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In fact, evolution can produce features that, while helping an individual, harm the species as a whole.
As evolution predicts, we never see adaptations that benefit the species at the expense of the individual—something that we might have expected if organisms were designed by a beneficent creator.
Such random change in the frequency of genes over time is called genetic drift. It is a legitimate type of evolution, since it involves changes in the frequencies of alleles over time, but it doesn’t arise from natural selection.
The almost complete absence of genes producing the B blood type in Native American populations, for example, may reflect the loss of this gene in a small population of humans that colonized North America from Asia around twelve thousand years ago.
Genetic drift can change the frequencies of alleles regardless of how useful they are to their carrier. Selection, on the other hand, always gets rid of harmful alleles and raises the frequencies of beneficial ones.
Even a tiny advantage, so small as to be unmeasurable or unobservable by biologists in real time, can lead to important evolutionary change over eons.
features whose evolution we don’t understand may reflect only our ignorance rather than genetic drift.
After a long period of cures and medical optimism, TB is once again becoming a fatal disease. This is natural selection, pure and simple.
Now, seventy years later, more than 95 percent of staph strains are resistant to penicillin.
when a population encounters a stress that doesn’t come from humans, such as a change in salinity, temperature, or rainfall, natural selection will often produce an adaptive response.
The Beak of the Finch: A Story of Evolution in Our Time),
Natural Selection in the Wild, a book by the biologist John Endler, documents over 150 cases of observed evolution, and in roughly a third of these we have a good idea about how natural selection was acting.
Indeed, we know of no adaptations whose origin could not have involved natural selection.
Philip Gingerich at the University of Michigan showed that rates of change in animal size and shape during laboratory and colonization studies are actually much faster than rates of fossil change: from five hundred times faster (selection during colonizations) to nearly a million times faster (laboratory selection experiments).
Nevertheless, the eye evolved very quickly: the entire process from rudimentary light-patch to camera eye took fewer than 400,000 years.
the earliest animals with eyes date back 550 million years ago,
In reality, eyes have evolved independently in at least forty groups of animals.
Traits that differ between males and females of a species—such as tails, color, and songs—are called sexual dimorphisms, from the Greek for “two forms.”
if traits differ between males and females of a species, the elaborate behaviors, structures, and ornaments are nearly always restricted to males.
“It is certain that with almost all animals there is a struggle between the males for the possession of the female.”
In his exhaustive book Sexual Selection, Malte Andersson describes 232 experiments in 186 species showing that a huge variety of male traits are correlated with mating success, and the vast majority of these tests involve female choice.
For males, mating is cheap; for females it’s expensive.
In more than 90 percent of mammal species, a male’s only investment in offspring is his sperm, for females provide all the parental care.
Selection then favors genes that make a male promiscuous, relentlessly trying to mate with nearly any female.
Females must make each opportunity count by choosing the best possible father to fertilize their limited number of eggs. They should therefore inspect potential mates very closely.
Almost all females, on the other hand, will eventually find mates.
We see this reversal in those most appealing of fish, seahorses, and their close relatives the pipefish. In some of these species the males rather than the females become pregnant!
Here, the male-female difference in reproductive strategy is reversed. And just as you might expect under sexual-selection theory, it is the females who are decorated with bright colors and body ornaments, while males are relatively drab.
Evolutionary theory shows that females should prefer any trait showing that a male will be a good father.
You can imagine many features that could show a male has genes for greater survival, or a greater ability to reproduce. Evolutionary theory shows that in these cases, three types of genes will all increase in frequency together: genes for a male “indicator” trait reflecting that he has good genes, genes that make a female prefer that indicator trait, and of course the “good” genes whose presence is reflected by the indicator. This is a complex scenario, but most evolutionary biologists consider it the best explanation for elaborate male traits and behaviors.
Offspring from long-callers grew faster and survived better as tadpoles, were larger at metamorphosis (the time when tadpoles turn into frogs), and grew faster after metamorphosis. Since male gray tree frogs make no contribution to offspring except for sperm, females can get no direct benefits from choosing a long-calling male. This test strongly suggests that a long call is the sign of a healthy male with good genes, and that females who choose those males produce genetically superior offspring.
If a mutant male appeared with a patch of red on his breast, he might be preferred by females simply because of this preexisting preference.
Maybe Darwin’s theory of animal aesthetics was partly correct, even if he did anthropomorphize female preferences as a “taste for the beautiful.”
Animal Species and Evolution,
A better title for The Origin of Species, then, would have been The Origin of Adaptations: while Darwin did figure out how and why a single species changes over time (largely by natural selection), he never explained how one species splits in two.
In sexually dimorphic species, as we saw in the last chapter, males and females can look very different.
early museum researchers working on birds and insects often misclassified males and females of a single species as members of two different species.
Mayr defined a species as a group of interbreeding natural populations that are reproductively isolated from other such groups.
How do you get one species to divide into two, separated by reproductive barriers? Mayr argued that these barriers were merely the by-products of natural or sexual selection that caused geographically isolated populations to evolve in different directions.
Different mutations affecting male behaviors or traits could appear in different places—say, longer tail feathers in one population and orange color in another—and sexual selection might then drive the populations in different directions. Eventually, females in one population would prefer long-tailed males, and females in the other, orange males. If the two populations later encountered each other, their mating preferences would prevent them from mixing genes, and they would be considered different species.
species are evolutionary accidents.
Like species, languages can diverge in isolated populations that once shared an ancestral tongue.
Languages are like biological species in that they occur in discrete groups rather than as a continuum:
The Language Instinct.
starting with one ancestor, it takes roughly between 100,000 and five million years to evolve two reproductively isolated descendants.
Genetic barriers between groups became strong enough to completely prevent interbreeding after about 2.7 million years of divergence.
we can still understand how they work by finding snapshots of the process at different evolutionary stages and putting these snapshots together into a conceptual movie.
We see young species, descended from a common ancestor, on either side of geographic barriers like rivers or the Isthmus of Panama, and on different islands of an archipelago.
geographic isolation of populations is the most common way that speciation takes place.
Farkli turde canlilarin evrimlesebilmesinin nedeni cografik engellerdir: deniz, nehir, dag gibi.
why a creator would produce similar species of birds or lizards on continents but not on isolated islands.
