Sometimes, we hear about cases of people born with a tail, claws, face hair or other traits that remember us about a distant evolutionary past.
These traits are called atavisms.
One of the most bizarre is the presence of two wombs in women.
More bizarre is that such a woman from UK gave birth to triplets, when usually this condition causes fertility problems. Hannah Kersey, 23, from Northam in Devon, had identical twins Ruby and Tilly, from one womb, and Grace, from the other. The girls had to stay in hospital for nine weeks after being born seven weeks early by caesarean.
The chances of having children from two wombs are about 25 million to one and those of a woman with two wombs having twins or two separate births are five million to one. Till now, worldwide only 70 women have been registered pregnant in two wombs.
The condition - which is called uterus didelphys ("opossum" in Latin) - affects one in 1,000 women in the UK. In primitive mammals, double womb is the common condition, and in marsupials even the vagina is double! In rodent females, male offspring develop in a womb, and female offspring in the other!
In the British case, the babies were conceived from two eggs, one in each womb, fertilized at the same time by two different sperm cells. One of the eggs then divided, producing identical twins, while the other produced a single baby. "There are very few world firsts nowadays, but it may be one", said Dr Simon Grant, a consultant at Southmead Hospital who delivered the babies.
"It is quite amazing. Women with two wombs have conceived a baby in each womb before but never twins in one and a singleton in the other", said Mr Ellis Downes, consultant obstetrician and gynecologist at Chase Farm Hospital in London.
"For a woman to spontaneously conceive and give birth in this way is a real rarity. They have been extremely fortunate", said leading expert Mr Peter Bowen-Simpkins.
Mr Richard Warren of the Royal College of Obstetricians and Gynecologists said the condition of two wombs - in most cases - is genetic: Hannah's mother and sister also have two wombs.
Image credit: SWNS