title: Multicellular organism

text: One hypothesis for the origin of multicellularity is that a group of function-specific cells aggregated into 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 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.


title: Multicellular organism

text: Because the first multicellular organisms were simple, soft organisms lacking bone, shell or other hard body parts, they are not well preserved in 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.


title: Multicellular organism

text: Until recently, phylogenetic reconstruction has been through anatomical (particularly embryological) similarities. This 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.


title: Multicellular organism

text: The evolution of multicellularity could have occurred in a number of different ways, some of which are described below:


title: Multicellular organism

text: This theory suggests that 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 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 the newly created species.


title: Multicellular organism

text: 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 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 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.


title: Multicellular organism

text: 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, 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 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.


title: Multicellular organism

text: 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 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 is also typically considered to involve cellular differentiation.


title: Multicellular organism

text: 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, 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".


title: Multicellular organism

text: Some authors suggest that 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.


title: Multicellular organism

text: 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 a single cell organism to one of many cells.


title: Multicellular organism

text: 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 cell and sperm.


title: Multicellular organism

text: Such fused cells are also involved in metazoan membranes such as those that prevent chemicals crossing the placenta and the brain body separation. Two viral components have been identified. The first is syncytin, which came from a virus.


title: Multicellular organism

text: The second identified in 2007 is called EFF1, 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 EFF1 protein and shown it does the work of linking one cell to another, in viral infections.


title: Multicellular organism

text: 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.


title: Multicellular organism

text: This theory suggests that 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 the Ediacaran is not necessary for complex life and therefore is unlikely to have been the driving factor for the origin of multicellularity.


title: Multicellular organism

text: 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.


title: Multicellular organism

text: The most recent snowball Earth took place during 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.


title: Multicellular organism

text: The snowball Earth hypothesis in regards to multicellularity proposes that the Cryogenian period in Earth 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 the Cambrian explosion shortly after the Marinoan.


title: Multicellular organism

text: The predation hypothesis suggests that in order 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 the presence of this predator, "C. reinhardtii" does indeed evolve simple multicellular features.


title: Multicellular organism

text: 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.


title: Multicellular organism

text: Whether all of these can be seen as advantages however 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.


title: Multicellular organism

text: 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.


title: Tim Jenkin

text: Timothy Peter Jenkin (born 1948) is a South African writer, former anti-apartheid activist and political prisoner. He is best known for his 1979 escape from Pretoria Local Prison (part of the Pretoria Central Prison complex), along with Stephen Lee and Alex Moumbaris.


title: Tim Jenkin

text: Jenkin was born in Cape Town and educated at Rondebosch Boys' Prep and Boys' High School, matriculating aged 17.


title: Tim Jenkin

text: After leaving school, he avoided conscription into the South African Defence Force, and worked at a variety of jobs for two years, with no particular interest in anything except motorcycle racing. He left for the UK in 1970, where, working in a fibreglass factory under poor working conditions and little pay, found the system unjust and developed an interest in sociology. This led him to learning more about the injustice in his own country. He later wrote that he had "grown up a 'normal' complacent white South African" who "unthinkingly accepted the system and for twenty-one years never questioned it".


title: Tim Jenkin

text: At the end of 1970 Jenkin enrolled at the University of Cape Town (UCT) and graduated with a Bachelor of Social Science degree at the end of 1973.


title: Tim Jenkin

text: Jenkin met Stephen Lee in a sociology class at UCT. They became friends and, in a South African version of Samizdat, Jenkins and Lee sought out literature banned by the ruling National Party. They then photocopied it and swapped it with other students. They both found their sociology course disappointing, as the material reinforced the status quo of apartheid. Through reading material banned by the government, they came to see the "naked reality" of apartheid and the undemocratic behavior of the ruling party, and felt a burning desire to effect positive change, which, Jenkin concluded, was only possible using unconstitutional means under the current regime. During this time they learnt of the activities of the African National Congress (ANC), which was an illegal organisation in South Africa.


title: Tim Jenkin

text: In February 1974, Jenkin and Lee left the country in order to join the ANC in London, with the intention of helping to bring about change in South Africa. Here, Jenkin met his future wife Robin. While awaiting clearance for membership, Jenkin worked as a social worker at a reform school in Swindon. After acceptance by the ANC, he and Lee received training from the ANC in various tactics, in particular how to spread their propaganda leaflets, and how to set up communication and financial structures.


title: Tim Jenkin

text: Upon return to Cape Town in July 1975, Lee and Jenkin bought a typewriter, duplicator and stationery to print and post pamphlets and leased first a garage and then a tiny apartment. Jenkin worked as a researcher for the Institute for Social Development at the University of the Western Cape, a university for South Africans of mixed racial ancestry, or Coloureds. In March 1976 Lee went to Johannesburg to look for work, and the ANC coincidentally sent them both on their first mission, to disperse leaflets urging support for the ANC via a leaflet bomb (using a new design developed by Jenkin) in Johannesburg, close to the anniversary of the Sharpeville Massacre on 21 March. They achieved this mission, managing to distribute hundreds of leaflets by means of several leaflet bombs, the text of which is reproduced in Jenkin's memoir.


title: Tim Jenkin

text: After the success of their first mission, Jenkin worked on refining the mechanism by adding a triggering system to the leaflet bomb, so that they did not have to be close to it when it went off. He successfully distributed leaflets this way on Cape Town's Grand Parade. Lee worked for the University of the Witwatersrand, while Jenkin ran the "cell" on his own in Cape Town. Jenkin went to London at the request of the ANC in May 1976, while Lee continued to plant leaflet bombs around Johannesburg. In July, four ANC operatives including author Jeremy Cronin were arrested doing similar work in Cape Town and were given prison sentences.


title: Tim Jenkin

text: Undeterred, Jenkin continued the work in Cape Town, finding a new premises and regularly changing their printing equipment, and both carried out further leaflet bombings in Johannesburg. There were a few worrying signs that Jenkin was being monitored, but he went to London to see Robin for six weeks and returned without incident. In September, he and Lee hung a 10-metre-long banner with the words "ANC LIVES" from a high building in the centre of Cape Town, along with a timed device which distributed hundreds of leaflets over the crowds below. Lee moved back to Cape Town in December after enrolling in a master's degree in sociology, and the two continued their undercover work, but unbeknownst to them they were by this time under surveillance by the Security Branch of the South African Police.


title: Tim Jenkin

text: At 3am the morning of 2 March 1978, Jenkin and Lee were both arrested, after being seen moving their printing equipment into their own dwelling. They were never told how the security police got onto them, and Jenkin concluded that it must have been the result of meticulous police work and long surveillance.


title: Tim Jenkin

text: They were taken to Caledon Square Police Station, the head office of the Security Branch in Cape Town, where they were separated, interrogated and put into cells, without being informed of the charges or their rights. This was legal under Section 6 of the Terrorism Act, which allowed detention without trial for up to 60 days, and was extendable. Lee made an escape attempt and nearly succeeded. After a spell in the notorious John Vorster Square in Johannesburg, they were returned to Cape Town and after four weeks, allowed to see family, and held at Pollsmoor Prison as they awaited trial. After Lee's father brought him a copy of the book "Papillon", the book inspired them to seriously consider the prospect of escape and they concentrated on rigorous observations of the world around them.


title: Tim Jenkin

text: Along with Lee, Jenkin was charged with "producing and distributing 18 different pamphlets on behalf of banned organisations" including the South African Communist Party, the ANC and its armed wing, Umkhonto we Sizwe, from 1975 to 1978, and urging people to join the liberation movement. The trial in the Cape Town Supreme Court went from 6 to 15 June 1978. Upon legal advice, both pleaded guilty to all charges. They were both found guilty on one charge, with Jenkin receiving a 12-year sentence and Lee eight.


title: Tim Jenkin

text: After their incarceration, Jenkin, Lee and several other inmates began plotting an escape, which would involve copies of several prison keys that Jenkin made from wood. Jenkin had smuggled some money into prison. The initial plan was that eight of the political prisoners would escape, leaving behind two who were nearing the end of their sentences. One of the intending escapees, Denis Goldberg, communicated with comrades in the ANC through coded letters sent to Baruch Hirson in London. Hirson then communicated with Joe Slovo in Mozambique and a date for the escape was set and an escape vehicle arranged.


title: Tim Jenkin

text: As the plan evolved it became clear that for the escape to be successful it would have to be restricted to three people, who would have to hide in a small closet at one point. The escape preparations brought some differences of opinion amongst the political prisoners, but they remained comrades and all contributed in some way to the escape effort. The fact that they were all in prison for their political activities and beliefs united them, and "as members of a revolutionary organisation [they] were disciplined and shared in [their] suffering collectively". Goldberg and the others decided to withdraw from the escape, with Goldberg continuing to be involved in the preparations.