Bio questions pt. 2?

Question

I've looked everywhere (my bio book & a few places online) and I can't seem to get the answer to two of my questions?

1. How variation within a species increases the chance that some organisms would survive a majoy enviornmental change (i.e. selective pressure)?

2. How does the fossil record provide evidence of biological diversity, episodic speciation, and mass extinction?

Thank you in advance!

mark

Answer 1

Well for the first question, the simple answers is that variation within a population will increase the whole population's chance of survival in a situation where the environment changes drastically.  If the population were genetically homogenous, and the traits that they all posessed were weak to the environmental change, the whole population would be wiped out.  On the flip side, if there was a lot of variation, there would be a greater chance that some of the traits that the individuals in the population posessed are advantageous in surviving the change.

On the second question, the fossils that archaeologists find can help with putting together phylogenetic trees which can then give evidence of the biological diversity and speciation.  They can date the fossils to group them according to their age and in combination with morphological features of the fossils, they can create the phylogeny.  As for mass extinction, I can think of one specific example: the Permean mass extinction.  There are virtually no fossils found in the estimated age where this supposed extinction occured, so researchers believe that 90-95% of the marine species on Earth were wiped out.  Mass extinction is usually tipped off because of a lack of fossils, instead of the presence of them.