Rise of wheat and milk allergies

New analysis of how humans expanded out of Africa could explain rise of wheat and milk allergies

  • New study draws together anthropological and genetic records for most-complete account yet
  • Shows how genes responsible for gluten and lactose intolerance emerged as Europeans embraced agriculture 10,000 years ago
  • Researchers also hope their work can inform medical treatment of groups susceptible to genetic diseases


Damien Gayle

Source - http://www.dailymail.co.uk/sciencetech/article-2221906/New-analysis-humans-expanded-Africa-explain-rise-wheat-milk-allergies.html?ito=feeds-newsxml

The emergence of wheat and milk allergies could be explained by a new account of the human race's 'out of Africa' expansion that began 60,000 years ago.

The comprehensive review of humans' anthropological and genetic records gives the most up-to-date story of how the global migration had a dramatic effect on human genetic diversity.

As small groups of modern humans migrated out of Africa in Eurasia and the Americas, the genetic diversity of their descendants was substantially reduced.

However, in studying these migrations, previous genomic projects haven't fully taken into account the rich archaeological and anthropological data available, and vice versa.

This latest review by three Stanford geneticists integrates both sides of the story and offers a foundation that could lead to a better understanding of ancient humans that could lead to medical advances.

'People are doing amazing genome sequencing, but they don't always understand human demographic history,' said review co-author Brenna Henn, a postdoctoral fellow in genetics at the Stanford School of Medicine.

'We wanted to write this as a primer on pre-human history for people who are not anthropologists.'

The anthropological information can inform geneticists when they investigate certain genetic changes that emerge over time.

For example, geneticists have found that genes for lactose intolerance and gluten sensitivity began to emerge in populations expanding into Europe around 10,000 years ago.

The anthropological record helps explain this. It was around this time that humans embraced agriculture, including milk and wheat production.

The populations that prospered – and thus those who survived to pass on these mutations – were those who embraced these unnatural food sources.

This is an example of how human movements drove a new form of natural selection, the researchers say.

The model of the Out of Africa expansion provides the framework for testing other anthropological and genetic models and will allow researchers to constrain various parameters on computer simulations, which will ultimately improve their accuracy, said Professor Henn.

Marcus Feldman, professor of biology at Stanford and co-author, added: 'The basic notion is that all of these disciplines have to be considered simultaneously when thinking about movements of ancient populations.

'What we're proposing is a story that has potential to explain any of the fossil record that subsequently becomes available, and to be able to tell what was the size of the population in that place at that time.'

Populations that expand from a small founding group can also exhibit reduced genetic diversity – known as a 'bottleneck'.

A classic example is the Ashkenazi Jewish population, which has a fairly large number of genetic diseases that can be attributed to its small number of founders.

When this small group moved from the Rhineland to Eastern Europe, reproduction occurred mainly within the group, eventually leading to situations in which mothers and fathers were related.

This meant that offspring often received the same deleterious gene from each parent and, as this process continued, ultimately resulted in a population in which certain diseases and cancers are more prevalent.

'If you know something about the demographic history of populations, you may be able to learn something about the reasons why a group today has a certain genetic abnormality – either good or bad,' Professor Feldman said.

'That's one of the reasons why in our work we focus on the importance of migration and history of mixing in human populations. It helps you assess the kinds of things you might be looking for in a first clinical assessment.

'It doesn't have the immediacy of prescribing chemotherapy – it's a more general look at what's the status of human variability in DNA, and how might that inform a clinician.'

The study is published in the current edition of the Proceedings of the National Academy of Sciences. Population geneticist Luigi Luca Cavalli-Sforza of the Università Vita-Salute San Raffaele in Italy also contributed.