A Thorn Tree And Its Questions

Every day, on our morning walk, the dogs and I pass a terrible tree of thorns.

It is a fearsome tree.  From its trunk far up into its branches, it is bursting with clusters of two- and three-inch long razor-sharp thorns.  If you tried to shinny up the tree, you’d be punctured in a hundred places before you got up into the branches.  It’s the ultimate form of protection against an unwanted tree invasion.

The thorn defense is formidable, but why does it exist?  I always understood thorns, and other biological and botanical defense mechanisms, to develop through the process of evolution and natural selection.  For some reason, trees with thorns must have been better suited to surviving than trees that weren’t bristling with dagger-like projections — but why?  Were there once bears in our sleepy suburban neighborhood, or other large, thick-furred mammals who were a threat to the tree and could only be discouraged by such long, sharp thorns?  And what kind of threat did they pose that required such menacing defenses?  Were they eating something the tree produced, or stripping its bark?

The thorn tree gives no answers.  It just stands there, silent and dreadful, posing its thorny questions with no obvious answers in the vicinity.

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Dogs At The Dawn Of Mankind

Tens of thousands of years ago, both humans and Neanderthals walked the Earth.  Humans, obviously, survived.  Neanderthals — except to the extent they mated with humans and left their genes behind — didn’t. Why did one humanoid species thrive, and the other fail?

New theories posit that the domestication of dogs was a significant part of the secret to success for humans, because dogs helped humans procreate more rapidly and crowd the Neanderthals out.  Paleolithic excavations show significant interaction between humans and dogs, and even indicate that early humans engaged in ritualistic canine worship that included special burials of man’s best friend.  Dogs also helped hunting humans identify and take down their prey and served as beasts of burden, carrying packs as they accompanied their human masters.  All of this allowed humans to eat more, carry more supplies, and survive to reproduce.  Under the laws of natural selection, that gave the humans an ultimately dispositive advantage.

Although the linked article doesn’t mention it specifically, I imagine that the special emotional bond between humans and dogs also was an important part of the humans’ secret.  It’s not hard to imagine dogs helping to keep ancient humans warm at night, providing early warnings when predators approached, and giving the kind of happy companionship that makes people feel good — and makes life a bit more worth living.  It’s one reason why companion dogs have been so successful at hospitals and retirement homes.

It’s hard to imagine Penny and Kasey as pack animals for early hunter-gatherers, but they would have liked the canine worship part.

Farmers On The Move

How did humans stop wandering and start farming?  It’s a crucial question, because farming allowed our ancestors to move beyond itinerant lifestyles into more permanent cultures.  When farming was adopted, and people saw the benefits of having food at the ready, early humans put down roots (pun intended), established long-term structures, and began to defend their territory and protect their possessions.  Civilization as we know it was the ultimate result.

There are two competing theories.  One is that early farmers migrated from their home area and brought their seeds, tools, and farming concepts with them.  The other posits that hunter-gatherers saw the benefits of farming and decided to adopt the farming lifestyle.  The latter theory seems a bit far-fetched, because it’s hard to imagine hardy hunter-gatherers appreciating the benefits of farming and radically changing their transient ways.

Now DNA studies have lent support to the former theory and indicate that farming was spread through Europe by migrants.  The study found that a Stone Age farmer was genetically distinct from hunter-gatherers of that era, and suggests that farming began in the area now known as Turkey and spread north and west, as farmers looked for tillable acreage where their crops could thrive.  The study also suggests that modern Europeans have more genes of the early farmers than they do of the hunter-gatherers.

In short, the farmers won the Darwinian contest.  Their lifestyle might have been boring compared to that of the hardy hunter-gatherers, but with their steady diets, domesticated animals, and focus on building for a better harvest next year, they were more likely to survive and pass down their genes.

Why Did Zebras Get Their Stripes?

Why do zebras have stripes?  It’s a question many kids have asked their parents, and one that many scientists have tried to answer.  Now researchers say they’ve solved the puzzle, and it has to do with . . . flies.

Awful, blood-sucking horseflies, to be precise.  The researchers contend that the patterns of stripes reflect light in a way that makes zebras unattractive to flies.  They conclude that the coats of black and brown horses, poor devils, reflect light in a horizontal way that horseflies love, whereas the coats of white horses don’t reflect light in that way and, as a result, white horses are less troubled by painful fly bites.  When stripes were added, the researchers found, even fewer flies were attracted.  Hence, they believe that stripes evolved to keep flies away.

Color me skeptical.  Much as it sucks to be bitten by blood-sucking flies — and it does — it’s not life-threatening and wouldn’t seem to be a sufficient cause for a significant evolutionary detour.  If it were, we wouldn’t be seeing black and brown horses romping through the pastures of Ohio, and elsewhere.  As I understand evolution, the process of natural selection works only if a genetic variation makes the individual with the variation more likely to survive and reproduce.  A variation that allows you to be more successful at avoiding non-life-threatening fly bites wouldn’t seem to fall into that category.

On the other hand, it could be that lady zebras long ago decided that black-coated males who were covered with biting flies were less attractive potential mates than those cool, laid-back striped dudes over by the watering hole who weren’t frantically twitching their tails at swarms of horseflies.  Or, alternatively, the black-coated lady zebras tormented by blood-sucking flies were less likely to be in a receptive reproductive mood than their serene, striped counterparts.