Friday, February 14, 2014

Change happens

When the first rains come long dormant seeds germinate.  Typically in a square foot of vacant lot soil, several hundred seeds will sprout.  If you return to the same space in July, you will find that only one or two plants still to be found.  For some its bad luck and they are eaten by a predator, for others it’s slight difference in sunlight or soil.  But the major deciding factor is that some have some sort of genetic advantage. 

The beauty of sexual reproduction is that it causes genes from two parents to recombine in a variety of different combinations.  Even a small genetic advantage promoting more rapid growth, resistance to drought, resistance to pests… can give the small advantage needed to allow better survival that for others in the group.

This is the basis for natural selection.  There are always more offspring produced than can survive.  Due to genetic recombination in sexual reproduction some of the offspring are better equipped for survival than others.  The survivors live to pass on their beneficial genetic information to later generations.

Sometimes when DNA, the cell molecules that carry genetic information, duplicates during cell division, small spontaneously changes occur.  The changes are included in all descendant cells.  The vast majorities of these changes (mutations) are detrimental to life – and diminish chances of survival.  Rarely a mutation occurs that benefits survival.  

These genes would be passed on while others can’t compete as well. Beneficial genes collect in the survivors.  It was once thought that vast amounts of time were needed for this process – now we see many examples of changes in organisms that occur as the result of a few mutations over  brief time periods  - most notably changes in virus, bacteria, insects, and birds.

In any environment – all of those organisms that are suited for survival will survive.  
Natural selection results in survival of new mutations when the environment is changing.  Take the case of White Sharks – the ocean has provided a stable unchanging environment… There is no advantage in receiving changes through new mutations.  If there is any limit in the environment, food supply, predators, etc. then natural selection would be at work… but sharks live in an environment that has not changed since well before the time of the dinosaurs – and the fossil record shows that shark design is also largely unchanged.  The same is true of any stable species living in an unchanging environment.

It was thought until recently that evolution of life was a continuous process dependent on the introduction of new genetic information as the result of random mutations.  Now evidence suggests that as long as any environment is stable the rate of genetic change will be very small.  Then during times of rapid environmental change the process of natural selection occurs ‘quickly'.  Changes in an individual species may occur within observable time, but for enough changes to add up to result in new species would require thousands of generations.*(bottom of page)

 The process of periods of stability followed by times of rapid change are called ‘”Punctuated Equilibrium”.  An example of this would be the long reign of dinosaurs on earth cut short by a comet or asteroid colliding with the earth – causing catastrophic climate change.  The fossil record shows a number of times of change that resulting in times of great dying off, followed by the slow emergence of new life forms suited for the new environment.  (The introduction of "punctuated equilibrium" in no way diminishes the theory of evolution - but it only serves to clarify the mechanism by which evolution occurs.)

Our current pattern of climate change is, in earth history terms, – very rapid.  We are experiencing the kind of change that would normally require many thousands of years to take place naturally.  This appears to constitute a change in our environment stability that will cause extinction of species.  At least 1000 species have been permanently lost in the last 500 years...Extinction is forever.

According to punctuated equilibrium, this appears to be a time when the ‘rapid’ (a few hundreds years) change in the earths environments will cause a rash of extinctions… followed by the next many thousands of years with the evolution of life forms suited for the next stable environment. Read more here; 

*A species is defined as a group of animals that can only produce fertile offspring by mating with others in that group.  So if two similar populations of salamanders, both descendants of the same group are different enough to no longer be able to mate and produce fertile offspring - they have become different species.