Tag Archives: biology

What are animals?

Though this question seems to be trivial, but in fact it is not. And if we want to introduce animal welfare legislation, we need to establish what organisms are animals.

In modern taxonomy animals (Animalia) are known as Metazoa. Animals are multicellular eukaryotes (i.e. animal cells have a nucleus), are heterotrophic (i.e. they don’t do photosynthesis, and chemical energy in the form of organic molecules to survive), and their cells don’t have a rigid cell walls (unlike plants, fungi and bacteria).

Taxonomists have divided the animal kingdom in three main groups: Eumetazoa, Mesozoa and Parazoa. The last subkingdom consists of multicellular animals who (unlike other animals) do not have tissues or organs. Currently only sponges belong to the Parazoans. The second group, Mesozoa, contains only worm-like parasites, and its actual status is subject of scientific dispute.

The first subkingdom, Eumetazoa, is by far the most interesting one, since it contains all other animals. Eumetazoans are animals with differentiated tissues and organs. Most aminals of this group of a symmetric body to a certain degree. Since only Eumetazoans are known to have nerve systems, and hence capable of suffering, it might be an idea to restrict animal welfare legislation to Eumetazoans rather to all Metazoans.

Many people have learned at school that life is divided into four kingdoms: bacteria, fungi, plants and animals. Only this system is now outdated due to new scientific (genetic!) research. There are two superkingdoms: Prokaryotes and Eukaryotes. The former is divided into Bacteria and Archaea. The latter is divided into: Unikonta and Bikonta. The latter contains plants, algae and similar organisms. Unikonta contains amoebozoa and opisthokonts.

Opisthokonts are further divided into main groups: Holomycota (includes among others fungi) and Halozoa. The latter group is then further divided into Mesomycetoea and Filozoa. Filozoans are divided into Filasterea, Choanoflagellata and Animalia. Choanoflagellata are a group of unicellular organisms, and they are the closest relatives of animals (most recent common ancestor living about 600 million years ago).

Can a child have multiple parents?

Yes, (s)he can. This question is relevant since the Dutch government is investigating whether the Dutch civil code should be changed to include the possibility of a child having more than one parent. However, this legal reform is aimed to loosen to connection between legal and biological parenthood. In this post we’ll discuss the possibility of having multiple biological parents.

One method to create a three-parent-child is the following. From an oocyte we can remove the nucleus, and replace it with the nucleus of another oocyte. The newly recombined oocyte will contain the DNA of two people: the mitochondrial DNA of the first oocyte donor, and the nuclear DNA of the second donor. Subsequently the recombined oocyte can be fertilized by a sperm cell, resulting a zygote with the DNA of three different people. The rationale of this technique is to prevent diseases caused by defects in mitochondrial DNA.

A second, more intriguing method is to create human chimeras. Basically a chimera is an organism which the result of the merger of two, or even more, embryos. We could say this a chimera is the opposite of an identical twin. More important chimeras, including human ones, occur in nature. And if a woman would have had sex with two different shortly after each other, such a chimera could have one mother and two fathers. The chance of this possibility is increased by the fact that sperm can survive up to seven days in the female body, and hence able of fertilizing an oocyte.

Most human chimeras are unaware of their condition, but they could be get into trouble because of this. Lydia Fairchild (an ironic name) was denied motherhood of her own child as result of a paternity test. After some investigation it was discovered that Ms. Fairchild was actually a chimera, and consequently in the possession of two different genomes.

It might happen that a female and a male embryo merge into one single human being. What sex should we assign such person? Or should leave that choice up to that person?

When we are writing down the civil code of space settlements, we have to take these things into account.