IMHO - Any animals on this planet could eventually become the humans.
That some primates were first to converge upon the “Humanoid Form” on
this planet is not very good evidence for the hypothesis that only one
species can ever become the humans.
Convergent Evolution
“...Convergent evolution is the independent evolution of similar
features in species of different lineages.
Convergent evolution creates analogous structures that have similar
form or function but were not present in the last common ancestor of
those groups...
...In morphology, analogous traits arise when different species live in
similar ways and/or a similar environment, and so face the same
environmental factors. When occupying similar ecological niches (that
is, a distinctive way of life) similar problems can lead to similar
solutions...”
Reference Article: A brief overview of convergent evolution.
Dolphins and sharks separately evolved very similar physical features
that have helped them become successful marine predators.(Image credit: Shutterstock)
Convergent evolution is when different organisms independently evolve
similar traits. For example, sharks and dolphins look relatively similar despite being
entirely unrelated. Sharks are egg-laying fish with the deadly ability to sniff out blood in
the water, while dolphins are curious mammals that navigate by making
clicking sounds and listening for their echoes. Those differences aren't
too surprising, considering that the duo's last common ancestor swam the
seas some 290 million years ago.
From that ancient common ancestor, one lineage struck out on land and
evolved into mammals, including the wolf-like Pakicetus, which would later return to the water and evolve into whales and
dolphins. Another lineage stayed put in the ocean, undergoing tweaks to
become the modern shark. Yet despite their winding paths, both animals
ended up in similar evolutionary niches: streamlined swimmers with
smooth skin and water-slicing fins ideal for chasing down
prey.
Each of Earth's habitats presents its own challenges. Sometimes,
different species develop the same solution to the same problem.
Biologists call this process — when two organisms share characteristics
that they didn't jointly inherit from a common ancestor — convergent
evolution.
Convergent vs. divergent evolution
The classical examples of evolution, such as Darwin's finches, demonstrate the opposite process:
divergent evolution. Popularized in the late 1800s by American missionary and naturalist J. T. Gulick, the term
describes one single species becoming many to fit different roles in a
given setting. Among the Galápagos finches, for instance, beak shape changed (or diverged) to better
match the different types of food available on various
islands.
By contrast, convergent evolution happens when species start out distinct
and then grow more similar. For instance, imagine you were to dump an
assortment of parrots and toucans onto the same island. Individuals with
beaks that were inefficient for snagging bugs might go hungry and die
without passing their bad-beak genes on to offspring. But the parrots and
toucans lucky enough to have beaks that were more successful at grabbing
bugs, would survive and pass on the genes for those bug-nabbing beaks.
Generations later, the descendents of both species could converge on the
same beak shape, as it's the most successful design for surviving in that
habitat.
The concepts underlying convergent evolution can be traced back to
Richard Owen, a British biologist who, despite doubting Darwin's theory of
evolution, in the mid 1800s pointed out the difference between animals with body parts that are built similarly
(homologues) and body parts that just have similar purposes (analogues). A
dolphin's fin and a human hand, for instance, are homologous because they
have the same bone structure, despite their functions diverging since our
last common ancestor. On the other hand, the dolphin's fin is an analogue
of the shark's fin — they have the same purpose but different shapes
because they evolved independently (and convergently).
Examples of convergent evolution abound, but they're easiest to see in
familiar animal species. For example, giant pandas have body parts resembling thumbs, which the animals use to grip
bamboo, as biologist Stephen Jay Gould described in Incorporating Nature Magazine in the 1970s. Both humans and octopuseshave camera-like eyes with an iris, a lens and a retina — all essential
parts of an imaging device. And both bats and birds have wings.
As similar as these traits may appear, a closer look reveals their
independent origins. A panda paw, with its five digits and a thumb-like,
stumpy bone jutting from its palm, looks nothing like a human hand. That
makes sense, given that primates evolved their opposable thumbs about 50
million years ago while pandas did it less than 20 million years ago (and our last common ancestor lived 65 million to 90 million years ago). Similarly, the unique wiring of octopus eyes means they lack blind
spots. And whereas bird wings are more akin to "arms," bat wings look more
like "hands" with spindly fingers. To use Owen's categories, these are analogous, not homologous, body
parts.
The driver of convergent evolution is the availability of specific roles
offered by the environment. Oceans cast swift-swimming predators, be they
sharks or dolphins. The skies need fliers, and creatures that live in or
deal extensively with trees need to be able to grab branches with a tail,
hands or claws.
One of the most dramatic modern-day examples is two whole convergent groups of animals: Australia’s marsupial mammals, who spend their early days in
pouches, and mammals born from placentas, which inhabit the rest of the
world. Because Australia split from the other continents tens of millions
of years ago, its animal species have evolved somewhat independently.
Nevertheless, many niches have been filled by animals that look very
similar to their counterparts in Africa, the Americas and
Eurasia.
For digging underground, there are moles and marsupial moles. For scampering along the ground, mice meet their match in
Australian mulgaras. And for hunting other small mammals, the now-extinct thylacine looked and walked exactly like a dog or a wolf, except it, too,
carried its young in a pouch as a kangaroo does. Because similar roles —
such as the digger, the scamperer and the hunter — existed on both sides
of the ocean, evolution converged on similar designs in both
locations.
The thylacine looks just like a dog, but it evolved many of the same
features independently. (Image credit: Shutterstock)
Is convergent evolution inevitable?
The fossil record reveals that the same patterns have played out across
eons and multiple extinction events, with fins, legs, armored shells and
claws appearing as familiar packages in similar environments. The
phenomenon has led evolutionary biologists to question to what degree evolution is a random process, and to what degree
its outcome is fixed by the environment. As Gould wondered, if we could
replay Earth's history from the beginning, would the tree of life take
the same shape?
Clearly delineating instances of convergent evolution, however, isn't
black and white. It is closely related to parallel evolution, in which a
species finds itself in two different environments and evolves the same
adaptation to each. Starting from the same body plan, evolution moves in
lockstep, not exactly "converging" on a new and similar adaptation. Some
scientists consider marsupial evolution to be parallel with that of placental mammals, while others debate whether
parallel evolution is just a less extreme form of convergent evolution.
Both convergent and parallel evolution serve as reminders that natural
selection has no favored path, no intrinsic arc from basic to advanced.
Species can diverge, converge and diverge again. Evolution insists only
that species adopt survival strategies that work in a given environment,
regardless of where those strategies come from.
Human beings tend think that we—as a species—are very special. We dominate
this planet that we're on, mostly due to our collective intelligence and
ability to adapt to this particular climate. But Harvard biologist Jonathan B.
Losos has an interesting theory that since there are so many Earth-type
planets in our galaxy alone it's possible that there's some humanoid looking
(at least in the bipedal sense) creatures out there, too. In fact, he posits,
they might not even be that far off from the kind we're used to seeing in
Hollywood movies. But he also dips into convergent evolutions, and presents
the opposite side of the argument: evolutionary singletons. If you're
interested in learning more, Jonathan's new book is called Improbable Destinies: Fate, Chance, and the Future of Evolution
Jonathan B. Losos: So this question about the inevitability of evolution, the extent to which the outcomes we see in the world today were destined to occur,
has a number of implications.
I mean just most generally it tells us whether how fated evolution was to occur, how the outcome today was destined in a way.
But it has other implications as well that people have long speculated
about, and that is: what would life be like on other planets if it is
evolved? Would it be like the world today here on Earth or would it be
completely different?
And this question has taken on some increased urgency or at least
interest in recent years because we now realize that there are many
planets out there that are like Earth. We used to think that Earth was
perhaps unique and so perhaps life as we know it is unique, because we’re
the only place that it could evolve.
But quite the contrary we’ve now discovered that there are lots of what
are called “habitable exoplanets”, Some people estimate millions, even
billions just in our own Milky Way galaxy. So if that’s the case, if there
are that many Earth-like planets – and by Earth-like I mean about the same
size, temperature, atmosphere somewhat similar, running water – roughly
similar conditions. If there are really that many Earth-like planets many
people think that it’s very likely that life has evolved on them.
And so the question is what will that life look like? Well there are
those who argue that from the argument of convergent evolution they argue
that species facing the same conditions here on Earth evolved the same
solutions by natural selection.
They extrapolate to say if conditions on other planets are similar to
here then we would see very similar lifeforms, that you arrive on whatever
planet you’ll see animal and plant-like organisms that look very familiar.
Some people have gone so far as to say that, in fact, human type
organisms, humanoids will occur on other planets. So there will be
intelligent beings that if we saw them they would be recognizable which,
of course, is what Hollywood tells us. If you watch almost any
science fiction TV show or movie the intelligent lifeform is bipedal, a
couple of arms, a mouth. Maybe they only have three fingers and pointy
ears and they’re green, but they’re pretty humanoid.
And so some people say yes, that’s actually very likely that humans are a
very successful lifeform here on Earth that we are extremely well adapted
to our environment which ancestrally was occurring on the plains of
Africa. But we have adapted so exquisitely that we now dominate the world.
And so if this is such a good adaptation here on Earth it would similarly
be a good adaptation on another planet and evolution would be likely to
take the similar course. That is the argument that is being made in some
quarters.
Not everyone is convinced by this argument that evolution is
deterministic. We recognize that convergent evolution does occur more than
we used to realize but still it is argued and I agree with this viewpoint,
it’s not inevitable. And the reason is that there are often multiple ways
to adapt to the same environmental circumstance. And so even though
species are faced with the same conditions they may find different ways to
adapt to them. And my favorite example of that has to do with a bird that
everyone knows – the woodpecker. And everyone’s heard the tat-tat-tat of a
woodpecker on a tree or on your garage siding or whatever. People don’t
actually know what the woodpecker is doing.
This is what the woodpecker is doing: It is using its beak to pound on
dead wood, listening for a hollow space, the echo indicating there’s a
hollow space in the wood which is where a grub, a larval beetle or some
other insect is eating the dead wood. And so it listens for the sound of a
hollow space. When it hears it, it then starts tapping very hard –
tat-tat-tat-tat-tat-tat – using its beak as a jackhammer to dig into the,
to chisel or to dig into the deep wood to get to the tunnel. Once it’s
there—the woodpecker has an extremely long tongue. So long, in fact, that
it wraps around its brain case. But it sticks out this long tongue that
has little prickles on it, and the tongue goes in and it snags the grub
which looks like a mealworm or a – snags the grub and pulls it out and
eats it. And that is how they capture the food that they eat.
Well woodpeckers are found on almost every continent in the world.
They’re very successful, but they don’t fly very well across water. They
don’t like to fly across water. And so isolated islands tend not to have
woodpeckers. And in their absence other species have evolved to fill the
same niche.
And the most extreme example of a different way of doing the same thing
is an animal on the island of Madagascar called an aye-aye. Now an aye-aye
is a type of lemur. Now people know lemurs from the TV show Zooboomafoo
and maybe they’ve seen them, the ring-tailed lemur. They hop around, very
cute, and so on.
The aye-aye is not very cute. It’s about the size maybe of a small
housecat and it’s kind of demonic looking. It has these big leathery ears
and these bright yellow eyes and a face that only a mother can love. And
the native people of Madagascar had all kinds of taboos and myths about
them because they look – and they only come out at night. But their most
extreme feature that I think really kind of freaks people out is that
their third finger is long and extremely thin. It looks skeletal, and it
can rotate in any direction. It’s this kind of finger that can wiggle
around.
Anyway, they live the same lifestyle as a woodpecker. They’re looking for
the same grubs in dead wood. But they do it in a completely different way.
Instead of tapping with their peak they tap with their finger. They go
around the wood going tap-tap-tap and their big ears are rotated forward
listening for the sound of an echo.
And when they hear the echo of an empty tunnel they have these teeth that
are – these teeth are kind of sticking out like this, these chiseling
incisors that are very strong. And they bite their way through the wood
and bite into the wood until they get the tunnel. And then once they get
there they then use their finger again. They stick it in there and they
snag the larvae and pull it out. And so they’re doing exactly the same
thing that the woodpecker is doing but they’ve evolved a completely
different set of adaptations. And so that’s just one example of how
species can adapt to do the same thing in very different ways.
And we see many examples of that in the world. Conversely we also see
many examples of species that have no evolutionary parallel. What we call
an evolutionary singleton. That is a species that is very well adapted to
where it lives but no other species has done the same thing. And my
favorite example of that is the duck-billed platypus, this extraordinary
animal in Australia. Now people like to make fun of the platypus but they
don’t realize that the platypus is exquisitely adapted to living in the
streams in eastern Australia. And so it has very lush fur that allows it
to swim in water that’s basically almost at freezing; It has a powerful
tail; It’s got webbed feet for swimming; And then most extraordinarily it
has this duck bill. Now it’s not actually – it kind of looks like a duck’s
bill, but it’s not hard like a duck’s bill.It’s actually
leathery.
But more importantly it’s covered with thousands of little receptors and
these receptors there’s two types of them. One of them can detect slight
variation in ripples of water. And so if something goes swimming by they
can detect it in the water But in addition they have electro receptors.
They can detect very slight electrical discharges. And so when an animal
moves its muscles there’s a little bit of electrical activity, and the
platypus can detect that. And so when it’s swimming under water it closes
its eyes, its ears and its mouth, but based on the receptors on its bill
it can find its way around and it can locate its prey—Remarkable
adaptation to eating crayfish and other food items like that.
Well so, the platypus lives in these streams that are in no way
remarkable. There are streams like that behind the house I grew up in
in St. Louis and they occur around the world. Yet nowhere else has a
duck-billed platypus evolved. Why is it that it evolved in Australia and
nowhere else? Well there are many examples of species extremely
well-adapted but no parallel. Things like the chameleon, elephants,
giraffes, many types of plants. Many evolutionary singletons. In fact,
humans are an evolutionary singleton. If we are so well adapted to our
environment, why didn’t something like us evolve anywhere else in the
world? Why didn’t they evolve on Madagascar or in South America where
monkeys colonized 40 million years ago?
And so this is the counterpart to the argument of evolutionary
determinism and convergence. We could probably make a list just as long of
species that have not converged. And so in many cases species – in many
cases evolution seemed not to be deterministic. That problems posed by
environment may elicit different evolutionary solutions.
That is the argument that is being made in some quarters... Read the
full transcript at
If nuclear war destroys humanity and most of the rest of life, a good
bet for survival in the short term, and for evolutionary ancestry in the
long term, is rats. I have a post-Armageddon vision. We and all other
large animals are gone. Rodents emerge as the ultimate post-human
scavengers. They gnaw their way through New York, London and Tokyo,
digesting spilled larders, ghost supermarkets and human corpses and
turning them into new generations of rats and mice, whose racing
populations explode out of the cities and into the countryside.
When all the relics of human profligacy are eaten, populations crash
again, and the rodents turn on each other, and on the cockroaches
scavenging with them. In a period of intense competition, short
generations perhaps with radioactivity enhanced mutation-rates boost
rapid evolution. With human ships and planes gone, islands become
islands again, with local populations isolated save for occasional lucky
raftings: ideal conditions for evolutionary divergence.
Within 5 million years, a whole range of new species replace the ones
we know. Herds of giant grazing rats are stalked by sabre-toothed
predatory rats.* Given enough time, will a species of intelligent,
cultivated rats emerge? Will rodent historians and scientists eventually
organise careful archaeological digs (gnaws?) through the strata of our
long-compacted cities, and reconstruct the peculiar and temporarily
tragic circumstances that gave ratkind its big break?
If correct, this blend of theory and factual evidence has brought us
closer to an understanding of what is truly distinctive about human change
and why it has been so quick. But
...there remains the nagging question of why man alone took the
fourth great step of organic evolution. The fossil beds are dotted
with the remains of large-brained animals that might have achieved the
same thing earlier.
One hundred million years ago, fifty times farther back in time than
the appearance of the earliest true men comprising Homo habilis, large
ammonites and other archaic relatives of the squid and octopus swam
the Jurassic seas. Their large saucer-shaped eyes surveyed the water
around them, and their tentacles played over the coralline and mud
surfaces of the ocean floor. What might they have been thinking?
Perhaps there was a mind of sorts, and their brains worked to enlarge
and exploit the limited amount of information already stored in their
associative nerve cells.
On the land lived human-sized dinosaurs who walked semierect on their
hind legs. They possessed relatively large brains and might have
manipulated objects in their three-fingered hands. Surely they were
prime candidates for the ascension to high intelligence and
culture.
"Dinosauroids," as the paleontologist Dale Russell has called their
imaginary brilliant descendants, could have beaten man to the tape by
a hundred million years, but the opportunity passed. The great
cepha-lopods and reptiles became extinct, and large-brained mammals
proliferated in their place. Ten times farther back than the origin of
man, the African savanna on which that unique event was to occur
swarmed with numerous elephantlike forms, hyenas, monkeys, and apes.
None managed to enter the self-propelling circuit of gene-culture
coevolution.
Millions of species passing through hundreds of millions of
generations comprised of uncountable billions of individuals, faced by
every conceivable environmental challenge and opportunity, shuffling
astronomical numbers of genes in microevolutionary experimentation -
all this immense ferment managed to push exactly one species across
the threshold and into the autocatalytic climb to advanced culture.
Something very peculiar and powerful must have been holding the
evolving systems back...
Promethean Fire: Reflections on the Origin of Mind by Charles
J. Lumsden & E.O. Wilson - 1983
if evolution is so deterministic, the expectation for life on planets
like our own is clear: Humanoid life forms should evolve and dominate,
just like here.
One thing for certain is that aliens from another world will be shaped
by the same evolutionary forces as here on Earth—natural
selection…
…The researchers suggest that evolutionary theory …can be used to make
some predictions about alien species. In particular, the team argues
that extraterrestrials will undergo natural selection, because that is
the only process by which organisms can adapt to their
environment.
Oxford Study Says Alien Life Would Evolve and Adapt Just Like Life on
Earth
