November 6, 2015

Domestication: An Introduction

CONSEQUENCES OF AGRICULTURE:

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central questions

Who? – The human cultures involved (demic vs cultural diffusion)

What? – The plant and animal (sub)species and their progenitor populations (first domesticated ancestor)

Where? – The origins, centres and number of domestications

When? – Timing of domestication and the speed of transition

How? – Domestication pathways (what path did they take) and the genes under selection

Why? – The motivations for domestication and the environmental/economic/cultural factors involved.

 

 

 

major stages

1. Aristotle’s Scala Naturae (Great Chain of Being) – Wiki

A ‘hierarchy’ of animals with man at the top – incorporated into religious dogma in the Middle Ages

Developed mostly by Aquinas = plants and animals cannot reason, therefore created for human use

2. Linnaeus (Carl von Linne) 1707 – 1778AD – Wiki

Developed immense catalogue of all living things – reflected divine plan of creation – animals unchanging

3. Georges-Louis LeClerc, Comte de Buffon – 1709-1788AD – Wiki

Created the Histoire Naturelle – a 44 volume encyclopedia describing everything known about the natural world.

Recognised the idea of wild and domestic (based on reproduction isolation), however saw domestic as degenerate

4. Evolutionary Theory 1859 – Wiki

Principles of Uniformitarianism = assumption that the same natural laws and processes that operate in the universe now have always operated in the universe in the past and apply everywhere in the universe

Theory of Natural selection

Variation of Animals and Plants under Domestication – Changes occur due to selective breeding – e.g. variation in domesticated pigeons

5. Mendelian Inheritance 1865 – Wiki

Development of three laws:

  • Law of Segregation – When gametes form, each pair of hereditary factors (alleles) segregates independently of the other pairs.
  • Principle of Uniformity – Hereditary factors (alleles) are dominant or recessive and heterozygotes will share the same phenotype
  • Law of Independent Assortment – Traits are inherited independently of other (i.e. new combinations can arise)

6. Nikolai Vavilov 1887-1943 – Wiki

Russian geneticist – Greatly advanced our knowledge of domestication (mostly plants)

Collected thousands of seeds – creation of modern seed bank – in order to:

  • Determine the geographic distribution of morphological and physiological variation
  • Identify regions with maximum diversity

 

 

 

approaches

Traditional Approaches:

  • Geographic centres of diversity or wild progenitor range identified as origin of domestication
  • Primarily based on earliest archaeological evidence, morphology or karyotyping
  • May be valid if species are domesticated within centre of ancestors range.

Difficult to identify when species are domesticated on periphery of ancestors range or with subsequent gene flow between wild and domestic forms

 

Genetic Approaches:

Compare DNA from domestic populations to various wild populations and assess their evolutionary relationship (phylogeography)

Traditionally focus on neutral, noncoding loci and organellar genomes

  • Animal mitochondrial DNA (mtDNA) – 5-10x faster mutation rate than nuclear  DNA
  • Plant chloroplast DNA and mtDNA – slower mutation rate than nuclear DNA
  • Microsatellites or short tanden repeats (non-coding nuclear DNA)

More recent focus on ‘domestication genes’ and whole genomes

  • Genome wide association studies (GWAS)
  • Quantitative Trait Loci (QTL)
  • Regulatory genes

 

 

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