Are humans different?

Are humans different from the rest of the natural world? Can biological mechanisms explain all aspects of human biology or do we need to call upon special processes?

We are used to thinking of human beings as the pinnacle of life. Christianity, Islam and Judaism all say that God created us in His own image. When Darwin published 'On the Origin of Species' he made no specific mention of human evolution - the idea that we evolved from apes was radical in the extreme.

And the idea that the extraordinary abilities of humans – language, intelligence, emotions, empathy, love – can be put down to random changes in DNA can seem difficult to accept.

Genes

But is there any reason to believe that these traits are 'special' one-offs that we alone have? The obvious thing to do is compare ourselves with other animals such as chimps, our closest living relatives.

We shared a common ancestor around seven million years ago. Since then, we have diverged markedly. We have less hair, bigger brains and are more intelligent.

By comparing genome sequences, researchers can identify genetic differences between the two species but also genes that are diverging rapidly in humans and chimps. It is noticeable that these are often genes influencing brain development (including HAR1F, the fastest evolving human gene yet discovered).

In addition, studies of human genetic variation around the world, such as the International HapMap Project, have identified differences that can act as a source of variation for natural selection to act upon.

Brain power

So much for genes, what about our mental and other skills? Here again, there is little that seems uniquely human. Other animals show simple ways of communicating with one another, mice have recently been shown to experience a type of empathy, crows have been seen to use tools, and rats have been shown to understand the motivations of others.

The most contentious area is consciousness. Is this what distinguishes us from other animals? Perhaps. But consciousness is difficult to define and study (see Big Picture on Thinking), and the difference may be one of degree rather than presence/absence.

Scientifically speaking then, purely biologically forces seem perfectly able to explain the creation of human beings.