Monday, August 19, 2019
Boundaries of the I-Function in Twins :: Biology Essays Research Papers
Boundaries of the I-Function in Twins Identical, conjoined, and half-twins are all examples of intrinsic variability in humans. Intrinsic variability exists in all animals and is an adaptive mechanism built into the nervous system in response to input. This mechanism allows humans to distinguish the same inputs as different from one another and therefore, the possible outputs vary with time. It is possible that due to identical genetic input, the twins could share identical neural pathways and identical I-Functions. This hypothesis could explain the identical behaviors and inter-connectedness of feelings and thoughts that twins share. Differences that are seen in twin behaviors could simply be due to intrinsic variability causing differing output or behaviors. During ovulation, when a woman releases an ovum, three different processes can occur. First, the ovum can remain in one piece all the way to the uterus where, if not fertilized, it will be shed out of the body along with the unused endometrium. Second, the ovum, if fertilized, can develop into a single embryo, which is the most common type of pregnancy in humans with about 99% of all births being singletons (1). Finally, the ovum can split into two separate halves resulting in genetically identical twins. The three types of twins previously mentioned are identical, which are created when the fertilized ovum separates into two complete, identical parts, conjoined, which occur as a result of a fertilized ovum not completing the equal separation resulting in two fetuses fused together in some way, and half-twins or polar body twins, which are made when an unfertilized ovum splits into two complete, identical parts and is then fertilized by two different sperm. The frequency of identical twins is 3.5 per 100 births (1) and the frequency of conjoined twins is 1 birth per 50,000 with only 100 known cases surviving their first year (5). There is no scientific explanation for why an ovum splits into two or more parts. It has been observed that ovum splitting can be hereditary but can also occur spontaneously. This spontaneity or unexplained divergence from normal egg growth and fertilization could be due to intrinsic variability. This intrinsic variability could also be connected to certain differences in behavior of two genetically and culturally identical twins. Ideally, one could say that twins with identical genetic information and environments would have extremely similar, if not the same neural pathways and central pattern generators (CPGs).