Kepler had 12 children and Kelvin none, a review finds

Scientists' children: Kepler had 12 and Kelvin none

How many children did Charles Darwin actually have? Ten. And Lord Kelvin? None. The list circulating online attributing offspring to some twenty figures of science falls apart as soon as you check it case by case, and that's where things get interesting: counting the children of geniuses is a minefield of badly copied data, children who died young, and offspring born outside marriage that biographers took decades to acknowledge.

The starting point is a table ranking the great names of science by number of children: Darwin at the top with ten, Santiago Ramón y Cajal with seven, Niels Bohr with six, and further down Einstein, Hawking, Galileo and Crick with three. It sounds like dinner-party trivia, but it doesn't stand up to scrutiny. Lord Kelvin had no children at all; he married twice and his barony died out with him precisely for that reason. And Kepler, far from the five the list gives him, is thought to have had around a dozen children across his two marriages, in an era when infant mortality was the norm in the seventeenth century.

The problem of counting children in the seventeenth century

The demography of early science can't be measured by today's standards. Kepler had children in two marriages and many never reached adulthood; Goethe had five and only one, August, survived him. Mendeleev, according to the most reliable counts, is thought to have had about six children between his two wives, twins included. These are figures that shift depending on the source, and the original table simplifies them into error.

There's one detail that complicates the inventory even further. Schrödinger's three daughters were all born outside marriage, to three different women. Of Einstein's first daughter, Lieserl, the trail goes cold while she was still a baby. The official biography of the geniuses has always had a problem with the fine print.

From anecdote to the debate on having children

The conversation quickly turned to the underlying issue: whether intelligence and offspring go hand in hand, or whether having children today is a bad economic decision. Some argue that in the past the smart move was to have children, and now it's the opposite, while others reply that having offspring means mortgaging freedom, time, rest and money for fifty years. The counterargument doesn't hold back: if anyone who thinks that way doesn't reproduce, the problem solves itself.

The striking fact is that most of the names on the list had numerous offspring in eras without contraception, when children arrived without any prior planning. Comparing that with a planned twenty-first-century decision is a trap. And yet the underlying question remains unanswered: does having children make you poorer, or does it just reorder your priorities?

In the end, the most exact science in the whole inventory is Lord Kelvin's: zero children and an extinct noble title. An impeccable thermodynamic legacy and an offspring that never came to exist.