Table 1.
Variables and parameters included in the model. CCE, cumulative cultural evolution.
| parameter/variable | symbol | definition | dimensions |
|---|---|---|---|
| human biomass | ϕ | human biomass expressed as a proportion of the maximum that can be held in a finite habitat (planet Earth) | dimensionless |
| growth rate of human biomass | r | rate of growth in human biomass | T−1 |
| habitat quality | ω | state of all ecosystem services required by humans expressed as a proportion of their maximum value for the habitat | dimensionless |
| habitat quality replenishment rate | λ | rate of supply of all ecosystem services that define the habitat quality | T−1 |
| habitat quality basal maintenance requirements | B | basal maintenance requirements for human biomass expressed as a proportion of the maximum amount of ecosystem services available in the habitat | dimensionless |
| habitat quality social maintenance requirements | Bs | social maintenance costs or the extra ecosystem services requirements that arise as a consequence of living in a group of individuals innovating through CCE, expressed as a proportion of the maximum amount of ecosystem services available in the habitat | dimensionless |
| habitat quality reproduction requirements | E | proportional efficiency with which humans convert ecosystem services into human biomass | dimensionless |
| technological stock | μ | number of technological items or technologies, defined as any cultural device, tangible or not, that is the product of innovation driven by CCE and aimed at increasing the proportional supply of ecosystem services | number of technological items (n) |
| rate of technological innovation | ρ | per capita innovation rate | n × n−1 × T−1 |
| rate of technology loss | l | per capita loss rate or rate at which technological items become obsolete. The reciprocal is the mean lifetime of a technology | n × n−1 × T−1 |
| minimum technological stock | ɛ | minimum technological stock needed to ensure basic human well-being | number of technological items (n) |
| scaling parameter | α | parameter that determines the relationship between technological stock (μ) and supply of ecosystem services (λ) | dimensionless |
| scaling parameter | β | parameter that determines the relationship between technological stock (μ) and social maintenance costs (Bs) | dimensionless |
| normalization parameter | c1 | normalization constant associated with the relationship between technological stock (μ) and supply of ecosystem services (λ) |  |
| normalization parameter | c2 | normalization constant associated with the relationship between technological stock (μ) and social maintenance costs (Bs) |  |
| technological impact |  |
net impact that technology has upon habitat quality | dimensionless |
| technological feedback |  |
net per capita impact that on average an extant technology has upon the production of new technologies before it disappears | n × n−1 × T−1 |
| technological feedback |  |
normalized technological feedback | dimensionless |