Diapers yield developmental data

By Robin Tricoles

With the help of babies and more than 5,000 of their diapers, Emory researchers have developed an accurate, noninvasive way to determine estrogen levels in infants. The method, described in the journal Frontiers in Systems Biology, will allow comparisons of estrogen levels in human infants and their long-term reproductive development as well as the development of sex-specific behaviors, such as toy preference or cognitive differences.


What’s more, the method will allow researchers to look at how early disruption of the endocrine system affects long-term maturation, a growing concern among physicians.

Surprisingly little is known about hormone levels during human infancy. Previous human research has focused on the measurement of hormones in blood, urine and saliva. The new data are the result of using fecal samples collected from cotton diapers. With this novel approach, the researchers successfully measured the fecal levels of estradiol, a type of estrogen.

The well-known importance of estradiol’s role in postnatal development of the body, brain and behavior has in recent years raised specific concerns about how exogenous estrogens, or environmental estrogens, such as those found in soy, fruits and vegetables, plastics and common household items, affect lifelong health.

“The development of robust, noninvasive methods to measure these hormones in infants allows us to further investigate the association between postnatal hormone production and the development of sex-specific biology and behavior,” says Emory anthropologist Michelle Lampl, senior author of the paper.

“The development of an assay to measure estrogen from diapers might initially strike one as unnecessary or strange, but the need is real,” says Sara Berga, chair of gynecology and obstetrics at Emory’s School of Medicine. “We understand very little about the hormonal dynamics that occur during early development precisely because we lack a reliable way to track hormones in neonates and very young children. Having a way to track this critical hormone that influences behavior and the development of many important tissues, including the brain, will allow us to understand normal. This really is a great leap forward.”

The paper’s authors include anthropologist Amanda Thompson at the University of North Carolina, Chapel Hill; Emory anthropologist Patricia Whitten; and Michael Johnson of the University of Virginia Health System.

Previous studies in primates have shown a close parallel between fecal levels of estradiol and serum values. Likewise, a comparison of fecal steroid levels between the study infants and previous studies of human adults shows an overlapping pattern, a pattern that is also seen in infant serum when compared with adult serum.

“These observations are the first report of human infant fecal estradiol levels and they provide a new tool for investigating early human development,” Lampl say, who also serves as associate director of the Emory/Georgia Tech Predictive Health Institute. “Because infant diapers are plentiful, fecal samples can be collected frequently and over a long period of time. Future longitudinal studies will allow the association between fecal levels of steroids and physiological measures to be assessed, and expand our understanding independent of serum measures.”

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Testes size correlates with men's involvement in toddler care

“Mothers definitely have more of an impact on child development, but fathers are also important and their role is understudied,” says anthropologist James Rilling.

By Carol Clark

Men with smaller testes than others are more likely to be involved in hands-on care of their toddlers, finds a new study by anthropologists at Emory University. The Proceedings of the National Academy of Sciences (PNAS) published the results of the study on Sept. 9.

Smaller testicular volumes also correlate with more nurturing-related brain activity in fathers as they are looking at photos of their own children, the study shows.

“Our data suggest that the biology of human males reflects a trade-off between investments in mating and parenting effort,” says Emory anthropologist James Rilling, whose lab conducted the research.

The goal of the research is to determine why some fathers invest more energy in parenting than others. “It’s an important question,” Rilling says, “because previous studies have shown that children with more involved fathers have better social, psychological and educational outcomes.”

Life History Theory posits that evolution optimizes the allocation of resources toward either mating or parenting to maximize fitness. “Our study is the first to investigate whether human anatomy and brain function explain this variance in parenting effort,” says Jennifer Mascaro, who led the study as a post-doctoral fellow in the Rilling lab.

“Although there are more households with no fathers, when the fathers are around, they tend to be much more involved than in previous decades,” Mascaro notes.

While many economic, social and cultural factors likely influence a father’s level of caregiving, the researchers wanted to investigate possible biological links.

They knew that lower levels of testosterone in men have been correlated with greater paternal involvement, and that higher levels of the hormone predict divorce as well as polygamy.

The testes, in addition to producing testosterone in males, also produce sperm. “Testes volume is more highly correlated with sperm count and quality than with testosterone levels,” Mascaro says.

The study included 70 biological fathers who had a child between the ages of 1 and 2, and who were living with the child and its biological mother.

The mothers and fathers were interviewed separately about the father’s involvement in hands-on childcare, including tasks such as changing diapers, feeding and bathing a child, staying home to care for a sick child or taking the child to doctor visits.

The men’s testosterone levels were measured, and they underwent functional magnetic resonance imaging (fMRI) to measure brain activity as they viewed photos of their own child with happy, sad and neutral expressions, and similar photos of an unknown child and an unknown adult. Then, structural MRI was used to measure testicular volume.

The findings showed that both testosterone levels and testes size were inversely correlated with the amount of direct paternal caregiving reported by the parents in the study.

"Previous studies have shown that children with more involved fathers have better social, psychological and educational outcomes," Rilling says.

And the father’s testes volume also correlated with activity in the ventral tegmental area (VTA), a part of the brain system associated with reward and parental motivation. “The men with smaller testes were activating this brain region to a greater extent when looking at photos of their own child,” Mascaro says.

While testosterone levels may be more related to pre-copulatory, intrasexual competition, testicular volume may reflect post-copulatory mating investment, the researchers theorize.

Although statistically significant, the correlation between testes size and caregiving was not perfect.

“The fact that we found this variance suggests personal choice,” Rilling says. “Even though some men may be built differently, perhaps they are willing themselves to be more hands-on fathers. It might be more challenging for some men to do these kinds of caregiving activities, but that by no means excuses them.”

A key question raised by the study findings is the direction of casualty. “We’re assuming that testes size drives how involved the fathers are,” Rilling says, “but it could also be that when men become more involved as caregivers, their testes shrink. Environmental influences can change biology. We know, for instance, that testosterone levels go down when men become involved fathers.”

Another important question is whether childhood environment can affect testes size. “Some research has shown that boys who experience childhood stress shift their life strategies,” Rilling says. “Or perhaps fatherless boys react to the absence of their father by adopting a strategy emphasizing mating effort at the expense of parenting effort.”

The study focused only on direct paternal care, and not indirect forms of care, such as protecting children and earning a living to provide for them.

In the decades since the 1960s, the number of women raising children on their own in the United States has risen dramatically. “Although there are more households with no fathers, when the fathers are around, they tend to be much more involved than in previous decades,” Mascaro says.

Much of the existing scientific literature on nurturing is focused on mothers, Rilling notes. “Mothers definitely have more of an impact on child development, but fathers are also important and their role is understudied,” he says.

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