**Etiology**

**Chapter 2**

**Provisional chapter**

**Twinning as an Evolved Age-Dependent Physiological**

**Twinning as an Evolved Age-Dependent Physiological** 

Multiple pregnancies occur in humans and other primates, which indicate that the twinning propensity is phylogenetically old. Factors such as decreased sexual dimorphism and size, rich and diverse nutrition and paternal care are related to multiple pregnancies in other animals. In human populations, despite its costs, twinning has a genetic basis and in Europe, Africa, and America, it was found that it increases mothers' fitness. Here, we explore the hypothesis that twinning represents an evolved physiological mechanism, particularly in mothers of higher age, as an 'all-or-nothing' last chance strategy for reproduction just before menopause. We present decade-long, large-scale population data about maternities from the city of São Paulo and the entire country of Brazil that indicate a considerable main effect of advanced age in promoting twinning, particularly dizygotic (DZ) twinning, but also monozygotic (MZ) twinning and higher order maternities. We also show that socioeconomic status is an important contextual factor increasing twinning. Besides the theoretical implications, these datasets establish a Brazilian countrywide twinning rate of 9.39‰ and highlight an increasing historical trend. This chapter promotes the importance of integrating proximate patterns from human and nonhuman animals and evolutionary factors in order to reach a comprehensive view about twinning.

**Keywords:** twinning rates, age dependence, physiological mechanism, evolutionary

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.79907

**Mechanism: Evidence from Large Brazilian Samples**

**Mechanism: Evidence from Large Brazilian Samples**

Marco Varella, Eloisa Fernandes, Jonas Arantes,

Marco Varella, Eloisa Fernandes, Jonas Arantes, Tiziana Acquaviva, Tania Lucci, Rafael Hsu,

Vinicius David, Vera Bussab, Jaroslava Valentova,

Vinicius David, Vera Bussab, Jaroslava Valentova,

Tiziana Acquaviva, Tania Lucci, Rafael Hsu,

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

theories, population data, socioeconomic status

Nancy Segal and Emma Otta

Nancy Segal and Emma Otta

**Abstract**

http://dx.doi.org/10.5772/intechopen.79907

#### **Twinning as an Evolved Age-Dependent Physiological Mechanism: Evidence from Large Brazilian Samples Twinning as an Evolved Age-Dependent Physiological Mechanism: Evidence from Large Brazilian Samples**

DOI: 10.5772/intechopen.79907

Marco Varella, Eloisa Fernandes, Jonas Arantes, Tiziana Acquaviva, Tania Lucci, Rafael Hsu, Vinicius David, Vera Bussab, Jaroslava Valentova, Nancy Segal and Emma Otta Marco Varella, Eloisa Fernandes, Jonas Arantes, Tiziana Acquaviva, Tania Lucci, Rafael Hsu, Vinicius David, Vera Bussab, Jaroslava Valentova, Nancy Segal and Emma Otta

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79907

#### **Abstract**

Multiple pregnancies occur in humans and other primates, which indicate that the twinning propensity is phylogenetically old. Factors such as decreased sexual dimorphism and size, rich and diverse nutrition and paternal care are related to multiple pregnancies in other animals. In human populations, despite its costs, twinning has a genetic basis and in Europe, Africa, and America, it was found that it increases mothers' fitness. Here, we explore the hypothesis that twinning represents an evolved physiological mechanism, particularly in mothers of higher age, as an 'all-or-nothing' last chance strategy for reproduction just before menopause. We present decade-long, large-scale population data about maternities from the city of São Paulo and the entire country of Brazil that indicate a considerable main effect of advanced age in promoting twinning, particularly dizygotic (DZ) twinning, but also monozygotic (MZ) twinning and higher order maternities. We also show that socioeconomic status is an important contextual factor increasing twinning. Besides the theoretical implications, these datasets establish a Brazilian countrywide twinning rate of 9.39‰ and highlight an increasing historical trend. This chapter promotes the importance of integrating proximate patterns from human and nonhuman animals and evolutionary factors in order to reach a comprehensive view about twinning.

**Keywords:** twinning rates, age dependence, physiological mechanism, evolutionary theories, population data, socioeconomic status

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
