| DeathDeath. Why it happens? Why do we die? | | | | animal, be it a mouse or a human, starts life |
| Why do animals die? Why do plants die? What | | | | as a single cell. That cell differentiates |
| is the need of this? In my opinion mechanism | | | | and develops into the complete animal. It |
| of death was selected during Evolution.From | | | | assures that a rare advantageous variant |
| the position of Darwin's theory of Natural | | | | sequence of DNA will be rapidly propagated by |
| Selection everything, that benefits survival | | | | natural selection. It is much easier to |
| of species and gives advantage in Natural | | | | reproduce and maybe get some new genes or |
| Selection, is preserved in following | | | | favourable mutations starting from a single |
| generations.Improvements were often left | | | | cell than starting from a whole multicellular |
| unchanged from the moment of life appearance. | | | | organism. Functions of most genes will have |
| Though there could be other ways, certain | | | | been optimized by random point mutation and |
| mechanisms were accidentally selected. These | | | | selection in any given species. Signalling |
| improvements are reproduced in the genome of | | | | between cells during the development process |
| more complex species. Billions of years ago, | | | | ensure that everything ends up in the right |
| according to the theory of evolution, | | | | place. Tiny changes in these Signalling |
| chemicals randomly organized themselves into | | | | processes can have very large effects on the |
| a self-replicating molecule.Lightings and | | | | resulting animal. Genome, with at most |
| UV-radiation helped to create first organic | | | | forty-sixty thousands genes, is able to |
| molecules. This phenomenon is reproducible in | | | | specify the creation of a human body |
| a lab. The experiments were described in | | | | containing trillions of cells, billions of |
| 1950-60.First self-replicating molecules were | | | | carefully wired neurons and hundreds of |
| probably RNA. First enzymes were probably RNA | | | | different cell types all amazingly sculpted |
| - enzymes. Then proteins, DNA and more | | | | into organs as diverse as the liver and the |
| complex lipid molecules and polysaccharide | | | | brain. This is why mechanism of proliferation |
| came to the scene.Death as it is did not | | | | of fertilized oocytes was selected.Hence, |
| exist at the stage of Primeval Soup . Sure | | | | having younger (smaller) and older (bigger) |
| some organic molecules were destroyed , some | | | | animals make sense.But there is the problem: |
| new created. But in general it was still that | | | | adult animals (or plants) consume all the |
| swirling and bubbling primary broth - quasi | | | | nutrition around and there is not much left |
| alive in our understanding as a mixture of | | | | for next generation.Then it is why mechanism |
| biochemical reactions.Everything in the | | | | of Death was selected as a mean for next |
| evolution was build from the previous blocks | | | | generation to establish.Imagine the |
| selected sometime by accident.Appearance of | | | | following:First, mechanism of proliferation |
| lipid membranes allows to compartmentalize | | | | was selected . If mono-cellular organism does |
| the primary broth and create first cells.At | | | | not have mechanism of reproduction it does |
| the cellular stage we could already talk | | | | not produce offspring with possible |
| about the Death. Cell is destroyed, membrane | | | | favourable mutations. Let say there are |
| is broken, everything leaked out. This is the | | | | primitive bacteria spontaneously created in |
| Death.Content of cell inside lipid membrane | | | | primeval soup. Just few of them. They consume |
| is irradiated. Process of crazy molecular | | | | nutrition, they live happily, practically |
| swirling is messed up by free radicals | | | | immortal but they do not divide. Then set of |
| irreversibly. This is also signs of Death.Yet | | | | enzymes appeared during mutations. The set |
| at the cellular stage we cannot talk about | | | | allows bacteria to split. Synthesis of the |
| Aging. Death at this stage is accidental, not | | | | new set is disadvantageous. It requires |
| programed.Organic molecules may age | | | | additional energy and nutrition. But |
| (oxidation, conjugation, etc.) and cell would | | | | advantage of splitting allows new mutants |
| die. But damaged molecule are repaired or | | | | immediately overgrow non-proliferating cells. |
| synthesized fresh usually. Hence, no good | | | | Selection is really cutthroat.Bacteria |
| reason for a single cell organism to age. | | | | growing in a tube represent mini evolution. |
| Irreparable damage from external cause leads | | | | Any bacteria that fit for the environment are |
| to Death, not Aging. This is accidental | | | | also selected on the ground of simplicity. In |
| death. For multicellular organisms, there is | | | | a toxic environment (antibiotics) mutant |
| a parental organism that ages and eventually | | | | bacteria having a new mechanism of |
| dies after next generation is born. For | | | | neutralisation would survive. But the more |
| mono-cellular organism, there is parental | | | | simple bacteria will eventually overgrow |
| organism that divides and becomes the next | | | | complicated ones. Unless complication gives |
| generation. There is no Aging leading to | | | | big advantage that outweigh the benefits of |
| death of parental organism.Mono-cellular | | | | simplicity. Another example: HIV virus is |
| organisms are practically immortal in a right | | | | very complex compare to some other viruses. |
| environment.Mechanism of division was | | | | But because of the complexity it evades |
| selected during evolution. Cell has volume | | | | immune response. This is why it is so |
| (3-D). Surface membrane is measured in square | | | | successful. For humans there was some |
| units (2-D). Growing beyond limits cause | | | | discussion that hernias are direct problem of |
| inadequate supply of nutrition from | | | | erect posture. So erect posture leads to |
| environment. Division solves the | | | | disadvantage. From the other hand erect |
| problem.Microbes, bacteria are immortal. Some | | | | posture frees the hand, that allows to |
| divide every 20 minutes. In a an hour they | | | | produce the tools and this gives huge |
| multiply 8 times.Tumour cells divide slower. | | | | advantage in the survival in natural world by |
| They are eukaryote. Most aggressive divide | | | | creating possibility to adapt to virtually |
| once a day. There is no need for Aging.They | | | | any condition.All high animals have just 4 |
| would die if you do not feed them. They die | | | | extremities. Obviously it is enough in |
| when you kill them with undiluted bleach in a | | | | cutthroat environment. Growing additional |
| flask. Otherwise they grow unstoppable. No | | | | couple of extremities will consume much more |
| aging.Multicellular organism supposedly has | | | | resources and take much more time, not giving |
| several control mechanisms to prevent | | | | big advantage in speed or protection of an |
| excessive growth and division, to kill an | | | | animal. Thus, danger of losing one of the |
| extra cell. Apoptosis, programmed death, is | | | | limb is not so big as the danger to not |
| used.Cancer cells often loose the control | | | | proliferate fast enough.Bilateral design of |
| mechanisms.A scientist from Yale once pointed | | | | majority of animals was chosen at the level |
| out to me that we can not say these cells are | | | | of primitive species. Though lower |
| immortal. Maybe they divide and parental cell | | | | multicellular organisms may have 3-side |
| dies. Indeed. We do not follow the fate of | | | | symmetry or 5-side symmetry like sea stars. |
| every individual cell during experiments. | | | | Often something chosen in the selection |
| They should give more children cells than | | | | becomes building blocks for higher species. |
| parental cells die. Otherwise there would not | | | | Maybe 5-side symmetrical tiger would be |
| be the multiplication. It is a possible | | | | possible but it requires intermediate |
| scenario. We do not follow the fate of | | | | chain.The same is true for the mechanism of |
| individual bacteria as well. Maybe they | | | | Death. Once chosen, it is replicated in all |
| actually undergo aging.From the other hand | | | | higher organisms. It should give an advantage |
| some experiments suggest that new cells | | | | in ultimate species survival. Otherwise it |
| contain roughly half of the parent cell after | | | | loses sense and species would be wiped |
| division. So it is not Death or Aging. Next | | | | out.So, what is advantage for Death?Immortal |
| generations contain 1/4, 1/8, 1/16 and so on | | | | and childless animals are growing and |
| of the parent cell. Any mechanism that is | | | | growing. Mutations lead to species producing |
| more complex than simple division would cause | | | | offsprings. They have disadvantage of been |
| disadvantage in evolution and would be | | | | more complex. But advantage of proliferating |
| quickly eliminated. On the level of | | | | animals is occupation of vaster areas. They |
| mono-cellular organism neither Aging nor | | | | displace immortal and childless species. Now, |
| Apoptosis make a lot of sense. Though Nature | | | | if proliferating animals are immortal they do |
| often have hidden reasons.Flick's phenomenon | | | | not give offsprings enough space or food. |
| and telomeres shortening make sense for a | | | | Next steps of mutation brought mechanism of |
| multicellular organism. Cells of | | | | programmed death at certain age.Let consider |
| multicellular organism do age. They stop | | | | situation when out of two species one is |
| dividing after 70 divisions or so.A | | | | immortal and producing offsprings, other is |
| multi-cell organism has clear cut advantage | | | | mortal with offspring production as well. |
| over a mono-cell.Why would mechanism of Death | | | | Mortality looks like an obvious disadvantage |
| selected for multicellular organisms? | | | | in stable environment. Adult organism are |
| Scenario could be the following.Big organism | | | | more powerful and more protected compare to |
| have more advantages compare to smaller one - | | | | juvenile.However, next catastrophe will wipe |
| stability, protection, etc. There are not so | | | | out all the species altogether. Only some |
| many natural enemies for whale or elephant | | | | mutants can adopt to new environment. But |
| because of their size. Large animals could be | | | | "mutant" for a multicellular organism imply |
| brought down by bacteria, viruses, small | | | | that the mutation happened when the organism |
| parasites, and lack of available food. Rare | | | | had only one cell (the stage of fertilized |
| predator attack whale or elephant.No wonder | | | | oocyte for example). Otherwise it needs |
| that evolution was going into the direction | | | | precisely the same mutations on the level of |
| of bigger animals - just look at giant bones | | | | several cells - infinitely impossible |
| of dinosaurs and you will feel some | | | | event.Thus, any species that had the |
| appreciation.Millions years ago not only | | | | mechanism to allow next generation to |
| Dinosaurs but also insects or crustacean were | | | | flourish (mechanism of programmed Death) will |
| enormous. Cockroaches, spiders or dragon | | | | have advantage. They produce more offspring |
| flies with size of one metre (3 feet). Going | | | | than immortal species. Death of parents |
| back in time we find shells of enormous | | | | spares the space and nutrition. Immortals can |
| molluscs. Many things imply that bigger | | | | die form accidents only. It is too long for |
| animal with unstoppable growth have a lot of | | | | children to expect a vacancy.Then, having |
| advantages compare to small ones. New species | | | | more offspring automatically means having |
| often evolve in their size. An example is | | | | more mutations (by mere number of events). |
| growth acceleration in humans. Females prefer | | | | Having more mutations means more probability |
| taller mates that lead to taller children. | | | | for adaptation to the new |
| Shorter plants usually cannot compete with | | | | environment.Immortal multicellular organisms, |
| the taller forms in the wild. A short mutant | | | | even if they existed in the past, were |
| in a patch of tall plants would be shaded | | | | quickly wiped out by accidents and overgrown |
| outMechanism of reproduction was also | | | | by mortal multicellular organisms.Again all |
| selected during the evolution. Any new | | | | this is just a hypothesis. |