38. You Make Me Sick...

Hi friends,

Welcome to the thirty-eighth dispatch of How Humans Flourish, a research-informed newsletter on how humans thrive.

I’m trying something new by releasing this on a Tuesday—do we like this? Feel free to respond with a simple yes or no.

This month, we’ve been diving into Dataclysm: Love, Sex, Race, and Identity–What Our Online Lives Tell Us about Our Offline Selves by Christian Rudder, a data scientist and technology founder. His work offers fascinating insights into how digital interactions reveal deep truths about human relationships and behaviors.

Today, I’m blending Rudder’s insights with the research of Dr. Nicholas Christakis, Yale Professor, sociologist, and physician, whose work centers on social networks and the biological, social, and evolutionary forces that shape our lives.

Dr. Christakis’s work, particularly with his colleague James Fowler in their book Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives, shows just how influential our social ties are. One of their key findings is that even behaviors like weight gain or smoking cessation ripple through our networks: if your friend’s friend’s friend gains weight or quits smoking, you’re more likely to do the same. Most importantly though, these discoveries show that social networks follow certain rules that govern their formation and flow.

Over the past few weeks, we’ve been exploring different aspects of sexuality—from the rejection faced by heterosexual Black women on dating apps to the social rejection and repression experienced by men who have sex with men. Though these two groups may initially seem disparate, they are connected by the way their social networks increase their vulnerability to HIV compared to other populations.

When we talk about social networks here, we are referring to specific patterns of connections between people. As Dr. Christakis and Fowler explain, the structure of these connections is often more important than an individual’s attributes. Communities aren’t defined by shared traits but by the web of ties linking their members, and understanding these connections is crucial to how social networks operate. This is also how Dr. Christakis and Fowler introduce the idea of contagion, describing how various things—germs, money, emotions like happiness or depression, or even obesity—spread through networks.

In the context of sexual networks, Dr. Christakis describes two types:

The first and most common involves what are called “highly sexually active cores,” where individuals at the center of the network are more likely to spread disease to less active individuals on the periphery. This is particularly significant in understanding differences in STD rates between Black and white populations.

Dr. Christakis and Fowler write, “Sociologist Dr. Ed Laumann and his colleagues proposed that STD rates were higher among blacks than whites because of differences in the two groups’ sexual network patterns. A peripheral black person (where peripheral is defined as having only one sexual partner in the past year) is five times more likely to choose a partner in the core (defined as having four or more partners in the past year) than is a peripheral white person. No one has yet discovered why this is the case, but the result is that STDs would be more likely to be contained within the white core, whereas they are more likely to spill out into the black periphery.” (Christakis and Fowler, pg. 102-103 - Kindle) 

(I don’t know if Dr. Christakis has read Dataclysm, but I’d be curious to hear his thoughts if he saw the data in the book.)

The broader takeaway is that individual intention often pales in comparison to the influence of social networks. Even if someone only has one sexual partner, they are still part of a larger web of connections that can place them at risk due to the behavior of people they literally do not know. This raises important questions for public health efforts: who should we be targeting with our messages?

Christakis argues that safe-sex campaigns would be most effective if they focused on those at the core of these networks—the highly active individuals who are most likely to spread disease—rather than trying to reach everyone equally.

As we discussed last week, the core for HIV transmission is often men who have sex with men, many of whom live in environments hostile to their identities, leading them to hide their sexuality. In 2008, a study found that 72.3% of African Americans believed homosexuality was "always wrong," a view that had remained largely unchanged since the 1970s, while the percentage among white respondents dropped from 70.8% in 1973 to 51.6% by 2008.* This overlap between the experiences of Black women, Black transgender women, and gay men makes prevention efforts more complex. How does one focus a campaign on a population in hiding? (Hint: AI can help)

The second social network can be seen in an HIV/AIDS epidemic that occurred in sub-Saharan Africa. Researchers studying seven villages in Malawi discovered that residents reported few sexual partners and that there was no distinction to be made between core and periphery… pretty much everyone had similar levels of sexual activity. They found that 65% of those aged 18-35 were instead part of a large interconnected sexual network, meaning while this community was not having sex with many people, they were having sex with the same people.

In such a network, Christakis recommends targeting prevention efforts at everyone since there is no clear core; if everyone takes protective measures, the entire community benefits.

It’s cliché to say, but few things bring to mind the phrase “what a tangled web we weave” than the dynamics of these networks.

With gratitude,

P.S. According to a 2017 Pew Report, while Black Americans have historically been less supportive of same-sex marriage compared to other racial groups, support has grown by 12 percentage points since 2015, rising from 39% to 51%. This shift, though slower than in other communities, is an important indicator of changing social norms.