question: Why do our hairs decide to split into two and become split ends?
comment: Our hairs don't decide to do anything. They are not sentient. They have no thoughts. Split ends happen because of heat, harsh chemicals, or brushing/manipulating them too much. Hair is kind of like clothes fiber, and the ends just get damaged over time.
passages: Another example may have happened in the early history of domesticating horses: tail-type hair grew instead of the wild-type short stiff hair still present in the manes of other equids such as donkeys and zebras.
  
  Section::::Heterotopy in molecular biology.
   Thermal, chemical or mechanical stress can cause split ends. For example, the use of curling irons and other heat treatments may cause split ends. Excessive application of hair products such as perms and hair coloring may strip protective layering off the outside of the hair's shaft and weaken the hair, making the hair prone to split ends. Mechanical stresses include pulling a comb forcefully through tangled hair and repeated combing. Split ends can be seen as a symptom of copper transport disorders such as Menkes disease and occipital horn syndrome. Rubbing the hair up towards the scalp does not cause split ends.
   The process is often called "rebonding" in some countries from Southeast Asia (e.g. Indonesia, Singapore, Malaysia and Philippines). The term "rebonding" was first used by REDS Hairdressing from Singapore in the late 1980s, which slowly spread to the rest of the region. If done often, flat irons and chemicals can be damaging to hair. Excessive straightening often results in split ends. However, heat protectant sprays can decrease the damage.
  
  Section::::Methods.
  
  Section::::Methods.:Temporary (non-chemical treatment).
   Section::::Evolution.:Texture.:The EDAR locus.
   Section::::Treatment of damage.
  
  Section::::Treatment of damage.:Split ends.
  
  Split ends, known formally as "trichoptilosis", happen when the protective cuticle has been stripped away from the ends of hair fibers.
  
  This condition involves a longitudinal splitting of the hair fiber. Any chemical or physical trauma, such as heat, that weathers the hair may eventually lead to split ends. Typically, the damaged hair fiber splits into two or three strands and the split may be two to three centimeters in length. Split ends are most often observed in long hair but also occur in short hair that is not in good condition.
   The hair follicle is a dynamic organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some new born babies. The process of hair growth occurs in distinct sequential stages. The first stage is called "anagen" and is the active growth phase, "telogen" is the resting stage, "catagen" is the regression of the hair follicle phase, "exogen" is the active shedding of hair phase and lastly "kenogen" is the phase between the empty hair follicle and the growth of new hair.
   Section::::Description.:Human hair growth.
  
  Hair grows everywhere on the external body except for mucus membranes and glabrous skin, such as that found on the palms of the hands, soles of the feet, and lips.
  
  Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases; all three occur simultaneously - while one strand of hair may be in the anagen phase, another may be in the telogen phase. Each has specific characteristics that determine the length of the hair.
   Section::::Cause of peach leaf curl.
   Although trimming enhances the hair's appearance by removing damaged or split ends, it does not promote faster growth or remove all damage along the length of the hair.
  
  Section::::Process.:Brushing and combing.
  
  Brushes and combs are used to organize and untangle the hair, encouraging all of the strands to lie in the same direction and removing debris such as lint, dandruff, or hairs that have already shed from their follicles but continue to cling to the other hairs.
   Each hair cell has a single, microtubular kinocilium. Before morphogenesis of the hair bundle, the kinocilium is found in the center of the apical surface of the hair cell surrounded by 20-300 microvilli. During hair bundle morphogenesis, the kinocilium moves to the cell periphery dictating hair bundle orientation. As the kinocilium does not move, microvilli surrounding it begin to elongate and form actin stereocilia. In many mammals the kinocilium will regress once the hair bundle has matured.
  
  Section::::Anatomy in humans.:Auditory system.
   Section::::Hair growth.:Anagen phase.
  
  Anagen is the active growth phase of hair follicles during which the root of the hair is dividing rapidly, adding to the hair shaft. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2–7 years; this period is genetically determined. At the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase.
  
  Section::::Hair growth.:Catagen phase.
   Hair on the top of the head was raised by backcombing or "teasing" it with a comb to create a pile of tangled, loosely knotted hair on the top and upper sides of the head. Then, unteased hair from the front of the head was lightly combed over the pile to give a smooth, sleek look, and the ends of the outer hair may be combed, cut, curled, or flipped in many distinctive ways. 
   In terms of development, the varying lengths of nectar spurs has been found to be based solely on the anisotropic elongation of cells. However, it still remains to be understood which genes underlie the elongation of cells to form a spur. Are the same genes being co-opted over and over again across the angiosperms to form spurs, or are there several developmental pathways to make a spur?
   Short internodes (the section of stem between nodes, i.e. areas where leaves are produced) help increase ramification in those plants that form branches at these nodes. Long internodes (which may be the result of over-watering, the over-use of fertilizer, or a seasonal "growth spurt") decrease a gardener's ability to induce ramification in a plant.
   Section::::Replication.
  
  Section::::Replication.:Division.
  
  Since obcells were cup-shaped and could expose their chromosomes to the harsh environment, to protect their genetic information and any signaling factors, obcells could attach to polyphosphate surfaces using local adhesin proteins. During division, division proteins would begin to pinch the obcell in half, separating the internal components between the two daughter obcells. As this pinching was occurring, the structural integrity of the membrane began to weaken and the two halves would migrate towards the polyphosphate surface. Adhesin proteins would attach these ends to the surface and division would be complete.
  
  Section::::Replication.:Fusion.
   The genetic determination of presence or absence of hair on the dorsal aspect of the middle phalanx was first suggested by Danforth (1921). From a study of 80 families with a total of 178 children, he suggested that 'a phylogenetically progressive loss of hair is brought about through the action of one or more recessive genes, or of one primary recessive gene with several modifying factors that regulate the distribution of hair when it is present.' Stated conversely, 'despite the fact that in evolutionary progress hair is disappearing from the mid-digital region, its presence...may be regarded as the manifestation of a dominant trait.'
   We can observe the difference between the last two figures which have different threshold values. Region growing provides the ability for us to separate the part we want connected.
  
  As we can see in Figure 3 to Figure 5, the segmented results in this example are seed-oriented connected. 
  
  That means the result grew from the same seed points are the same regions. And the points will not be grown without being connected with the seed points.
   Section::::Participation in hair follicle development.
   Sometimes the extensions, also called processes, come off from opposite poles of the cell, and the cell then assumes a spindle shape; in other cells both processes emerge at the same point.
  
  In some cases where two fibers are apparently connected with a cell, one of the fibers is really derived from an adjoining nerve cell and is passing to end in a ramification around the ganglion cell, or, again, it may be coiled helically around the nerve process which is issuing from the cell.
  
  Section::::See also.
  
  BULLET::::- Bipolar cell of the retina
  
  BULLET::::- Interneuron
  
  BULLET::::- Multipolar neuron
   Bernstein and Burks (1942) 
  
  suggested that 5 allelic genes, A-0 to A-4, 'control the inheritance and distribution of middigital hair involving but a single gene substitution (the subscript denoting the number of fingers affected with middigital hair),' and that the genes for the presence of hair are dominant over the genes for its absence.
   Section::::In Botany and Ecology.
   Section::::Complications and other considerations.
   The highly regulated process of formation of somites from the unsegmented presomitic mesoderm (PSM) is called somitogenesis. Somitogenesis involves three basic steps: - metameric pattern generation, labelling each somite with its antero-posterior identity, and forming a somatic border. The regularity in the arrangement of somites is due to the activity of a set of dynamically and rhythmically expressed genes in the PSM, namely c-hairyl and lunatic fringe. These genes are arguably related to the Notch signalling pathway which provides evidence for the presence of a molecular segmentation clock that is linked to the process of somitogenesis. The Notch signalling pathway is a crucial step in the embryonic segmentation in vertebrates playing multiple roles as it is one of the significant pathways involved in the regulation of the segmentation clock. Somitogenesis is a vital process that forms the foundation of the nervous system segmentation pattern.
   A club hair is formed during the catagen phase when the part of the hair follicle in contact with the lower portion of the hair becomes attached to the hair shaft. This process cuts the hair off from its blood supply and from the cells that produce new hair. When a club hair is completely formed, about a 2-week process, the hair follicle enters the telogen phase.
  
  Section::::Hair growth.:Telogen phase.
   Hair grows in cycles of various phases: anagen is the growth phase; catagen is the involuting or regressing phase; and telogen, the resting or quiescent phase (names derived using the Greek prefixes ana-, kata-, and telos- meaning up, down, and end respectively). Each phase has several morphologically and histologically distinguishable sub-phases. Prior to the start of cycling is a phase of follicular morphogenesis (formation of the follicle). There is also a shedding phase, or exogen, that is independent of anagen and telogen in which one or several hairs that might arise from a single follicle exits. Normally up to 90% of the hair follicles are in anagen phase, while 10–14% are in telogen and 1–2% in catagen. The cycle's length varies on different parts of the body. For eyebrows, the cycle is completed in around 4 months, while it takes the scalp 3–4 years to finish; this is the reason eyebrow hair have a much shorter length limit compared to hair on the head. Growth cycles are controlled by a chemical signal like epidermal growth factor. DLX3 is a crucial regulator of hair follicle differentiation and cycling. Specifically, colocalization of phosphorylated Smad1/5/8 complex and DLX3 regulate role for BMP signaling to Dlx3 during hair morphogenesis in animal models.
  
presuppositions: Question stated the "hair decides" that its ends split into two. Hairs decide to split into two and become split ends.
corrections: Our hairs can't decide to do anything. Hairs are not sentient, thus they do not decide to split into split ends; rather, they get damaged over time by heat, harsh chemicals, or over-brushing.
raw_presuppositions: Question stated the "hair decides" that its ends split into two. Hairs decide to split into two and become split ends.
raw_corrections: Our hairs can't decide to do anything. Hairs are not sentient, thus they do not decide to split into split ends; rather, they get damaged over time by heat, harsh chemicals, or over-brushing.