The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
Personally I think it's photosynthesis. Life itself developed and spread but photosynthesis started an inevitable chain of ever-greater and more-efficient life. I think a random chain of mutations that turns carbon-based proto-life into something that can harvest light energy is wildly unlikely, even after the wildly unlikely event of life beginning in the first place.
We propose that the global environmental crises of the Anthropocene are the outcome of a ratcheting process in long-term human evolution which has favoured groups of increased size and greater environmental exploitation. To explore this hypothesis, we review the changes in the human ecological niche. Evidence indicates the growth of the human niche has been facilitated by group-level cultural traits for environmental control. Following this logic, sustaining the biosphere under intense human use will probably require global cultural traits, including legal and technical systems. We investigate the conditions for the evolution of global cultural traits. We estimate that our species does not exhibit adequate population structure to evolve these traits. Our analysis suggests that characteristic patterns of human group-level cultural evolution created the Anthropocene and will work against global collective solutions to the environmental challenges it poses. We illustrate the implications of this theory with alternative evolutionary paths for humanity. We conclude that our species must alter longstanding patterns of cultural evolution to avoid environmental disaster and escalating between-group competition. We propose an applied research and policy programme with the goal of avoiding these outcomes.
Figure 2. Dimensions of environmental management create an attractor landscape for long-term human evolution. Environmental sustainability challenges (curved frontiers) require a minimum level of cooperation in a society of a certain minimum spatial size. Alternative potential paths move humanity toward different long-term evolutionary outcomes. In path B, competition between societies over common environmental resources creates cultural selection between groups for increasingly direct competition and conflict. Path A, growing cooperation between societies facilitates the emergence of global cultural traits to preserve shared environmental benefits.
A Great Filter is way, way bigger than that. Something that prevents a civilization from being able to expand into space. This includes things like "you can't make fire on this planet and therefore are never able to learn to work metal" and "supernovas sterilize regions of space before species can leave them".
Even the worst ecological disaster - one that kills billions - will not prevent humanity from eventually recovering, rebuilding, and expanding.
Under no circumstances (even Cold War mutually assured destruction) can human politics be a Great Filter. Thinking that it can be is small-minded and petty.