In the kitchen of 51勛圖窪蹋 Davis Professor Emerita , overlooking a long dining table, hangs a by artist .
In the artwork, meerkats stare at a group of African wild dogs; a double-wattled southern cassowary and a duo of pukekos tend to their chicks; and frogs, including the highly endangered Darwins frog, the Australian marsupial frog and the Hoogmoeds harlequin frog, hang along a creekbank, where inside swim Lake Tanganyika cichlids. A golden lion tamarin father reaches to grab one, as his mate and her twins wait in the tree above. Nearby, an owl monkey father watches as his baby clings to him.
And thats just naming some of the species depicted in this imaginary menagerie.
The oil painting derives from evolutionary anthropologist Hrdys 2024 book (Princeton University Press) and focuses on a phenomenon thats absorbed Hrdys recent scholarship. Namely, the role males play in parental care and its evolutionary basis. The 26 animals depicted in Kirklands painting are all species in which males are important caregivers.
That same biological potential for nurture exists within human males as well.
In her book, Hrdy takes us back through evolutionary time to show how these biologically ancient nurturing proclivities linger in modern man. The instincts are there; they just require awakening.
And now, the book has inspired a 52-minute documentary.
Directed by Jacqueline Farmer, Father Time: Why Men Are Born to Nurture premiered in January on the European public service channel , airing in France, Switzerland and Spain, with an expected premiere in Japan soon.
I worked very closely with the filmmakers, and it was how I think films about science should be made in collaboration with the scientists who are doing the research, said Hrdy. I love Jacquelines sensibilities and it was a joy to work with her.
On a foggy day in mid-January, Hrdy welcomed a 51勛圖窪蹋 Davis writer to her home on in Winters for a screening of the working version of the documentarys English language edition.
How fatherhood changes men's hormones
The film, like Hrdys book, is a wide-ranging scientific exploration of the biological changes that occur in men who spend prolonged time in intimate proximity to babies.
Viewers learn about the work of , the director of the Hormones, Health, and Human Behavior Laboratory at Notre Dame University. Gettler joined a long-term study of fatherhood in the Philippines decades ago. The study spanned an economic recession in the country, which led to a shift in family dynamics resulting in men more involved in their childrens lives.
Gettler along with colleagues from Northwestern University and the University of San Carlos traced 600 men since birth, many of whom are fathers now, documenting hormonal shifts in those new fathers.
Gettlers research revealed that levels of testosterone, oxytocin and cortisol all shift in men following the birth of a child.
Cortisol, a hormone linked to stress, rises before the birth of a child but drops substantially once a father makes physical contact with a newborn baby.
Oxytocin, sometimes called the love hormone, surges in tandem with this.
Testosterone, commonly associated with stereotypically masculine traits (although it exists in women in small amounts), also drops, dipping during pregnancy and then nosediving following birth.
A similar drop in testosterone has also been documented other species with paternal care.
As the narrator says, These hormonal shifts are evidence of profound changes, a biological Big Bang in male bodies.
A follow-up study of 300 Filippino fathers revealed a correlation between testosterone levels the day after a childs birth and how consistent a father was with bottle feeding and diaper duty.
Not only does testosterone decrease in men who have become fathers, but fathers who are the most actively involved with their kids consistently show the lowest levels, the narrator says.
What neuroscience reveals about the parental brain
Another standout nugget in the documentarys rich trove is the research of neuroscientist , the director of the Center for Developmental Social Neuroscience at Reichman University in Israel.
Feldman studies how parental brains function. Her research has revealed that the amygdala, the part of the brain involved in emotional responses and danger detection, is four times more active in mothers than in fathers. But in the same situation, the superior temporal sulcus, an evolutionarily newer brain area involved in reading and interpreting the behavior of others, is three times more active in fathers than in mothers.
However, this doesnt seem to be hardwired.
When the Feldman team monitored the brains of 48 gay fathers serving as primary caretakers of babies right from birth, with no mother involved, their amygdala was four times more active than the amygdala of fathers just helping, almost on a par with those of mothers.
The findings testify to the amazing plasticity of the human brain. Occupying the role of primary caretaker, it seems, leads to a fuller activation of a mans parental toolkit.
A persistent urban legend claims that mens brains simply arent wired to respond to a babys cries. But famed French bioacoustician, Nicolas Mathevon, challenges this idea.
As Mathevon explains in the film, it only takes three to four exposures to an infants cries for an adult to begin to discern what his own child sounds like. Gender wasnt the deciding factor; the amount of the time spent with the baby was.
With many 21st century fathers spending , its clear that increased time spent with infants is expanding mens caretaking sensibilities.
Do men have a maternal instinct?
Hrdy also appears in the documentary, discussing her foundational research on mothers and mothering, and how she expanded her research to fathers and fathering.
Growing up in Texas in the 1950s, I had no sense of males as potential nurturers, Hrdy says in the documentary. I had never so much as seen a man change a diaper. That only came much, much later.
Hrdys epiphany came when she witnessed her son-in-law become immersed in nurturing her grandson. She soon found herself puzzled, then obsessed, with wanting to understand the origin of this quantum of tenderness.
Thats what took me back to thinking about some of Darwins early musings, Hrdy states in the documentary. Darwin himself had briefly entertained the thought that our ancestors had had these hermaphroditic capacities. That there was a maternal instinct lurking in males.
Male caregiving across the animal kingdom
The documentary eventually expands its scope, tracing male parental care across the natural world.
We learn about the variable poison frog, whose offspring cannibalize each other when theyre tadpoles. To keep tadpoles hydrated and avoid cannibalization, the male frog transfers each tadpole to its own separate mini pond.
We also spend time with , Ph.D. 96, who takes us through an Argentinian forest to spend time with the owl monkeys he has spent decades studying.
Extensive male care of infants among this species results in the highest rate of infant survival (around 90%) ever reported for nonhuman primates in the wild.
Whats more, these owl monkeys live in the same environment as howler monkeys, a species with exclusively female care of babies. Howler infant survival rates never get much above 62%.
But why is this the case?
Fernandez-Duque speculates that the reason involves access to food and spatial distribution of owl monkey versus howler monkey females.
Unlike howler monkeys, which live in harems, owl monkey females are intolerant of nearby females who would compete with them for food. A strictly monogamous family system provides male owl monkeys a degree of certainty about paternity, which is uncommon among primates. Its thought that this contributed to the evolution of devoted male nurturing for every baby their mate produces.
While humans last shared a common ancestor with owl monkeys over 35 million years ago, their intimate family lives, with males spending a lot of time in intimate proximity to babies, resembles that of many humans. This represents a marked departure from our closest relatives, the great apes.
How society shapes men's roles as caregivers
Humans last shared a common ancestor with other apes some six million years ago. The collective lifestyle developed by our ancestors since then probably played a role in modern human males caretaking propensities.
As Hrdy has long argued, humans must have evolved as cooperative breeders, a term that describes species in which other group members, as well as the parents, help care for offspring. Historically, and in quite a few modern instances, care for a child extends beyond the biological parents, including support from siblings, grandparents and others.
Men in modern hunter-gatherer societies spend much more time with their children than their counterparts in industrialized societies. And that time spent with children affects a mans biology, shifting him towards greater tolerance and susceptibility to infant cues.
Society, it seems, sets the stage for the way male caretaking potentials get expressed.
As Farmer shows us in the film, these potentials date far, far back in time, drawing on molecules and neural circuits that evolved in vertebrates long before the first mammals even appeared 200 million years ago.
To return to the earliest manifestations of parental care, Hrdy says we need to consider fish, and other early vertebrate ancestors. Hrdy references this idea in the film, saying that back in their watery worlds, males were mothering long before mammals and with them internal fertilization, gestation and lactation even evolved.
We contain multitudes of remnants from our past, Hrdy said in her interview with 51勛圖窪蹋 Davis. Im so grateful to the film, because even convincing people that there is a nurturing potential in man can be a hard sell for some audiences, and I want to convince people, No, we need to consider, you know, not only that its there, but its a part of a much larger kind of tree of life.
The book Father Time has received numerous accolades, winning the 2025 PROSE Award in Biological Anthropology and Archaeology from the American Association of Publishers and being long-listed for the 2025 PEN/E.O. Wilson Literary Science Writing Award. It was also listed as a Financial Times Best Summer Science Book, a Telegraph Best Book to Read This Summer and included in the 2024 New Statesman Best of Academic Presses list.