In ecology, the Fisher-KPP equation is often motivated by the
proliferation of a population of randomly moving individuals in an
environment with finite ressources. In this talk, I will show that this
equation also appears as the limit of a Stefan problem originating from
an active gel model of a proliferating cell monolayer with a free
boundary. The advancement of the leading edge still relies on cell
proliferation and protrusive activity at the tissue margin but the
effective diffusion coefficient has now a direct mechanical interpretation.
