Relationships might be a lot spikier were it not for small genetic changes which mark humans out from other mammals, research has shown.

One patch of DNA missing from humans but present in chimpanzees, monkeys and mice produces tactile penile spines.

Loss of the structures allows humans to enjoy longer-lasting sexual intercourse and may have aided the evolution of mono-gamous partnerships, say scientists.

If humans still had these elements of DNA, they might not only possess spiny penises but whiskers too.

Another key area of genetic difference is believed to have helped humans develop larger brains.

But it could also make them more susceptible to brain tumours.

Chimpanzees share 96 per cent of their DNA with humans, but the differences between them obviously have far-reaching effects.

Scientists from Stanford University School of Medicine in California conducting the new study identified 510 segments of DNA in chimps, macaque monkeys and mice that were absent in humans.

The researchers, whose findings are reported in the journal Nature, pinpointed two key regions of deleted DNA that appeared to have made a big impact on human evolution. One was thought to regulate an “androgen receptor” gene that contributes to the development of sensory whiskers on the faces of many mammals, as well as penile spines.

The other was believed to inhibit a tumour suppressor gene that may have held back brain development in non-human mammals. If the gene is missing entirely, it leads to unchecked cell growth and pituitary tumours. But dampening down its effect could allow more brain growth.

The loss of penile spines in humans reduced sensitivity and increased the duration of sexual intercourse in humans compared with other species.