04.03 - Evolución: Variabilidad, su importancia y la presión selección

Understanding Variability in Evolution

The Origin of Variability

• Discussion on how variability is produced today, emphasizing its genetic origin. Darwin faced criticism for not explaining the source of variability in his theory.

• Darwin observed variations, such as birds with different beak shapes based on their island habitats, acknowledging that natural selection acts on heritable variations.

Mechanisms of Variability

• Current understanding attributes variability to two main factors: mutations and sexual reproduction. Mutations introduce new variants while sexual reproduction mixes existing ones.

• Clarification that mutations create new genetic variants (like adding new cards to a deck), whereas sexual reproduction shuffles existing variants (like shuffling cards).

Types of Mutations

• Explanation of mutations as random alterations in genetic material. Only germline mutations (in gametes) are inherited; somatic mutations (in body cells) are not passed to offspring.

• Three types of mutations discussed:

• Harmful Mutations: Decrease survival and reproductive chances, often eliminated from the population.

• Beneficial Mutations: Increase survival and reproductive success, likely to persist in the population.

• Neutral Mutations: Have no significant effect on survival or reproduction; their persistence is due to chance.

Reproductive Variability

• Sexual reproduction leads to genetic recombination during meiosis and random assortment during fertilization, contributing to variability without creating new genes.

Selection Pressure and Natural Selection

• Introduction of selection pressure as factors negatively impacting an individual's survival. For example, predators can reduce the likelihood of certain traits being passed down.

• Natural selection occurs when selection pressures persist over many generations, favoring individuals with advantageous traits that enhance survival and reproductive success.

Adaptation Through Time

• Over time, sustained selection pressure leads to adaptation within populations as beneficial traits become more common through successive generations.

• Example provided illustrating how a mutation can lead to advantageous adaptations by chance—highlighting the role of environmental context in evolutionary processes.

Natural Selection and Genetic Variability

The Role of Color in Survival

• Brown and green colors affect visibility to predators; brown individuals are more easily spotted, leading to higher predation rates.

• A mutation resulting in a green color allows for better camouflage, increasing the chances of survival and reproduction for those individuals.

Adaptations Through Mutations

• Further mutations can lead to shapes resembling leaves, enhancing concealment from predators and improving survival odds.

• While mutations may seem random, the majority of species have gone extinct due to lack of advantageous traits that enhance survival.

Evolutionary Arms Race

• Predators also evolve alongside prey, developing new adaptations to locate and capture them, creating an ongoing evolutionary competition akin to an arms race.

Importance of Genetic Variability

• Genetic variability within a population is crucial; it provides resilience against changing environmental pressures.

• A lack of variability can lead to extinction if conditions change unfavorably for the existing traits.

Environmental Changes and Adaptation

• If vegetation changes color (e.g., from green to brown), previously advantageous traits may become liabilities without genetic diversity.

• Individual disadvantages can turn into population advantages when environmental conditions shift, highlighting the importance of genetic diversity.

The Necessity of Genetic Diversity

• Continuous environmental changes mean that genetic variability is essential for long-term species survival; it allows populations to adapt over time.

• The metaphorical representation of genetic variability as liquid illustrates that more "liquid" (variability) leads to better adaptability in changing environments.

Selection Pressure Dynamics

• High selection pressure can reduce genetic variability; thus, maintaining some level of diversity is critical for species endurance amidst fluctuating conditions.