Originally, scientists thought that intelligent life should be somewhat common in the universe. All one had to do was to estimate the number of planets in the habitable zones of their stars in our galaxy, and there were an unlimited number of candidates. The prebiotic molecules that help kick-start life can be found throughout the universe. So life made up of single cells is probably common on many planets.

Part I of this series covered the Obstacles to intelligent life based on sun type, planet formation, and simple cell biology. There we learned that unless eukaryotes developed, no intelligent life was possible. Assuming, however, that eukaryotes do appear, we now discuss what further obstacles to intelligent life are present after complex multicellular lifeforms evolve.

Obstacle 4 – Lack of Primates

Animals that have reached a human level of intelligence, and able to extensively manipulate their environment, have only been certain primates. Living in trees, they first used their legs to walk upright on tree branches while holding on to higher tree branches with their arms, then walked on the ground with their arms free to carry provisions. No other animal form on Earth has reached human intelligence capabilities.

It was very unlikely that the asteroid that struck the Earth and led to the dinosaur's demise would land where it did. Half of the Earth's surface is deep water where an asteroid strike would not have much significance. So the evolution of primates on Earth was a fluke caused by an asteroid landing in the worst possible place to cause mass extinction of large animals.

The primate genus homo, which appeared 2.8 million years ago, happened 4.3 billion years after the Earth first formed. It took a long time to get that far, and there was no guarantee it would happen. What we have to conclude is that another Obstacle to the development of a technologically intelligent species is the absence of primate-like animals.

Obstacle 5 – Lack of Permanent Towns and Farming

Most of human history is that of bands of roaming foragers living off the land. When human populations grew too dense to sustain themselves foraging food in the wild, farming and a more settled way of life in villages appeared. However, Neanderthals and Denisovans never produced growing populations that required settlements and farming. If a species like modern humans with its rapid population growth does not appear, permanent settlements with the motivation to develop a writing system and recorded information may never develop.

Obstacle 6 – Religion

The first modern human philosophy explaining how the world came about was religion. Religion is not only widespread in all human cultures, it is easy to understand by the simplest of men. It tends to lead away from a rational, logical approach to the world to one that is more subjective. It is also very effective in combating other philosophies, such as science, and will often drive them out of society, by killing, or banishment of, its advocates.

Obstacle 7 – Lack of Science

Science is the methodical study of the observable universe for the purpose of understanding the laws by which the universe is governed. This philosophy was developed in Greece over many centuries and culminated in the teachings of the Greek philosopher Aristotle. Greece was the only country in the world to develop science and pass it to others. Without the Greek philosophical approach, would science have been invented and accepted by society anywhere else?