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Most of the birds that evolved flightlessness did so on islands—the
one of the notable features of remote islands is their lack of mammals and reptiles—species that prey on birds.
Vestigial eyes are also common. Many animals, including burrowers and cave dwellers, live in complete darkness, but we know from constructing evolutionary trees that they descended from species that lived aboveground and had functioning eyes.
There is even a blind cave crayfish that still has eyestalks, but no eyes atop them!
Darwin himself, an avid beetle collector in his youth, pointed out that some flightless beetles still have vestiges of wings beneath their fused wing covers (the beetle’s “shell”).
our appendix is simply the remnant of an organ that was critically important to our leaf-eating ancestors, but of no real value to us.
before the days of surgical removal, more than one person in a hundred died of appendicitis. That’s pretty strong natural selection.
if you can wiggle your ears, you’re demonstrating evolution. We have three muscles under our scalp that attach to our ears. In most individuals they’re useless, but some people can use them to wiggle their ears.
Tiny, nonfunctional wings, a dangerous appendix, eyes that can’t see, and silly ear muscles simply don’t make sense if you think that species were specially created.
about one whale in five hundred is actually born with a rear leg that protrudes outside the body wall.
Modern horses, which descend from smaller, five-toed ancestors, show similar atavisms.
vertebrae normally fused together in our tailbone. Some tails are an inch long, others nearly a foot. And they aren’t just simple flaps of skin, but can have hair, muscles, blood vessels, and nerves. Some can even wiggle!
recent genetic work has shown that we carry exactly the same genes that make tails in animals like mice, but these genes are normally deactivated in human fetuses.
Some atavisms can be produced in the laboratory.
the chicken tissue eventually produced toothlike structures, some with distinct roots and crowns.
birds do indeed have genetic pathways for producing teeth,
You’ll remember that birds evolved from toothed reptiles. They lost those teeth more than 60 million years ago, but clearly still carry some genes for making them—genes that are remnants of their reptilian ancestry.
there should be vestigial genes. In contrast, the idea that all species were created from scratch predicts that no such genes would exist, since there would be no common ancestors in which those genes were active.
A gene that doesn’t function is called a pseudogene.
Virtually every species harbors dead genes, many of them still active in its relatives.
Out of about thirty thousand genes, for example, we humans carry more than two thousand pseudogenes.
Why would a creator put a pathway for making vitamin C in all these species, and then inactivate it? Wouldn’t it be easier simply to omit the whole pathway from the beginning? Why would the same inactivating mutation be present in all primates, and a different one in guinea pigs? Why would the sequences of the dead gene exactly mirror the pattern of resemblance predicted from the known ancestry of these species? And why do humans have thousands of pseudogenes in the first place?
some of these remnants sit in exactly the same location on the chromosomes of humans and chimpanzees. These were surely viruses that infected our common ancestor and were passed on to both descendants. Since there is almost no chance of viruses inserting themselves independently at exactly the same spot in two species, this points strongly to common ancestry.
we still carry a total of eight hundred OR genes, which make up nearly 3 percent of our entire genome. And fully half of these are pseudogenes, permanently inactivated by mutations.
Unneeded genes eventually get bumped off by mutations. Predictably, primates with color vision, and hence greater discrimination of the environment, have more dead OR genes.
Why should dead genes show such a relationship, if not for evolution? And the fact that we harbor so many inactive genes is even more evidence for evolution: we carry this genetic baggage because it was needed in our distant ancestors who relied for survival on a keen sense of smell.
if you look at the DNA sequences of these dead dolphin genes, you’ll find that they resemble those of land mammals. This makes sense when we realize that dolphins evolved from land mammals whose OR genes became useless when they took to the water.
mammals like ourselves still produce a yolk sac—but one that is vestigial and yolkless, a large, fluid-filled balloon attached to the fetal gut (figure 15). In the second month of human pregnancy, it detaches from the embryo.
the platypus of Australia is bizarre in many ways. If ever a creature seems unintelligently designed—or perhaps devised for a creator’s amusement—it would be this one.
platypus genome contains two pseudogenes for enzymes related to digestion. No longer needed, they’ve become inactivated by mutation, but still testify to the evolution of this strange beast.
all vertebrates begin development in the same way, looking rather like an embryonic fish. As development proceeds, different species begin to diverge—but in weird ways. Some blood vessels, nerves, and organs that were present in the embryos of all species at the start suddenly disappear, while others go through strange contortions and migrations.
German embryologist Karl Ernst von Baer became confused by the similarity of vertebrate embryos. Von Baer wrote to Darwin:
the puzzling features of development suddenly made perfect sense under the unifying idea of evolution:
In fish and sharks, then, the development of gills from the embryonic arches is more or less direct: these embryonic features simply enlarge without much change to form the adult breathing apparatus.
in other vertebrates that don’t have gills as adults, these arches turn into very different structures-structures that make up the head.
Sometimes the embryonic gill slits fail to close in human embryos, producing a baby with a cyst on its neck.
In fish and sharks, the embryonic pattern of vessels develops without much change into the adult system. But as other vertebrates develop, the vessels move around, and some of them disappear.
Why do mammals form their heads and faces from the very same embryonic structures that become the gills of fish?
Embryonic and adult fish have six pairs of arches; this is the basic ground plan that appears at the beginning of development of all vertebrates.
During development, the human embryo actually forms three different types of kidneys, one after the other, with the first two discarded before our final kidney appears. And those transitory embryonic kidneys are similar to those we find in species that evolved before us in the fossil record—jawless fish and reptiles, respectively. What does this mean?
one species evolves into another, the descendant inherits the developmental program of its ancestor:
“biogenetic law”
Some say incorrectly that 'Evolution is only a theory'. So, how a law like this happens to use evolution to be a law. That brings us to the conclusion that evolution is also a fact.
Embryonic whales and dolphins form hindlimb buds—bulges of tissue that, in four-legged mammals, become the rear legs. But in marine mammals the buds are reabsorbed soon after they’re formed.
which lack teeth but whose ancestors were toothed whales, develop embryonic teeth that disappear before birth.
Around sixth months after conception, we become completely covered with a fine, downy coat of hair called lanugo.
fetal monkeys also develop a coat of hair at about the same stage of development.
fetal whales also have lanugo,
the idea of perfect design is an illusion. Every species is imperfect in many ways. Kiwis have useless wings, whales have a vestigial pelvis, and our appendix is a nefarious organ.
Perfect design would truly be the sign of a skilled and intelligent designer. Imperfect design is the mark of evolution; in fact, it’s precisely what we expect from evolution.
New parts evolve from old ones, and have to work well with the parts that have already evolved. Because of this, we should expect compromises: some features that work pretty well, but not as well as they might, or some features-like the kiwi wing—that don’t work at all,
