Environmental demands that influence an organism's survivability. Can be positive (beneficial) or negative (detrimental). 

Selection Pressures 

One theory suggests human brain growth is related to the need for creativity in order to attract a mate. 

Sexual Selection Influence on Hominin Brain Evolution

Humans and chimpanzees, who share nearly 99% of DNA, still differ in a plethora of physical, behavioral and cognitive ways- this may be because we differ in the specific sequences of our DNA, as well as in how genes express themselves in us. 

Gene Expression

The evolution of a large cortex, the outer covering of the cerebral hemispheres,  occurred rapidly and recently due to a multitude of possible factors, including some that promoted certain behaviors/capabilities: selection pressures, sexual selection, and gene expression. 

Villanova University

There is a link between the increased size of specific brain structures and the necessity of the behavior/capability it is responsible for in some species (i.e., those that rely heavily on their sense of smell possess a relatively large olfactory bulb). Likely occur through the process of natural selection favoring individuals that adapted to improve that capability.

Brain Size & Behavior 

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

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