|
1630
|
|
William Harvey concluded that
plants and animals alike reproduce in a sexual manner: males contribute
pollen or sperm; females contribute eggs. However, two hundred years
passed before the first mammalian eggs were observed.
|
| 1665 |
|
Robert Hooke observed the cellular structure of cork. But it wasn't
until almost 200 years later that scientists, armed with better microscopes,
realized that all of us are divided into very small compartments.
|
| 1668 |
|
Francesco
Redi (born 1626) used an experiment to compare two competing ideas
that seek to explain why maggots arise on rotting meat. He observed
that meat covered to exclude flies did not develop maggots, while
similar uncovered meat did. This is regarded as the first disproof
of spontaneous generation, and was among the first uses of a controlled
experiment. |
| 1748 |
|
Turbevill
Needham heated various soups or "infusions" all of which eventually
teem with life; he concluded "there is a vegetative Force in every
microscopical Point of Matter..." in support of the idea of spontaneous
generation. |
| 1859 |
|
Charles Darwin (1809 - 1882) hypothesized
that animal populations adapt their forms over time to best exploit
the environment, a process he referred to as "natural selection."
As he traveled in the Galapagos
Islands, he observed how the finch's beaks on each island were adapted
to their food sources. He theorized that only the creatures best
suited to their environment survive to reproduce.
Darwin also inferred the process
of adaptive radiation, wherein populations spread out into the environment
to exploit specialized resources. Charles Darwin's landmark book,
"On the Origin of Species," was published in London. It effectively
drowned out all other scientific voices, including Mendel's, for
decades.
|
| 1865 |
|
Gregor Mendel (1822 - 1884), an
Augustinian monk, presented his laws of heredity to the Natural
Science Society in Brunn, Austria. Mendel proposed that invisible
internal units of information account for observable traits, and
that these "factors" - which later became known as genes - are passed
from one generation to the next.
Mendel's work remained unnoticed,
languishing in the shadow of Darwin's more sensational publication
from five years earlier, until 1900, when Hugo de Vries, Erich Von
Tschermak, and Carl Correns published research corroborating Mendel's
mechanism of heredity.
|
| 1868 |
|
Fredrich Miescher, a Swiss biologist,
successfully isolated nuclein, a compound that includes nucleic
acid, from pus cells obtained from discarded bandages. Meischer,
however, was not investigating heredity. Instead, he was trying
to identify the chemicals in cells.
Several generations of scientists
would pass before the connection would be made between the DNA found
by Miescher and the laws of heredity described by Mendel just three
years previously.
|
| 1870 |
|
W.
Flemming discovered mitosis.
|
| 1871 |
|
DNA was isolated from the sperm of trout found in the Rhine River.
Darwin published "The Descent of Man and Selection Relation to Sex"
applying his ideas of evolution to the origins of humans. |
| 1875 |
|
Charles Darwin proposed the idea of "gemmules" as a mechanism of inheritance.
|
| 1879 |
|
In
Michigan, Darwin-devotee William James Beal developed the first clinically
controlled crosses of corn in search of colossal yields. Albrecht
Kossel began his studies of nuclein, leading to his discovery of nucleic
acids. |
| 1882 |
|
Walther Flemming reported his discovery of chromosomes and mitosis. |
| 1883 |
|
August Weismann, a German physiologist, coined the term "germ-plasm."
He asserted in his book of the same name that the male and female
parent contribute equally to the heredity of the offspring; that sexual
reproduction thus generates new combinations of hereditary factors;
and that the chromosomes must be the bearers of heredity. His books
were translated promptly into French and English. |
| 1887 |
|
Edouard-Joseph-Louis-Marie
van Beneden discovered that each species has a fixed number of chromosomes;
he also discovered the formation of haploid cells during cell division
of sperm and ova (meiosis). |
