Somewhere around 150 million years ago everything in order. Lactation already existed and the secretion had the ingredients of milk. The pre-mammal was warm-blooded; the placenta had developed. Live birth began. Lactation, which started developing a hundred million years ago, was available to those toothless newborns. The baby’s source of food was not very far away.
A critical element in the process is that the pre-mammals were prey, not predators, small, not big. Generation after generation, the parents must have stayed with the eggs and then the babies, providing warmth and moisture while all these critical transitions developed.
Using the information which can be found, a Darwinian explanation can be cobbled together. The closeness of the parents first to eggs and then to a new-born baby may have been pre-determined by the instinct to just stay alive. However, if “just surviving” were dominant, the female could have laid the eggs and sought the safest place to hide all day – these were still reptiles so the parents did not necessarily have to be with the eggs. Parenting has been seen earlier in the evolutionary line; should it not be a key element in the Darwinian interpretation?
This is a little bit off-topic, but it is sort of interesting that about the same time mammals experienced live birth, birds also evolved from reptiles. Like mammals, birds became warm-blooded, and, relative to their size, birds have quite a large brain. They display a good deal of intelligence, communicate with complex songs and signals better than any other animal.
This complex transition from reptile to mammal when the mammal was the prey, not the predator. Reptiles ruled. The animals stayed small, as out-of-sight as they could be.
Take just a couple minutes to review the role of parenting in these steps to lactation, warm blooded, placenta developed, live birth started, and the newborn needed parental help to stay alive. The process leading to lactation relied heavily on parental effort. .
As those the eggs were held longer and longer, the body temperature was turned up, demanding more energy. Is there a chance holding the baby inside was in some manner satisfying to the female, thereby allowing internal development to continue? Remember, the parents had to eat, too. They could easily concentrate on finding food, letting the eggs die in the process. In a dog-eat-dog world, who cares? Obviously they did care. Was there no time when leaving the eggs was more attractive to the parents, in terms of personal survival, than staying with eggs? Live birth followed, demanding attendant parenting. Every step of the way, across 130 million years, the female was holding the embryo inside her further and further into the birth process. And, across that same time span, the female – and apparently the male also – stayed quite close to the entire birth process, from beginning to end.
Again and again since the beginning, origin of change seems to include more than mutation followed by natural selection. A factor seems to have existed from the beginning which always seems to be connected to words like “feeling” or “reward” or “expectation of satisfaction.” The consistent picture shows gender seeking one another; genders together taking steps included under the heading “parenting.”
The earth now contained mammals. The mammals had little opportunity to branch out – they were just little animals in a world of really big animals. But 65 million years ago, mammals got their chance. The dinosaurs’ reign came to a sudden death, not from an internal but an external threat.
A comet or asteroid, moving at a speed 40 times faster than the speed of sound, hit Earth. On impact, when its bottom touched Earth, the top was still five miles high in the sky. The crater caused by the impact, nearly 60 miles across, is located on Mexico’s Yucatan Peninsula. More than 75% of animal and plant species on Earth, including all dinosaurs, were eliminated by this event. At this time, general agreement, based on accumulating evidence, is that the extinction was caused by an asteroid or comet collision.
Data suggest fast-moving debris from the impact caused anything flammable to burst into flames. No place existed for the bigger animals to hide or escape as their environments burned to the ground. Fires of that intensity and breadth are killing events. Although the demise of dinosaurs and others was fairly sudden after the extinction event, the debris flew around for a long time. As you can imagine, the world was dark and, with the sunlight obscured, cold as well.
Recovery took some time. Pretty soon, the climate was generally warm as those little mammals stepped in where dinosaurs were no more. At that time, temperatures were high but some plate movement led to a global cooling event about ten million years later. Interestingly, those lower temperatures caused the body sizes of mammals to increase.
Mammals released from jail. Mammals got their chance to take over; and they did!
Three kinds of mammals appear – actually, they had appeared before the big extinction. One had hair, produced milk, but still laid eggs. That group’s only remaining examples are in Australia and New Guinea; the most common survivor is the duck-billed platypus. The second group, marsupials, include kangaroos, koalas, and opossums Marsupials have a maternal pouch and, in reproduction, were sort of half way between egg layers and live birth. Their newborns spend a while in a maternal pouch before being on their own.
The third evolutionary line is ours, called the placentas. Fortunately, far from the impact site, surviving species includes placentas. Flowering plants, which had expanded across the land masses, survived, as did many amphibian and reptile groups. The burst of flowering plant groups coincided with their partners, the bees and wasps as well as ants and beetles. Those little bugs provided the fertilization plants need.
Just about the first line to spin off after the extinction were the insects. Right behind them, less than five million years after the extinction, came the flying lemurs, bats, and the line that led to us, the primates. About the same time, another evolution line led to carnivores or meat eaters, like bears, dogs, lions.
Just a little later, in the water, came the whales, dolphins, and porpoises. Next, along the same line, came elephants, manatees, and sea cows. How quickly the mammal took over. All these new species happened less than five million years after the extinction. Mammals stepped right up to the plate.