In 1847, the German biologist Christian Bergmann noted that mammals and birds living at higher latitudes (farther from the equator) are on average larger and bulkier than related species living at lower latitudes. Suggest an evolutionary hypothesis to explain this observation.

Question

Accepted Answer

Hi everyone, welcome back, Here's our next problem. It says according to blank species that live in hot climates tend to have smaller hearts relative to their body weight. Then closely related species that live in colder climates, when we look at our answer choices, we have four different choices of rules. Bergman's rule rule, Allen's rule and charge offs rule Well the first three Bergman's, Hess's and Alan's do have to do with body characteristics of closely related species that live in cooler versus warmer climates. But we can rule out choice the char gas rule right away and that's because it doesn't have anything to do with this is completely unrelated. Um That's the rule that has to do with D. N. A. That doesn't any species that the amount of Adnan must equal the amount of timing. The amount of wanting must equal the amount of cytosine and that pairings and perimeter things must exist in a 1 to 1 stored geometric ratio. So allowed us to think about the nature of D. N. A. Doesn't have anything to do with our question here. So now we've just got to recall which of these rules is which among our top three choices And just put a quick and dirty guide here, Bergman's rule has to do with general body size. And Bergman's rule says that in general um members of a species that live in a colder habitat tend to have larger body sizes compared to closely related species that live in warmer climates. Um This has to do with a larger body size um maintaining its temperature better. So in a colder climate, you need to stay warm and a larger body is going to be better at doing that. So that is not what we want, because we're specifically talking about heart size. So we're gonna eliminate choice. A choice B has a rule. Well, jesus says that in the colder habitat, um species will have larger hearts relative to their body size as compared to closely related species in warmer climates. And that is what the question is asking about. It's phrased the reverse way saying in hot climates, they tend to have smaller hearts, but that is what we're looking for. Hess's rule. And this is because to keep warm in a cold climate and animal has to keep pumping its blood around, circulating it to keep the heat moving around and spreading from the core out to the appendages, and a larger heart will be more efficient at pumping blood. So animals in the colder habitats need larger heart relative to their relatives in warmer climates. And finally, Allen's rule uh says in colder habitats, species tend to have shorter, thicker limbs and body appendages compared to their close relatives and warmer climates. Again, the it's all about maintaining heat. So long, thin limbs, long, thin appendages will lose heat more. So, of course, animals and warmer climates can use that to their advantage, but in colder habitats, they'll have shorter, thicker limbs and body appendages, but we're talking about heart size, not limbs. So we eliminate choice. See so again, according to choice B has this rule, species that live in hot climates tend to have smaller hearts relative their body weight. And closely related species that live in colder climates hope to see you in the next video.

In 1847, the German biologist Christian Bergmann noted that mammals and birds living at higher latitudes (farther from the equator) are on average larger and bulkier than related species living at lower latitudes. Suggest an evolutionary hypothesis to explain this observation.

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Key Concepts

Bergmann's Rule

Natural Selection

Thermoregulation