Pros & Cons of Neanderthal & Denisovan Genes

Many of us have genes from extinct human species in our DNA. Some of these genes have been helpful, but others seem to be destructive.

When modern humans moved out of Africa between about 60,000 and 100,000 years ago, they met other types of humans who had already made the move to Europe and Asia.

Whatever else went on between Homo Sapiens and these earlier people, some got together and had children, whose genes many of us carry.

Today, the genetic makeup of most people born outside Sub-Saharan Africa is 1 to 4 percent Neanderthal.

Neanderthal Father

And then, to make things even more interesting, along came the Denisovans. What we know of Denisovans is very recent, coming from a finger bone and two teeth found six years ago in Siberia. The Denisovans also left Africa early, and, like their Neanderthal relatives, they interbred with Homo Sapiens.

With time, we are learning that modern humans are indebted to these extinct human species for some of the abilities and some of the problems we find coded into our DNA.

The Altitude Gene

The higher you climb in Earth’s atmosphere, the lower the air pressure gets. This goes on until you reach space, where there’s no air. Every breath we take at high altitudes gives us less air, and less oxygen than at sea level.

Our DNA has an app for that though. At high altitude, our EPAS1 gene fires up, pushing other genes to make extra red blood cells, improving our oxygen take up. The trouble is, these extra cells thicken our blood, making our blood pressure rise unhealthily.

So what happens if you want to live three miles up? Your DNA will need a better app for that!

Tibet is a country whose average elevation is 4900 meters – about 3 miles. It turns out that most people in Tibet have a variant of EPAS1 that allows them to deal with low oxygen with fewer red blood cells than the rest of us. Their blood stays thin and healthy 3 miles up.

And where did this variant come from? It turns out it came from Denisovans; they shared this gene with people who now live in Tibet.

Tibet Children

Life 3 miles up is easier with a little help from Denisovan genes. Image by Antoine Taveneaux.

The Immunity Gene

HLA is a gene that helps white blood cells destroy micro-organism intruders in our bodies.

At least one version of HLA is basically absent in Sub-Saharan people. Researchers think that people carrying this gene can thank Neanderthals and Denisovans for it. These hominids had already adapted to infections and diseases found outside Africa. This gene gave any modern humans born with some Neanderthal and Denisovan ancestry a survival advantage.

European people get more than 50 percent of of one HLA genetic variant from interbreeding with Neanderthals and Denisovans. For Asian people it’s as much as 80 percent, and Papua New Guineans 95 percent.

The Hair and Skin Gene

Genes for keratin – the protein in our skin, hair and nails – can have an especially strong Neanderthal influence. Two-thirds of East Asian people have the Neanderthal skin gene POU2F3, while almost three-quarters of European people have the Neanderthal skin-color gene BNC2.

We don’t know exactly what advantages these genes gave people, but the persistence of these genes indicates that they offer quite a powerful boost to survival. It’s possible that Neanderthal adaptations to colder weather encoded in these genes were important.

Even Genetic Ointments Have Flies in Them

The DNA of Homo Sapiens and Neanderthals didn’t mix very well. Long, long stretches of human DNA have no Neanderthal gene input at all. This indicates that genetic modifications in these regions proved negative for survival.

For example, the FOXP2 gene for motor coordination and language and speech has no Neanderthal input.

Large regions of human DNA have no Neanderthal input

Neanderthal input is entirely absent from large sections of the human DNA molecule.

Furthermore, human male X chromosomes are particularly lacking in Neanderthal input, meaning there’s a good chance that male children of a Human-Neanderthal union had lower fertility than average.

Perhaps only a tiny fraction of the descendents of Human-Neanderthal unions actually prospered.

As if that weren’t enough, auto-immune disorders like type 2 diabetes and Crohn’s disease seem to be more likely if you carry Neanderthal influence.

The Future

Other human groupings besides Neanderthals and Denisovans left Africa before Homo Sapiens. Researchers are seeking to obtain their DNA too. Ultimately science would like to determine just how big an effect interbreeding with other species has had on us.

 

Archimedes Makes his Greatest Discovery

archimedes small sphere

Archimedes was fascinated by curves. His powerful mind had mastered straight line shapes in both 2D and 3D.

He needed something more intellectually challenging to test him. This came in the form of circles, ellipses, parabolas, hyperbolas, spheres and cones.

Calculation of the Volume of a Sphere

He rose to the challenge masterfully, becoming the first person to calculate and prove the formulas for the volume and the surface area of a sphere.

The way he found his formulas is both amazingly clever and shows him to be a mathematician of the first rank, far ahead of others of his time, doing mathematics within touching distance of integral calculus 1800 years before it was invented.

Taming Curves in 3-Dimensions – Not for the Timid

The surface of a sphere is incredibly hard to get to grips with compared with a shape like a cube. Cubes only change at the corners and edges. The surface of a sphere changes its direction at every point. How could you work with this?

sphere cut into hemispheres

Sphere cut into hemispheres.
Image by Jhbdel

First, Archimedes imagined cutting a sphere into two halves – hemispheres.

Taking one hemisphere gave him a shape with a flat surface to work with – easier than a sphere, and if he could find the volume of a hemisphere, doubling it would give him the volume of a sphere.

He then imagined placing the hemisphere face down on a flat surface.

Next, in his mind’s eye, he fitted a cylinder around his hemisphere.

The circle at each end of the cylinder was the same size as the circle at the bottom of the hemisphere, and the cylinder’s height was equal to the hemisphere’s height, as shown in the image below:

hemisphere within cylinder

Archimedes imagined a hemisphere within a cylinder

Salami Tactics

Archimedes then did something incredibly clever. To anyone who has studied university mathematics, you’ll recognize something very similar to integral calculus.

Archimedes imagined cutting horizontal slices through the cylinder.

He took his first slice of mathematical salami at the very top of the cylinder. Here the hemisphere is at its smallest. Looking at this first slice from above, the radius of the circle from the very top of the hemisphere is infinitesimally small.

Then, in his mind’s eye, he moved his attention a tiny bit lower down the cylinder and took another salami slice through the cylinder and hemisphere. In this slice, the hemisphere circle had grown a little larger.

Then he moved his attention a little lower again, cutting another salami slice. The cylinder circle stayed the same size, while the hemisphere circle was again a little larger than the previous slice.

He then moved down the cylinder, taking slices all the way to the bottom. In each slice, the size of the inner circle got larger, while the size of the outside circle stayed the same, as shown in these images.

Archimedes takes salami slices

The cross sections Archimedes imagined of the hemisphere and the cylinder.

Putting Everything Together

Archimedes considered each salami slice. In particular, he was interested in the gap between the two circles in each slice – shown in blue in the images above.

He took all of these blue areas – there were as many of them as he liked to imagine, with the depth of each slice as close to infinitesimally thin as he liked. He then multiplied the areas of the blue rings by their depths to find the volume represented by all of the blue salami rings stacked up on one another. (He didn’t consider an infinite number of infinitely thin slices, because if he had, he would have invented integral calculus over 1800 years before Isaac Newton did it.)

Archimedes found that the volumes of the blue rings added up to the volume of a cone whose base radius and height were the same as the cylinder’s.

This meant the volume of the hemisphere must be equal to the volume of the cylinder minus the volume of the cone.

The formula for the volume of the cylinder was known to be πr2h and the formula for the volume of a cone was known to be 13πr2h. In this example, r and h are identical, so the volumes are πr3 and 13π r3.

Subtracting one from the other meant that the volume of a hemisphere must be 23πr3, and since a sphere’s volume is twice the volume of a hemisphere, the volume of a sphere is:

V = 43πr3

Archimedes also proved that the surface area of a sphere is 4πr2.

Archimedes saw this proof as his greatest mathematical achievement, and gave instructions that it should be remembered on his gravestone as a sphere within a cylinder.

More about Archimedes

Archimedes - the sphere within the cylinder

The sphere within the cylinder. Image by André Karwath.