Today we reflect on the lives of two very famous men, arguably the two most influential of the 19th century, whose influence is likely to last as long as there are thinking and democratic peoples. By one of the great coincidences of history, both were born on the same day — Feb. 12 — 200 years ago.

Abraham Lincoln shaped the world’s dominant democracy, the United States. Our present ideas of a country indivisible, with a strong executive branch, are to some large measure due to Lincoln.

Charles Darwin explained the relationships among organisms. His work also incorporated humans, previously considered something separate from nature, into the natural process.

These were two vastly different personalities, born to very separate environments and circumstance, but their histories have much in common. Like their births, the progress of their careers was similar.

Abraham Lincoln was born in a log cabin on a 348-acre farm in Kentucky. Lincoln called his early life the “short and simple annals of the poor.” Popular understanding of Lincoln’s early poverty is to some degree exaggerated, as his father owned land and was well respected in his community.

As a boy, Lincoln received the rudiments of a school education at the age of six to seven years, and again for several months at small schools in 1822 and 1824. At age 12 he started borrowing books and to some degree taught himself to read, write and do arithmetic. He read “Pilgrim’s Progress,” “Robinson Crusoe” and later, Shakespeare.

At age 22, Lincoln settled in the frontier village of New Salem, Illinois. Lincoln served as laborer on a flatboat trip to New Orleans and as a storekeeper, postmaster and surveyor. In 1834, he was elected to the state legislature and took up the self-study of law. He was licensed to practice law in 1836 and embarked on the career that would take him to fame.

Charles Darwin was born to a fairly wealthy society doctor. Unlike Lincoln, Darwin had advantages of education, family connections and some financial independence.

Darwin seems to have been a bit lazy about his studies at Cambridge, but in 1831 graduated 10th in a class of 178. Darwin also developed an interest in natural history and after graduation was recommended as an unpaid naturalist on board the HMS Beagle. This voyage, from 1831 to 1836 — the same years as Lincoln’s time in New Salem — would be the formative experience of Darwin’s life.

Darwin’s observations on this voyage were as much geology as biology. That the Earth’s geological history showed a sequence of change with time had only recently been appreciated. Darwin saw abundant evidence of geologic change that came to influence his biologic interpretations.

The most important portion of Darwin’s voyage was the Galapagos. These are a series of isolated islands with a limited biota: mockingbirds, finches, giant tortoises, iguanas. By the time Darwin returned in October 1836 — three weeks after Lincoln received his legal license — some of his writings had already been published, and his reputation as a scientist had been established.

Abraham Lincoln had an extraordinary appearance, very lanky with simple and ill-fitting cloths and unkempt hair, this at a time of Victorian prim-and-proper. He had a folksy demeanor with a high-pitched voice and archaic mannerisms. Lincoln’s size and strength were matched by an exaggerated melancholy.

Lincoln’s sadness was offset by a remarkable sense of humor. He told jokes and stories throughout his life, and was famous for them. Lincoln made remarkable political use of this sense of humor. A comical tale seemed to lessen the pain of a “no,” or deflected a criticism.

After eight years in the Illinois state legislature and two years as a congressman, Lincoln retired from politics and concentrated on his legal practice.

Lincoln was brought back to politics by the Kansas-Nebraska Act of 1854, which established two new territories whose citizens could vote to establish slavery. In 1858, Lincoln’s campaign and debates with Illinois senator and Kansas-Nebraska author Stephen Douglas, published in the newspapers of the day, brought Lincoln to prominence.

When Charles Darwin returned from his voyage around the world, he quickly tended to the organization of his notes and specimens. On the Galapagos there were very similar but different finches, and separate islands had unique species. Why would the species be different?

For the 20 years following his return with the Beagle, Darwin pondered the subject of species change. Clues were provided to him by Thomas Malthus, who decades earlier had written of the importance of competition among human populations. Was there such competition in nature? There was. Could that competition select winners and losers?

Darwin’s work on the species question was published in a short article, with a similar but less extensive study by Alfred Wallace, in 1858. Darwin’s most famous book was published the following year.

These two men, through diligent self-study, ultimately changed their world. Happy 200th birthday to them both!

Kevin McCartney is a professor of geology at the University of Maine at Presque Isle.