|MadSci Network: General Biology|
Can I answer the easiest question first? If a mammal is large, believe me it takes a long time to reach a ton in weight! So whales and elephants gestate for ages so that the calves can be the correct mass for that particular species. Smaller elephant species in the past had shorter gestations, for that reason. In the case of whales, the young must be born with a huge amount of insulation to combat the freezing temperatures they have in the polar oceans. Their fat is blubber, of course, which insulates just like the filled air cavities in house walls.
Animals and plants with short life cycles often live as annuals. This means that they take advantage of annual cycles in weather and climate to avoid the extreme cold or heat. Butterflies are a fine example. If youíd like to know about them, they exist as an egg of pupa (or sometimes caterpillar) over-winter, hatch in the spring (or start feeding again) then pupate if they havenít already. This all prepares them for the breeding season in summer or whenever, so that the adults can feed and breed and often die quite quickly. Then the cycle starts again. Biennial plants have modified this to a two year cycle, but I think you will understand that annual plants are like these annual animals!
As far as long-lived animals are concerned, we are very interested in trying to copy them. Again, itís usually large organisms that live long. They say if your heart beats fast, like a shrew, you will be a very short lived creature. If it beats slowly like an elephant, you will live a long time. So every species, if you work it out, has almost exactly the same number of beats in its life, on average. If you have to grow to be big, a lot of energy is needed, and it takes many years to take in so much energy. That is why plants and animals can live for so long, and indeed, some HAVE to live long before they can breed and produce the next generation.
Ask some more if you like Leow, as you always have such an mature and enquiring mind!
Try the links in the MadSci Library for more information on General Biology.