<P> There are two types of twins: identical and fraternal . Identical twins have exactly the same genes; fraternal twins are no more similar than regular siblings . Often, twins with a close relationship will develop a twin language from infanthood, a language only shared and understood between the two . Studies suggest that identical twins appear to display more twin talk than fraternal twins . At about 3 years of age, twin talk usually ends . </P> <P> Researchers were interested in subjects who were in the later years of life . They knew that past studies suggested that genetics played a larger role in one's personality in the earlier years of their life . However, they were curious about whether or not this was true later on in life . They gathered subjects with a mean age of 59, who included 99 pairs of identical twins, and 229 pairs of fraternal twins who were all reared apart . They also gathered twins who were reared together: 160 pairs of identical twins, and 212 pairs of fraternal twins . They studied the most heritable traits in regard to personality, which are emotionality, activity level and sociability; also known as EAS . This study found that identical twins resembled each other twice as much as fraternal twins, due to genetic factors . Furthermore, environment influences personality substantially; however, it has little to do with whether they are reared together or apart . This study also suggests that heritability is substantial, but not as substantial as for younger subjects; it has less significance later on in life . </P> <P> Half - siblings are people who share one parent but not both . They may share the same mother but different fathers (in which case they are known as uterine siblings or maternal half - brothers / half - sisters), or they may have the same father but different mothers (in which case, they are known as agnate siblings or paternal half - brothers / half - sisters . In law, the term consanguine is used in place of agnate). They share only one parent instead of two as full siblings do and are on average 25% related . </P> <P> Theoretically, there is a chance that they might not share genes . This is very rare and is due to there being a smaller possibility of inheriting the same chromosomes from the shared parent . However, the same is also theoretically possible for full siblings, albeit (comparatively) much less likely . </P>

What is the meaning of half brother or sister