D4.1.1—Natural selection as the mechanism driving evolutionary change

The theory of evolution by natural selection can be explained with the following statements:

• Organisms produce more offspring than the environment can support.
• Among these offspring, there is variation.
• Some variants are better suited to the environment and have a higher chance of surviving to reproductive age.
• Survivors of the fittest, from less fit or less well-adapted-are sometimes have a higher risk of mortality from predation or other factors. This is sometimes called survival of the fittest.
• The heritable features of the population change frequently, so the population can adapt to the environment.

While evolution can occur rapidly in response to sudden changes in the environment, the process is often gradual. Evolution by natural selection, over the billions of years that life has existed, has resulted in the immense biodiversity now present on Earth.

Lamarckism:

An older theory, Lamarckism, proposed that organisms acquire advantageous traits during their lifetime and pass those traits on to their offspring. (e.g., a giraffe stretching its neck to reach leaves would have offspring with longer necks). This theory has been disproven.

Paradigm Shift: Darwin’s theory of evolution by natural selection represented a paradigm shift in scientific understanding. It challenged the existing ideas about species evolution and provided a new framework for interpreting observations in biology.

In summary, natural selection, driven by variation, differential survival, and inheritance, is the mechanism driving evolutionary change.

D4.1.2—Roles of mutation and sexual reproduction in generating the variation on which natural selection acts

Mutation is the original source of new alleles. It introduces genetic diversity into a population by changing DNA sequences.

Meiosis shuffles existing alleles through crossing over and independent assortment of chromosomes. This creates a wide range of possible combinations of alleles in gametes, leading to genetic variation among offspring.

Sexual reproduction combines gametes from two different parents, bringing together mutations that occurred in different individuals. This increases the genetic diversity within a population and provides more raw material for natural selection to act upon.

The text highlights that species that reproduce asexually rely solely on mutation for generating genetic variation. It is generally believed that this might not be sufficient for rapid adaptation to changing environmental conditions, as compared to sexually reproducing species.

In essence, the interplay of mutation, meiosis, and sexual reproduction is crucial in generating the diverse genetic variations that fuel evolutionary processes.

D4.1.3—Overproduction of offspring and competition for resources as factors that promote natural selection

Organisms vary in the number of offspring they produce. Some species, like the southern ground hornbill, have slow breeding rates, while others, like the coconut palm and the fungus Calvatia gigantea, produce a large number of offspring. Most species produce more offspring than the environment can support. This overproduction leads to competition for resources like food and space. Not all individuals will survive and reproduce due to this competition. Only those with traits best suited to the environment will be able to thrive and pass on their genes. This competition for resources is a key factor in natural selection, as it favors individuals with advantageous traits.