Before Darwin: Deep Time, Extinction, Lamarck and Malthus

Standing on the shoulders of giants

Charles Darwin did not come up with evolution out of nowhere. When he set out on his famous voyage in 1831, he carried a new geology book. He later read an essay on human population that changed his thinking. Scientists before him had already argued that Earth was very old, that species could go extinct, and even that species could change.

In this lesson you will meet the thinkers whose ideas Darwin built on, and see how science progresses: each idea is tested against evidence, kept, changed or thrown out.

Linnaeus: naming life (1735)

You met Carl Linnaeus in the Diversity of Living Things unit: the Swedish naturalist who gave us binomial nomenclature and the ranks of classification. Linnaeus first published his system in 1735. Like most scientists of his time, he started out believing in the fixity of species: species were created as they are and do not change. His careful grouping of similar organisms, however, made it easier for later scientists to ask why some species are so alike.

Cuvier: extinction is real (1796)

The French anatomist Georges Cuvier compared the bones of mammoths with those of living elephants. He showed they were different species and that mammoths no longer existed anywhere. He proved that extinction really happens, which many people had doubted.

Cuvier also noticed that different rock layers contain different fossils, with deeper (older) layers holding organisms less like today's. He explained this with catastrophism: sudden disasters, such as floods, wiped out the species of one period, and other species then filled the land. Cuvier did not accept that species change into new species. Still, his evidence for extinction and for a changing fossil record was essential to evolution.

Hutton and Lyell: deep time (1788 and 1830)

The Scottish geologist James Hutton studied rock layers and erosion. He realized that slow processes, such as rivers wearing down mountains and sediment piling up, would need enormous amounts of time to build the rocks we see. Earth must be far older than people had thought.

Charles Lyell expanded this idea in his book Principles of Geology (1830 to 1833). His principle of uniformitarianism says that the same natural processes we can watch today worked in the past at similar rates. Small changes, added up over vast time, produce huge results.

Darwin read Lyell's book on the Beagle. He applied the same thinking to living things: if small geological changes can build mountains, perhaps small biological changes, added up over a very long time, can build new species.

Lamarck: the first full theory of evolution (1809)

The French naturalist Jean-Baptiste Lamarck published the first detailed theory that species change over time, in Philosophie zoologique (1809). He deserves credit for saying clearly that species are not fixed and that they change in response to their environment. His proposed mechanism, however, was wrong. He suggested:

1. Use and disuse: body parts that are used a lot become larger and stronger; parts that are not used shrink.
2. Inheritance of acquired characteristics: changes gained during a lifetime are passed on to offspring.

In his most famous example, giraffes stretched their necks to reach higher leaves, their necks got slightly longer, and their offspring were born with longer necks.

Why Lamarck's mechanism fails

• Acquired changes do not change the DNA in eggs or sperm. A weightlifter's muscles grow, but the DNA in their reproductive cells does not change, so their children are not born muscular.
• Experiments. In the 1880s the German biologist August Weismann cut the tails off mice for five generations in a row. Every new generation was still born with normal tails.
• Many traits cannot be "used" into existence. The colour of a moth's wings or the shape of a seed cannot be changed by effort.

Biologists today do study epigenetics, chemical tags that change how genes are switched on, and some of these effects can last into the next generation. This is an active research area, but it does not support Lamarck's idea that using a body part makes it grow in the next generation.

Malthus: more mouths than food (1798)

In An Essay on the Principle of Population (1798), the English economist Thomas Malthus argued that human populations tend to grow geometrically (1, 2, 4, 8, 16, ...: they multiply), while food supplies can only grow arithmetically (1, 2, 3, 4, 5, ...: they add). He suggested a population could double about every 25 years if nothing held it back. Sooner or later, a population outgrows its food, and famine, disease and competition hold numbers down.

Darwin read Malthus in 1838, and so did Alfred Russel Wallace some years later. Both realized the same thing applies to every species: far more offspring are born than can survive. There must be a struggle for existence, and the individuals best suited to their environment are most likely to win it.