Eggs and embryos

1826

Eggs and embryos

The book of science

Tom Sharp

Karl Ernst von Baer embryology

Eggs and embryos

Homunculi

Having come from an egg, one should never belittle them; from tiny eggs mighty mammals grow.

The typical adult human body is made of trillions of cells. Each of these arises by cellular division from a single cell. The embryo of any animal that produces sexually grows by cellular division or mitosis from a single fertilized cell called a zygote (pronounced with two syllables), which is the union of two gamete cells (a sperm cell from the male and an ovum from the female).

In 1744 Albrecht von Haller coined the term evolution to describe the then prevailing theory (also known as preformation) that every human was preformed by God at once, each person nested inside the sperm of his or her father, which was nested inside the sperm of his father, and so forth back to Adam.

I am amazed that it wasn't until Von Baer's work in 1826 that anyone proved that mammals grew from eggs, maybe because of the inherent difficulty of observing the process in the laboratory, or because humans believed that mammals like us were not like other animals. Ever one's own biases blind one to the truth.

Von Baer went on to study the embryonal development of animals, and discovered the blastula stage and the notochord.

The biologist Gregor Mendel, who published the laws of genetic inheritance in 1865, coined the term gamete.

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