For all living things on Earth that practice sexual reproduction, the next generation can only be born in one of two ways: either oviparous or viviparous, birds, reptiles in general, most fish and insects are almost oviparous, while fetal beings are generally mammals, which is a manifestation of more mature evolution. Of course, there are also some organisms that are oviparous, such as sharks, and shark eggs are born from the mother after they develop into new individuals in the mother's body.
However, scientists have rarely found a creature that can both spawn and give birth, and this is the three-toed stone dragon, an Australian reptile that can be described as an outlier of animal evolution.
According to a study published last month in the American journal Molecular Biology, a three-toed stone dragon completed an extraordinary feat: it laid three eggs and gave birth to a live fetus during the same pregnancy.
In the eggs laid by this stone dragon, the embryos are almost fully developed and hatch much faster than other egg-laying lizards. The incubation time of the eggs that are born may only take 5 days, compared to 35 days under normal circumstances.
This situation can be said to break through the understanding of scientists, it is well known that fetal animals evolved from oviparous ancestors, the evolution of vertebrates: primitive fish→ primitive amphibians→ primitive reptiles→ birds and mammals.
In the beginning, mammals, like reptiles, used oviparous reproduction, and after the extinction of the dinosaurs, mammals underwent a cruel survival of the fittest, and the viviparous species replaced oviparous and single-porous mammals, occupying the advantage of the earth's ecological niche.
The viviparous animal develops in the mother's body, thus avoiding the risk of the eggs being destroyed by the outside world. Viviparous animals can get sustained energy from the mother, so they can have a long period of development. , the birth of the carcass development is more completely mammalian and then through the way of maternal breastfeeding, the cub grows rapidly, the newborn larvae obtain nutrients from the mother's milk to maintain growth, sucking milk does not require chewing ability, before weaning the upper and lower jaws have a chewing function, the permanent teeth are gradually sprouted, thus forming a strong individual, which is conducive to survival after birth. And this way is conducive to the formation of highly complex (especially highly complex brains) individuals, is conducive to population reproduction.
The common features of more primitive reptiles are: (1) the body surface is covered with dry keratinous scales and nails, (2) the body temperature is not constant (cold blood), (3) the heart has three chambers (the ventricular septum is incomplete), (4) lung respiration, (5) there are amniotic eggs (egg shells are hard), and reproductive development is free from the restriction of water. It does not have the ability to evolve into a fetus.
Over the course of time, reptiles overcome the physiological limitations of gas exchange, and embryos developing in vivo acquire the ability to tolerate the effects of maternal movement on their development. Soft fetuses evolved, compared to mammals, they did not simply stay in the womb to supply nutrients by the placenta, but developed in the egg, grew on the nutrients in the egg, and then slid into the womb, and finally landed on the ground.
The costs of oviparous birth include the loss of whole offspring due to decreased feeding capacity of pregnant females and death from predator attacks, low fertility, and stable embryonic development environment that prevents genetic diversity from maximizing: the benefits of oviparous birth include decreased embryonic mortality, the temperature regulation of pregnant females to optimize the phenotypic characteristics of offspring (morphology, behavior and physiology), and the provision of embryonic material and energy.
That's why scientists are so surprised to observe the three-toed stone dragon giving birth to a live fetus, having never seen a species lay both an egg and a live fetus during a single pregnancy. This is the first time this behavior has been recorded in vertebrates. It also means that this lizard species is in a rare transition phase between oviparous and fetal animals.
We need to understand that the living organism refers to a self-evolutionary system that can spontaneously change entropy for the purpose of reproduction, so any evolution it makes is for better reproduction, including human beings, although human beings have been born with self-consciousness, but human human instincts attach great importance to appearance. If we exclude acquired influences (money, power), humans prefer to associate with good-looking people.
The good gene theory holds that people's evaluation of faces stems from evolution, and attractive faces are considered to be signs of healthy genes, better immunity, and reproductive advantage, so we prefer people with attractive faces. Conversely, a bad face seems to mean unhealthy, difficult to guarantee the continuation of the race, so we deliberately avoid them.
The same is true of living things, and the reason why the three-toed stone dragon has evolved such an ability may be adhering to the principle of not putting eggs in one basket, and animals have formed their own reproductive strategies in the long process of evolution. Reproductive strategy is determined by heredity, is also an adaptation to habitat conditions, and is an important condition for population stability and continuation. When it masters both oviparous and viviparous methods, it gains an advantage in an unpredictable environment and quickly switches reproductive strategies, thus ensuring the reproduction of the population.
However, in what direction the last three-toed stone dragon will evolve, it is still "impossible" to determine.