Online Journal of Anthropology

evolution

 

Researchers find differences between ethnic groups living as farmers and those engaged in traditional hunter-gatherer activities

 

Scientists have long thought that the rate with which mutations occur in the genome does not depend on cultural factors. The results of a current study suggest this may not be the case. A team of researchers from France and Germany analysed more than 500 sequences of the male Y-chromosome in southern African ethnic groups living as farmers and in population groups engaged in traditional hunter-gatherer activities. The study found that the agriculturalists had a comparatively higher rate of change than the hunter-gatherers did. The researchers explain this by the significantly older average age of paternity among the agriculturalists. Furthermore, the study finds a much older age for the most recent common ancestor of the human Y-chromosome than was previously assumed.

 

By sequencing stretches of the Y-chromosome of 500 African males, scientists have been able to show for the first time that the chromosome, which is inherited only in the paternal line, changes at different speeds in different population groups. The researchers compared, on the one hand, members of the Khoisan ethnic groups who traditionally live as hunter-gatherers and, on the other hand, speakers of a Bantu language living in Botswana, Namibia and Zambia who have long worked as farmers.
Interestingly, the different mutation rates can be explained by cultural differences between the two population groups: men from farming societies tend to have children for a longer period of time, leading to an older average age of fathers and a higher mutation rate than is typical for men from foraging societies.

 

“On average, paternal age in southern African foraging societies is 36 years, and 46 years in southern African agriculturalist societies”, explains Chiara Barbieri, scientist at the Max Planck Institute for the Science of Human History and one of the lead authors of the study. “A 15-year increase in age of paternity results in a 50% increase of mutations – so these differences in lifestyle can have a huge impact on the rate of change of the Y-chromosome.”

 

Farmers often marry twice

 

Brigitte Pakendorf, scientist at the laboratoire Dynamique Du Langage in Lyon who coordinated the study added: “Farming societies often allow men to marry more than one wife, so that men often have children at a relatively advanced age with a younger woman. This is one of the factors behind this difference in paternal age and the resulting difference in mutation rate.”

 

The study also reveals a much older age than was previously thought for the most recent common ancestor of the human Y-chromosome. Whereas previous studies estimated an age of approximately 140,000 years, the current investigation estimates an age of 180,000 to 200,000 years. “Previous analyses studied mainly Eurasian individuals in their dating efforts and so missed much of the genetic variation found in southern African populations”, said co-author Mark Stoneking, professor at the Max Planck Institute for Evolutionary Anthropology. “Overall, our results demonstrate the importance of expanding genetic studies to non-Eurasian populations.”

 

(Text & Images’ Source: Max Planck Institute for Evolutionary Anthropology)

 

 

 

 

 

 

Researchers find evolution of human teeth to be much simpler than previously thought, and can predict the sizes of teeth missing from hominin fossils

 

A new study led by evolutionary biologist Alistair Evans of Monash University in Australia, took a fresh look at the teeth of humans and fossil hominins. The research confirms that molars, including ‘wisdom teeth’ do follow the sizes predicted by what is called ‘the inhibitory cascade’ – a rule that shows how the size of one tooth affects the size of the tooth next to it. This is important because it indicates that human evolution was a lot simpler than scientists had previously thought. The international team included researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany: The analysis of digital data on fossil hominins generated by the Department of Human Evolution made this large-scale study on dental development possible.

 

Alistair Evans explains how our fascination with where we come from, and what our fossil ancestors were like, has fuelled our search for new fossils and how we can interpret them. “Teeth can tell us a lot about the lives of our ancestors, and how they evolved over the last 7 million years. What makes modern humans different from our fossil relatives? Palaeontologists have worked for decades to interpret these fossils, and looked for new ways to extract more information from teeth,” says Evans.

 

He then discusses how this new research has challenged the accepted view that there was a lot of variation in how teeth evolved in our closest relatives. “Our new study shows that the pattern is a lot simpler than we first thought – human evolution was much more limited,” says Evans. He led an international team of anthropologists and developmental biologists from Finland, USA, UK and Germany, using a new extensive database on fossil hominins and modern humans collected over several decades, as well as high resolution 3D imaging to see inside the fossil teeth.

 

The team then took the research a step further by applying the findings to two main groups of hominins: the species in the genus Homo (like us and Neanderthals), and australopiths, including specimens like Lucy, the famous fossil hominin from Africa. Evans explains that while it was discovered that both groups follow the inhibitory cascade, they do so slightly differently. “There seems to be a key difference between the two groups of hominins – perhaps one of the things that define our genus, Homo,” says Evans.

 

“What’s really exciting is that we can then use this inhibitory cascade rule to help us predict the size of missing fossil teeth. Sometimes we find only a few teeth in a fossil. With our new insight, we can reliably estimate how big the missing teeth were. The early hominin Ardipithecus is a good example – the second milk molar has never been found, but we can now predict how big it was,” says Evans, who is also a research associate at Museum Victoria.

 

The findings of the study will be very useful in interpreting new hominin fossil finds, and looking at what the real drivers of human evolution were. As well as shedding new light on our evolutionary past, this simple rule provides clues about how we may evolve into the future.

 

Original article:
Alistair R. Evans, E. Susanne Daly, Kierstin K. Catlett, Kathleen S. Paul, Stephen J. King, Matthew M. Skinner, Hans P. Nesse, Jean-Jacques Hublin, Grant C. Townsend, Gary T. Schwartz and Jukka Jernvall, A simple rule governs the evolution and development of hominin tooth size, Nature, 25 February 2016

 

(Text & Images’ Source: Max Planck Institute for Evolutionary Anthropology)