The development of understanding of genetics and evolution

Biology · Inheritance, variation and evolution. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Darwin proposed evolution by natural selection after years of observation and experiment. Wallace reached the same idea on his own, and their work was published together in 1858. Lamarck had an earlier, wrong idea: that changes gained during an organism's life are passed on.

Darwin's theory was accepted slowly. It challenged the belief that God made all living things, there was not much evidence at the time, and nobody yet knew how characteristics are inherited. Mendel's work with pea plants later supplied that mechanism.

Fossils and antibiotic-resistant bacteria are evidence for evolution. Fossils show how organisms changed over millions of years. Bacteria evolve quickly because they reproduce very fast.

Rules to remember

Darwin published On the Origin of Species in 1859. Wallace also worked on warning colouration and speciation.
Speciation: populations become isolated → each has variation → natural selection differs in each place → they become so different that they cannot interbreed to produce fertile offspring.
Mendel: characteristics are decided by 'units' that are passed on unchanged. These units are now called genes.
Fossils form when hard parts are replaced by minerals, when decay cannot happen (no oxygen, too cold, too acidic), or as preserved traces such as footprints and burrows.
The fossil record is incomplete: early life was soft-bodied and many fossils were destroyed by geological activity.
Extinction can follow a new predator, new disease, new competitor, a change in the environment or a catastrophic event.
To slow antibiotic resistance: do not prescribe antibiotics for viral or mild infections, complete the whole course, and restrict their use in farming.

Common mistake

Antibiotics do not cause bacteria to become resistant. The resistance mutation happens by chance; the antibiotic kills the non-resistant bacteria and the resistant ones survive and multiply.

Worked example

Fossils of horse-like animals are found in rock layers of different ages. The oldest are small with four toes on the front foot. Younger ones are larger with fewer toes. The most recent have one toe, like a modern horse. What does this show?

Deeper, older rocks hold older fossils, so the layers put the animals in time order.
The features change step by step from the oldest layer to the youngest.
Gradual change in a line of related organisms over millions of years is evolution.

Answer: The fossils are evidence that the modern horse evolved gradually from smaller ancestors with more toes.

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