Milch mares
The mother who ran dry of milk, saw foals getting milk from the mares, and would have mare's milk for her child. The mares who gave most milk were preferred to others. From this came the natural idea of breeding from good milch mares to improve the strain, and get a larger yield. And thus the use and value grew of mare's milk with its many preparations as a staple food for children, then of grown-ups, until the practice of herding tame horse stock became general among the hordes of Asia. Since then it has been found that cows gave more and better milk than mares.
As the wild game migrated between their high summer range and their lowland wintering grounds the savage tribes followed in search of meat. With the beginning of the pastoral age the need was urgent of moving the flocks and herds between the summer and the winter pastures. But as yet there were no beasts of draught or burden to carry the tribal camp. That meant the keeping of two camp equipments, or maybe a camp upon the highlands to supplement the village in the lowlands; and it was doubtful policy to leave valuable tents as a prey for marauding rivals. A larger and a bitter need arose when the tribe must move, and old folk who lacked the strength to travel must be left behind. There is nothing so terrible in savage life as the necessity of leaving old men and women exposed upon a hilltop after the tribe has moved. The poor old thing is provided with warm robes, a fire, fuel, water and some food, but as the days pass the last cinders, carefully raked together, sink to dust, and the cautious wolves close in for the final rush. Savages love as we do, think as we do, and their life which has for us some glamour of romance is full for them of sordid realism. So we may reckon well that some good matron grudged the loss, at moving time, of tent poles, the cutting of which had cost her heavy labour, done as it was without steel tools like ours.
The travois
She saw the tent poles left behind when the milch-pony herd moved off. She told the herders to lash a pair of her poles, one on either side of each pony's neck with the ends trailing astern. The next idea was to lash a couple of cross bars across the trailing poles behind the pony's hocks, and that was enough to keep them at a proper angle. It was easy then to lash a skin robe in position between the trailing poles and the two cross bars, making a sort of basket, something to carry the old mother, who must otherwise be left behind to perish. Here then was transport which enabled the tribe to march with its tent poles, old folk and baggage. One can imagine how the medicine men protested against so shocking a violation of the laws of nature, which decree that the aged shall be left as a meal for our hunting companions, the range wolves. But here the priests would find themselves opposed by the common sense of every man and woman; so they would doubtless yield with an ill grace, after enacting a law that this new means of transport was a special privilege for aged clergymen. The travois came into general use for transport.
The cart
The next step was less obvious, an idea which would appeal to men of inventive minds; and I have noticed that it is only in civilisation that the inventor is treated as a public enemy. The savage actually admires a man with new ideas. The travois frame was a heavy drag, and the draught pony was apt to delay the march. Why not have a round log as a roller under the trailing ends of the poles? Too heavy. Cut away the bulk of the roller, fining it down to a mere axle bar, with a disc at either end to roll along the ground. The larger the disc the better it rolled, so disc wheels were built, with a hole in the middle into which the ends of the axle bar were bolted.
As one may see in the many countries where disc wheels are used by farmers, the first idea of lightening the disc was to cut out four large holes, leaving the timber shaped like a rough cross with a rim. But that cross was too weak to carry weight, so its arms had to be strengthened with four spokes, lashed on with raw-hide; next the four spokes replaced the arms of the cross, and a rim was built enclosed in a raw-hide tyre. The raw hide, put on wet, and shrinking as it dried, made a quite serviceable tyre. So was the wheel invented, and the first four-spoke pattern gave place to the six and eight-spoke methods of strengthening the rim. The whole process from roller to four-spoke wheel would easily occur to one inventor in his experiments.
The chariot
Meanwhile the skin basket in the travois frame was changed to a floor of raw-hide lacing, on which a man could stand with bent knees driving. He needed shelter, so a dashboard was made of oiled bull-hide, quite translucent but proof against spears, arrows and pony kicks. As a curved surface made weapons glance when they hit, this dash-board was rounded at the front, and carried along the sides enclosing the driver's stand.