In ~ 5,000 BCE there was a radical change in the composition of the Y chromosomes on the planet, while the XX distribution (by analyzing mitochondrial DNA) remained relatively unaltered (see Fig. 1; Karmin et al. 2015; Poznik et al. 2016; Zeng et al. 2018). Between 5,000 and 3,000 BCE, the Neolithic era, there were many wars between different clans intent on expanding their territory mainly in Europe and Central and East Asia (Zeng et al. 2018; Meyer et al. 2015), which led to the creation of private property and later nations as we understand them today (Bowles and Choi 2019; see Footnote 1). Protracted warfare during the Neolithic period resulted in the dominant clans extending their territory at the expense and extinction of other groups, which has been attributed to the Y-chromosome distribution change (Zeng et al. 2018). During this conquest, the women and children were commonly spared and absorbed by the dominant clans, which explains why the XX distribution did not change. Note that at this time, violence did not induce a global population collapse; the population size varied between 5 and 10 million inhabitants (see Fig. 2).

Edward O. Wilson (2012) believed that humans and ants are quite alike (despite the difference in their brain size) in that they are programmed to grow their populations until all the resources are depleted. Once depleted, this propensity of humans will be such that the most violent members will fight to their death to survive, as documented for the Neolithic period (Horn and Molloy 2025; Meyer et al. 2015; Novak et al. 2021; Schroeder et al. 2019; Szeverényi and Kiss 2018). Human-induced climate change may accelerate the desertification of the Amazon basin, which would further reduce the world’s viable agricultural land and put further stress on human populations (see Footnote 2 and Fig. 3). Thomas Paine (1776), a student of history, was very aware that many of the autocrats (i.e., mainly male monarchs) of his time had come to power through extreme violence and it will be this violence and an inability to sustain agricultural resources that will extinguish Homo sapiens, especially if they cannot quell their genetically endowed urge for conspecific killing (also see Hudson 2023). Let’s hope that the sane amongst us can regulate this urge to extinction.

Footnote 1: The knowledge of the hunter-gatherer societies about plant and animal biology was central to the agricultural revolution during the Neolithic period (Bowles and Choi 2019).

Footnote 2: Climate change was behind the desertification of North Africa which became the Sahara Desert post-5,000 BCE (Martineau 2013).

Figure 1. Shown is the distribution of the Y chromosomal composition and the mitochondria DNA composition from different regions of the world. Notice the dip in the Y chromosome function at about 5,000 BCE followed by a change in the composition of the Y chromosomes. Data from Karmim et al. (2015).

Figure 2. The population of the planet between 10,000 BCE and 2,000 CE. Data from Wikipedia, Estimates of Historical World Population.

Figure 3. Shown are the regions of the planet that are prone to arid conditions (McSweeney 2019), the expansion of which through climate change would put further stress on a planet that will soon need to support 10 billion individuals.