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Incredible twin statistics: Why do some ethnic groups have such high rates of twin births?
Twins are two offspring resulting from the same pregnancy. These twins can be monozygotic (identical), meaning they developed from one fertilized egg that split to form two embryos, or dizygotic (fraternal or sibling), meaning each Twins are conceived from different eggs and their own sperm. Identical twins will have the same gender, while fraternal twins may be different. According to statistics, in the United States, the birth rate of twins increased by 76% between 1980 and 2009, from about 9.4 pairs of twins per 1,000 births to 16.7 pairs. This has drawn attention to the high twin birth rates in certain ethnic groups.
The differences in twin birth rates among different ethnic groups around the world are almost a mystery.
For example, the Yoruba people in Nigeria have the highest twin birth rate in the world, with 45 to 50 twins per 1,000 live births. Research has found that this may have something to do with their diet, specifically a certain type of yam that contains natural phytoestrogens, which may stimulate their ovaries to release multiple eggs. This trend is also significant in Central Africa, with about 18 to 30 twins per 1,000 births, while in South America, South Asia and Southeast Asia, the birth rate is lower, with only about 6 to 9 twins per 1,000 births. North and Central America and Europe are in the middle, with about 9 to 16 twins per 1,000 births.
The genetic factors that cause women to give birth to twins are an ongoing topic of research. Women who have twins in their family are more likely to have twins because there is a genetic tendency to ovulate multiple times. For singletons, their gestation period is usually longer. The average gestation period for twins is 37 weeks, which is 3 weeks shorter than singletons.
The birth rate of twins is affected by multiple factors, including age, diet and fertility treatments.
As for the types of twins, most twins are fraternal, while monozygotic twins are relatively rare. Fraternal twins may be female twins, male twins, or a combination of one boy and one girl, indicating up to 50% gender reassortment at birth. Due to the random nature of gene assignment, the sex of twins born in some areas remains highly variable.
In research so far, it has been found that the birth of twins is not only affected by genes, but also restricted by the environment. Some scholars have pointed out that women who suffer from nutritional imbalances and environmental changes may not have a higher chance of twins being born at the beginning of pregnancy. Modern reproductive technologies and treatments have also increased the birth rate of twins significantly compared with the past. According to a 2021 study, twins conceived through fertility treatments have a higher chance.
These observations sparked interest in further exploration of the twin phenomenon.
With the growth of the global population and the continuous advancement of fertility methods, there seems to be a certain "epidemic" trend in the birth rate of twins, including in some specific ethnic communities. For example, the villages of Kodinhi in India and Igbo-Ora in Nigeria both show above-average twin birth rates. There are some common genetic characteristics among the residents of these places, which may be one of the reasons why the birth rate of twins is generally high in this area.
The same situation can be observed in some studies. For example, in a small village in Brazil called Cândido Godói, data collected showed an alarming twin birth rate, one in every five pregnancies. Give birth to twins. Compared with other places, this ratio is "abnormal."
What cultural or genetic reasons are hidden behind the high birth rate?
Currently, the scientific community has not fully clarified the specific reasons for these abnormally high birth rates, whether they are diet, environmental, genetic factors, etc. In future research, we may be able to uncover the deeper sociological or biological implications of the phenomenon of twins.
With the passage of time, the emergence of twins not only makes family structures more diverse, but also makes society face the understanding and challenges of twins in different cultural backgrounds. In the face of twin phenomena like this, can future research help us gain a deeper understanding of the wonders of life itself?
