week 2 Flashcards
(49 cards)
What are crop plants?
defined as any plants grown for economic reasons. This definition is broad and can include trees grown for economic purposes, not just typical field crops like wheat
What is domestication?
defined as a change in the morphological appearance of plants that fits the needs of the farmer. This change in appearance corresponds to an underlying change in the genetic makeup of the wild ancestor. Domestication is considered distinct from later genetic improvement which occurs after the crop has been domesticated in its centre of origin. While domestication involves changes to the plant genome by humans, it is not the same as Genetic Modification (GM), which has a specific legal definition usually involving in vitro steps or non-natural techniques, unlike the processes used during Neolithic domestication.
What were original modern humans like (hunter gatherers)?
Original modern humans were hunter-gatherers, who we can assume had a healthy diet but were likely subject to seasonal food shortages. The human population remained very small on the planet for a long time during this period
What about current humans like? (farmers)
largely transitioned from hunter-gatherers to farmers, which began about 10,000 years ago. Farmers started cultivating specific plant species, leading to a narrower diet but also surpluses that helped them survive winters. This shift enabled social stratification, hierarchical societies, and increased population size.
Why did we invent agriculture?
about 10,000 years ago. The consensus is that it was more of an opportunity than a forced necessity:
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There was some climate change about 11,000 years ago, leading to drier conditions in some areas and more annual plants, which are ideal for agriculture.
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It likely occurred in ecologically rich areas with a lot of species to choose from for domestication.
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There was probably an abundance of wild seeds, tubers, or fibres that could be stored.
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One hypothesis, called the rubbish heap hypothesis, suggests that people storing seeds and throwing them outside their settlement observed plants growing nearby, leading to the realisation that they could grow plants close by instead of walking long distances.
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Although possibly starting as an opportunity, agriculture is thought to have become a one-way street, as food production now sustains the large global population, making a return to non-agricultural lifestyles impossible on a large scale.
Where did our crops come from?
different areas around the world, each domesticated by different populations, and most domestication events happened around the same time period, roughly 10,000 years ago (defined as 1950 BP + 10,000 years).
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The Russian scientist Vavilov in 1926 proposed ideas to identify the centres of origin (areas where crops were first selected). He suggested that finding a wild relative in an area or observing large genetic variation for a specific crop in a region likely indicated a centre of origin. He also proposed using linguistic clues.
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More recently, archaeology and DNA analysis play significant roles in identifying centres of origin. DNA analysis, in particular, has become very important for identifying where and when domestication occurred.
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Examples of centres of origin include: Maize in Mexico, Yam and Potato in South America, Rice in Asia and Africa, Sunflower in parts of America, Wheat and Barley in the Fertile Crescent, and Banana in Indonesia.
How has agriculture changed over the last 100,000 years at various places on the planet? What were the patterns in domestication?
Domestication events occurred independently in different regions globally around the same time.
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While most crops were domesticated in a single region, a few, like cotton, rice, and yams, were selected independently in more than one region.
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Interestingly, in each region, similar types of plants were often selected. For example, cereals (deficient in lysine) and beans/pulses (deficient in methionine) were selected, suggesting early domesticators were aware of combining these for a balanced diet. Selection also occurred for fibres, fruits, and tubers in different areas.
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After initial domestication, an estimated 6,000 crops were available, but many became extinct or remained confined to their centres of origin. A few crops took over large production zones, with about 30 crops now grown widely
What crops are we most dependent on? How much of the global food supply do they account for? Why does this create challenges?
dependent on a small number of crops to feed the growing population.
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About 30 crops supply 90% of the energy we get from food.
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Specifically, cereals like Maize, Rice, and Wheat constitute about 75% of crop production and account for 60% of the global food supply.
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This dependence creates challenges for food security, biodiversity, and nutrition, highlighting the need for diversifying crops.
Where did the domestication of wheat and some other early crops begin?
In the Fertile Crescent — a relatively humid, grassland region including parts of modern-day Iraq, the Zagros Mountains, Syria, Jordan, and Israel.
Which cereal crops were first domesticated in the Fertile Crescent?
Einkorn wheat
Emmer wheat
Barley
How did modern bread wheat originate?
It likely originated from a spontaneous natural hybridization between domesticated Emmer wheat and a wild grass called wild goat grass.
What was one of the most significant changes in wheat during domestication?
The development of a non-shattering seed head, making seeds remain attached for easier harvesting.
How does seed shattering differ between wild and domesticated wheat?
Wild wheat: Seeds shatter and disperse easily at maturity.
Domesticated wheat: Seeds remain attached to the spike and require threshing.
What genetic mutation underlies the non-shattering trait?
A single mutation that prevents the formation of the abscission zone (the tissue that allows seeds to fall off).
Was the non-shattering mutation common in wild wheat populations?
No, it was rare, but early farmers selected for it because it made harvesting easier.
Besides non-shattering, what other traits changed during cereal domestication?
Reduced seed dormancy — domesticated cereals germinate more quickly and uniformly.
Loss of environmental germination delay — wild cereals stagger germination as an adaptation to uncertain conditions.
What is the term for the collective traits selected during domestication?
This group of traits is called the domestication syndrome.
How can archaeologists tell wild wheat from domesticated wheat in ancient sites?
By examining the scar at the base of the grain:
Smooth scar = wild grain (natural abscission).
Rough scar = domesticated grain (manually broken off).
Burned grains, often found in archaeological sites, preserve these features.
What did early genetic studies propose about wheat domestication?
That it occurred rapidly at a single geographic location, likely in the Karakadag region, based on phylogenetic analysis showing close genetic similarity between wild and domesticated Einkorn there.
What is the counterargument from archaeologists to the single-origin (monophyletic) model?
Archaeological findings suggest:
A gradual selection process.
Multiple locations showing mixed wild and domesticated wheat.
A temporal increase in domesticated traits over time, indicating a slow, diffuse domestication rather than a rapid, singular event.
What are centres of origin and genetic diversity?
Centres of origin are regions where a crop was first domesticated and where its greatest genetic diversity is found.
These regions often still harbor wild ancestors and traditional landraces of the crop.
Wild ancestors are crucial sources of genetic traits that may have been lost during domestication or modern breeding.
Such traits include resistance to pests, diseases, drought, and other environmental stresses, which are valuable for crop improvement.
Why is it important to study domestication?
Investigating the process of domestication helps scientists understand how plant traits (e.g., seed size, fruit shape, flowering time) have evolved under human selection.
It reveals the genetic and molecular mechanisms that control important phenotypes in crops.
These studies also provide insight into human history and cultural evolution, as plant domestication is closely linked to the development of agriculture and civilizations.
What is the relevance of centres of origin in the context of genetically modified (GM) crops?
Knowing a crop’s centre of origin is important when planning the release of GM varieties.
One major ecological concern with GM crops is the risk of gene flow (cross-pollination) between GM crops and their wild relatives.
This gene flow can potentially introduce transgenes into wild populations, threatening genetic diversity and ecosystem stability.
Low-risk scenario: If GM crops are cultivated far from their centre of origin (e.g., GM maize grown in Europe, Africa, or Asia), where wild relatives are absent, the risk of cross-pollination is minimal or non-existent.
High-risk scenario: If GM crops are introduced into their centre of origin (e.g., GM maize in Mexico), where wild relatives and traditional varieties coexist, there is a significant risk of gene flow.
This can lead to the unintentional spread of transgenes, potentially reducing the genetic integrity and diversity of local landraces and wild populations.
Therefore, greater caution and regulatory oversight are needed when introducing GM crops in or near their centres of origin.
What is seed shattering, and how does it differ between wild and domesticated wheat?
In wild wheat, seeds detach easily at maturity (shattering). Domesticated wheat seeds stay attached and must be threshed.
