Question

How can evolutionary fitness be estimated? a. Document how long individuals survive. b. Count the number of healthy, fertile offspring produced. c. Determine which individuals are strongest. d. Determine which phenotype is the most common.

Short answer

b. Count the number of healthy, fertile offspring produced.

Step-by-step solution

Eliminate irrelevant options

We can eliminate options that don't focus on measuring the actual impact of an individual's genetic traits on its ability to produce offspring and therefore contribute to the next generation. Option (a) - Document how long individuals survive: Although survival is an important aspect to consider, it doesn't directly refer to the individual's ability to produce offspring. Option (c) - Determine which individuals are strongest: Strength can be an important factor in certain contexts, but it doesn't directly provide any information on an individual's ability to produce viable offspring. Option (d) - Determine which phenotype is the most common: The frequency of a phenotype in a population doesn't necessarily mean that it is the most fit and contributes more to the next generation.

Choose the best option

After eliminating the irrelevant options, we are left with the one option that directly measures an individual's impact on future generations. Option (b) - Count the number of healthy, fertile offspring produced: This is the most accurate method to estimate evolutionary fitness because the ability to produce viable offspring is a direct measure of an individual's adaptation to their environment and contribution to future generations. Therefore, the correct answer to estimate evolutionary fitness is: b. Count the number of healthy, fertile offspring produced.

Key concepts

Natural Selection

Natural selection is a fundamental mechanism of evolution, described by Charles Darwin. It explains how traits that enhance survival and reproductive success become more common in subsequent generations. The core idea is that individuals with characteristics better suited to their environment tend to survive longer and have more opportunities to reproduce. Over time, these advantageous traits accumulate in the population, while less beneficial traits may diminish or disappear.

For instance, consider a population of moths where some are light-colored and others are dark. If the environment has dark trees due to industrial soot, dark-colored moths are less visible to predators and have a higher chance of survival. As a result, they reproduce more successfully, passing on their dark coloration to their offspring. This demonstrates how natural selection operates on the principle of 'survival of the fittest', where 'fitness' refers to an individual's genetic contribution to subsequent generations through reproduction.

Reproductive Success

Reproductive success is a measurement of the number of offspring an individual produces and supports. It's a crucial component of evolutionary fitness because only traits that are successfully passed on to offspring can spread through a population. In biological terms, an individual’s success is not judged by its strength or longevity alone, but by its ability to reproduce and ensure the survival and reproductive capability of its offspring.

For example, a peacock's elaborate tail may not be practical for survival, but if it attracts peahens and leads to more offspring, it is considered a contributor to the peacock's reproductive success. It's important to note that reproductive success is not just about quantity but also quality; if offspring are not healthy or fertile, they won't continue the lineage, and thus those traits would have a limited impact on the gene pool.

Genetic Contribution to Future Generations

An individual's genetic contribution to future generations, commonly known as 'heritable fitness', is a key measure in understanding evolutionary processes. It represents the extent to which an individual's genetic material is passed down. This is not only dependent on producing offspring but also on the offspring's capacity to survive and reproduce themselves.

Consider a tree that produces thousands of seeds. If only a few seeds grow into trees that also produce seeds, the original tree's genetic contribution may be considered low. Conversely, a tree that produces fewer seeds, but with a higher survival rate, may make a greater genetic contribution in the long-term. This showcases why quantity does not necessarily trump quality in terms of evolutionary success. Evolutionary fitness, therefore, is determined by an organism's overall ability to propagate its genes through successive generations, influencing the genetic makeup of its population over time.