The theory of evolution is an established premise and an explanation for the many vast and diverse species on this planet. Not a single species has never in some way adapted to its environment through natural or artificial selection. Darwinian evolution states that selective pressures in an organism's environment will allow only the members of species who are able to reproduce in such conditions survival - in other words, the survival of the fittest. Humans are not exempt from this, and are of course taxonomically animals themselves. Humans did not come to become the most dominant species on the planet without adaptation to their environments - without evolution and natural selection working to provide them with the traits necessary to reproduce and carry on their genes for generations. The entire discipline of neuroscience focuses on tying the more subjective notions of emotion and cognition to physical and biological aspects of the brain and has through techniques like brain imaging proven that emotions and mental processes logically have a biological (cellular, hormonal or biochemical basis). Therefore, it is not farfetched to state that natural selection can act upon an organism neurologically and thus psychologically.

Humans are referred to as homo sapiens by biologists for a reason - they homo in their scientific name refers to their genus of Hominids. Humans are the only hominids left alive today. This was not the case hundreds of thousands of years ago, with many species of Hominids (like Neanderthals, Denisovans and Cro Magnids) living on the planet at the same time. Humans evolved from earlier Hominids in the horn of Africa, and eventually set out to Europe, where the Neanderthals had already beaten them to it. The two species lived together for some tens of thousands of years, but eventually the Homo Neanderthalensis became extinct. Neanderthals were very similar to humans in terms of appearance and mental faculties. Their increased brain capacity has lead some anthropologists to claim they may have been more intelligent and capable of a greater capacity for language, and their bone structure is indicative that they were shorter, but much more stockier and powerful than humans.
So it appears that Homo Neanderthalensis had evolved over time to have great intellect, strength and stockiness to deal with the harsh nature of the European climate, which frigid at the time and undergoing an ice age. Yet, despite these superior traits, they still became extinct. The answer, evolutionary psychologists believe, is due to social psychology and natural selection meeting in the middle.

The best analogy between Neanderthals and Humans that may be drawn is to compare them to lions and tigers. Neanderthals were much more solitary, and lived in small social groups localised to small areas and did not tend to travel. Humans on the other hand relied on safety in numbers; the humans who did not have large social groups tended to fall prey to other predators (and were unable to defend themselves compared to the stronger Neanderthals) and did not pass their genes. Thus, humans learned to stick together through natural selection, and learned to work together and co-operate for food, shelter and resources - this lead the way to hunter gatherer societies. Biologists could only speculate as to how this caused humans to out-compete or outbreed Neanderthals. Recent DNA evidence reported in Time Science  has proven that European people have on average 4% Neanderthal DNA, which suggests that humanity was able to interbreed with Neanderthals, and slowly breed them out of existence in addition to their own social nature causing them to become extinct by natural selection. The social nature of human beings also gives us clues as to how this may have happened; since hunter gatherer societies tended to hunt by having a group of males swarm prey together, humans may have ganged up on Neanderthals, perhaps even stealing their resources or females.  The social nature of human beings preferring larger groups for companionship most probably lead to the domestication of animals also; it is very possible (according to biologists) that the domestication of the dog from the wolf 100,000 years ago allowed humans to gain an edge on both hunting for food and defence against possible Neanderthal attacks. Thus, the early evolution of humans has brought about this need for social structure and social groups, and has allowed us to wipe out all of our like-minded competition. The sequencing of our DNA to early hominids is a new and emerging discipline, and who knows what other early human we will find in the blood of current groups of humans today. Australoid peoples such as Aboriginals, for instance, have been found to contain small amounts of Denisovan DNA and new evidence for a 'new archaic Hominid species' being found in the depths of the DNA of native Africans is emerging and has been published in the New York Times and Popular Archaeology. Each of these findings tells a similar story; that because of our need to stick to social groups for survival and to develop our intellect and cunning through natural selection, we have managed to emerge victorious from our competitors.

In addition to Hominids acting upon the psychological evolution of humanity, human populations themselves have managed to evolve or change psychologically in slight, but very marked ways through geographical isolation, forming human subspecies or races. Two events in human history have had the most sway on our psychological evolution, both of them causing what is called a population bottleneck, where conditions in the environment (for instance a natural disaster or disease) cause the population to plummet to ridiculously low levels, from which only the most hardy or smartest survive. The first is the migration of homo sapiens from the horn of Africa through the Sahara desert. The Sahara desert is of course a very harsh and extreme environment. To be able to cross it, humans would have needed to ration supplies, plan ahead, hone their directional skills and become even more socially cohesive to stick together. Only those who could be exceptional at these traits survived the migration; thus the environment facilitated the selection of mental traits that enabled them to survive. The same may be said for the humans in Europe at the time of the Ice Age, which formed another bottleneck. The Ice Age and Sahara migrations (particularly the former) naturally selected for humans with traits that would later allow them to become agricultural societies, rather than hunter gatherers, and thus Darwinian theory of evolution and natural selection shaped their behaviour and psychology.

This evolutionary history has enabled us to develop theories as to why certain individuals or populations differ from one another. The Neanderthal Theory proposed by developmental psychologist Leif Eckblad in 2006s states that Autism is believed to be from the aforementioned human-Neanderthal interbreeding; since Neanderthals were generally quite intelligent and had a large cranial capacity, but also very asocial and unable to empathise and develop emotions on the level of Humans, the traits we associate with Autism are believed to come from the DNA we have in common with Neanderthals. Similarly, the transition from hunter gatherer society to agricultural society in the North of Africa and in Europe may be responsible for the disease we know of as ADHD; this is what is known as the 'Hunter vs. farmer hypothesis' proposed by psychotherapist Thom Hartman. The theory states that humans without ADHD are descended from farming societies, whereas humans with ADHD retain some of the genes that hunter gatherers have, which manifest themselves in the symptoms of ADHD; restlessness, etc. These finds have very recently been backed up more biochemically in neurological and brain imaging studies.

As I said earlier, subspecies of humans have also managed to evolve slightly differently over time in their psychology through natural selection, and evolution can explain why certain races or ethnicities behave in certain ways or have certain traits on average. According to studies by Rogoff (1998) and Vgotsky (1978), Children descended from Bushmen in Western Australia (or even those living similar lifestyles in Africa), which follow a more hunter gatherer culture have visual spatial reasoning much greater than any population on the planet, most probably because natural selection has made it so that the individuals in the group that reproduce are those who are able to locate food quickly and memorize locations quickly to survive. Similarly, a study by Lea and Chambers (2007) notes that the more exploratory culture in ethnicities the Maori population has produced individuals (56%) with what scientists call the 'warrior gene' or Monoamine oxidase A, a gene that promotes 'risky decision making and outgoingness, as well as aggression' through degrading amine neurotransmitters, such as dopamine, and serotonin. . It's easy to see why a proud warrior and navigator culture which colonized the tropics would select for such a gene and such traits over time.

Perhaps most interesting are the evolutionary explanations for IQ in human populations (which is of course a very important psychological aspect of humans), which I could literally start a whole other debate on. According to the books The Bell Curve and IQ and the Wealth of Nations  East Asians possess the second highest IQ on average on the planet at 105, and this was believed to come from both their braving a slightly colder Ice Age than Europeans, and their early adoption of agriculture. Remarkably, they possess a high visual spatial reasoning too; this is most probably due to the logographic writing style that arose from their peoples' culture, an excellent example of culture shaping evolution and vice versa. According to a 2005 scientific paper, "Natural History of Ashkenazi Intelligence, the highest IQs on the planet belong to the Ashkenazi Jewish population, which is an excellent example of artificial rather than natural selection working similar to evolution to shape a population psychologically. IQ has been theorized to be at least 85% heritable through studies of identical twins. ", Ashkenazi Jews have long been persecuted throughout history, particularly in medieval times, where they were forced to take less menial labourer jobs and instead were forced into jobs which required more intellectual pursuits; banking, finance, philosophy, writing, science - this meant that it was encouraged that the most intelligent breed to avoid persecution and thus over only a few generations raised their IQ by two standard deviations at 115. Interestingly, the same studies observe that the verbal and mathematical reasoning ability of the Ashkenazi population is also quite high, suggesting that artificial selection of mental traits which favour their environment also occurred.

As you can see, humanity has changed throughout the course of history, both at a species and subspecies level. It is na￯ve to say that evolution stopped at the neck, and that our mental processes are independent of the environment around us and that this environment cannot in some way force us to have certain breeding trends. Human history and human evolutionary history provides us with the powerful reasoning needed to explain why we as a whole and as groups on average behave, think and act the way we do. Thank you.