Environmental Engineering Reference
In-Depth Information
netic trait to predominate—hardly a desirable solution
to the environmental problems we face.
Fruit and seed eaters
Insect and nectar eaters
Greater Koa-finch
Kuai Akialaoa
Two Commonly Misunderstood
Aspects of Evolution
Evolution is about leaving the most descendants,
and there is no master plan leading to genetic
perfection.
There are two common misconceptions about bio-
logical evolution. One is that “survival of the fittest”
means “survival of the strongest.” To biologists,
fitness
is a measure of reproductive success, not strength.
The fittest individuals are those that leave the most
descendants.
The other misconception is that evolution involves
some grand plan of nature in which species become
more perfectly adapted. From a scientific standpoint,
no plan or goal of genetic perfection has been identi-
fied in the evolutionary process.
Amakihi
Kona Grosbeak
Crested Honeycreeper
Akiapolaau
Maui Parrotbill
Apapane
Learn more about two special types of natural selection,
one stabilizing and the other disruptive, at Environmental
ScienceNow.
Unkown finch ancestor
Figure 4-6
Natural capital:
evolutionary divergence of honey-
creepers into specialized ecological niches. Each species has
a beak specialized to take advantage of certain types of food
resources.
4-4 SPECIATION, EXTINCTION,
AND BIODIVERSITY
Speciation: How New Species Develop
A new species arises when members of a
population are isolated from other members for so
long that changes in their genetic makeup prevent
them from producing fertile offspring if they get
together again.
Under certain circumstances, natural selection can
lead to an entirely new species. In this process, called
speciation,
two species arise from one. For sexually re-
producing species, a new species is formed when
some members of a population can no longer breed
with other members to produce fertile offspring.
The most common mechanism of speciation (es-
pecially among animals) takes place in two phases:
geographic isolation and reproductive isolation. In
geographic isolation,
different groups of the same pop-
ulation of a species become physically isolated from
one another for long periods. For example, part of a
population may migrate in search of food and then be-
gin living in another area with different environmental
conditions, as shown in Figure 4-7. Populations can be-
come separated by a physical barrier (such as a moun-
tain range, stream, lake, or road), by a change such as a
volcanic eruption or earthquake, or by a few individu-
als being carried to a new area by wind or water.
First,
a change in environmental conditions can
lead to adaptation only for genetic traits already pres-
ent in a population's gene pool. You must have genetic
dice to play the genetic dice game.
Second,
even if a beneficial heritable trait is present
in a population, the population's ability to adapt may
be limited by its reproductive capacity. Populations of
genetically diverse species that reproduce quickly—
such as weeds, mosquitoes, rats, bacteria, or cock-
roaches—often adapt to a change in environmental
conditions in a short time. In contrast, species that can-
not produce large numbers of offspring rapidly—such
as elephants, tigers, sharks, and humans—take a long
time (typically thousands or even millions of years) to
adapt through natural selection. You have to be able to
throw the genetic dice fast.
Here is some
bad news
for most members of a pop-
ulation. Even when a favorable genetic trait is present
in a population, most of the population would have to
die or become sterile so that individuals with the trait
could predominate and pass the trait on. As a result,
most players get kicked out of the genetic dice game
before they have a chance to win. Most members of the
human population would have to die prematurely for
hundreds of thousands of generations for a new ge-
