Why do some people give birth to abnormal human beings?

Answer 1

First of all, the term abnormal is a little offensive and should be avoided when looking for terms to discuss humans. It's also vague, so my answer will include a variety of possible interpretations of "abnormal."

If you mean physical abnormalities, such as additional fingers/toes or missing limbs, it's either a very rare recessive gene, or it's a birth development problem, of which Fetal Alcohol Syndrome is the most common due to the high rate of alcohol use (and abuse). The rare recessive gene would have to be carried by both parents (since it's recessive), both of whom only have one (unless they exhibit the trait themselves) and would require the gene to be selected from the 2 possibilities in both the mother's egg and the particular sperm cell from the father that fertilizes that egg - a 25% chance, assuming each has 1 recessive, 1 dominant "normal) gene. The odds of both parents even carrying the gene are low because it is a rare gene (otherwise people with more or less than 5 fingers/toes per limb would be more common). Fetal Alcohol Syndrome causes a variety of problems with child development - in severe cases, caused by significant alcohol consumption by the pregnant mother throughout the pregnancy, this can include non-developed limbs or other severe problems of that sort. FAS also causes major mental instability, especially if the mother is drinking in the first few weeks of her pregnancy (and since this is before pregnancy can be detected, it is far wiser for women hoping to get pregnant to avoid alcohol altogether, and the possibility of FAS should be considered in decisions about abortion in the case of unplanned pregnancies.

As for mental issues, many are related to genetics at least somewhat. Certain genes have been identified as requirements in various significant mental disorders, including sociopathy (though that particular one has a number of other requirements during early childhood). Other genetics-related issues are a set of conditions, including Downs Syndrome, involving mismatched chromosome pairings. Most males are born with the XY chromosome pair, while females are born with the XX pair. Some other possible combinations that arise from errors in the cell division process that produces egg and sperm cells are XXX, XXY, XYY, XXXY. I believe there is always at least one X in the groupings, as the X chromosome carries a bunch of important genes (called sex-linked genes, since they're connected to the pairing that determines gender). The X chromosome, or the combination of available X chromosomes in the case of females or some of the above unusual combinations, provides a default for these traits, while the Y chromosome makes only the changes necessary to make a person male (which accounts for men being more succeptible to many genetic traits like baldness, since women have a second X chromosome, thus reducing the chances that baldness (linked to a recessive gene) will be expressed).

Many other mental traits are caused during development of mental pathways. Those that happen in the womb are, as far as I know, completely random, like winning a lottery (though being selected might be better termed "losing" with some lotteries, such as in the story "The Lottery") Post-birth development is governed primarily by nurture rather than nature - how well the kid is raised rather than genetics or in the womb. This category includes a large number of mental traits, probably far more than the genetic or in-the-womb categories, so good parenting is essential. Most people who grow up with an alcoholic father who beats his wife and children do not end up with a good result (though it has happened, and in those cases I am inclined to believe those people have to wrestle with some pretty major inner demons). On the other hand, most children growing up in a good family do end up with a good result (though the reverse is true in this case as well).

If there's a specific issue you're concerned about, I suggest you look it up. On the other hand, if your question was prompted by immediate concerns (like impending parenthood), I suggest you talk to a doctor (either a GP or a Pediatrician, probably)...though I suggest a more politically correct wording for your question.

Of course, everyone is somewhat abnormal, since we all have differing personalities.