Encyclopedia of Evolution.pdf - Online Reading Center

Hardy-Weinberg equilibrium
with his sister Naomi and studied their genetics. Here he
discovered for himself a phenomenon now known as genetic
linkage, in which two different characteristics are passed
down together from one generation to another because they
are linked on the same chromosome (see Mendelian genetics).
With a father so fearless, and who researched such
diverse phenomena, and with his own childhood experience
in scientific research, it is little wonder that J. B. S. Haldane
made important contributions to more than one field of
scholarship.
J. B. S. Haldane fought in World War I. After the war he
attended Oxford and majored in classics, and for the rest of
his life he would recite long passages of Milton, or of Homer
in the original Greek. However, in his spare time, he also
studied physiology, mathematics, evolution, and the origin of
life. He became so accomplished in these and other scientific
fields that they became his principal work when he joined the
faculty of Oxford:
• Physiology: Following in the footsteps of his father, J. B.
S. Haldane studied the reaction of the human body to
extreme conditions such as high pressures that would be
experienced in submarines. He built a chamber for studying
the effects of pressure on human volunteers, including
himself. One time, when he was in this chamber, rapid
decompression caused the fillings in his teeth to pop out.
Another time, he went into seizures from experiencing high
oxygen pressure. Due to the importance of this research to
understanding the human body under combat conditions,
he received Admiralty funding for the work.
• Mathematics and evolution: Haldane became interested
in Darwinian evolution and in Mendelian genetics. During
the 1920s, many scientists (such as DeVries, Hugo)
considered Darwinism and Mendelism to contradict one
another. Haldane’s proficiency with mathematics allowed
him to make important contributions, along with others
(see Fisher, R. A.; Wright, Sewall), to a theoretical
reconciliation of the two. Haldane’s The Causes of Evolution
was published in 1933. The mathematical works
of Haldane, Fisher, and Wright were essential precursors
to the modern synthesis proposed by biologists (such
as Dobzhansky, Theodosius; Mayr, Ernst; Simpson,
George Gaylord). He published a paper in 1924 in
which he calculated the effects of natural selection on
the peppered moths. This paper astonished the scientific
community because it showed that natural selection could
be an extremely powerful force. He also took the first
steps in working out the mathematics of the evolution of
altruism. He pointed out that an individual’s genes could
be passed on to the next generation by his own offspring,
or by the offspring of his relatives. Therefore an individual
who sacrificed himself to save two of his brothers
would have just as high an evolutionary fitness as if he
had his own children, since he was related by a genetic
factor of one-half to his brothers. The same would be true
of a man who sacrificed himself to save eight cousins.
“I would die for two brothers or ten cousins,” said Haldane—using
ten, not eight, just to be on the safe side.
• Origin of life: Haldane was, along with the Russian chemist
Aleksandr I. Oparin, the principal defender of the idea
that the first cells evolved in a soup of chemicals in the primordial
oceans of the Earth, before oxygen became abundant
in the atmosphere (see life, origin of). This theory
is now called the Oparin-Haldane Hypothesis.
Haldane published two dozen books and hundreds of
articles. Many of the articles were in a communist newspaper,
The Daily Worker. He especially enjoyed attacking religious
people. He was particularly incensed at his fellow Oxford
faculty member and famous defender of Christianity, Clive
Staples Lewis. One of his newspaper articles was “Anti-Lewisite,”
in which he compared C. S. Lewis to the poison gas
used in the Great War. In 1924 he presented a paper before
the Heretics Society in which he speculated about the possibility
of ectogenesis (birth outside the body). Although he was
ridiculed for these ideas, it was his intellectual fearlessness
that enabled him to make so many important contributions
to evolutionary science. Haldane died December 1, 1964.
Hardy-Weinberg equilibrium See population genetics.
hominid See hominin.
hominin Hominin is the term that is preferred by most scientists
for the unique evolutionary lineage of human ancestors,
since the divergence of the human from the chimpanzee
lineages. The previously employed term hominid referred to
the family Hominidae, as opposed to the chimpanzee family
Pongidae. Because of the genetic closeness of humans and
chimpanzees, both are now classified in the family Hominidae.
The term hominid, therefore, now refers to humans
and chimpanzees (which includes the pygmy chimpanzee, or
bonobo; see primates). The common ancestor of humans
and chimps would look like a chimp to a human observer,
because chimps have undergone fewer evolutionary changes
of anatomy than have humans since the time of the common
ancestor.
Homo sapiens is the only surviving hominin. This
simple fact of history has permitted humans to consider
themselves entirely separate from “the animals.” Human
uniqueness is of recent origin; for all but the last 20,000
years, two or more species of hominins have coexisted.
Hominin evolution corresponds closely to, and may
have been stimulated by, climatic changes in Africa. When
ice ages occurred in northern latitudes, droughts as well as
cooler temperatures occurred in Africa, transforming forests
into savannas. Periods of drier climate occurred about five
million, 2.7 million, and 1.8 million years ago, which corresponded
to the origin of hominins, of the genus Homo, and
of advanced Homo (the immediate ancestors of H. sapiens),
respectively. Part of the hominin adaptation to new climates
was through technology. Technology (such as clothes and
fire) allowed members of the genus Homo to live in cold climates.
Many scientists consider this to be the first and only
time that a species has migrated to an entirely different climate
without evolving into another species.