Migration Theories and Patterns

Spec mapping (AQA 7037): Paper 2 (Human Geography), §3.2.4 Population and the Environment and the migration components of Global systems and global governance (§3.2.1) — the causes, patterns and theories of population movement at local, national and international scales. This depth lesson moves beyond cataloguing types of migration to evaluating the theoretical frameworks that explain it: Ravenstein's laws, Lee's push–pull model, the gravity model, Todaro's expected-income model, Stark's new economics of labour migration, and Zelinsky's mobility transition. It exercises AO1 (precise knowledge of each model's mechanism), AO2 (applying frameworks to real-world flows and explaining their drivers) and AO3 (manipulating migration data — net migration, the gravity equation, expected income — and interpreting patterns). Synoptic links run to the migration case studies lesson that follows, to the DTM (Zelinsky couples to it directly), to Changing places (the local imprint of migration) and to Global systems (globalisation, remittances, governance of flows).

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Defining migration precisely

Migration is the permanent or semi-permanent change of usual residence across a defined boundary. It is distinct from circulation (commuting, tourism, seasonal movement) where the person returns to a fixed home. Precision in classification earns AO1 marks:

Axis	Categories	Worked example
Scale	Internal vs international	Rural–urban (China) vs Poland→UK
Choice	Voluntary vs forced	Economic migrant vs refugee
Duration	Temporary vs permanent	Gulf labour contract vs settlement
Pattern	Step / chain / return / circular	Village→town→city; Turkish→Germany; post-Brexit returns

Legal terms matter because they carry rights: an asylum seeker has applied for protection; a refugee has been recognised as fleeing persecution under the 1951 Geneva Convention; an Internally Displaced Person (IDP) is forced to move but has not crossed an international border (and so lacks Convention protection). Conflating "migrant," "asylum seeker" and "refugee" is a common error that the strongest answers avoid.

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Ravenstein's Laws of Migration (1885)

Ernst Georg Ravenstein, a German-British geographer, mined the 1871/1881 census of England and Wales to derive eleven empirical generalisations — the first systematic "laws" of migration. Over 130 years on, several remain strikingly robust, which is why they still anchor the topic.

The core laws:

1. Distance-decay — most migrants move only short distances; the number falls as distance rises.
2. Long-distance migrants head for major centres of commerce and industry.
3. Migration proceeds step by step (village → town → regional city).
4. Every stream produces a counter-stream — flows generate return movement.
5. Urban dwellers migrate less than rural dwellers.
6. Gender differs by distance — (in 1885) women dominated short-distance moves, men long-distance.
7. Most migrants are adults; families with children move less.
8. Large towns grow more by migration than by natural increase.
9. Migration increases with economic development, transport and industry.
10. The dominant motive is economic.

Evaluation. Laws 1, 3, 8, 9 and 10 hold up remarkably well — distance-decay, step migration, the economic motive and the link to development are all visible in contemporary flows. But the model is dated: it ignores forced migration (Ravenstein's England was peaceful), its gender law has reversed (women now dominate many long-distance and even international flows — the "feminisation of migration"), and modern transport and digital information have weakened the friction of distance he assumed. It is best treated as an enduring empirical baseline that later theory explains and updates.

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Lee's Push–Pull Model (1966)

Everett Lee reframed Ravenstein as a decision model. Migration results from the interplay of four sets of factors:

• Push factors at origin — unemployment, low wages, poverty, conflict/persecution, environmental hazard (drought, flood, desertification), poor services, discrimination.
• Pull factors at destination — jobs, higher wages, stability and freedom, better services, family/community links (chain migration), perceived quality of life.
• Intervening obstacles — distance and transport cost, immigration law and visas, language and culture, physical barriers (seas, deserts), lack of information.
• Personal factors — age, education, gender, family status, risk tolerance, ambition — which determine how an individual weighs the same push/pull set.

flowchart LR
  O["ORIGIN<br/>+ and - factors<br/>(push)"] -->|"intervening obstacles<br/>distance · law · cost · barriers"| D["DESTINATION<br/>+ and - factors<br/>(pull)"]
  P["PERSONAL FACTORS<br/>age · education · gender · risk"] -.filters perception.-> O
  P -.filters perception.-> D

Evaluation. Lee's strengths are its simplicity and breadth: it captures non-economic motives, recognises obstacles, and — crucially — its insistence that perception is filtered by personal factors anticipates later behavioural geography. Its weaknesses are real: it implies perfect information (migrants rarely have it), assumes rational, individual decision-making (Stark, below, shows decisions are often made by households), and it is essentially descriptive — a checklist that does not explain why particular flows form or who moves. It also handles forced migration poorly, where "decision" is barely meaningful.

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The Gravity Model

Borrowing from Newton, the gravity model predicts the volume of migration between two places as proportional to the product of their populations and inversely proportional to the square of the distance between them:

$M_{ij} = k \frac{P_i \, P_j}{d_{ij}^{2}}$Mij​=kdij2​Pi​Pj​​

where $M_{ij}$Mij​ is migration between places $i$i and $j$j, $P$P their populations, $d$d the distance, and $k$k a constant. It is a quantitative expression of Ravenstein's distance-decay and the size attraction of large cities, and it predicts real flows tolerably well at the regional scale. Its limitations are instructive: it is purely spatial, treating people as inert particles; it ignores wages, networks, language, colonial ties and immigration law, all of which can override raw distance (the UK–Australia flow vastly exceeds what $d^{2}$d2 alone predicts, because of shared language and history). It is a useful AO3 tool, not a theory of why people move.

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Todaro's Expected-Income Model (1969–70)

Michael Todaro (with John Harris) solved a paradox: why does rural–urban migration continue when urban unemployment is high? The answer is that migrants respond not to the actual urban wage but to the expected wage — the wage discounted by the probability of getting a job:

$\text{Expected urban income} = W_{urban} \times P(\text{employment})$Expected urban income=Wurban​×P(employment)

Worked logic. Suppose rural income is £1,000, the urban wage £3,000, and the chance of landing an urban job only 0.5. Expected urban income = $3{,}000 \times 0.5 = £1{,}500 > £1{,}000$3,000×0.5=£1,500>£1,000. Migration remains rational despite 50% unemployment, because the prize (a high-wage job) outweighs the risk.

Predictions: migration persists while expected urban income exceeds rural income; urban unemployment can be an equilibrium, not a disequilibrium; raising urban wages without creating jobs paradoxically increases migration and unemployment; and the policy lever is to raise rural incomes and create urban jobs together.

Evaluation. Powerful and well-supported (it explains the persistence of mega-city in-migration across the Global South), but it assumes migrants can estimate employment probabilities, treats income as the sole motive, ignores the informal economy that absorbs most arrivals, and cannot explain return migration.

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Stark's New Economics of Labour Migration (1980s)

Oded Stark's new economics of labour migration (NELM) is the most important correction to the individual-rational tradition, and a top-band discriminator. Its central claims:

1. The decision unit is the household, not the individual. Families send a member abroad as a collective strategy.
2. Migration is a risk-management device. By placing a worker in a different (uncorrelated) labour market, the household diversifies its income — if the local harvest fails, remittances cushion it. This is portfolio theory applied to families.
3. Relative deprivation matters as much as absolute income. Households migrate to improve their position relative to neighbours, not merely to maximise absolute earnings — which explains why migration often rises in moderately prosperous (not the poorest) villages.
4. Remittances are the point, not a by-product: they finance investment, education and consumption back home.

NELM explains what Todaro and Lee cannot: why the poorest often do not migrate (they cannot afford the risk or fare), why migration clusters in particular sending communities, and why remittances flow so reliably. It reframes migration from individual gamble to household investment.

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Zelinsky's Mobility Transition (1971) — coupling migration to the DTM

Wilbur Zelinsky tied the type and volume of migration to the stages of the Demographic Transition Model, repairing the DTM's neglect of migration:

Phase	DTM stage	Dominant mobility
1 Pre-modern traditional	1	Minimal; only circular/seasonal (herding, trade, pilgrimage)
2 Early transitional	2	Mass rural→urban; emigration and frontier colonisation begin
3 Late transitional	3	Rural→urban slows; inter-urban and inter-regional rise
4 Advanced	4	Inter-urban and suburban dominate; immigration of labour; counter-urbanisation begins
5 Super-advanced	5	International and skilled mobility dominate; residential deconcentration; some "virtual" mobility

Evaluation. Its great merit is integration — it makes migration a function of development, generating the powerful prediction that countries pass from net emigration (Stage 2–3) to net immigration (Stage 4–5), which fits Europe's history and Asia's present. But it inherits the DTM's flaws: it is Eurocentric and unilinear, it underplays forced migration and political shocks, and its Phase-5 prediction that virtual mobility would replace physical movement has only partly materialised (remote work substitutes for some commuting, not for international migration).

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Age-selective migration and the demographic imprint

Migration is sharply age-selective, and this is what gives it demographic consequences. The mobility curve peaks among 18–30 year-olds (moving for education, work and partnership), with a secondary retirement peak (55–70, for amenity), and a trough among families with school-age children. The consequence is that migration redistributes the young and economically active, transforming the age structure at both ends:

	Source (sending) area	Destination (receiving) area
Age structure	Ages; loses 20–35s → rising dependency	Gains working-age cohort → youthful
Economy	Brain drain but remittances; lost services	Labour supply, dynamism but infrastructure strain
Society	Gender imbalance (if male-led); "left-behind" elders/children	Diversity and innovation but possible tension
Fertility	CBR falls (young adults gone)	CBR may rise (young in-migrants)

This is why migration must be read alongside the DTM: it is the mechanism that lets a Stage-4 country (sub-replacement fertility) still grow, and that drains a Stage-2 country of the very cohort needed to capture its demographic dividend.

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AO3 skills exemplar: net migration and the gravity model

Net migration. $\text{Net migration} = \text{Immigration} - \text{Emigration}$Net migration=Immigration−Emigration. In the UK, net migration was estimated at ~606,000 in 2022 (later revised) — far exceeding natural increase, so migration, not births minus deaths, drives UK population growth. This single fact exposes the closed-system DTM's central blind spot.

Gravity calculation. Suppose City A has population 2,000,000, City B 500,000, and they are 100 km apart, with $k = 1$k=1. Then

$M_{AB} = 1 \times \frac{2{,}000{,}000 \times 500{,}000}{100^{2}} = \frac{1 \times 10^{12}}{10{,}000} = 1.0 \times 10^{8}\ \text{(index units)}.$MAB​=1×10022,000,000×500,000​=10,0001×1012​=1.0×108 (index units).

Now double the distance to 200 km: the denominator becomes $200^{2}=40{,}000$2002=40,000, so predicted migration quarters to $2.5 \times 10^{7}$2.5×107 — the inverse-square law in action. Evaluate: the model would under-predict an A→B flow if the cities shared a language, a motorway and family networks, and over-predict it if a closed border or hostile politics intervened. The lesson is that gravity captures the geometry of migration but none of its political economy — exactly the critical point the top band must make about quantitative models.

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Specimen exam question (20 marks)

"Assess the extent to which economic theories provide the most convincing explanation of contemporary international migration." (20 marks: AO1 10 / AO2 10)

Mid-band response (extract). "Economic theories like Todaro and Lee's push–pull say people move for jobs and higher wages, for example Poles moving to the UK for work after 2004. This is convincing because most migrants are economic migrants. However, some migration is forced, like Syrian refugees, which economics does not explain. So economic theories are quite convincing but not for all migration. Overall they are the most convincing for voluntary migration." (Knows the theories and a case each side, but treats "economic" as one undifferentiated block and asserts the verdict.)

Stronger response (extract). "Economic models are powerfully convincing for labour migration. Lee's push–pull and Todaro's expected-income model explain why Poles moved to the UK after 2004 (a 3–4× wage gap, immediate labour-market access) and why rural–urban migration persists despite urban unemployment. Stark's new economics adds that households migrate to diversify risk and send remittances — $63bn a year to Mexico — explaining the persistence and selectivity that pure wage models miss. But two limits matter. First, forced migration (13.5 million displaced Syrians) is driven by conflict, not wages, and economic models barely apply. Second, even economic migration is shaped by non-economic structures — colonial ties, networks, immigration law — that gravity and Todaro ignore. So economic theory is the best single lens for voluntary migration but incomplete overall." (Differentiates within "economic," deploys Stark, weighs voluntary vs forced.)