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Darwin doubters have sometimes questioned evolutionary theory by asserting that no “missing link” exists between humans and other primates. But the fossil record shows that there was no instant leap to humanity: rather our species’ physical hallmarks appeared gradually over the past several million years. “Humans did not suddenly come into existence, but we share features with many other [species],” John G. Fleagle, an anatomist at Stony Brook University, has said. Fingernails evolved 54 million years ago (mya) and the opposable thumb 25 mya, for instance. The pelvis shape needed for walking upright as well as the knee appeared more than 3.5 mya, and the foot arch arose around 1.8 mya. Although skull construction was set around 35 mya, brains only ballooned in size between 2 and 1 mya, and the chin dates from around 200,000 years ago. With apologies to Shakespeare’s Hamlet: what a patchwork is a man.
One feature that visibly separates us from most other mammals is our lack of fur. As Nina G. Jablonski explains in our cover story, “The Naked Truth,” the transition of hirsute to hairless helped to set the stage for the emergence of large brains and symbolic thought. The appearance of bare skin was one of a suite of adaptations that allowed our ancestors to thrive on the savanna as grasslands expanded in Africa starting about three million years ago.
Our forebears abandoned their easier foraging habits, traveling longer distances through a tropical landscape to acquire sufficient food to survive. Adding meat to their diets meant more calories, but finding prey also took more work. Their activity level increased and with it their need to dissipate body heat to avoid tissue damage. By 1.6 mya, protohumans had long legs for sustained walking and running. Along with that trait came naked skin and a large number of eccrine sweat glands, which produce moisture that removes body heat through evaporative cooling. The hairs on our head also help to combat overheating, by shielding our big brain from direct sun.
Although the board of editors didn’t plan it this way, many of the other feature articles in this issue also examine changes over time. The connection is most direct in “The Art of Bacterial Warfare,” by B. Brett Finlay, which describes the ancient battle between infectious agents and their human hosts. But other articles also describe “evolution” in various areas.
Whereas Finlay’s article focuses on inner space, for instance, “Cloudy with a Chance of Stars,” by Erick T. Young, looks at outer: how stars arise and change over time, a seemingly simple question that has long puzzled astronomers. “The Prolific Afterlife of Whales,” by Crispin T. S. Little, explores how sunken whale carcasses today—and dinosaurs millions of years ago—support a series of ecosystem oases on the seafloor. Even “Better Mileage Now,” by Ben Knight, looks at how internal-combustion engines are changing, creating improved performance. By explaining such advances, Scientific American strives to fulfill its mission of demystifying a changing world.
This article was originally published with the title Continuum of Change.
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18 Comments
Add CommentHow does she explain that, unlike elephants, pigs, manatees, whales, dolphins, and rhinos, humans are the only mamalian species that became hairless without spending millions of years as an aquatic animal?
Reply | Report Abuse | Link to thisWe did spend millions of years as an aquatic animal. This article is just another piece from the rubbish-bin of academic reactionaries to Desmond Morris' thesis. The Scars of Evolution by Elane Morgan lays it out better than Morris.
Reply | Report Abuse | Link to thisWe were aquatic. We are the only swimming/diving ape besides proboscis monkeys. And what we have completed our transition to - upright posture - proboscis monkeys only do when walking in water.
Alone among the great apes our fat distribution is generalized like other aquatic animals. Alone among the great apes we like the seaside and like to go in the water. Etc.
I do not think these homosapien paleontologists are qualified to speculate on the origons of the human species. Human scientists have proven that our DNA and skeletal structure is even different from the homosapiens...similiar, but noticablely different.
Reply | Report Abuse | Link to thisThey would probably never believe that we arrived here in stasis on an astroid from a nearby star cluster. Go ahead and laugh and pin labels on me, but after you pull your head out of that darkmatter and think a little, you may see and accept the truth.
Look at the precision of some of these ancient sturctures and milliam old computers; like the Mayen calendar. Do you think homosapiens had the knowledge, skill, or machines, at that time, to build these puzzling wonders of the world?
I still find it humorous that evolutionists suppose that upright walking evolved to aid in faster locomotion. Anyone who has ever chased a chimp will know that a lie. Anyone who has tracked the migration of anilams will also know that upright walking isn't condusive to long distances. In short two legs instead of four or two legs and knuckle walking even puts us at a disadvantage. Sorry Evolution once again doesn't wash
Reply | Report Abuse | Link to thisI'm no expert, but I wouldn't knock the evolutionists so fast.
Reply | Report Abuse | Link to thisLife on the savanna was dangerous at best, to get a good view, one must stand to see and avoid predators. Also we were gatherer's, to carry food, early hominids had to master bipedalism, speed is not the issue here, there is not much we can out run.
Carrying food, forced us to become bipedal, and then carrying weapons for defence and hunting became an easy task.
But I do see some validity, in the aquatic hominid theory, the buoyancy of water would assist in the transition. But it's only a theory.
But I'm not buying into, that we arrived here in stasis on an astroid from a nearby star cluster.
Growing hairs requires a lot of aminoacids, and so hairy people have higher food intake needs than hairless, equally as fair skinned and blonde people uses less aminoacids in building hair and skin pigment, the skin colour loss giving an additional advantage in not so sunny environments, as sun produced Vit D has many important physiological roles. Saving always pays
Reply | Report Abuse | Link to thisSciAm: You people must be wicked smaat...
Reply | Report Abuse | Link to thisIt's hilarious how many people keep attributing the "aquatic ape" hypothesis to Desmond Morris. Have any of you actually read The Naked Ape? He only briefly references the hypothesis as proposed by Alister Hardy. Elaine Morgan read The Naked Ape, saw the reference to Hardy's hypothesis, and felt that the explanation of us evolving as hairless, sweating, long distance savanna hunters was too male centric and didn't explain why women are also relatively hairless and also sweat. Hmm..probably for the same reason men have nipples even though they don't produce milk for young, because we're the same species so we've developed the same structures and organs which when necessary do develop differently based on hormonal cues up to adulthood. Difficult to imagine why sweat glands and relative lack of hair would need to be hormonally suppressed in females. So no, not buying the aquatic ape hogwash.
Reply | Report Abuse | Link to thisBut keep the nonsense coming you whackos!
Our ancestors had the same brain as us. Why should they not be just as clever?
Reply | Report Abuse | Link to thisAlthough I completely believe evolution is how species adapt/change, for a long time I haven't bought the "expanding grassland" theory of EVERY difference b/w H sapiens and other apes. I think a semi-aquatic period that involved a lot of seafood (high quality protein at low risk of being eaten), catching fish and maybe even primitive fish farming, may explain several things. It may take time, research and scientists from other fields to finally sort this out.
Reply | Report Abuse | Link to thisI remember when the asteroid hypothesis of dinosaur extinction was derided as "goofball" science when I was in college - but it's now largely accepted. It seems that scientific thought also evolves, and those ideas which last the longest and produce the most viable progeny (valid, repeatable outcomes) tend to win out.
I wonder if we haven't got the question backwards. Did humans become hairless or did the unprotected apes that lost their hair have to become smarter, and human, in order to continue to survive? I also wonder if this does not tie into another story here that talks about humans facing an extinction about a milliion years ago. Major stresses like these would seem to me to have the potential to induce some evolutionary changes. And the ones best suited for the new conditions or those that were best able to adapt, survived.
Reply | Report Abuse | Link to thisWell done, Conrad. You caught and questioned presumptions in the question that most of us (incl. me) missed. It's a little sad for SciAm when the comments get me thinking more than the article did - but I'm happy for it either way.
Reply | Report Abuse | Link to thisPeople like Sacha Baron Cohen have a shocking look for many human races, and are also costly in food and energy demands compared to hairless persons, an anti-ecological trait. When invading Russia, Napoleon noticed that bald people died sooner under freezing conditions, scalp hair giving protection for heat losses. The only advantage in being furry is that when aminoacid levels in blood go down, and growing hair is a constant challenge on AA pools, people become aggressive, and this can be an advantage in some circunstances. Somebody seems having shown that "macho" men, get on average higher salaries than others
Reply | Report Abuse | Link to thisAn argument can be made that humans losing their bodily hair was aided by our development as long distance runners. Compared to other species we are much better suited as distance runners - our bipedal stance, respiration, etc. - and having less hair means we sweat better, thermoregulate more properly and can sustain a good running pace for hours. Many arguments exist for an evolutionary advantage to distance running - we would chase down our prey to exhaustion and could be sustained that way. We could also outrun predators due to both our enlarged brains and running abilities and migrate to more bounteous areas by running longer distances. See a 2009 paper written by Dr. Lieberman et al. from Harvard for a lot more info about other reasons parts of the body (legs, arms, head, etc.) are the way they are because we evolved as runners. Combine that with the swimming primate and amino acid saving theories and you have some good arguments for why we're hairless.
Reply | Report Abuse | Link to thisNina Jablonski fails to mention:
Reply | Report Abuse | Link to thisThe second-sweatiest priimate, the patas monkey, uses sweat
cooling withoiut shedding its hair.
If greater size explains the nakedness of elephants and rhinos, why no naked buffalos?
if whales became naked to swim faster by "reducibg ndrag", what about the hippopotamus?
If we became naked to run fast after prey, why didn't the prey have to do the same?
Why would head hair keep the brain cool, and back hair make the back hot?
She suggests our ancestors shed twelve litgres a day in sweat. Where were the crocodiles when they they were thirstily imbibing twelve litres a day by the rivers and water-holes?
My beef is with people who put the cart before the horse: "Carrying food, forced us to become bipedal" -- that's ridiculous, supposing there was a Caesar or Hitler with a whip forcing apes to carry food and presto, suddenly they stood up and had arms and saw that they were naked.
Reply | Report Abuse | Link to thisDarwinism is about advantage. It still is. I remember an excellent science fiction short story, a re-visit of "In the land of the blind, the one-eyed man is king." No, in the land of the blind, a one-eyed man is a mutant. The story is set on a hot planet, the natives come out only at night, their houses are windowless adobe. Our astronaut has crashed on this planet. He could not see at night or day and spends the rest of his life being treated as an invalid.
So, it isn't that an ape was trying to carry food and sprouted arms; rather, you had a deformed primate who figured out what to do with his long legs and short arms and in some way proved himself superior, or "more fit", and thus started a new subspecies or species.
"Nina Jablonski fails to mention:" -- a nearly infinite repertoire.
Reply | Report Abuse | Link to this"The second-sweatiest priimate, the patas monkey, uses sweat
cooling withoiut shedding its hair." Yukk! Give that monkey a razor.
"If greater size explains the nakedness of elephants and rhinos, why no naked buffalos?" There were some, but they froze to death. Occasionally any animal will be hairless, a mutation, but is not usually an advantage. Hairless cats, hairless dogs, even a hairless chimpanzee. Some humans are quite hairy.
"if whales became naked to swim faster by "reducibg ndrag", what about the hippopotamus?" I have no idea why whales chose to become naked and neither do you. Maybe it just happened that way, jumping genes, mutation, that sort of thing. Quite likely the whale did not notice although his mates may have teased him a bit.
"If we became naked to run fast after prey, why didn't the prey have to do the same?" Obviously they chose not to. Anyway, seems unlikely that Ogg decided one day to shave so that he could run faster. More likely Ogg was born hairless, he was teased mercilessly and had to run to escape the torment, only then discovering that he could outrun his mates. He never did figure out WHY, but he was glad for it just the same.
"Why would head hair keep the brain cool, and back hair make the back hot?" Neither. Head hair is an insulator; keeps the sun off the top of your head. Your brain is still hot and you need to radiate the heat somewhere, preferably an area with broad surface and less vulnerable to attack. Chest also radiates but is vulnerable to frontal assault.
When I visit the desert, I am covered head to toe with white or light cotton. I am protected from sunlight and radiant heat. What I must not do is build up a lot of metabolic heat at the same time. Tourists frequently wear shorts and short sleeve shirts in the desert; they get overheated much more rapidly than I do.
"She suggests our ancestors shed twelve litgres a day in sweat. Where were the crocodiles when they they were thirstily imbibing twelve litres a day by the rivers and water-holes?" Australia.
Disclosure: I believe in evolution and I believe in God. Exactly what each word means is itself "evolving" for me as I continue to learn everything that is learnable in my lifetime. I encourage balance between belief and skepticism. Healthy skepticism is cautious and thorough; good and true books being stored on the shelves of one's mind. Unhealthy skepticism is "blind disbelief" and discards everything.
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