Quizzes & Puzzles1 min ago
Evolution
17 Answers
I read a puzzle in the paper asking why zebra are black and white in a colourful environment, the answer being that lions, their main predators are colour blind. Given that these are totally different species, how did the zebra evolve like this? How would its DNA / genes / whatever "know" that its main predator doesn't see in colour to develop the patterning?
Answers
1 to 17 of 17
Best Answer
No best answer has yet been selected by badhorsey. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.
-- answer removed --
I see some problems with andy hughes scenario. Firstly, unless the striping seen in zebras arrived full blown, it would have a detrimental effect on the survival of the species. If, as andy postulates, the striping gained prominence over a period of time, the progenitors with only some striping would be more visibile, not less. They would have little chance of survival since they would attract undue attention. Secondly, at least in historic records, the primary predator of zebras (what's the difference between an abra and a zebra? About 25 sizes...) is lions. Lions hunt, almost exclusively at night. Thus, the striping on zebras would add little, if any survival advantage for the individual zebra. This is especially true considering the quality of the big cat's night vision, which is equivalent to our night vision goggles. Lastly, many other species, especially in Africa, that have historically been concurrent with the zebra, are partially striped. Some of the large antelope and other varieties have prominent striping only on some body parts. This doesn't seem to offer much in the way of survival from predators, but do serve other functions. There do appear to be some advantages in the heat reflecting and absorbtion of the color pattern. It's known that the black part of the stripes has fatty layers underneath that aid in heat dissipation, which assists the white portions in reflecting heat. But, again, unless this occurred full blown, little, if any benefit would be drived... In my humble opinion only...
Animals evolve to fill a niche. The zebra niche is "an animal which finds food in that habitat, but will not be totally devoured by lions." Lions have a big advantage. They are fast and will beat any zebra on a one to one bout.
The zebras are present in a group. When the lion attacks, they do not flee in different directions. They flee in a pack. Any attacking lion has to pick out an individual zebra for supper. This presents problems. If you just charge in, you can get a nasty, even life-threatening kick in the face. You need to pick out one.
Way way back, in pre-stripey days, two zebras mated. Mating produces random variation, in this case, a wee bit different coat colour, which conferred just enough advantage in that 'running away' situation to give that genetic line a survival advantage over those with a regular coat. Over a long period of time, this process continued, in very small steps, here and there. The reason why you end up with something very identifiable, like stripes, is that although the genetic mutation is random, the natural selection process is not: it picks the fittest for survival (and thus reproduction). Stripes make it very hard for a lion to pick out an individual member of the pack.
Although the effect is mediated via a group process, it still confers survival advantages to any individual which happen to possess those genes (genotype) which confer the stripes (phenotype).
Oh, and I should add, they were present in a DIFFICULT niche. Even when you have a few stripes here and there, the world is still a very difficult place to be for a zebra, and the lions are still going to be taking out a decent percentage of the pack. Thus, the upward pressure towards the best camouflage* possible is very heavy: a zebra with a mutation towards a slightly higher degree of stripeyness will have a small but significant advantage over some others Small advantage, just a slightly better striping: but one lion is out for one kill, and if your small advantage is enough to ensure that someone else gets it in the neck, not you, then this of course is a huge result.
*Camouflage here means 'blending in with the group', not the environment.
Another possibility is that the stripes evolved not through competition between zebras, but between zebras and an outgroup. Zebras could only fill that niche for that food when they were of such a colour that would prevent mass devouring by lions.
When zebras are standing in tall grass, their stripes serve to break up their outline, so making them fairly inconspicuous until they move. When they are being chased by lions they become one big packed herd of moving stripes , which is very confusing to the lions , as they need to pick out just one for a successful kill. The pattern of each zebras' stripes is unique, which helps the members of the herd to identify each other. In fact you do find very dark zebras occasionally but they tend to get ostracised by the rest of the herd and don't fare well in the survival stakes.
All wrong, zebras were made by God when he was in a funny mood to enable questions like this to be asked 6010 years later (the earth was created in 4004 BC). Evolution could never have come up with a zebra, nor a spider that lives underwater and takes bubbles of air down with it.
He was not in such a ticklish mood when he created Croydon however.
"I look magnificant, leave it at that!"
http://www.visions-of-africa.com/ZebraMigration0893.jpg< /P>
1 to 17 of 17
