against Prussia , and was awarded a commission for bravery on the battlefield. Posted to Monaco , Lamarck became interested in natural history and resolved to study medicine. He retired from
14518-476: Was clearly hostile to the materialistic overtones of current transformist theorizing, but it does not necessarily follow that he regarded species origin as supernatural; certainly he was careful to use neutral language to refer to the causes of the origins of new forms of life, and even of man. Lamarck gradually turned blind; he died in Paris on 18 December 1829. When he died, his family was so poor, they had to apply to
14640-566: Was in his teenaged years. Yielding to the wishes of his father, Lamarck enrolled in a Jesuit college in Amiens in the late 1750s. After his father died in 1760, Lamarck bought himself a horse, and rode across the country to join the French army, which was in Germany at the time. Lamarck showed great physical courage on the battlefield in the Seven Years' War with Prussia , and he was even nominated for
14762-435: Was that the environment gives rise to changes in animals. He cited examples of blindness in moles, the presence of teeth in mammals and the absence of teeth in birds as evidence of this principle. The second principle was that life was structured in an orderly manner and that many different parts of all bodies make possible the organic movements of animals. Although he was not the first thinker to advocate organic evolution, he
14884-496: Was the first to develop a truly coherent evolutionary theory. He outlined his theories regarding evolution first in his Floreal lecture of 1800, and then in three later published works: Lamarck employed several mechanisms as drivers of evolution, drawn from the common knowledge of his day and from his own belief in the chemistry before Lavoisier . He used these mechanisms to explain the two forces he saw as constituting evolution: force driving animals from simple to complex forms and
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