Problem 6 - Biology

Question

The modern synthesis (a) is based on the sequence of fossils in rock layers (b) uses genetics to explain the source of hereditary variation that is essential to natural selection (c) was first proposed by ancient Greek scholars (d) considers the influence of the geographic distribution of organisms on their evolution (e) is reinforced by homologies that are explained by common descent.

Step-by-Step Solution

Answer

The modern synthesis primarily involves genetics explaining variation essential to natural selection.

Step 1: Understanding the Modern Synthesis

The modern synthesis refers to the fusion of Mendelian genetics with Darwinian evolution, resulting in a unified theory of evolution. It emphasizes the role of genetic variation and its impact on natural selection.

Step 2: Evaluating Statements A and C

Statement (a) about fossils in rock layers does not directly relate to the main focus of the modern synthesis, which is genetics and selection. Similarly, Statement (c) referring to ancient Greek scholars proposing modern synthesis is incorrect, as Greek scholars did not have the knowledge of genetics intertwined with evolution.

Step 3: Analyzing Statement B

Statement (b) accurately describes a key aspect of the modern synthesis. It uses genetics to explain the source of hereditary variation, which is crucial for natural selection to operate, thus aligning with the modern synthesis principles.

Step 4: Considering Statement D

Statement (d) considers geographic distribution influencing evolution. While it can be a factor in evolutionary biology, the primary contribution of the modern synthesis focuses on genetic variation and natural selection rather than geographic distribution's role.

Step 5: Examining Statement E

Statement (e) describes the reinforcement of common descent through homologies, another important element of evolutionary theory supported by genetic evidence, which aligns with the modern synthesis.

Step 6: Conclusion

Summarizing the above analysis, the statement that best describes the basis of the modern synthesis is (b). This is due to its focus on genetics as a source of hereditary variation essential for natural selection.

Key Concepts

Genetic Variation

Genetic variation refers to the differences in genetic makeup among individuals within a population. These differences arise due to mutations, gene shuffling during sexual reproduction, and other mechanisms.
Genetic variation is crucial because it provides the raw material on which natural selection acts.

• Without variation, all individuals might be equally susceptible to diseases or environmental changes.
• This diversity ensures that some individuals might have advantageous traits, leading to better survival chances.

The modern synthesis highlights the importance of understanding genetic variation as it combines the principles of Mendelian genetics with Darwinian evolution, showing how genetic diversity drives evolutionary change.

Natural Selection

Natural selection is a process where individuals with traits better suited to their environment tend to survive and reproduce more than those without these traits. This concept, proposed by Charles Darwin, is central to evolutionary theory.
The modern synthesis explains natural selection by incorporating genetic knowledge, illustrating how advantageous traits become more common in a population over generations.

• For example, in a population of beetles, if green beetles are less visible to predators than red ones, green beetles will have a survival advantage.
• Over time, the green gene becomes more prevalent due to these survival and reproduction advantages.

Natural selection, therefore, acts on existing genetic variation within a population, shaping the evolution of species.

Evolutionary Theory

Evolutionary theory describes the process by which organisms change over time due to changes in heritable physical or behavioral traits.
Prior to the modern synthesis, evolutionary theory primarily focused on organism morphology. The modern synthesis expanded this view to include genetic mechanisms, providing a more comprehensive understanding of how evolution operates.

• It combines natural selection, mutation, genetic drift, and gene flow to explain how populations evolve and adapt to their environments.
• This synthesis bridges the gap between Darwin's ideas of natural selection and the genetic foundation necessary to propagate those changes through generations.

Hence, evolutionary theory as understood today owes much to the integration of these genetic principles, enhancing our knowledge of the dynamics of life on Earth.

Common Descent

Common descent is the principle that all living organisms share a common ancestor. This idea is supported by a wide range of evidence, including genetic similarities and fossil records.
The modern synthesis reinforced this concept by demonstrating how genetic information is passed down through generations, maintaining relationships between species.

• Homologies, or shared characteristics between different organisms, further illustrate common descent. These traits can be anatomical, like the structure of limbs, or molecular, such as DNA sequences.
• For instance, the basic genetic code is shared among all living organisms, pointing to a shared lineage.

By linking genetics with common descent, the modern synthesis provides a robust framework for understanding the unity and diversity of life.