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Politics : Evolution -- Ignore unavailable to you. Want to Upgrade?

To: Brumar89 who wrote (62581)	11/12/2014 3:44:53 PM
From: TigerPaw	1 Recommendation Recommended By 2MAR$ Read Replies (2) \| Respond to of 69300

earth is unchanging most of the time It would be more accurate to say "slowly changing" especially compared to the timescale of generations for organisms. Surely this should have brought vast increases in new creatures. But did it? Yes Indeed! In the last ice age there were Wooly Mammoths, and giant ground sloths, long toothed cats, and Neanderthals. When the ecosystem changed so did the types of organisms. The buffalo are different from those of the ice age. The end of the ice age was very much a time of punctuated change north of the tropics but as we would expect, not much change south of the tropics where the climate shift was far less dramatic. In Texas we have an interesting relic that illustrates some of forces which lead to equilibriums following the punctuated change. The Texas Pronghorn can run much faster than any predator from which it needs to escape. During the ice age there was a cat in Texas with bones similar to an African Cheetah. During the ice age it would chase pronghorn at high speed, the pronghorn competed primarily against each other (to not be the slowest pronghorn in the herd) and developed a gene pool with little diversity. When the fast cat went extinct the pronghorn did not rapidly change. First of all, since the pronghorn had little diversity in genes the next generation did not exhibit many changes to be selected. Second of all, running much much faster than wolves or coyotes or mountain lions is not a great disadvantage so there is little selection pressure on that trait.

To: Brumar89 who wrote (62581)	11/12/2014 4:17:06 PM
From: TigerPaw	Read Replies (1) \| Respond to of 69300

"The organisms are now changing faster." But why do they change faster? When the ecosystem changes to the point that organisms are now at a disadvantage, they either die out, or have offspring which are better able to tolerate the changes in the ecosystem. There are many ways for an ecosystem to change besides changes in the Earth (or Sun). An ecosystem is more defined by the total population of organisms it contains, so a change, even a random change, to one organism can have a ripple effect through the whole group of surrounding organisms.