Natural selection and genetic modification Revision Notes

Core Principles of Natural Selection

Natural selection is based on several key observations:

1. Variation: Individuals within a species show variation in their characteristics.
2. Overproduction: Organisms produce more offspring than can survive.
3. Competition: There is competition for resources, leading to a struggle for survival.
4. Differential Survival/Reproduction: Individuals with advantageous traits are more likely to survive and reproduce, passing on those traits.

Mechanism of Change

Over generations, the frequency of beneficial alleles (genes coding for advantageous traits) increases in the population. This gradual change leads to populations becoming better adapted to their environment. If environmental conditions change, different traits may become advantageous, driving further evolutionary adaptation. This long-term process can lead to the formation of new species.

Definition and Purpose of Genetic Engineering

Genetic engineering refers to altering the genetic material (genome) of an organism by introducing a gene from another species or individual. The aim is to provide the recipient organism with a desirable trait, such as resistance to disease, enhanced nutritional value, or the ability to produce a useful protein. This process differs from selective breeding because it is much more targeted and can involve genes from unrelated organisms.

Basic Steps in Genetic Engineering (Foundation and Higher Tier)

At foundation tier, the process involves locating the gene responsible for a desired trait, removing it from the donor organism, and transferring it into the target organism, which then develops the desired characteristic. For higher tier, this process may include using specific enzymes to cut and insert the gene, using a vector (like a plasmid) to transfer the gene, and selecting successfully modified cells. A well-known example is inserting the human insulin gene into bacteria, enabling them to make insulin for medical use.

Ardi (Ardipithecus ramidus) - 4.4 MYA

Ardi, dating back 4.4 million years ago (MYA), represents one of the earliest known hominins. Fossil evidence, particularly from a skeleton discovered in Ethiopia, suggests Ardi had features adapted for both tree climbing and walking upright (bipedalism). Its foot structure, including a grasping big toe, indicates arboreal locomotion, while its pelvis structure shows adaptations for walking on two legs, though perhaps not as efficiently as later hominins. This discovery is crucial for understanding the transition to bipedalism, showing it might have developed in a woodland environment rather than purely in open savannas as previously thought.

Lucy (Australopithecus afarensis) - 3.2 MYA

Lucy, discovered in Ethiopia and dated to 3.2 million years ago, is an iconic fossil of Australopithecus afarensis. A significant proportion of her skeleton was recovered, providing extensive information. Her pelvis and leg bones clearly indicate that she was fully bipedal, meaning she habitually walked upright on two legs. However, her brain size was still relatively small, comparable to that of modern chimpanzees, and she retained some features, such as relatively long arms, that suggest she might have still spent some time in trees. Lucy provides key insights into the development of efficient bipedalism before significant brain enlargement.

Richard Leakey's East African Discoveries - from 1.6 MYA

Richard Leakey's expeditions in East Africa, particularly around Lake Turkana, yielded numerous significant hominin fossils, including those from approximately 1.6 million years ago. These discoveries include remains of Homo erectus, such as 'Turkana Boy', a nearly complete skeleton of a juvenile male. These fossils show a larger brain capacity compared to earlier hominins like Lucy and a body proportion closer to modern humans, indicating more efficient bipedalism over long distances. The tools associated with these fossils suggest increased cognitive abilities and complex behaviours, linking human evolution to technological advancements and further changes in lifestyle.

Summary of Evolutionary Trends

Over millions of years, the fossil record shows a clear trend towards increased bipedalism, allowing for hands-free locomotion. This was followed by a significant increase in brain size and complexity, alongside a reduction in jaw size and tooth prominence. The development of tool-making and culture further distinguishes later hominins. Each fossil discovery, from Ardi to those made by Leakey, adds pieces to the puzzle of how hominins adapted and evolved to become modern humans, showcasing a gradual progression of traits.

Natural Selection and Antibiotic Resistance

Natural selection explains the rise of antibiotic-resistant bacteria. Within any bacterial population, some individuals may have random genetic mutations that make them resistant to an antibiotic. When this antibiotic is applied, it kills non-resistant bacteria, while the resistant ones survive. These survivors then reproduce, passing on their resistance genes, leading to a higher proportion of resistant bacteria in subsequent generations.

Darwin's Theory and Bacterial Evolution

Charles Darwin's theory of evolution by natural selection posits that individuals with advantageous traits are more likely to survive and reproduce. In the context of antibiotic resistance, the 'advantageous trait' is the ability to withstand an antibiotic. The antibiotic acts as a 'selective pressure' that filters out the non-resistant bacteria. This process causes the bacterial population to evolve, becoming increasingly resistant over time, illustrating evolution in action.

Impact of Overuse of Antibiotics

The overuse and misuse of antibiotics accelerate the process of natural selection for resistance. Every time antibiotics are used, there's an opportunity for resistant strains to be selected and multiply. This has led to a critical public health issue where a growing number of bacterial infections are becoming difficult or impossible to treat with conventional antibiotics, highlighting the urgent need for responsible antibiotic use and the development of new treatments.