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Related Concept Videos

Biological Clocks and Seasonal Responses02:45

Biological Clocks and Seasonal Responses

The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod.
Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
Hormonal Regulation of the Menstrual Cycle01:22

Hormonal Regulation of the Menstrual Cycle

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Related Experiment Video

Updated: Jul 13, 2026

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures
06:53

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures

Published on: November 11, 2016

Toward a general analysis of endogenous Easterlin cycles.

C Y Chu, H Lu

    Journal of Population Economics
    |January 1, 1995
    PubMed
    Summary

    This study models fertility cycles using labor market dynamics and self-generating mechanisms. The US fertility limit cycle solution is unstable, meaning population trajectories will not converge to it.

    Keywords:
    AmericasBirth RateCohort AnalysisDemographic FactorsDeveloped CountriesEasterlin HypothesisEconomic FactorsFertilityFertility MeasurementsFertility RateHuman ResourcesLabor ForceMicroeconomic FactorsModels, TheoreticalNorth AmericaNorthern AmericaPopulationPopulation DynamicsResearch MethodologyTheoretical StudiesUnited States

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    Last Updated: Jul 13, 2026

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    Published on: November 11, 2016

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    Published on: August 30, 2021

    Area of Science:

    • Demography
    • Labor Economics
    • Economic History

    Background:

    • The Easterlin hypothesis suggests fertility cycles are linked to labor market conditions and are self-generating.
    • Previous cohort and period models, while analyzed, are shown to be restricted versions of a more general framework.
    • Statistical tests have previously rejected both the cohort and period models.

    Purpose of the Study:

    • To develop a general model incorporating both labor market influences and self-generating properties of fertility cycles.
    • To analyze the stability of potential fertility limit cycles within this general framework.
    • To extend previous research by examining the US fertility limit cycle solution.

    Main Methods:

    • Construction of a general production function model for age-specific labor cohorts.
    • Estimation of coefficient values from the unrestricted version of the model.
    • Bifurcation analysis to investigate the stability of the fertility limit cycle solution.

    Main Results:

    • The general model encompasses previous cohort and period models as restricted cases.
    • The estimated US fertility limit cycle solution is demonstrated to be unstable.
    • Population trajectories are shown to diverge from, rather than converge to, the limit cycle.

    Conclusions:

    • The proposed general model provides a more comprehensive framework for understanding fertility cycles.
    • The instability of the US fertility limit cycle suggests that population dynamics are not bound to such cycles.
    • Future research should consider the implications of unstable limit cycles for long-term population forecasting.