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Understanding how traits improve an organism's chance of survival and reproduction.
Why does a polar bear thrive in the freezing Arctic while a desert camel would perish in days? It isn't just luck—it's a biological 'perfect fit' developed over millions of years.
In everyday language, 'fitness' usually means how fast you can run or how much you can lift. In biology, Biological Fitness has a very specific meaning: it is a measure of an individual's reproductive success. It is not just about surviving; it is about passing your genes to the next generation. If an organism lives for 100 years but never has offspring, its biological fitness is effectively . Conversely, an organism that lives only a year but leaves behind dozens of healthy offspring has high fitness. We often represent relative fitness with the variable , where the most successful genotype in a population is assigned .
Quick Check
If a lion is the strongest in the pride but is sterile and cannot have cubs, what is its biological fitness?
Answer
Its biological fitness is zero because it cannot pass its genetic information to the next generation.
An adaptation is a heritable trait that increases an organism's fitness in its environment. These are categorized into three types: 1. Structural: Physical features of an organism's body (e.g., the shape of a bird's beak). 2. Behavioral: The way an organism acts to survive (e.g., birds migrating south for winter). 3. Physiological: Internal processes or chemical changes (e.g., a snake producing venom or a desert animal producing highly concentrated urine to save water).
The Wood Frog lives in cold climates and demonstrates multiple adaptations: 1. Structural: Camouflaged skin that looks like dead leaves. 2. Behavioral: Burrowing under leaf litter to stay insulated. 3. Physiological: It produces a 'natural antifreeze' (glucose) in its blood that allows its heart to stop and its body to partially freeze without dying.
Quick Check
A pufferfish inflating its body to look larger to predators is which type of adaptation?
Answer
Behavioral (the action of inflating) and Structural (the ability to expand and the presence of spines).
1. Before the Industrial Revolution, light-colored moths had higher fitness because they blended with light-colored trees. 2. Soot from factories turned trees black. 3. The light-colored moths' survival probability () decreased because they were easily seen by birds. 4. Rare dark-colored moths now had a higher , leading to a population where most moths became dark over several generations.
Bacteria reproduce rapidly, allowing us to see evolution in real-time. 1. A population of bacteria is exposed to an antibiotic. 2. Most die, but a few have a physiological adaptation (an enzyme that breaks down the drug). 3. Their relative fitness becomes , while the others become . 4. Within hours, the entire population consists of resistant bacteria. This is a 'challenge' because it combines physiological adaptation with rapid environmental change.
Which of the following best defines biological fitness?
A desert fox having large ears to dissipate heat is an example of what?
An adaptation that is beneficial in one environment will always be beneficial in any other environment.
Review Tomorrow
In 24 hours, try to list one structural, one behavioral, and one physiological adaptation for an animal of your choice.
Practice Activity
Look at a common pet (like a dog or cat). Identify three structural adaptations they have and hypothesize what kind of environment those traits were originally 'designed' for.