Category: human

Monogamy may have evolved to keep baby-killers away

On By A.P.In Carel van Schaik, gibbon, human, Human Behavior, infanticide, Kit Opie, monogamy, Nature, New World monkey, pair-bonding, PNAS, primatology, Proceedings of the National Academy of Sciences, Relationship, social monogamy, Susanne Shultz, University College London, University of Manchester, University of ZurichLeave a comment

monogamy

Social monogamy – when a male and female of the species stick together for the long term, although may mate with others – is rare in mammals generally. However, it occurs in over a quarter of primate species, including humans, gibbons and many New World monkeys, such as titis.

To investigate what originally drove us to establish such pair bonds, a team led by Kit Opie of University College London and Susanne Shultz from the University of Manchester, UK, gathered data on the mating behaviour of 230 primate species. They selected behavioural traits associated with several possible evolutionary drivers of monogamy, including the risk of infanticide, the need for paternal care and the potential for guarding female mates.

Using data on the genetic relationships between the species, the team ran millions of computer simulations of the evolution of these traits to work out which came first.

All three were linked to the evolution of monogamy but only behaviours associated with infanticide actually preceded it, suggesting that this was the driver. Suckling infants are most likely to be killed by unrelated males, in order to bring the mother back into ovulation.

With pair-bonding in place, not only would a mother have a male to help protect the infant from marauding males, but there would then be the opportunity for the male to help care for it by providing extra resources. This means the infant can be weaned earlier, again reducing the chance of it being killed.

“Until recently, reconstructing how behaviour evolves has been very tricky as there are few behavioural traces in the fossil record. The statistical approach we have used allows us to bring the fossils to life and to understand the factors that have led to the evolution of monogamy in humans and other primates,” says Shultz.

Carel van Schaik, a primatologist at the University of Zurich in Switzerland says the results are solid but questions whether they can be extrapolated to humans. He says evidence suggests that humans were never really monogamous and that the monogamy we see today in many cultures is socially imposed.

Shultz counters that there is fossil evidence pointing to monogamy in australopithecines, the hominin genus from which modern humans descended.

“Although we suggest that infanticide may help explain the evolution of monogamy in humans, we do not argue that it is the only factor nor that monogamy is universal,” Shultz says. “I would suggest that where infanticide risk is high, as it would be with our ancestors, having a father provide protection and care would facilitate the evolution of the modern human extended childhood.”

Journal reference: PNAS, DOI: 10.1073/pnas.1307903110

Did Neanderthals go extinct because they couldn’t learn to catch rabbits?

On By A.P.In Bunny, Durrell Wildlife Conservation Trust, extinction, France, human, Hunting, John Fa, Nature, Neanderthal, New Scientist, rabbit, Science, SpainLeave a comment

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Neanderthals became extinct as they were unable to adapt their hunting skills to catch small animals like rabbits, a new study has claimed.

For the study, John Fa of Durrell Wildlife Conservation Trust in Trinity, Jersey, and his colleagues counted skeletons of animals that were found in three excavation sites in Spain and southern France.

The team found that up until 30,000 years ago, the skeletons of larger animals like deer were plentiful in caves.

But around the same time, coinciding with Neanderthals’ disappearance, rabbit skeletons became more abundant.

The team postulated that humans succeeded far more at switching to capturing and eating rabbits than Neanderthals, New Scientist reported.

Fa said that it is still not clear as to why Neanderthals had trouble changing their prey.

He said that maybe the Neanderthals may have been less able to cooperate and rather than using spears, early humans probably surrounded a warren and flushed out rabbits with fire, smoke or dogs.

http://www.phenomenica.com/2013/03/inability-to-catch-rabbits-may-have-led-to-demise-of-neanderthals.html

Mother-Child Connection: Scientists Discover Children’s Cells Living in Mothers’ Brains, Including Male Cells Living in the Female Brain for Decades

On By A.P.In Alzheimer's disease, bond, breast cancer, Chimera, chimerism, Communication, DNA, fetus, human, immune system, Microchimerism, mother-child connection, multiple pregnancies, Multiple Sclerosis, Nature, Neuropsychiatric Disease, Neuroscience, neuroscientist, nursing, Placenta, Pregnancy, Relationship, Science, Scientific American, stem cells, The Brain, twinsLeave a comment

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The link between a mother and child is profound, and new research suggests a physical connection even deeper than anyone thought. The profound psychological and physical bonds shared by the mother and her child begin during gestation when the mother is everything for the developing fetus, supplying warmth and sustenance, while her heartbeat provides a soothing constant rhythm.

The physical connection between mother and fetus is provided by the placenta, an organ, built of cells from both the mother and fetus, which serves as a conduit for the exchange of nutrients, gasses, and wastes. Cells may migrate through the placenta between the mother and the fetus, taking up residence in many organs of the body including the lung, thyroid muscle, liver, heart, kidney and skin. These may have a broad range of impacts, from tissue repair and cancer prevention to sparking immune disorders.

It is remarkable that it is so common for cells from one individual to integrate into the tissues of another distinct person. We are accustomed to thinking of ourselves as singular autonomous individuals, and these foreign cells seem to belie that notion, and suggest that most people carry remnants of other individuals. As remarkable as this may be, stunning results from a new study show that cells from other individuals are also found in the brain. In this study, male cells were found in the brains of women and had been living there, in some cases, for several decades. What impact they may have had is now only a guess, but this study revealed that these cells were less common in the brains of women who had Alzheimer’s disease, suggesting they may be related to the health of the brain.

We all consider our bodies to be our own unique being, so the notion that we may harbor cells from other people in our bodies seems strange. Even stranger is the thought that, although we certainly consider our actions and decisions as originating in the activity of our own individual brains, cells from other individuals are living and functioning in that complex structure. However, the mixing of cells from genetically distinct individuals is not at all uncommon. This condition is called chimerism after the fire-breathing Chimera from Greek mythology, a creature that was part serpent part lion and part goat. Naturally occurring chimeras are far less ominous though, and include such creatures as the slime mold and corals.

 Microchimerism is the persistent presence of a few genetically distinct cells in an organism. This was first noticed in humans many years ago when cells containing the male “Y” chromosome were found circulating in the blood of women after pregnancy. Since these cells are genetically male, they could not have been the women’s own, but most likely came from their babies during gestation.

In this new study, scientists observed that microchimeric cells are not only found circulating in the blood, they are also embedded in the brain. They examined the brains of deceased women for the presence of cells containing the male “Y” chromosome. They found such cells in more than 60 percent of the brains and in multiple brain regions. Since Alzheimer’s disease is more common in women who have had multiple pregnancies, they suspected that the number of fetal cells would be greater in women with AD compared to those who had no evidence for neurological disease. The results were precisely the opposite: there were fewer fetal-derived cells in women with Alzheimer’s. The reasons are unclear.

Microchimerism most commonly results from the exchange of cells across the placenta during pregnancy, however there is also evidence that cells may be transferred from mother to infant through nursing. In addition to exchange between mother and fetus, there may be exchange of cells between twins in utero, and there is also the possibility that cells from an older sibling residing in the mother may find their way back across the placenta to a younger sibling during the latter’s gestation. Women may have microchimeric cells both from their mother as well as from their own pregnancies, and there is even evidence for competition between cells from grandmother and infant within the mother.

What it is that fetal microchimeric cells do in the mother’s body is unclear, although there are some intriguing possibilities. For example, fetal microchimeric cells are similar to stem cells in that they are able to become a variety of different tissues and may aid in tissue repair. One research group investigating this possibility followed the activity of fetal microchimeric cells in a mother rat after the maternal heart was injured: they discovered that the fetal cells migrated to the maternal heart and differentiated into heart cells helping to repair the damage. In animal studies, microchimeric cells were found in maternal brains where they became nerve cells, suggesting they might be functionally integrated in the brain. It is possible that the same may true of such cells in the human brain.

These microchimeric cells may also influence the immune system. A fetal microchimeric cell from a pregnancy is recognized by the mother’s immune system partly as belonging to the mother, since the fetus is genetically half identical to the mother, but partly foreign, due to the father’s genetic contribution. This may “prime” the immune system to be alert for cells that are similar to the self, but with some genetic differences. Cancer cells which arise due to genetic mutations are just such cells, and there are studies which suggest that microchimeric cells may stimulate the immune system to stem the growth of tumors. Many more microchimeric cells are found in the blood of healthy women compared to those with breast cancer, for example, suggesting that microchimeric cells can somehow prevent tumor formation. In other circumstances, the immune system turns against the self, causing significant damage. Microchimerism is more common in patients suffering from Multiple Sclerosis than in their healthy siblings, suggesting chimeric cells may have a detrimental role in this disease, perhaps by setting off an autoimmune attack.

This is a burgeoning new field of inquiry with tremendous potential for novel findings as well as for practical applications. But it is also a reminder of our interconnectedness.

http://www.scientificamerican.com/article.cfm?id=scientists-discover-childrens-cells-living-in-mothers-brain

Chimp and human gut bacteria are nearly identical

On By A.P.In Andrew Moeller, chimp, chimpanzee, enterotypes, Gomber Stream National Park, gut bacteria, Howard Ochman, human, immune system, inflammatory bowel disease, Medicine, Obesity, Tanzania, Yale UniversityLeave a comment

 

Humans share about 99 percent of our genomes with chimpanzees. Now, research finds we share something else: gut bacteria.

The bacterial colonies that populate the chimpanzee intestinal tract are mirror images of those found in the human gut, researchers report today (Nov. 13) in the journal Nature Communications. The findings suggest gut bacteria patterns evolved before chimps and humans split and went their evolutionarily separate ways.

Human gut bacteria are crucial to health, with infants relying on healthy microbe populations to influence the developing immune system. Problems with microbe populations may also contribute to obesity and inflammatory bowel diseases. 

Three intestinal ecosystems

In 2011, researchers learned that everyone’s gut bacteria fall into one of three different types, almost analogous to blood types. In each type, certain bacteria dominate. These types weren’t linked to any personal characteristics such as geographic area, age or gender. Researchers dubbed these distinct bacterial ecosystems “enterotypes.” (“Entero” means gut or intestine.)

“No one really knows why these three enterotypes exist,” said study researcher Andrew Moeller, a doctoral student at Yale University.

Along with his adviser Howard Ochman and their colleagues, Moeller want to understand how these enterotypes arose. They could be distinctly human, he told LiveScience, which would suggest they arose relatively recently, perhaps in response to the development of agriculture. Or they could be ancient, shared among our closest primate relatives.

The researchers analyzed gut bacteria samples from 35 chimpanzees from Gombe Stream National Park in Tanzania. The chimpanzees were all in the subspecies Pan troglodytes schweinfurthii, the eastern chimpanzee, which arose approximately the same time as Homo sapiens.

Shared bacteria

The researchers found that, just like humans, chimps’ guts harbor one of three distinct types of bacterial colonies. Even more intriguingly, these enterotypes matched humans’ precisely. In type 1, for example, both humans and chimps show a predominance of Bacteroides, Faecalibacterium and Parabacteroides.

There were some differences. For example, in humans and chimps, enterotype 2 is marked by an overabundance of bacteria called Lachnospiraceae. In humans, the bacteria Prevotellae is also prevalent in type 2. In chimps, Prevotellae appears in significant numbers in all three enterotypes, perhaps because it is associated with a high-carbohydrate diet.

Other differences could help explain certain human health issues. By comparing human and chimpanzee gut bacteria, the researchers found many of the bacteria present only in humans are linked to diseases such as inflammatory bowel diseases, conditions that cause pain, diarrhea and vomiting.

Seven of the chimps in the study were tested repeatedly over eight years, and their gut microbes were found to change from type to type over that time period. No one has ever tested humans for changes over a period longer than two weeks, Moeller said, but the results suggest our enterotypes may shift over time, too.

Our shared history

The similarities between chimp and human colonies suggest enterotypes predate our species, which in turn suggests that none of the three ecosystems are better than the others, Moeller said. [Gallery: Tiny, Nasty Bugs That Make Us Sick]

“Before we found this in chimpanzees, there was a possibility that enterotypes were a product of modernization, which could mean they have some negative effects on health,” he said. “I don’t think there’s any reason to think one enterotype is going to have an effect on health that’s going to be better” than the others.

Moeller and his colleagues are now examining gorilla fecal samples to find out where they stand as slightly more distant primate relatives to humans.

“The next step is to try to find out the processes and mechanisms responsible for producing these three community states,” Moeller said, “which is kind of a lofty goal, but I think more sampling will actually reveal why these communities exist.”

http://www.livescience.com/24738-chimp-human-gut-bacteria-identical.html