Checks and balances present in nature guarantee that these species are just successful enough. We will set aside aspects of the two ends of the spectrum for now, and look at general clan classifications.
Human infants require years of care before they gain the ability to fend for themselves.
Mankind groups by religion, political affiliation, geographical region, race, gender, class, recreational pursuit, age, and by any other detectable difference. The most damaging to harmony within the human race is nationalism. The entire political system that drives nationalism is in place because the vast majority of people have no interest in managing the infrastructure necessary to make our technological world function. A relatively small number of individuals manage society as proxies for the masses, and direct world events from a perspective that is quite alien to most people. In a totally natural environment, these people could not provide for the basic needs of shelter and sustenance, nor could they provide themselves with clothing, nor successfully give birth to and raise infants without outside intervention.