Question

Compare and contrast how evolution by inheritance of acquired characters and the theory of evolution by natural selection would explain the observation of white mice living on light soil and brown mice living on dark soil.

Short answer

Inheritance of acquired characters suggests that white mice living on light soil and brown mice living on dark soil would have changed their fur color during their lifetime as a direct response to their environment, and their offspring would inherit these acquired traits. In contrast, evolution by natural selection suggests that the white and brown mice originated from a common ancestor with varying fur colors, with those better suited to their environment having a higher survival and reproduction rate over generations, leading to a higher prevalence of white mice on light soil and brown mice on dark soil.

Step-by-step solution

1. Understanding Evolution by Inheritance of Acquired Characters

Evolution by inheritance of acquired characters, also known as Lamarckism, states that individuals can acquire certain traits during their lifetime, which would eventually be passed on to their offspring. In this theory, these acquired traits are expected to better suit the organism for its environment. It implies that mice can suddenly change their fur color to better blend into their environment during their lifetime, and their offspring will inherit the same trait.

2. Understanding Evolution by Natural Selection

Evolution by natural selection, proposed by Charles Darwin, suggests that species evolve over generations due to the survival and reproduction of organisms with advantageous traits. In this theory, individuals with beneficial characteristics to their environment are more likely to survive and reproduce successfully compared to those with less advantageous traits. Over time, these advantageous traits become more prevalent in the population, leading to the evolution of species.

3. Applying Inheritance of Acquired Characters to the Mice Scenario

According to the theory of inheritance of acquired characters, the white mice living on light soil would have gradually changed their fur color as a direct response to their environment. Likewise, the brown mice living on dark soil would have developed their brown fur to better match the dark soil. The acquired traits (white and brown fur) would then be inherited by their offspring, leading to a population of white mice on light soil and brown mice on dark soil.

4. Applying Natural Selection to the Mice Scenario

According to the theory of evolution by natural selection, the white mice and brown mice likely originated from a common ancestor with a variation of fur colors. As the mice lived in different environments (light soil and dark soil), the individuals with fur colors better suited to their respective environments would have a higher probability of surviving predation and reproducing. Over generations, the proportion of white mice on light soil and brown mice on dark soil would increase due to their higher survival and reproduction rates relative to mice with other fur colors.

5. Comparing and Contrasting the Two Theories

Inheritance of acquired characters suggests that individual organisms can change their traits during their lifetime to adapt to their environment, and these acquired traits are then inherited by their offspring. This theory implies a direct cause-effect relationship between the environment and the traits of an organism. On the other hand, natural selection focuses on the variation in traits within a population and the differential survival and reproduction of organisms with advantageous traits in a given environment. This theory suggests that evolution occurs over generations as a result of selection pressure favoring specific traits. In the case of the white mice living on light soil and brown mice living on dark soil, inheritance of acquired characters would involve individual mice changing their fur color during their lifetime, while natural selection would involve the gradual increase in the proportion of white or brown mice in their respective environments over generations due to their increased survival and reproduction rates.

Key concepts

Inheritance of Acquired Characters

The concept of the inheritance of acquired characters, often associated with the ideas proposed by Jean-Baptiste Lamarck, is a classical evolutionary theory. It posits that traits developed by an organism during its lifetime can be passed down to its offspring. For example, if a mouse living on light-colored soil acquired white fur to blend in and avoid predators, according to this theory, it could then pass this trait to its progeny, leading to a population of white-furred mice in that environment.

While this theory has historical significance, it doesn't hold up scientifically today. Modern genetics has shown that traits are passed through genes and DNA, not by direct transmission of characteristics acquired from the environment. This suggests that while the theory is an interesting part of the history of evolutionary thought, it is not accepted as a mechanism for how species evolve over time.

Natural Selection

Natural selection is a cornerstone of modern evolutionary theory. Introduced by Charles Darwin, it explains how species adapt and evolve through differential survival and reproduction. Organisms that have beneficial traits for their environment are more likely to survive and pass these adaptive traits on to future generations.

Using our mice example, over many generations, mice with white fur in a light soil environment would be less likely to be preyed upon, thus having more chance to reproduce. Their genes, which include the code for white fur, would become more common in the population. This process naturally selects traits that improve survival and reproduction. Unlike the inheritance of acquired characters, this theory is widely supported by empirical evidence and is a fundamental principle of biology.

Adaptive Traits

Adaptive traits are characteristics that enhance an organism's ability to survive and reproduce in a particular environment. These traits can range from physical attributes, like the fur color in mice, to behaviors or physiological responses. The process of adaptation occurs over many generations, with beneficial traits becoming more prevalent in the population due to natural selection.

For instance, white fur in mice living on light soil is an adaptive trait because it camouflages them from predators, increasing their survival odds. Over time, this trait becomes more common as these mice have higher reproductive success. Adaptive traits are key to understanding how populations evolve in response to their surroundings.

Variation in Populations

Variation within a population is essential for natural selection to operate. It refers to the differences among individuals in a population, which can be due to genetic variation or the result of environmental factors. These variations lead to a range of traits among the individuals, some of which may provide an advantage in specific environments.

Continuing with our mice scenario, the initial population would display variation in fur color. This diversity allows natural selection to favor those colors better adapted to their environment—white for light soil and brown for dark soil. Over generations, this leads to an increased frequency of the advantageous fur color variant in each respective environment. Genetic variation is the fuel for evolutionary change and is crucial for the adaptability and survival of species.