give any two points of difference between Darwinism and Neodarwinism?
Answers
The major difference involves the incorporation of Mendelian genetics. Neo-Darwinism incorporates recent discoveries of inheritance and genes, explains why variations occur, considers populations rather than individuals and follows the success of individual genes rather than organisms.
Darwin didn't know about heritable factors being discrete units of inheritance called genes. In the past it was thought that traits could mix and were a spectrum but we now know that genes come in discrete units and blending does not occur. It may appear that traits from mating pairs "blend" e.g. red flowers mating with white flowers and producing pink flowers. But, this is really just because the pink flowers have red and white pigments, each because of a pigment provided by a particular gene. The pink flowers have 1 red gene + 1 white gene not 1 pink gene. Plus, genetic information is not lost in these matings. In this example, two pink flowers could have offspring that are all red or all white flowers.
The cause of variations is mutation combined with differential reproductive success (natural selection), which is just a fancy way of saying some critters have more babies than others. Darwin thought that a creature could develop a trait in it's lifetime because of necessity and pass that trait on to its offspring. An example of this would be someone working out and growing really big muscles and then having a child that just naturally has huge muscles and growing from there. This is not the case. Instead, the source of genetic variation in a population is cause by mutations or "errors" in the genetic sequence of an organism that gets passed on to its offspring. I think you read my other answer explaining mutation and recombination and how those create genetic diversity in different ways. Keep in mind that environment absolutely can affect phenotypic expression of genes (see epigenetics) but this doesn't actually change the genome of that organism. An exception is genetic damage due to carcinogens such as radiation or other toxic chemicals that damage the DNA itself and cause cancer. Anyway, if these mutations are neutral or beneficial, they will be passed on. A creature can't develop a useful trait on purpose; evolution doesn't look ahead. If a mutation makes a creature better able to survive, it has more offspring. That creature's relative may have a mutation that causes it to have less offspring or die before having any. The first creature's genes will become more common and the other's will disappear from the gene pool. Eventually, the descendants of the original organism will have a wide variety of traits but will be separated from their cousins by extinction. This isn't my best explanation of natural selection and speciation but it'll do.
Also, Darwin only considered the success of individual organisms rather than populations of organisms. Darwinian "survival of the fittest" doesn't explain seemingly altruistic acts such as helping other members of your species or even of another species. Giving your sister some food doesn't help you survive so Darwin wouldn't expect to see such acts in nature. Neo-Darwinian evolution does explain this, however. Giving your sister some food makes them more likely to survive. Since you likely share roughly the same genes, these genes will be more likely to survive and get passed on. Cooperation will also be reciprocated within a familial group since all of the organisms in that group share approximately the same genes and therefore will be inclined towards similar behaviors. Mutually beneficial symbiotic relationships between species is even possible with Neo-Darwinistic evolution. This is co-evolution. I help you survive, you help me survive, we both survive and our descendants continue the same partnership. Genes can survive in a group despite the death of any one organism so, when looking at evolution and natural selection, we need to look at populations not just individuals. This leads to my last point which is the survival of genes.