The answer lies in a well known concept in biology, termed r/K Selection Theory. r/K Theory examines how all populations tend to adopt one of two psychologies as a means of adapting their behavior to the presence or absence of environmental resources. The two strategies, termed r and K, each correlate perfectly with the psychologies underlying Liberalism and Conservatism.
One strategy, named the r-strategy, imbues those who are programmed with it to be averse to all peer on peer competition, embrace promiscuity, embrace single parenting, and support early onset sexual activity in youth. Obviously, this mirrors the Liberal philosophy's aversion to individual Darwinian competitions such as capitalism and self defense with firearms, as well as group competitions such as war. Likewise, Liberalism is tolerant of promiscuity, tolerant of single parenting, and more prone to support early sex education for children and the sexualization of cultural influences. Designed to exploit a plethora of resources, one will often find this r-type strategy embodied within prey species, where predation has lowered the population's numbers, and thereby increased the resources available to it's individuals.
The other strategy, termed the K-strategy, imbues those who pursue it with a fierce competitiveness, as well as tendencies towards abstinence until monogamy, two-parent parenting, and delaying sexual activity until later in life. Obviously, this mirrors Conservatism's acceptance of all sorts of competitive social schemes, from free market capitalism, to war, to individuals owning and carrying private weapons for self defense. Conservatives also tend to favor abstinence until monogamy, two parent parenting with an emphasis upon "family values," and children being shielded from any sexualized stimuli until later in life. This strategy is found most commonly in species which lack predation, and whose population's have grown to the point individuals must compete with each other for the limited environmental resources that they are rapidly running out of.
Meticulously substantiated with the latest research in fields from neurobiology to human behavioral ecology, this work offers an unprecedented view into not just what governs our political battles, but why these battles have arisen within our species in the first place. From showing how these two strategies adapt in other more complex species in nature, to examining what genetic and neurostructural mechanisms may produce these divergences between individuals, to showing what this theory indicates our future may hold, this work is the most thorough analysis to date of just why we have two political ideologies, why they will never agree, and why we will tend to become even more partisan in the future.