Evolution "killed" twins: why the birth of two babies at once has become a rarity today.

Children of every generation have certain differences. However, millions of years ago, the ancestors of humans and primates had a distinct trait — they almost always gave birth to twins and multiples.

Scientists believe that the birth of twins was the norm for primates around 60 million years ago. Currently, this is a relatively rare occurrence with natural conception, and evolution is to blame for this shift.

Modern humans primarily give birth to a single child — a notably large child with an even larger head. The size of the human brain and body is linked to the ability to learn and develop. For both primates and humans, childhood learning is crucial. Researchers argue that the transition from twins to a single child was pivotal for the evolution of contemporary human infants with larger brains.

The shift from giving birth to many twins to having singleton births occurred several times in the primate lineage — indicating that it was beneficial for primates to develop only one fetus per pregnancy. Since multiple pregnancies require more energy from the mother, and the offspring are often smaller and born prematurely, early primate ancestors who gave birth to only one child likely had a survival advantage.

Current Trends in Twin Birth Rates

Over the past 50 years, the twin birth rate has increased by 70%. This rise is attributed to the use of IVF protocols and the trend of having children at an older age. For women over 35, multiple pregnancies are more common compared to younger mothers. Overall, there is one instance of twins or multiples for every 250 births. Having more than two children at once is extremely rare.

Previously, "Telegraph" reported on the changes in human traits influenced by evolution. Dark skin, large eyes, and even curly hair have their explanations.