Modern Synthesis in Evolution

multiplied. There are even MRSA strains that have become resistant to the antibiotics used to kill them as well—leading to even more resistant “superbugs” in the environment. This is also seen in insect populations that have become resistant to pesticides.

Natural selection can only result in evolutionary changes if the new traits and new species coming out of it have differences in fitness that allow them to survive. Things like genetic recombination, changes in karyotype number, and changes in the size and arrangement in chromosomes may have an advantage or a disadvantage to the organism. Some genetic changes have no effect because there is synonymous substitution of a DNA base pair or because the change occurred in non-coding DNA. Most changes in regulatory genes in the DNA will be lethal to the embryo or will have a mutation that doesn’t affect survival.

MODERN SYNTHESIS IN EVOLUTION

Evolutionary theory did not end with Darwin. Remember, he knew nothing of genetics and of the theories of Gregor Mendel and others that have come to understand the way genetics and evolution work. Darwin was successful in convincing most biologists since then that evolution actually occurred but wasn’t as successful in convincing scientists that natural selection was how evolution occurred. There were other theories, such as Lamarckism (inheritance of acquired characteristics), orthogenesis (the presence of progressive evolution), saltationism (evolution by jumps in speciation), and mutationism (evolution driven by mutations).

Remember that Darwin believed in blending inheritance rather than gene-related inheritance. With blending inheritance, any new generation of changes in an organism would be diluted out by half with each successive generation. This negated the idea that blending actually took place. The other theory of Darwin, that of pangenesis, was wrong. This was the theory that gemmules were flowing from all parts of the reproductive body in order to create the gamete.

Weismann argued the theory of germ plasm. He said that there were two aspects of an organism: germ plasm and the soma (or the rest of the body). Only the germ plasm

determined what was inherited. This turned out, of course to be true. Germ plasm or reproductive cells influence the offspring. He proved his theory by cutting the tails off of mice and proving that the baby mice grew normal tails. In this way, the body or soma did not influence the offspring.

Individuals who believed in Mendelian theory rejected the ideas of natural selection—a problem that was solved by researchers who studied and developed the ideas of population genetics. Evolutionary genetics applied genetics to natural populations. Over time, there have been many other additions to theories of evolution that add to the natural selection theories.

The modern synthesis theory of evolution indicates that populations contain genetic variation that is random and is from random mutation and from recombination. Natural selection, gene flow, and random genetic drift produces population variances over time. Diversification into different species comes when there is reproductive isolation among populations that give rise to differences that ultimately become different species.

The main differences between Darwinism and modern synthesis in evolution include these three things:

• In modern synthesis, there are several mechanisms in evolution besides natural selection, such as genetic drift.

• There are heritable units called genes (which did not exist in Darwin’s theories) with variations in a population occurring because of the numbers of different alleles in the population.

• Speciation usually happens due to the gradual accumulation of small genetic changes with macroevolution being microevolution over a long period of time.

The thing most controversial is the idea that gradual changes in genetic makeup cause speciation. This is because fossil records do not show gradual changes in organisms but a more rapid speciation occurring. This is called “punctuated equilibrium”, which is believed to be a fact that may or may not directly oppose the microevolution-tomacroevolution theory. In other words, both things may be in play at the same time.