Exercises: Evolutionary theories

Explain what biological evolution is and what it means to state that present-day species descend from other species of the past.

Summarise Lamarck's two main ideas (use and disuse of organs and inheritance of acquired characteristics) and explain how he interpreted the long neck of giraffes.

Summarise the key ideas of Darwinism: variation among individuals, the struggle for existence and natural selection of the best adapted.

Explain what fixism or creationism claimed about the origin and the permanence of species, and why fossils of animals that no longer exist were a problem for that idea.

Explain what a fossil is, how it usually forms and what two kinds of information it provides about evolution: what living things of the past were like and how old the rocks containing them are.

Explain the sentence "individuals do not evolve, populations evolve": what happens to individuals over their lifetime and what it is that changes in the population from generation to generation.

During his voyage on the Beagle, Darwin made observations that made him doubt fixism. Name two of them (for example, fossils of extinct species similar to present-day ones, or different species on each Galápagos island) and explain what each one suggested to him.

Define adaptation and give two examples of adaptations of living things to their environment, explaining what the advantage of each one consists of.

Look at the diagram, which shows two different explanations (A and B) of how giraffes came to have long necks. State which corresponds to Lamarck and which to Darwin, and point out the fundamental difference between the two regarding what is inherited.

What does Neo-Darwinism or the synthetic theory add to Darwin's ideas? Explain how genetics (mutations and inheritance) completed the theory of natural selection.

Name and briefly describe three lines of evidence for evolution: fossils, comparative anatomy (homologous bones) and biogeography.

Lamarck's theory seemed reasonable in its time. Explain what fact about heredity Lamarck did not know that today allows us to reject the inheritance of acquired characteristics, and what a Lamarckist and a Darwinist would each say about why gazelles run fast.

Distinguish between homologous organs and analogous organs using the wing of a bird, the wing of a bat, the human arm and the wing of a butterfly, and explain which of the two cases is evidence of evolutionary kinship and why.

Explain what vestigial organs are and give two examples (for example, the human appendix or the remains of a pelvis in whales), reasoning why they constitute evidence of evolution.

Arrange these milestones in chronological order and explain in one sentence what each one contributed: the publication of "On the Origin of Species", the rediscovery of Mendel's laws, Lamarck's theory, the voyage of the Beagle and the formulation of the synthetic theory.

After years of using the same insecticide, the mosquitoes in an area have become resistant to it. Explain why it is incorrect to say that "each mosquito has adapted to the insecticide during its lifetime" and how natural selection explains it correctly.

On a small island, a prolonged drought wipes out soft-seeded plants, and only those with large, hard seeds survive. A team of biologists measures beak depth in a finch population before the drought (mean of 8,8 mm) and one year later among the survivors (mean of 9,8 mm). A) Justify using the synthetic theory what has happened in the population at the phenotypic and genotypic levels. B) A student comments: "The finches had to strive to crack the hard seeds, which caused their beaks to grow 1 mm during their lifetime, and that is why their offspring were born with larger beaks." Refute their statement by pointing out why it falls into Lamarckism and how natural selection actually operates.

In an English industrial region, the proportion of dark (carbonaria) and light (typica) peppered moths (Biston betularia) was measured. After anti-coal pollution laws were passed in 1960, records showed: in 1960, 90% dark moths; in 1980, 50%; and in 2000, only 10%. A) Interpret these data by identifying the natural selection factor and explaining why the allele frequencies changed. B) Predict with reasoned arguments what would happen to the proportion of both varieties if a new nocturnal predator were introduced that locates its prey exclusively by smell and not by sight.

Analyze the following two situations: 1) If the tails of mice are surgically amputated for several successive generations, all offspring in subsequent litters continue to be born with intact tails. 2) If the testes of male mice are irradiated with X-rays, many of their offspring are born with tail malformations. A) Justify these results based on the difference between somatic cells and germline cells. B) If a bodybuilder were to use gene therapy to modify the DNA of their arm muscle fibers to induce hypertrophy, would their descendants inherit that muscle mass? Justify your answer.

On a social network you read the following comment: "If humans are descended from monkeys, why do current chimpanzees still exist instead of all having transformed into humans?". Write a scientific response that refutes this doubt: A) Identify the two conceptual errors about how biological evolution operates contained in the sentence. B) Use the phylogenetic tree model to explain the real relationship between chimpanzees, humans, and their common ancestor, justifying why chimpanzees are "evolutionary cousins" and not "ancestors."

The orchid Angraecum sesquipedale accumulates nectar at the bottom of a spur nearly 30 cm deep, and only the moth Xanthopan morganii, with a proboscis of similar length, is able to feed on it and pollinate it. A) Explain the evolutionary "arms race" (coevolution) between the two: what selective advantage did it confer on the plant for its spur to be longer than the average proboscis, and what selective pressure forced the moth to lengthen its own? B) If a disease were to suddenly drive this moth to extinction, predict the evolutionary fate of the orchid and refute the idea that the plant could "voluntarily modify its nectar to attract other insects."

When studying a series of marine strata spanning 12 million years, a paleontology team discovers that a mollusk species maintains exactly the same morphology for 10 million years. However, in a layer representing an abrupt change of barely 40 000 years, the species disappears and two very distinct derived species emerge, remaining stable for the rest of the time. A) Compare how Darwinian phyletic gradualism and Gould and Eldredge's punctuated equilibrium theory would explain this fossil record. B) Justify why the "rapid" pace supported by punctuated equilibrium does not contradict natural selection or imply instantaneous changes.

The famous "March of Progress" illustration shows a line where quadrupedal primates gradually stand upright step by step until culminating in the human being, conveying the idea that evolution is a ladder toward perfection. A) Dismantle this idea using as counterexamples the evolutionary success of bacteria (simple single-celled organisms for more than 3500 million years) and internal parasites like tapeworms (which have lost complex organs such as the digestive system). B) Justify why in biology the concept of "adaptive success" does not equate to "greater complexity" and explain why natural selection lacks goals or intrinsic purpose.

A laboratory analyzes an unknown cellular organelle found in the cytoplasm of an amoeba and obtains the following data: it has a double membrane (the inner one without cholesterol, similar to bacterial membranes), contains 70S ribosomes, and possesses a closed circular DNA molecule capable of replicating independently of the nucleus. In addition, an antibiotic that blocks bacterial protein synthesis halts the organelle's function. A) Interpret these results by giving a reasoned justification of how they support Lynn Margulis's endosymbiotic theory. B) Explain what paradigm shift this theory represented compared to the traditional evolutionary view based exclusively on competition between living organisms.