A4.1 Evolution and Speciation

Evolution is the change in the inherited characteristics of a population over successive generations. It occurs because genetic variation exists within populations and environmental selection pressures favour some traits over others.

Scientists discovered fossils of organisms that were: Similar to living organisms Completely unlike any living species Found in different geological layers These observations suggested that species changed over time and that some species had become extinct.

Early scientists had difficulty interpreting dinosaur fossils because: Fossils were often incomplete or damaged There were few specimens for comparison DNA technology did not exist Knowledge of evolution and genetics was limited Scientists often compared fossils only to modern reptiles

Lamarck proposed that: Organisms change during their lifetime in response to environmental needs Acquired characteristics can be passed to offspring Structures used frequently become stronger, while unused structures shrink Example: giraffes stretched their necks to reach food, causing longer necks to be inherited.

Lamarck’s theory was incorrect because acquired traits are not inherited genetically. Changes occurring during an organism’s lifetime do not alter the DNA in gametes.

Lamarck was important because he: • Proposed that species change over time • Challenged the idea that species are fixed • Suggested adaptation occurs in response to the environment Although his mechanism was wrong, his ideas contributed to later evolutionary theory.

Darwin proposed that: • Variation exists within populations • Some variations increase survival and reproductive success • Individuals with advantageous traits reproduce more successfully • Beneficial traits become more common over generations This process is called natural selection.

During his voyage, Darwin observed: * Variation between species in different environments * Island species resembling mainland species * Organisms adapted to local conditions * Fossils resembling living organisms These observations helped him develop the theory of evolution by natural selection.

Fitness refers to an organism’s ability to survive and reproduce successfully in its environment.

A scientific theory is: • A well-supported explanation • Based on extensive evidence and observations • Scientifically testable • Able to be modified if new evidence emerges

In everyday language, a theory may mean a guess or opinion. In science, a theory is a thoroughly tested explanation strongly supported by evidence.

Darwin’s theory was modified because later discoveries in genetics explained how traits are inherited. The combination of natural selection and genetics became Neo-Darwinism.

Neo-Darwinism is the modern evolutionary theory combining: • Darwin’s theory of natural selection • Mendelian genetics • Modern understanding of DNA and mutation

DNA sequencing determines the exact order of nucleotides in a DNA molecule.

DNA sequencing allows scientists to compare genetic similarity between organisms. Closely related species have fewer sequence differences.

Few DNA differences indicate: * A recent common ancestor * Close evolutionary relationship

Many DNA differences indicate: * A distant common ancestor * Greater evolutionary divergence

Bioinformatics is the use of: * Computer science * Mathematics * Statistics * Engineering to analyse and interpret biological data such as DNA sequences.

Highly conserved sequences are DNA or protein sequences that change very little over time because they perform essential biological functions.

Because they mutate slowly, differences in their sequences reflect major evolutionary divergences between groups.

Homologous proteins are proteins in different organisms that originated from a common ancestor and have similar structures or sequences.

Hox genes are regulatory genes that control body plan development and the positioning of body structures during embryonic development.

Similar Hox genes are found across many animal groups, suggesting they evolved from a common ancestor.

Haemoglobin is found in many vertebrates and is highly conserved, making it useful for comparing amino acid differences between species.