Hypotheses linking climate change and hominin evolution are based on indications that large-scale shifts in climate or climate variability altered the landscape ecology which, in turn, presented specific adaptive or speciation pressures that led to genetic selection and innovation.
In addition, climate change can impact evolution by altering patterns of hybridization, changing population size, and altering patterns of gene flow in landscapes.
A large brain, long legs, the ability to craft tools, and prolonged maturation periods were all thought to have evolved together at the start of the Homo lineage as African grasslands expanded and Earth's climate became cooler and drier.
Two different types of environment – dense woodlands and open bushland – occurred in the same areas of East Africa during the period of human evolution. Climate fluctuation altered the proportion of these habitats, and thus led to repeated changes only in population density and variable conditions of natural selection.
Climate change is likely to favor the evolution of traits that promote stress tolerance or escape. For example, the evolution of higher thermal tolerance could reduce species' vulnerability to climate change in regions projected to experience increases in temperature (Thompson et al., 2013).
During the period of climatic fluctuations in the Holocene era, humans began to domesticate plants and animals and subsequently adopted agriculture. These adjustments later led to sedentary settlements and the expansion of urban-based societies.
Extinction is often caused by a change in environmental conditions. When conditions change, some species possess adaptations that allow them to survive and reproduce, while others do not. If the environment changes slowly enough, species will sometimes evolve the necessary adaptations, over many generations.
Humans began to work with and occasionally against their environment to create a stable way to acquire food as well as a more stable lifestyle. On the other hand, the environment, the climate in particular, definitely dictated the movement and survival methods of early humans.