Tag Archives: Offspring

Chimps, unlike humans, are more likely to choose genetically-dissimilar mates

A new study found that while chimps sleep around a lot, they’re pretty selective about who they make little chimps with. The team found that these primates are more likely to conceive with the individuals that most differ from them genetically.

Image credits Pascal Renet / Pexels.

A couple of days ago we’ve talked about how humans tend to pick their mates after similarities in genome — a practice called assortative mating. From a biological point of view, it gives couples a higher chance of passing on desirable traits to their offspring, such as height, intelligence, and so on. It does, however, also come with potential drawbacks.

So let’s take a look at the opposite mating strategy — negative assortative mating. Postdoc associate in evolutionary anthropology Kara Walker and her team at Duke University found that chimps, our closest living relatives, are more likely to reproduce with genetically-different mates.

They took DNA samples from roughly 150 adult chimps from the Gombe National Park in Tanzania, and examine between 8 to 11 variable sites in their genome. They used this data to estimate the genetic similarity between every possible pairing of mates.

Getting some strange

Chimps get down a lot. But their adventures don’t always lead to offspring. The team compared the pairings that produced infants to those that didn’t, and found that females conceived with males that were genetically less similar to them than the average male. They were somehow able to determine genetic similarity among unfamiliar mates who were far removed from them in the family tree, the team concluded.

The female chimps of Gombe NP usually leave their family group when they reach adolescence, seeking a new group (with new males) to reproduce with. These females, even though they had few or no male relatives in the community they immigrated to, showed an even stronger preference for genetically-dissimilar mates than the native females. The researchers say that the females’ mate choices are driven by inbreeding depression — which is the drawback I was referring to earlier.

When two genetically-similar individuals have offspring, they have a higher chance of passing on beneficial genes — but they also have a higher chance of passing on harmful one. In the absence of another gene version to override it, this harmful gene will become active. Over time, the process increases whole populations’ vulnerability to certain pathogens or environmental factors. That is inbreeding depression in a nutshell — a whole group sharing one or more Achilles’s heel because everyone is related to everyone else.

Gene-dar on the ready

Instinctually, this is what makes you and chimps not cool with parent-offspring or sibling-sibling pairing. Such pairings are rare in chimps, and when it occurs it’s less likely to produce individuals that survive to maturity than their peers.

However, while we can determine the genetic makeup of our mate through DNA tests (you should probably not suggest that on your first date), chimps can’t. The researchers are now trying to find out how the chimps can recognize genetically-distant mates. They suggest that the primates do more than simply avoid potential mates they grew up with, being able to distinguish even among unfamiliar partners. It’s not sure yet exactly how they discriminate but it might be a best guess based on appearance, smell, or sound, said professor of evolutionary anthropology at Duke and senior author of the paper Anne Pusey.

Timing could also play a factor. The females might be pickier about partners during their most fertile period. The team is also considering processes that take place after mating, such as a female unconsciously choosing some males’ sperm over others or influencing the outcome of a pregnancy, Walker said.

The full paper “Chimpanzees breed with genetically dissimilar mates” has been published in the journal Royal Society Open Science.


Male chimpanzees take an active interest in their offspring’s well-being, suggests early humans did the same

Male chimps take an active role in protecting their offspring, new research suggests, by prioritizing time and effort into the task rather than focusing only on future mating options. The study challenges our traditional view of the primates, that of a highly promiscuous species whose males may not even recognize their own offspring.

Image via Wikimedia.

A new study by George Washington University anthropologists looked at male chimps to try and answer why human fathers invest so much time and energy in offspring. The team used data acquired at the Gombe Stream National Park, Tanzania over a period of more than 25 years. They examined the behavioral patterns of 17 father chimpanzees and 49 mother-infant pairs to see if the males recognized their offspring and if they showed a difference in behavior around them.

The researchers found the males associated with mothers of their offspring early in infancy and interacted with their infants more than expected. The fact that the males spent time with nursing mothers even though this didn’t increase their chances of fathering the next infant supports the paternal effort hypothesis, according to which males associate more with mothers in order to protect their offspring, not for sexual gain.

“As anthropologists, we want to understand what patterns could have existed early in human evolution that help explain how human behavior evolved,” said Carson Murray, assistant professor of anthropology at the GWU and lead author of the paper.

“This research suggests that males may sometimes prioritize relationships with their offspring rather than with potential mates. For a species without pair-bonds where it was assumed fathers didn’t know which infants were their own, this is an important finding.”

The researchers also found that the males would spend time grooming and caring for their offspring. Chimpanzees are one of the closes living relatives modern humans have. Discovering that they not only have paternal recognition, but also take an interest in raising and caring for their offspring rather than only focusing on future mating opportunities, offers insight into how early human fathers behaved.

“Our findings are not only further evidence that chimpanzee fathers recognize their offspring in a promiscuous species, but also that fathers behave differently around their offspring,” said Margaret Stanton, postdoctoral scientist at GW’s Center for the Advanced Study of Human Paleobiology and co-author of the paper.

But, while the paper offers some valuable insight, it cannot answer the overall question of how human paternal behavior evolved by itself.

The full paper “Chimpanzee fathers bias their behaviour towards their offspring” has been published in the journal Royal Society Open Science.

Good fathers’ testosterone level drops when expecting a baby

A news study found that men show shifts in behavior from mating-oriented to parent-oriented while their partners’ pregnancy develops. These changes are determined by changes in testosterone levels across pregnancy and hormonal linkage with their partner.

Image credits Chris Price / Flickr

It’s almost hard to imagine that every caring dad was once a skirt-chasing ball of hormones — but it’s true. Somewhere along their transition to parenthood, biology puts a stop to men’s carefree days of sowing wild oats and turns their attention towards nurturing children. This is a very solid strategy from an evolutionary point of view, but we didn’t know exactly how it happened.

A new study found that the answer may be testosterone. While high levels of this androgenic steroid hormone have been associated with aggression and competitive behavior, lower levels promote nurturing behaviors, particularly those related to caring for offspring.

Previous studies show that fathers who are in a relationship and are more involved with children’s care show lower testosterone levels that men who don’t have children. Lower levels of salivary testosterone have also been tied to higher self-reported levels of relationship satisfaction and commitment, a lower interest in sex outside of marriage and a lower chance of divorce. So it would seem that a father’s decrease in testosterone levels during the transition to parenthood leads him from exploring new mating opportunities towards investment into the current relationship and caring for offspring.

Led by Darby Saxbe of the University of Southern California, the study followed 27 couples expecting their first child during pregnancy and first few months after birth. The parents’ testosterone levels were measured during this pregnancy, and participants rated their investment, commitment, and satisfaction with their partner a few months after their child’s birth.

The team found that fathers showed significant declines in testosterone while the pregnancy progressed, and a significant positive correlation with the mother’s testosterone levels. A better correlation between the mother’s and father’s testosterone levels during pregnancy was associated with higher levels of father involvement after the child’s birth —  the degree of synchrony between the parents predicted the fathers’ investment, commitment, and satisfaction in the couple relationship.

Interestingly, they also found that testosterone levels before the birth of the child predicted the relationship outcomes after the birth, even after adjusting for fathers’ scores of investment early on in the pregnancy.

“The direction of our effects suggests that hormonal change and synchrony predict relationship investment, not the other way around; that is, relationship investment at the first prenatal assessment was not significantly associated with testosterone change or coordination with mothers,” concluded the authors.

The full paper, “Fathers’ Decline In Testosterone And Synchrony With Partner Testosterone During Pregnancy Predicts Greater Postpartum Relationship Investment” has been published in the journal Hormones and Behavior.

older fathers

Older dads birth offspring that end up having fewer kids of their own

Evolution is not kind to older dads, a new research suggests. University of Göttingen, Germany researchers found that older fathers end up having fewer grandchildren. Apparently, mutations that appear in old age are transferred to the offspring. To improve the fitness of the gene pool, evolutionary processes limit the number of children these offspring can have of their own.

older fathers

Image: Pixabay

Previously, geneticists showed that older fathers have genetic mutations. Most of these are harmless, but some can be harmful. The first hints were reported in the 1930s by J. B. S. Haldane who noticed a peculiar inheritance pattern in families with long histories of haemophilia. He noticed that the mutation that causes the blood-clotting disorder was much likelier to be found in the X chromosomes that fathers passed to daughters. Haldane then proposed that children inherit more mutations from their fathers than from their mothers.

Much later, in 2012, researchers found the age at which a father sires children determines how many mutations those offspring inherit. By starting families in their thirties, forties and beyond, men could be increasing the chances that their children will develop autism, schizophrenia and other diseases often linked to new mutations. “

The older we are as fathers, the more likely we will pass on our mutations,” says lead author Kári Stefánsson, chief executive of deCODE Genetics in Reykjavik. “The more mutations we pass on, the more likely that one of them is going to be deleterious.”

So why dads and not mothers? Sperm is constantly renewed from dividing precursor cells, which acquire new mutations with each division. Women, on the other hand, are born with their lifelong basket of eggs.

German researchers now suggest that evolution is weeding out these mutations by inhibiting child bearing, they report in  bioRxiv.org.

They analyzed the census records from 17th and 18th century Germany, Canada and Sweden, as well as data from 20th century Sweden national population registry. About 1.3 million people were included in the analysis, in total. Researchers found that both in preindustrial and modern times children born to older fathers had fewer kids that survived past the age of 5. For every decade that a father aged from the baseline measurement, his children had between 5% (20th century Sweden) and 13% (preindustrial Germany) fewer children of their own. This effect seems to be magnified when millions of children are involved. Over many breeding cycles, potentially harmful mutations are kept at bay in the gene pool.

“We can use this understanding to predict the effect of increasingly delayed reproduction on offspring genetic load, mortality and fertility,” the researchers conclude in their paper.

The findings might concern many older fathers, but you should not worry that much. On average U.S. married men have their first child by age 25, while the average age of single men as first-time fathers is 22, according to the U.S. Department of Health and Human Services.  That’s a lot later than a hundred years ago, or only three generations. Men are also living longer, so the same mechanisms that are inhibiting child bearing might adapt. As such, the researchers emphasize that prospective fathers shouldn’t be dissuaded from having kids by the findings.

Menopause appeared by accident, evolved due to stay-at-home males

The evolution of the menopause was ‘kick-started’ by a fluke of nature, but then boosted by the tendency for sons and grandsons go on living close to home, a new study by Liverpool scientists suggests. The full paper, titled ‘Patterns of philopatry and longevity contribute to the evolution of post-reproductive lifespan in mammals’ is published in the journal Biology Letters here.

When you think about it from a biological point of view….Menopause doesn’t make that much sense, does it? All life is an embroidery of the fierce competition each living thing finds itself in in order to pass on its genes (for the most part). And yet, the females of some mammal species (including humans) spend up to one third of their lifespan unable to conceive offspring. So what’s the point in slamming the breaks early on one’s reproductive ability?

Now also available in musical form.
Image via flickr

In an effort to understand why this happens, University of Liverpool and Liverpool John Moores University researchers applied phylogenetic principles to see how the most common theories of why menopause evolved stand up to scrutiny. They used data from 26 different mammal species (including three distinct human populations) to test the effects lifespan, group size and each sex’s tendency to remain within family groups have on post-reproductive lifespan (PRLS)

This study, published in Biology Letters, used data from 26 different mammal species, including three different tribal or historical human populations, to test for the effects of lifespan, group size and male and female philopatry (the tendency to remain within a family group) on post-reproductive lifespan (PRLS).

First was the so-called “Grandmother hypotheses,” probably the most widely-believed explanation for the advent of menopause. According to it women outlive their reproductive period to help with raising their grandchildren. This way, they increase their chances to reach maturity and have children of their own — making the grandmother’s genes more likely to be passed on.

Another theory they looked into is that evolution didn’t actually make menopause happen — we did. Because menopause offers no obvious advantage to the female, some hold that it’s just a ‘mismatch’ that stems from the desynch between our long lifespans in the modern world compared to what we were likely to get in the wild.

The team determined that no one hypothesis could, by itself, adequately explain why menopause sets in. They suggest a new scenario, in which “non-adaptive origins followed by evolutionary tinkering” would bridge the two theories and finally explain menopause.

“Our results suggest that the menopause arose through a non-adaptive ‘mismatch’ between lifespan and reproductive span. Subsequently we think that in populations where males remained at home and females dispersed to reproduce, an adaptive benefit drove the extension of this post-reproductive period,” said evolutionary biologist, Dr Kevin Arbuckle, from the University of Liverpool.

“This adaptive benefit could have come from grandmothers looking after their sons and grandsons at home. As females tend to reproduce more reliably than males, this additional family support could have made it more likely that their grandsons successfully reproduced. ”

Co-author Dr Hazel Nichols, from Liverpool John Moores University, added: “Conflicting views in science can be challenging to reconcile, but our study suggests that both adaptive and non-adaptive ideas may be correct – it’s just that they apply to different parts of the evolution of this most unusual reproductive trait.”